Composition and abundance of weed populations often change in response to new or extensively used weed management practices. Glyphosate-resistant (GR) technology is one such weed management practice now used extensively. A recent survey of weed scientists was conducted to address weed shifts in GR corn, cotton, and soybean. Twelve scientists in 11 states responded to the survey. Averaged over estimates from scientists, GR corn, cotton, and soybean were planted on 15, 90, and 88% of the hectarage in 2003, respectively. Acreage of GR corn is expected to rise, whereas only minor changes in acreage of GR cotton or soybean are expected. Weed shifts have not been observed in GR corn but have occurred in GR cotton and soybean. In GR cotton, Amaranthus, Commelina, Ipomoea, and Cyperus species as well as annual grasses were noted as becoming more problematic. Similar to cotton, Ipomoea and Commelina species are becoming more troublesome in GR soybean. In addition, in GR soybean, various winter annuals, lambsquarters species, and waterhemp species were noted as becoming more problematic. All scientists felt that weeds shifts were occurring, and two-thirds of these scientists noted that weed shifts are currently of economic concern. The scientists recommend the following to help manage weed shifts: additional herbicides in mixture with glyphosate, rotation to herbicides other than glyphosate, rotation to non–GR crops, and greater use of soil-applied herbicides.

Nomenclature: Glyphosate; waterhemp species, Amaranthus tuberculatus and Amaranthus rudis; corn, Zea mays L.; cotton, Gossypium hirsutum L.; soybean, Glycine max (L.) Merr.

Additional index words: Invasive weeds, noxious weeds.

Abbreviation: GR, glyphosate-resistant.

Resistance to the herbicide glyphosate is currently known in at least eight weed species from many countries. Some populations of goosegrass from Malaysia, rigid ryegrass from Australia, and Italian ryegrass from Chile exhibit target site–based resistance to glyphosate through changes at amino acid 106 of the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene. Mutations change amino acid 106 from proline to either serine or threonine, conferring an EPSPS weakly resistant to glyphosate. The moderate level of resistance is sufficient for commercial failure of the herbicide to control these plants in the field. Conversely, a nontarget site resistance mechanism has been documented in glyphosate-resistant populations of horseweed and rigid ryegrass from the United States and Australia, respectively. In these resistant plants, there is reduced translocation of glyphosate to meristematic tissues. Both of these mechanisms are inherited as a single, nuclear gene trait. Although at present only two glyphosate-resistance mechanisms are known, it is likely that other mechanisms will become evident. The already very large and still increasing reliance on glyphosate in many parts of the world will inevitably result in more glyphosate-resistant weeds, placing the sustainability of this precious herbicide resource at risk.

Nomenclature: Glyphosate; goosegrass, Eleusine indica (L.) Gaertn. #³ ELEIN; horseweed, Conyza canadensis (L.) Cronq. # ERICA; rigid ryegrass, Lolium rigidum Gaud. # LOLRI; Italian ryegrass, Lolium multiflorum Lam. # LOLMU.

Additional index words: EPSPS, herbicide resistance, herbicide translocation.

Abbreviations: ACCase, acetyl-coenzyme A carboxylase; ALS, acetolactate synthase; ESPS, 5-enolpyruvylshikimate-3-phosphate synthase.

Glyphosate, a nonselective herbicide and also the world's most widely used herbicide, inhibits 5-enol-pyruvylshikimate-3-phosphate synthase (EPSPS), an enzyme in the aromatic amino acid biosynthetic pathway. Because of its broad-spectrum and potent weed control and favorable environmental characteristics, attempts to engineer glyphosate resistance have been intensive in the past few decades. The use of at least three different mechanisms has conferred glyphosate resistance in normally sensitive crop species. Early work focused on progressive adaptation of cultured plant cells to stepwise increases in glyphosate concentrations. The resulting cells were resistant to glyphosate because of EPSPS overexpression, EPSPS gene amplification, or increased enzyme stability. Further work aimed to achieve resistance by transforming plants with glyphosate metabolism genes. An enzyme from a soil microorganism, glyphosate oxidoreductase (GOX), cleaves the nitrogen– carbon bond in glyphosate yielding aminomethylphosphonic acid. Another metabolism gene, glyphosate N-acetyl transferase (gat), acetylates and deactivates glyphosate. A third mechanism, and the one found in all currently commercial glyphosate-resistant crops, is the insertion of a glyphosate-resistant form of the EPSPS enzyme. Several researchers have used site-directed mutagenesis or amino acid substitutions of EPSPS. However, the most glyphosate-resistant EPSPS enzyme to date has been isolated from Agrobacterium spp. strain CP4 and gives high levels of resistance in planta. Weeds resistant to glyphosate have offered further physiological mechanisms for glyphosate resistance. Resistant field bindweed had higher levels of 3-deoxy-d-arbino-heptulosonate 7-phosphate synthase, the first enzyme in the shikimate pathway, suggesting that increased carbon flow through the shikimate pathway can provide glyphosate resistance. Resistant goosegrass has reduced translocation of glyphosate out of the treated area. Although glyphosate resistance has been achieved by numerous mechanisms, currently the only independent physiological mechanism to give adequate and stable resistance to glyphosate for commercialization of glyphosate-resistant crops has been glyphosate-resistant forms of EPSPS.

Nomenclature: Glyphosate, N-phosphonomethyl glycine; field bindweed, Convolvulus arvensis L.; goosegrass, Eleusine indica L.

Additional index words: EPSPS, gene amplification, glyphosate, glyphosate N-acetyl transferase, glyphosate oxidoreductase, herbicide metabolism, herbicide resistance, shikimate pathway.

Abbreviations: AMPA, aminomethylphosphonic acid; CP4-EPSPS, 5-enol-pyruvylshikimate-3-phosphate synthase isolated from Agrobacterium spp. strain CP4; CTP, chloroplast transit peptide; DAHP synthase, 3-deoxy-d-arabino heptulosonate-7-phosphate synthase; EPSPS, 5-enol-pyruvylshikimate-3-phosphate synthase [E.C. 2.5.1.19]; gat, glyphosate N-acetyl-transferase gene; gox, glyphosate oxidoreductase gene.

Recent shifts in herbicide use patterns can be attributed to rapid, large-scale adoption of glyphosate-resistant soybean and cotton. A dramatic increase in glyphosate use is the most obvious change associated with the adoption of glyphosate-resistant crops. Consequently, the diversity of herbicides used for weed management in these crops has declined, particularly in soybean. To date, the availability of glyphosate-resistant corn has limited the use of glyphosate in corn. While exploiting the benefits of glyphosate-resistant crops, many growers have abandoned the principles of sound weed and herbicide-resistance management. Instead of incorporating glyphosate into a resistance management strategy utilizing multiple herbicide sites of action, many growers rely exclusively upon glyphosate for weed control. Although it is difficult to establish a clear relationship between the adoption of glyphosate-resistant crops and changes in other crop production practices, the increase in no-till and strip-till production of cotton and soybean between 1995 and 2002 may have been facilitated by glyphosate-resistant crops.

Nomenclature: Glyphosate; corn, Zea mays L.; cotton, Gossypium hirsutum L.; soybean, Glycine max L.

Additional key words: Application timing, herbicide-resistance management, mode of action, site of action, tank mixtures, tillage, weed management strategies.

Populations of eastern black nightshade suspected of being resistant to acetolactate synthase (ALS) inhibitors have been reported since 1999 in different locations in Ontario, Canada. This event has threatened the use of ALS inhibitors for control of this species. The objectives of this study were to evaluate the spectrum of resistance to different ALS-inhibiting herbicides and to examine the effectiveness of alternative modes of action herbicides. Growth room experiments were conducted to determine the response to imazethapyr and atrazine in seven suspected ALS inhibitor– resistant populations. One resistant and one susceptible population were further characterized for their response to ALS inhibitors and chloroacetamides. Seven populations were able to survive imazethapyr at 100 g ai/ha, while there was no resistance to atrazine. Compared to a susceptible (S) population, resistant (R) population SOLPT 1 had 726-, 31-, 6-, and 4-fold resistance to postemergence (POST) applied imazethapyr, imazamox, primisulfuron, and flumetsulam, respectively. Preemergence (PRE) application of imazethapyr, flumetsulam, cloransulam, nicosulfuron, prosulfuron, and rimsulfuron did not provide control of the R population, whereas they totally controlled the S population. The chloroacetamide herbicides metolachlor, dimethenamid, and flufenacet all provided at least 90% control of both R and S populations when applied PRE at the recommended field rates. The ALS inhibitors will not provide adequate control of these resistant populations, but acceptable control could be achieved with chloroacetamides or with atrazine.

Nomenclature: ALS-inhibiting herbicides; eastern black nightshade, Solanum ptycanthum Dun. #³ SOLPT.

Additional index words: Spectrums of resistance, chloroacetamide herbicides, dose–response curves.

Abbreviations: ALS, acetolactate synthase; GR₅₀, dose required to reduce plant dry weight by 50%; POST; postemergence; PRE, preemergence; R, resistant; S, susceptible.

Field studies were conducted to determine the effect of season of the year, sunlight exposure time, and mulch color on paraquat photodegradation rate on polyethylene mulch. Experiments were established in winter, spring, and summer, with white and black polyethylene mulch, and paraquat-applied films were exposed to sunlight for 1, 4, 8, 24, 30, 48, 72, or 96 h after herbicide application. There was significant effect of the season by mulch color by time of exposure interaction on paraquat concentration recovered from mulch eluants. Winter paraquat photodegradation was lower than during the other seasons. At 48 h of sunlight exposure, predicted photodegradation on white mulch was 67, 83, and 88%, during winter, spring, and summer, respectively, whereas these values were 66, 82, and 84% on black mulch. The difference in paraquat photodegradation in winter with respect to the other seasons may be attributed to reduced ultraviolet radiation in winter, when solar radiation has to penetrate a larger atmosphere mass. In practical terms, transplanting on paraquat-applied mulch requires a minimum of 96 h during the spring and summer seasons, when concentrations were 5% or less, whereas a longer waiting period might be necessary in the winter.

Nomenclature: Paraquat; tomato, Lycopersicon esculentum Mill.

Additional index words: Tomato, Lycopersicon esculentum, herbicide breakdown, ultraviolet radiation.

Tillage is used in sugarcane to control weeds, eliminate ruts caused by harvest, destroy residue from the previous crop, and incorporate fertilizer. The effect of weed control and tillage programs on sugarcane growth and yield and on economics was evaluated over two growing seasons. In the first study, weeds were effectively controlled with a March application of hexazinone at 0.59 kg ai/ha plus diuron at 2.10 kg ai/ha either banded or broadcast. When tillage of row shoulders and middles in March was eliminated, soil temperature in the sugarcane drill early in the season was equal to that where March tillage was performed. Sugarcane early and late season stalk population and sugarcane and sugar yield were each equivalent for the full season tillage (tillage of row shoulders and middles in March and in May) and the no-till programs. Elimination of a single tillage operation reduced cost $16.28/ha, and herbicide applied as a band rather than broadcast reduced cost $30.49/ ha. For the no-till program, with herbicide banded in March, net return was increased $32.56/ha. In a subsequent study conducted at five locations, weed control was excellent when either pendimethalin at 2.77 kg ai/ha plus metribuzin at 1.26 kg ai/ha or hexazinone plus diuron at 0.59 kg/ha and 2.10 kg/ha was used. When the March tillage was eliminated, sugar yield was increased 8.6% (620 kg/ ha), and net return was increased $152.68/ha compared with March tillage. When the May tillage was eliminated sugar yield was increased 8% (580 kg/ha), and net return was increased $143.88/ha compared with May tillage. A reduction in tillage cost accounted for only $16.28 of the increase in net return per hectare, with the remainder due to increased yield with the elimination of the tillage operation.

Nomenclature: Diuron, hexazinone, metribuzin, pendimethalin; sugarcane, Saccharum spp. hybrids ‘HoCP 85–845’ and ‘LCP 85–384’.

Additional index words: Conservation tillage, crop residue, net return, no-till, production cost, soil temperature.

It has been previously reported that POST-applied isoxaben can effectively control established hairy bittercress. Experiments were conducted to determine the relative importance of root vs. foliar entry of POST-applied isoxaben. At a common isoxaben rate of 0.56 kg/ha, foliar-only and foliar plus soil applications provided 10.5 and 23.3% control, respectively, as determined by fresh weight reduction. In contrast, soil-only application provided 47.0% control. Hairy bittercress foliar absorption of ¹⁴C–isoxaben did not exceed 15% of the amount applied after 72 h. Therefore, the comparatively less effectiveness of foliar-only applications may be attributed primarily to limited absorption. Minimal isoxaben concentration required to inhibit root growth of hydroponically grown hairy bittercress was 0.0025 mg/L. Higher concentrations were required to produce a response in the foliage. Sorption of isoxaben by pine bark rooting substrate, typical of what is used in container nursery production, exceeded 99% of amount applied after 36 h. Even with 99% sorption, the probable concentration within the aqueous phase remains sufficient to inhibit hairy bittercress root growth. Additional studies with ¹⁴C–isoxaben established that approximately 35% of the root-absorbed isoxaben was translocated into the foliage. Translocation from the roots into the foliage was reduced to 16% when the experiment was repeated during environmental conditions less favorable for vegetative growth (i.e., longer day length and higher temperature). Results indicate that the control of hairy bittercress with POST-applied isoxaben is likely the result of root absorption and root-growth inhibition. Expression of phytotoxicity within the foliage is also a component, but is dependent upon the root-absorbed isoxaben being translocated into the foliage. Extent of this translocation is dependent upon plant maturity and prevalent environmental conditions.

Nomenclature: Isoxaben; hairy bittercress, Cardamine hirsuta L. #³ CARHI.

Additional index words: Herbicide sorption, hydroponics, organic rooting substrates.

Abbreviations: K_d, distribution coefficient.

Experiments were conducted at three locations in Louisiana in 2002 and 2003 to evaluate flumioxazin (36, 72, or 109 g ai/ha) applied pretransplant (PRE) or post-transplant (POST) to sweetpotato. All treatments were applied immediately before or after sweetpotato transplanting to weed-free beds. PRE applications caused 4% or less injury with any rate of flumioxazin at 9 or 18 d after transplanting (DATr) compared with 18 to 20% injury at 9 DATr and 6 to 14% at 18 DATr with 72 or 109 g/ha POST, respectively. Injury from PRE applications of flumioxazin were not different from injury with clomazone (840 g ai/ha) applied POST. Injury at Chase, LA, in 2002 was 8% and less with flumioxazin PRE, but 35 to 83% with flumioxazin POST and appeared to be due to the use of greenhouse-grown cuttings instead of field-grown cuttings, which were used in the other two experiments. There was no interaction between experiments for sweetpotato yield. Plots treated with flumioxazin PRE or 36 g/ha POST yielded greater than sweetpotato treated with clomazone for U.S. No. 1 and 2 grade yield as well as total marketable yield. No differences were observed in yellow nutsedge control with any rate of flumioxazin. At 34 or 50 DATr, flumioxazin controlled yellow nutsedge 73 to 85% with 72 or 109 g/ha applied PRE or POST. Flumioxazin, regardless of application timing or rate, controlled carpetweed and spiny amaranth at least 86%. A similar experiment in Mississippi evaluated tank-mixes of flumioxazin (36, 72, or 109 g/ha) and clomazone (840 g/ha) applied PRE or POST. No sweetpotato injury was observed with flumioxazin PRE. However, injury from flumioxazin POST increased with increased rates (18 to 50% at 18 DATr and 16 to 93% at 25 DATr). Weed control was greater than 80% with all treatments.

Nomenclature: Clomazone; flumioxazin; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #³ BRAPP; carpetweed, Mollugo verticillata L. # MOLVE; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray # IPOHE; pitted morningglory, Ipomoea lacunosa L. # IPOLA; redroot pigweed Amaranthus retroflexus L. # AMARE; spiny amaranth, Amaranthus spinosus # AMASP; yellow nutsedge, Cyperus rotundus L. # CYPES; sweetpotato, Ipomoea batatas (L.) Lam. ‘Beauregard’.

Additional index words: Clomazone, Amaranthus retroflexus, Amaranthus spinosus, Brachiaria platyphylla, Cyperus rotundus, Ipomoea hederacea var. integriuscula, Ipomoea lacunosa, Mollugo verticillata, AMARE, AMASP BRAPP, CYPES, IPOHE, IPOLA, MOLVE.

Abbreviations: DATr, days after transplanting; PRE, pretransplant; POST, post-transplant.

Creeping bentgrass infestations in cool-season turfgrass are unsightly and difficult to control. Field tests were conducted at Stoney Creek Golf Course in Wintergreen, VA, in 2002 and 2003 on a Kentucky bluegrass rough and at the Turfgrass Research Center in Blacksburg, VA, in 2003 on a perennial ryegrass lawn to determine the efficacy of imazaquin, isoxaflutole, and mesotrione for creeping bentgrass control and turfgrass tolerance. Isoxaflutole and mesotrione each applied in two sequential applications at 280 g ai/ha or three sequential applications at 170 or 60 g/ha and imazaquin in two sequential applications at 390 g/ha controlled bentgrass at least 92% 14 wk after initial treatment (WAIT) at all locations. Sequential applications were applied at 2-wk intervals. Isoxaflutole and mesotrione, regardless of rate or sequential treatment, injured turfgrass less than 20% at all rating dates and locations. Imazaquin in two sequential applications at 390 g/ha injured Kentucky bluegrass and perennial ryegrass greater than 50% at all locations 14 WAIT. Results indicate isoxaflutole or mesotrione could be used for selective bentgrass control in Kentucky bluegrass or perennial ryegrass.

Nomenclature: Imazaquin; isoxaflutole; mesotrione; creeping bentgrass, Agrostis stolonifera L. #³ AGRST; Kentucky bluegrass, Poa pratensis L. ‘Blacksburg’ and ‘Midnight’; perennial ryegrass, Lolium perenne L. ‘Prosport’.

Additional index words: Golf course rough, turfgrass injury, weed control.

Abbreviations: SCG, Stoney Creek Golf Course; TRC, Turfgrass Research Center; WAIT, weeks after initial treatment.

Field studies have shown that rimsulfuron can move laterally with mower tires and injure neighboring cool-season grasses, indicating that persistent chemical can dislodge from turfgrass foliage. Laboratory studies were conducted to evaluate persistence and stability of ¹⁴C rimsulfuron on perennial ryegrass and annual bluegrass foliage. Rimsulfuron was absorbed by annual bluegrass and perennial ryegrass equivalently, and persisted equally on foliage of each species. When extracted with a water rinse, 57% of applied rimsulfuron was recovered after 10 min, and 42% of applied rimsulfuron was recovered after 96 h. Rimsulfuron was stable 4 d after application based on comparison of rinse water chromatograms to stock solution chromatograms. These data indicate that appreciable rimsulfuron persists on turf foliage for 4 d. Thus, limiting traffic on treated areas for several hours to allow drying is not a viable method to prevent lateral relocation of rimsulfuron, and subsequent injury to cool-season turfgrasses.

Nomenclature: Rimsulfuron; annual bluegrass, Poa annua L. #³ POAAN; perennial ryegrass, Lolium perenne L. ‘Pennant II’.

Additional index words: Absorption; herbicide degradation; herbicide relocation; herbicide stability; sulfonylurea.

Abbreviations: HAT, hours after treatment; LSS, liquid scintillation spectrometry; TLC, thin-layer chromatography.

Torpedograss is a serious problem in southern turfgrass, especially along the U.S. gulf coast. Studies were conducted in 1999, 2000, 2002, and 2003 to evaluate single and sequential applications of trifloxysulfuron-sodium for torpedograss control in bermudagrass turf. In 1999/2000, single applications of trifloxysulfuron-sodium at 75 g ai/ha provided at least 10% better torpedograss control than 25 g/ha 7 and 15 wk after initial treatment (WAIT). When evaluated 15 WAIT, sequential applications of trifloxysulfuron-sodium provided 87% control, similar to 84% control observed with quinclorac diclofop-methyl, each applied at 840 g ai/ha. Both treatments controlled torpedograss better than a single trifloxysulfuron-sodium application (61%) in 1999/2000. Torpedograss control was less in 2002/2003 than in 1999/2000 because of high rainfall, which encouraged aggressive torpedograss growth and possible movement of trifloxysulfuron-sodium below its rooting zone. No differences were noted among trifloxysulfuron-sodium rates or number of applications in 2002/2003. Quinclorac diclofop-methyl controlled torpedograss greater than trifloxysulfuron-sodium 15 WAIT in 2002/2003, but neither treatment provided greater than 45% control. These results suggest that trifloxysulfuron-sodium controls torpedograss when rainfall is not excessive.

Nomenclature: Bermudagrass, Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davey ‘Tifway’; torpedograss, Panicum repens L. #³ PANRE.

Additional index words: Application rate, application frequency.

Abbreviations: WAIT, weeks after initial treatment.

Small broomrape is an annual holoparasitic weed that was recently discovered in red clover production fields in Oregon. Imidazolinone herbicides such as imazamox control small broomrape; however, the mechanism of uptake by the parasite is largely unknown. Studies were conducted to determine the imazamox route of uptake by small broomrape in red clover, and to determine the potential for imazamox to be exuded from red clover and the subsequent effect on small broomrape. Small broomrape control was best at 90% when imazamox was foliar-applied, and worst at 42% or less when imazamox was soil-applied. The presence of activated charcoal to adsorb imazamox at the soil surface did not affect efficacy of broadcast foliar treatment. Small broomrape control was also evaluated when a foliar-treated red clover plant was grown in the same pot as a nontreated, parasitized red clover plant that was bagged during herbicide application. Activated charcoal was spread on the soil surface to adsorb imazamox, thus limiting herbicide uptake routes to the foliage of one of two red clover plants in the pot. Small broomrape attachment decreased on nontreated red clover when the other red clover plant in the pot was treated, suggesting roots exuded the herbicide or an active metabolite.

Nomenclature: Imazamox; small broomrape, Orobanche minor J. E. Smith. # ORAMI; red clover, Trifolium pratense L. # TRFPR.

Additional index words: Parasitic plant, imazamox.

Abbreviations: DAT, days after treatment.

Eclipta is a seed-borne summer annual that is problematic in the production of container-grown landscape plants. Halosulfuron at 70 g/ha is registered as a directed application to landscape areas but not to container-grown landscape plants. Halosulfuron was applied preemergence (PRE) to seeded eclipta and postemergence (POST) to progressively older eclipta seedlings at rates ranging from 0.18 to 100 g/ha. For halosulfuron PRE treatments, eclipta control was determined from the foliage weight of surviving seedlings. For halosulfuron POST treatments, control was determined from the weight of foliage regrowth following the removal of the treated foliage 2 wk after treatment. Nonlinear regression and log-logistic analysis indicated that the rate required for 90% control (I₉₀) for halosulfuron PRE was 45 g/ha. For halosulfuron POST, the I₉₀ was 60 g/ha for plants having five or fewer true leaves and 98 g/ha for plants that had lateral branching from the basal crown. Analysis estimated the I₉₀ for flowering-sized eclipta exceeded 300 g/ha. Selective placement studies revealed that the phytotoxicity resulting from POST treatments occurs by foliar and root uptake, with foliar exposure having greater activity. For POST treatments that were limited to foliage-only contact, a split application increased control up to 25% compared with a single application of the same total dosage. However, control remained inadequate because the rate required for 75% control (I₇₅) was 157 and 121 g/ha for single and split applications, respectively. Halosulfuron sorption by a pine bark–based rooting substrate, as used in container production, was 96% of the amount applied. The propensity for surface-applied halosulfuron to be leached in this substrate was evaluated by eclipta bioassay. After 2 wk, with 23 cm of cumulative irrigation and rainfall, halosulfuron was detected 12 cm below the substrate surface. The propensity for substrate-adsorbed halosulfuron to return to the water phase may also contribute to PRE activity for eclipta control.

Nomenclature: Halosulfuron; eclipta, Eclipta prostrata L., #³ ECLAL.

Additional index words: Herbicide sorption, log-logistic analysis, organic rooting substrates.

Abbreviations: I_x, x% growth inhibition; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

Experiments were conducted in Florida in 2000 through 2003 to evaluate weed management systems in single- and twin-row peanut utilizing either conventional or strip tillage. Diclosulam or flumioxazin preemergence (PRE) or 2,4-DB or imazapic mid-postemergence (MPOST) or late-postemergence (LPOST) was needed for greater than 95% common cocklebur control in conventional- and strip-tillage peanut. In both tillage systems, paraquat bentazon early-postemergence (EPOST) followed by (fb) 2,4-DB or imazapic MPOST, 2,4-DB or chlorimuron LPOST, or both was required for more than 80% late-season control of Florida beggarweed and control in twin-row was 5 to 10 percentage points above that observed with single-row peanut. Paraquat bentazon EPOST preceded by a diclosulam or flumioxazin PRE or fb MPOST or LPOST applications provided 80% or greater control of ivyleaf morningglory, and no differences were observed between peanut planting pattern. Paraquat bentazon EPOST fb imazapic MPOST was the only treatment that provided 90% or greater late-season sicklepod control across all years and tillage methods, and, regardless of tillage, sicklepod control was 7 percentage points better in twin- than single-row peanut. Treatments that contained diclosulam or flumioxazin PRE and paraquat bentazon EPOST fb a MPOST or LPOST herbicide application increased peanut yield compared to nontreated in conventional- and strip-tillage peanut. Averaged over all herbicide treatments, years, and tillage methods, peanut seeded in twin rows yielded 300 kg/ha more than in single rows.

Nomenclature: 2,4-DB; bentazon; diclosulam; chlorimuron; flumioxazin; imazapic; imazethapyr; paraquat; pyridate; common cocklebur, Xanthium strumarium L. #³ XANST; Florida beggarweed, Desmodium tortuosum (Sw.) DC. # DEDTO; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq.; sicklepod, Senna obtusifolia L. # CASOB; peanut, Arachis hypogaea L. ‘Georgia Green’ and ‘C-99R’.

Additional index words: Narrow-row; double-row; tillage.

Abbreviations: EPOST, early-postemergence; fb, followed by; LPOST, late-postemergence; MPOST, mid-postemergence; POST, postemergence; PRE, preemergence; TSWV, tomato spotted wilt tospovirus; WAP, weeks after planting; WAT, weeks after treatment.

Experiments were conducted in Florida from 1998 through 2000 to evaluate trifloxysulfuron-sodium applied POST for weed control in cotton. The addition of 0.25% (v/v) nonionic surfactant (NIS) to trifloxysulfuron-sodium, regardless of rate, increased sicklepod control 10 to 50% 6 and 19 wk after planting (WAP). All trifloxysulfuron-sodium treatments controlled Florida beggarweed and redweed 70 to 100% 6 and 19 WAP. Pitted morningglory was controlled 68 to 100% by trifloxysulfuron-sodium treatments; however, control was higher for treatments that contained 0.25% v/v NIS. Trifloxysulfuron-sodium provided poor control of smallflower morningglory. A sequential application of fluometuron PRE followed by trifloxysulfuron-sodium POST provided better control of smallflower morningglory than trifloxysulfuron-sodium alone 19 WAP. Cotton treated with trifloxysulfuron-sodium yielded higher than the nontreated check and early POST treatments that included 0.25% v/v NIS yielded approximately 20% higher than non-NIS treatments. Trifloxysulfuron-sodium applied POST provided season-long control of Florida beggarweed, pitted morningglory, redweed, and sicklepod with the addition of 0.25% v/v NIS but did not control smallflower morningglory in cotton.

Nomenclature: Fluometuron; trifloxysulfuron-sodium; Florida beggarweed, Desmodium tortuosum (Sw.) DC. #³ DEDTO; pitted morningglory, Ipomoea lacunosa L. # IPOLA; redweed, Melochia corchorifolia # MEOCO; sicklepod, Senna obtusifolia L. # CASOB; smallflower morningglory, Jacquemontia tamnifolia (L.) Griseb. # IAQTA; cotton, Gossypium hirsutum L.

Additional index words: CGA-362622, adjuvant, timing.

Abbreviations: ALS, acetolactate synthase; EPOST, early postemergence; fb, followed by; NIS, nonionic surfactant; WAP, wk after planting; WAT, wk after treatment.

Experiments were conducted from 1998 to 2000 at Rocky Mount, NC, in weed-free environments to determine soybean tolerance to preplant (PP) applications of trifloxysulfuron and the potential for trifloxysulfuron applied preemergence (PRE) and postemergence (POST) to cotton to injure soybean grown in rotation the following year. Trifloxysulfuron at 3.75 and 7.5 g ai/ha applied PP 2 wk before seeding injured conventional soybean less than 5%, whereas no injury was observed when seeding was delayed 4 or 6 wk after PP treatment. No injury to sulfonylurea-resistant soybean (SR) was observed for any treatment. Soybean yields were not influenced by trifloxysulfuron treatment. Cotton injury was 7% or less with trifloxysulfuron applied PRE or POST at 3.75 and 7.5 g/ha. Trifloxysulfuron at 15 g/ha PRE or POST injured cotton a maximum of 14 to 18%. Trifloxysulfuron did not reduce cotton lint yields regardless of method or rate of application. Both conventional and SR soybean were not injured nor were yields influenced by trifloxysulfuron applied PRE or POST the previous year to cotton.

Nomenclature: Trifloxysulfuron; cotton, Gossypium hirsutum L.; soybean, Glycine max (L.) Merr.

Additional index words: Carryover, crop injury, sulfonylurea herbicide.

Abbreviations: ALS, acetolactate synthase; LPOST, late postemergence; POST, postemergence; PP, preplant; PRE, preemergence; SR, sulfonylurea-resistant.

Greenhouse research was conducted to evaluate shoot and root growth response of imidazolinone-tolerant (IT) rice cultivars to imazethapyr applied postemergence at various rates and application timings. Imazethapyr was applied at 70, 140, and 280 g ai/ha to IT cultivars ‘CL 121’ and ‘CL 161’ in the one- to two-leaf and three- to four-leaf growth stages. Imazethapyr applied to one- to two-leaf or three- to four-leaf rice at 70, 140, and 280 g/ha was more injurious to CL 121 than to CL 161. At 3 wk after treatment (WAT), CL 121 was injured 23 to 38% regardless of application timing. In contrast, CL 161 was injured no more than 11% at 3 WAT. Shoot:root ratio for CL 161 was not affected by imazethapyr application. For CL 121, shoot:root ratio was lower following imazethapyr at 280 g/ha than at 70 or 140 g/ha. Based on shoot fresh weight following imazethapyr at 70 g/ha, CL 161 was 1.8 times more tolerant than CL 121 at 2 WAT and 1.3 times more tolerant at 3 WAT. The IT rice cultivar CL 161 is inherently more tolerant to imazethapyr than is CL 121 based on visual injury and shoot and root growth.

Nomenclature: Imazethapyr; rice, Oryza sativa L. ‘CL 121’, ‘CL 161’.

Additional index words: Application timing, rice injury, shoot:root ratio.

Abbreviations: ALS, acetolactate synthase; IT, imidazolinone-tolerant; WAT, weeks after treatment.

Two studies were conducted near Bronson, MI, to determine gladiolus tolerance and weed control with flumioxazin and other herbicide treatments. The first study was conducted in 2002, 2003, and 2004 to evaluate weed control and gladiolus injury with flumioxazin and 14 other preemergence treatments. Crop injury over the 3-yr period was less than 6% and was considered commercially acceptable with flumioxazin, linuron, oryzalin, pendimethalin, prometryn, S-metolachlor, and sulfentrazone. Gladiolus stand count, height, and flower count were similar to those of the nontreated control with these treatments. Clomazone, halosulfuron, imazamox, imazapic, mesotrione, oxyfluorfen, rimsulfuron, and trifloxysulfuron resulted in unacceptable crop injury. Of the acceptable treatments, only flumioxazin controlled common ragweed, yellow nutsedge, and foxtail species at least 68%. The second study was conducted in 2003 and 2004. Flumioxazin was evaluated at four rates, in mixtures with S-metolachlor and oryzalin, and in comparison with isoxaben plus oryzalin. Gladiolus injury did not exceed 6%. Common ragweed, annual grass, and yellow nutsedge control were at least 63% with all flumioxazin treatments.

Nomenclature: Clomazone; flumioxazin; halosulfuron; imazamox; imazapic; isoxaben; linuron; mesotrione; oryzalin; oxyfluorfen; pendimethalin; prometryn; rimsulfuron; S-metolachlor; sulfentrazone; trifloxysulfuron; common ragweed, Ambrosia artemisiifolia L. #³ AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; purple robust foxtail, Setaria viridis var. robusta-purpurea Schr. # SETVI; stinkgrass, Eragrostis cilianensis (All.) E. Mosher # ERACN; yellow nutsedge, Cyperus esculentus L. # CYPES; gladiolus, Gladiolus spp.

Additional index words: Crop tolerance, floriculture, herbicide efficacy.

Abbreviation: WAT, weeks after treatment.

Glyphosate-resistant corn was grown in 38- and 76-cm row spacings at two locations in 2001 to examine the effect of weed competition and row spacing on soil moisture. Volumetric soil moisture was measured to a depth of 0.9 m in 18-cm increments. Glyphosate was applied when average weed canopy heights reached 5, 10, 15, 23, and 30 cm. Season-long weed interference reduced soil moisture compared with the weed free controls. At Clarksville, MI, where common lambsquarters was the dominant weed species, weed interference reduced soil moisture in the 0- to 18-cm soil depth from late June through early August and at the 54- to 72- and 72- to 90-cm depths from mid-July through the end of the season. At East Lansing, MI, where giant foxtail was the dominant weed species, weed interference reduced soil moisture at the 18- to 36-, 36- to 54-, and 54- to 72-cm soil depths from mid-June to the end of the season. Season-long weed competition reduced yields more than 90% at each location. Weeds that emerged after the 5-cm glyphosate timing reduced soil moisture and grain yield at both locations. Delaying glyphosate applications until weeds reached 23 cm or more in height reduced corn yield at both locations and soil moisture at East Lansing. Grain yields in the 10- and 15-cm glyphosate-timing treatments were equal to the weed-free corn, even though soil moisture was less during pollination and grain fill. Row spacing did not affect grain yield but did affect soil moisture. Soil moisture was greater in the 76-cm row spacing, suggesting that corn in the 38-cm row spacing may have been able to access soil moisture more effectively.

Nomenclature: Glyphosate; common lambsquarters, Chenopodium album L. #³ CHEAL; giant foxtail, Setaria faberi Herrm. # SETFA; corn, Zea mays L.

Additional index words: Narrow-row corn, glyphosate-resistant, weed interference, weed competition, time domain reflectometry, soil water.

Abbreviations: DAP, days after planting; FC, field capacity; PRE, preemergence; PWP, permanent wilting point.

In an effort to find safe natural products to function in traditional agricultural chemical roles, short-chain fatty acids were evaluated as desiccants for dry beans. Desiccation was evaluated in greenhouse studies on three dry bean cultivars: ‘Montcalm’ kidney, ‘Midnight’ black turtle, and ‘Vista’ navy bean. Caprylic (C8) and pelargonic acid (C9) were the most effective in the C2 through C10 range. Effective emulsifiers with C8 were Henkel Emsorb 6900 and Henkel Emsorb 6915. Organosilicone, saponified, methylated, and ethylated seed oil activator adjuvants enhanced the efficacy of the caprylic acid. C8 was also phytotoxic to velvetleaf, giant foxtail, and common lambsquarters; esters of C6, C8, and C10 fatty acids were comparatively less effective than C8.

Nomenclature: Common lambsquarters, Chenopodium album L. #³ CHEAL; giant foxtail, Setaria faberi Herrm. #SETFA; velvetleaf, Abutilon theophrasti Medic. #ABUTH; dry beans, Phaseolus vulgaris L.

Additional index words: Caprylic acid, adjuvants, emulsifiers.

Abbreviations: AMS, ammonium sulfate; C2 to C10, carbon chains of 2 through 10; DAT, days after treatment; HFCS, high-fructose corn syrup.

Growers from three counties in Virginia have recently experienced difficulty controlling shattercane in corn with acetolactate synthase (ALS)–inhibiting herbicides. Seed was collected from these locations and from a susceptible biotype and tested for resistance to imazethapyr, imazapyr, and nicosulfuron in greenhouse trials. Seedlings from these locations were also treated with glufosinate and glyphosate. Greenhouse experiments indicated that one of the four shattercane biotypes was resistant to ALS-inhibiting herbicides. Effective control of the resistant biotype was possible with glufosinate or glyphosate. Field experiments were conducted in 2003 and 2004 to determine the most effective herbicide program utilizing herbicide-tolerant/-resistant corn hybrids for the control of shattercane. Early postemergence (EP) and late postemergence (LP) applications of imazethapyr plus imazapyr or EP nicosulfuron did not control shattercane, and yield from the imidazolinone-tolerant (IT) hybrid was equivalent between these treatments and was equivalent to yield from the weedy control (WC). At 23 wk after planting (WAP), EP applications of glyphosate controlled shattercane 71 and 75% compared to only 21 and 66% with EP applications of glufosinate in 2003 and 2004, respectively. In both years, LP applications of glufosinate or glyphosate controlled shattercane better than did EP applications of glufosinate or glyphosate. Treatment timing with respect to corn yield within either the glufosinate-resistant (LL) or glyphosate-resistant (RR) corn hybrid was critical. EP treatments of glufosinate or glyphosate resulted in yields that were equivalent to yield from the weed-free control (WFC) of each hybrid. LP treatments of glufosinate or glyphosate, however, resulted in yields that were equivalent to only 90 and 91% of yield from the WFC of each hybrid, respectively.

Nomenclature: Glyphosate; glufosinate; imazapyr; imazethapyr; nicosulfuron; shattercane, Sorghum bicolor (L.) Moench. #³ SORVU; corn, Zea mays (L.) # ZEAMX.

Additional index words: Herbicide-resistance management.

Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); AMS, ammonium sulfate; EP, early postemergence; IT, imidazolinone-tolerant; LL, glufosinate-resistant; LP, late postemergence; POST, postemergence; PRE, preemergence; RR, glyphosate-resistant; WAP, weeks after planting; WC, weedy control; WFC, weed-free control.

Herbicide evaluation trials are typically conducted with the objective of rating herbicide efficacy and assessing crop yield loss. There is little if any attempt to quantify the economic risk associated with each treatment. The objective of this research was to use second-degree stochastic dominance to evaluate the economic stability of corn and soybean weed management systems between two contrasting environments. Weed management systems were evaluated in small-plot replicated trials over a 3-yr time period at two locations in southern Minnesota. One location (Waseca) had a slightly cooler and wetter environment than the second location (Lamberton). The Waseca location also had higher weed density and greater weed species diversity. Adjusted returns from weed management were calculated for each system by measuring economic returns, as determined by deducting weed management costs from the product of crop price and grain yield. Stochastic dominance is a technique that considers the entire distribution of net returns from weed management and compares these cumulative distributions as a basis for analyzing risk. Climate, soils, and weed diversity dictated differences in risk efficiency and effectiveness of the various weed management systems evaluated between the Waseca and Lamberton sites. Stochastic dominance testing is a useful tool for understanding long-term risk across environments. Results can be used to develop effective long-term weed management systems that minimize risk while maximizing profit potential.

Nomenclature: Corn, Zea mays L.; soybean, Glycine max (L.) Merr.

Additional index words: Risk efficiency, net returns.

Abbreviations: ALS, acetolactate synthase; GDU, growing degree units; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; SSD, second-degree stochastic dominance.

Persian darnel control options are limited and unmanaged populations can cause substantial crop yield loss. Integrating crop diversification and higher crop seeding rates into a cropping system might improve Persian darnel management. Field experiments were conducted to determine the effect of different crops and increased crop seeding rates on Persian darnel fecundity. Persian darnel produced up to 2,800 seeds per plant and 53,000 seeds/m² when grown without competition. Increasing crop density reduced Persian darnel tillers per plant, seed weight, and fecundity. Increasing crop density reduced Persian darnel fecundity 0.4 to 0.2% per spring wheat plant, 0.6 to 0.1% per canola plant, and 16 to 8% per sunflower plant. Persian darnel fecundity was impacted the greatest by reduced weed seedling establishment, which was caused by crop competition and seeding sunflower late in the spring preceded by a nonselective herbicide application. Results indicated delaying the seeding of spring crops or including a late-seeded warm season crop, like sunflower or safflower, in the cropping system is an effective weed management tool for reducing Persian darnel fecundity.

Nomenclature: Glyphosate; Persian darnel, Lolium persicum Boiss. & Hoh. #³ LOLPS; canola, Brassica napus Koch.; spring wheat, Triticum aestivum L.; sunflower, Helianthus annuus L.

Additional index words: Fecundity, preplant herbicide, seedling establishment, seeding date, seeding rate, stale seedbed, weed interference, yield components.

Experiments were conducted to investigate the effects of depth and duration of burial on seasonal germination, primary and secondary dormancy, viability, and seedling emergence of ivyleaf speedwell (Veronica hederifolia L.) seeds. The seeds were buried at 0, 5, 10, or 20 cm and retrieved from the field at monthly intervals. The exhumed seeds were germinated at 5 C. In the second experiment, seeds were stored in the laboratory after harvest and tested for germination at monthly intervals. In each experiment, nongerminated seeds were treated with triphenyltetrazolium chloride at monthly intervals to test their viability. The effects of stratification and burial depth on seedling emergence were observed for 1 yr. The seeds exhumed from the soil were dormant at the beginning of the experiment and exhibited dormancy/nondormancy/conditional dormancy cycling throughout the experiment. Depth of burial and time affected seed germination. Seeds retrieved from the soil surface germinated well initially, but germination decreased as depth of burial increased. In the dry storage experiment, seeds had a high level of primary dormancy, and viability decreased over time. Seedling emergence decreased when depth of burial increased. Seedlings emerged nonuniformly throughout the year and demonstrated typical winter annual characteristics.

Nomenclature: Veronica hederifolia, Ivyleaf speedwell, #³ VERHE

Additional index words: Primary/secondary dormancy, weed management, wheat, germination ecology.

Abbreviations: TTC, triphenyltetrazolium chloride.

In the Southern Great Plains, producers of hard red winter wheat seek sustainable methods for controlling cheat and improving economic returns. Experiments were conducted at two sites in north-central Oklahoma to determine the effect of cheat management programs, with various weed control strategies, on cheat densities and total net returns. The cheat management programs, initiated following harvest of winter wheat, included conventionally tilled, double-crop grain sorghum (Sorghum bicolor L.) followed by soybean (Glycine max L.); and continuous winter wheat. Rotating out of winter wheat for one growing season increased yield of succedent wheat up to 32% and 42% at Billings and Ponca City, respectively. Dockage due to cheat in the succedent wheat was reduced up to 78% and 87% by rotating out of winter wheat for one growing season at Billings and Ponca City, respectively. Cheat management programs including a crop rotation with herbicides applied to the grain sorghum, except for an application of atrazine metolachlor at Ponca City, improved total net returns over the nontreated continuous wheat option. Cheat panicles in the succedent wheat were reduced up to 87% by rotation out of winter wheat for one growing season.

Nomenclature: Atrazine metolachlor; cheat, Bromus secalinus L. #³ BROSE; grain sorghum, Sorghum bicolor (L.) Moench ‘Pioneer 8500’, ‘Dekalb DK28E’; soybean, Glycine max (L.) Merr., ‘Dekalb CX367RR’; wheat, Triticum aestivum L. ‘2137’.

Additional index words: Economics, net returns, Oklahoma.

Abbreviations: Fb, followed by; NSD, no significant difference; OM, organic matter.

Experiments were conducted between 2002 and 2004 at multiple locations in Florida to determine the efficacy of aminopyralid and other herbicides on tropical soda apple (TSA) control. Aminopyralid applied at rates ≥0.08 kg ai/ha consistently provided >96% TSA control up to 335 d after treatment (DAT), while applications <0.06 kg/ha were less effective as well as inconsistent. Control of TSA with aminopyralid was often not statistically different from control with triclopyr, picloram, or dicamba. However, these responses were likely due to the variability in TSA control by triclopyr, picloram, or dicamba across several locations. For example, the standard error of the mean for TSA control with picloram at 335 DAT was 8, compared to 1 for aminopyralid. Herbicides were applied in April, January, and June, but time of year did not affect the efficacy of aminopyralid. Aminopyralid possesses soil residual activity and controlled 98% of germinating seedlings at 75 DAT, compared to 0% control for triclopyr or 2,4-D dicamba. Therefore, aminopyralid controlled TSA from foliar applications and soil residual activity more consistently than any other herbicide evaluated in these experiments.

Nomenclature: Aminopyralid, 4-amino-3,6-dichloropyridine-2-carboxylic acid; tropical soda apple, Solanum viarum Dunal. #³ SOLVI.

Additional index words: Preemergence control.

Abbreviations: DAT, days after treatment; TSA, tropical soda apple.

Corn inbreds are often more sensitive to herbicides than hybrids. Field experiments were conducted with three corn inbreds to (1) evaluate inbred sensitivity to the acetamide herbicides acetochlor, dimethenamid, flufenacet, and metolachlor, (2) compare the effects of various crop safeners in combination with acetochlor and metolachlor, and (3) measure the effect of herbicide microencapsulation on acetochlor injury. Herbicides were applied preemergence at the registered rate and at two, three, or four times the registered rate in corn. Injury ratings, plant population, and the percentage of plants showing acetamide injury symptoms were used to measure herbicide effect. The inbreds ‘Mo17’ and ‘Great Lakes 15’ (GL15) were sensitive to acetamide injury. Reductions in plant population and increases in the injury rating and the percentage of injured plants were caused by acetochlor, dimethenamid, flufenacet, metolachlor, and flufenacet metribuzin when applied at three times the registered rate. The inbred ‘B73’ was not injured. The safeners benoxacor and dichlormid reduced injury caused by metolachlor. The percentage of plants injured by metolachlor 15 days after treatment (DAT) was lower when benoxacor was the safener compared to dichlormid. By 28 DAT, plants treated with safeners recovered from injury, and there were no differences between the treatments. The safeners dichlormid and furilazole reduced, but did not always eliminate, injury caused by acetochlor applied at three times the registered rate. Microencapsulation of acetochlor reduced injury to GL15. When the safeners dichlormid or furilazole were included in an acetochlor formulation, microencapsulation did not further reduce corn injury.

Nomenclature: Acetochlor; benoxacor; dichlormid; dimethenamid; flufenacet; furilazole; metolachlor; metribuzin; corn, Zea mays L.

Additional index words: Controlled release formulation, herbicide antidote, microencapsulation, safener.

Abbreviations: DAT, days after treatment; GL15, ‘Great Lakes 15’.

Putatively resistant (PR) and putatively susceptible (PS) common waterhemp populations were grown in the greenhouse and sprayed at the three- to four-leaf stage with glyphosate (0.63 kg ae/ha). Surviving plants from PR populations and randomly selected plants from PS populations were clonally propagated and the clones were sprayed with 0.1 to 10.0 kg/ha glyphosate. The glyphosate rates required to reduce growth by 50% (GR₅₀) among the clones were relatively similar, but the concentration required to reduce growth by 90% (GR₉₀) ranged from 1.5 to 16.3 kg/ha. The concentration of glyphosate required to kill 90% of plants (LD₉₀) ranged from 2.3 kg/ha to over 10.0 kg/ ha. This range of responses to glyphosate in common waterhemp clones from different parts of the Midwestern United States indicates a risk of evolution of resistance in common waterhemp populations that are repeatedly selected by applications of glyphosate in the field.

Nomenclature: Glyphosate; common waterhemp, Amaranthus rudis Sauer #³ AMATA.

Additional index words: Dose response, herbicide resistance, herbicide tolerance.

Abbreviations: GR₅₀, the concentration of glyphosate required to reduce dry weights by 50%; GR₉₀, the concentration of glyphosate required to reduce dry weights by 90%; LD₉₀, the concentration of glyphosate required to kill 90% of plants; PR, putatively resistant; PS, putatively susceptible.

Spring wheat competitive ability has recently been demonstrated to co-vary with seed size. The objective of this study was to determine if spring wheat seed size would influence the effects of variable tralkoxydim rates on wild oat control, wheat yield, and economic returns. The factorial treatment arrangement consisted of three spring wheat seed size classes and five tralkoxydim rates. Wild oat density, panicles, and biomass decreased as spring wheat seed size and tralkoxydim rate increased, with the combined effect being additive. Wild oat variables decreased in a log-logistic manner as tralkoxydim rate increased during both years. However, tralkoxydim was less effective in 2000 than 2002, as indicated by the higher dosage required to reduce the wild oat variables by 50% (greater I₅₀ values). In contrast, the effect of large seeded wheat in suppressing wild oat was more consistently expressed, with wild oat variables decreasing linearly as seed size increased. Wheat yield and economic returns increased exponentially as tralkoxydim rate increased. At the same time, wheat yield and economic returns were greater for wheat plants derived from large seed compared to those derived from small seed. Averaged over all other factors, adjusted gross returns of 578, 657, and 703 $/ha were realized for the small, medium, and large seed size classes, respectively. The combined use of large seeded wheat plus tralkoxydim applications provided greater wild oat control than did either single tactic. The use of large seeded wheat had a stabilizing effect that increased the consistency and durability of the weed management system while simultaneously improving economic returns.

Nomenclature: Tralkoxydim; wild oat, Avena fatua L. #³ AVEFA; wheat, Triticum aestivum L. ‘McNeal’.

Additional index words: Seed size, dose response, integrated weed management.

Abbreviations: AGR, adjusted gross return; TKW, thousand kernel weights.

Decision support systems (DSSs) have been developed to assist producers and consultants with weed management decisions. WeedSOFT is a DSS currently used in several states in the north-central region of the United States. Accurate estimates of crop yield loss due to weed interference are required for cost-effective weed management recommendations. WeedSOFT uses competitive indices (CIs) to predict crop yield loss under multiple weed species, weed densities, and relative times of weed emergence. Performance of several WeedSOFT versions to predict soybean yield loss from weed competition was evaluated using CI values in WeedSOFT version 9.0 compared to new CI values calculated from weed dry matter, weed volume, and soybean yield loss in two soybean row spacings (19 and 76 cm) and two relative weed emergence times (at soybean emergence and first trifoliate leaf stage). Overall, new CI values improved predictions of soybean yield loss by as high as 63%. It was especially true with using new CI values based on yield loss compared to those based on weed dry matter or weed volume. However, there were inconsistencies in predictions for most weed species, suggesting that additional modifications are needed to further improve soybean yield loss predictions.

Nomenclature: Soybean, Glycine max (L.) Merr.

Additional index words: Crop modeling, competition, decision support systems, simulation, Abutilon theophrasti, Amaranthus retroflexus, Amaranthus rudis, Ambrosia trifida, Echinochloa crus-galli, Helianthus annuus, Setaria faberi, Setaria glauca, Xanthium strumarium, ABUTH, AMARE, AMATA, AMBTR, ECHCG, HELAN, SETFA, SETLU, XANST.

Abbreviations: AE, average error; ACI, adjusted competitive index; CI, competitive index; DM, WeedSOFT version based on weed dry matter; DSS, decision support systems; RCBD, randomized complete block design; TCL, total competitive load; TDM, total dry matter; V1, soybean first trifoliate leaf stage; VE, soybean emergence; VP, soybean planting; VOL, WeedSOFT version based on weed volume; WS, WeedSOFT version 9.0; YL, WeedSOFT version based on yield loss.

Phenoxy herbicides are frequently used to control volunteer canola populations. However, there have been claims that poor control could be due to cold acclimation of canola plants in the spring. The objective of this study was to determine whether cold acclimation or growth stage affected the response of canola volunteers to herbicides. In a growth room experiment, canola plants were prehardened and cold acclimated or were grown at 20/12 C and treated with one of six 2,4-D doses. Cold acclimation as achieved by this experiment affected upper and lower asymptotes of the dose–response curve but not the herbicide dose required to reduce canola weight by 50% relative to the nontreated control (GR₅₀), indicating limited cold-related effects on canola tolerance to 2,4-D. Field experiments, conducted in the provinces of Québec and Saskatchewan, examined the effects of canola growth stage on the efficacy of 2,4-D, MCPA, and carfentrazone. Comparisons of the estimates from the dose–response curves confirmed that herbicide efficacy was consistently greater when canola plants were treated at an early growth stage, regardless of cultivar or herbicide used. The GR₅₀ estimates for canola plants treated at a later growth stage exceeded the recommended rates. Some canola plants grown as volunteers in a wheat crop survived 2,4-D or MCPA treatments at 0.5× and 1× rates and produced up to 148 seeds/m². Efficient control of canola volunteers will be obtained when plants are sprayed at an early growth stage, but near-total control will be highly desirable in order to restrict seedbank buildup, particularly when dealing with canola cultivars with different herbicide-resistant traits.

Nomenclature: Canola, Brassica napus L.; wheat, Triticum aestivum L.

Additional index words: Phenoxy herbicides, 2,4-D, MCPA, carfentrazone, Brassica napus, volunteer canola.

Abbreviations: CA, cold acclimated; DAE, days after emergence; GR₅₀, herbicide dose required to reduce canola weight by 50% relative to the nontreated control; NA, nonacclimated; PAR, photosynthetic photon flux density.

Herbicide-resistant cultivars account for over 90% of the canola grown in western Canada and cultivars resistant to glyphosate dominate the market. Field experiments were conducted at three locations in Alberta to compare the glyphosate system with more traditional herbicide regimes. Glyphosate applied before seeding in spring resulted in better weed control, lower dockage, and higher canola yield and net return than 2,4-D applied in the fall. Glyphosate applied once (two- to four-leaf canola) or twice (two- to four-leaf followed by five- to six-leaf canola) in-crop provided similar weed control, dockage, and canola yield as ethalfluralin applied PRE in the fall followed by an in-crop mixture of sethoxydim, ethametsulfuron, and clopyralid; and superior weed control and canola yield and lower dockage than ethalfluralin alone or an in-crop mixture of sethoxydim and ethametsulfuron. The in-crop glyphosate applications resulted in higher net revenues than the other treatments. There was little or no advantage to applying glyphosate twice compared with once in-crop. The amount of active ingredient entering the environment varied with the herbicide regime but was lower with the glyphosate system than with most of the traditional regimes, especially when glyphosate was applied only once in-crop.

Nomenclature: Clopyralid; 2,4-D; ethalfluralin; ethametsulfuron; glyphosate; sethoxydim; canola, Brassica napus L. ‘LG 3235’ and ‘DKL 3235’.

Additional index words: Conventional canola; dockage; economics; environmental impact; GMO; herbicide-resistant canola; weed biomass.

Reduced-rate zone herbicide application (ZHA) consists of banding reduced herbicide rates between crop rows (≤ full broadcast registered rate, 1×) and banding much reduced herbicide rates over crop rows (≪ 1×). The objective of this research was to compare the mechanically complicated dual-boom ZHA sprayer with a much simpler, single-boom ZHA sprayer for controlling giant foxtail and common waterhemp in field corn in 2003 and 2004 in Missouri. The dual-boom ZHA sprayer employed two different herbicide solutions, which were propelled through two booms on separate sprayer systems to apply different herbicide rates over in-row and between-row areas while maintaining similar carrier volumes and coverage through two booms. In contrast, the single-boom ZHA sprayer is a mechanically simpler system in which both herbicide rates and carrier volumes were varied across one boom over in-row (IR) and between-row (BR) areas. In single-boom ZHA, two different nozzle tips were alternated on one boom over in-row and between-row areas, the number of nozzles per boom was doubled, and the distance between nozzles was halved compared with a conventional sprayer boom. In a 2-yr study, these different ZHA sprayers were used to apply preemergence atrazine S-metolachlor between and over crop rows at various reduced rates (1× = 2,240 1,750 g ai/ha, respectively). Among all single- and dual-boom ZHA sprayer treatments and the weed-free checks, corn yields and in-row total weed cover were statistically indistinguishable for both years and for between-row total weed cover in 1 of 2 yr. In both years, a single-boom ZHA system prevented yield loss from competing weeds as effectively as the dual-boom ZHA system. The new single-boom ZHA system is a mechanically simple, inexpensive, generic alternative for reducing herbicide rates and lowering input costs.

Nomenclature: Atrazine; S-metolachlor; common waterhemp, Amaranthus rudis Sauer #³ AMATA; giant foxtail, Setaria faberii (L.) Beauv. # SETFA; corn, Zea mays L., ‘Pioneer 33G28’ and ‘Pioneer 34M92’.

Additional index words: Band application, banding, chloroacetamide, reduced rate, triazine, weed.

Abbreviations: BR, between-row; IR, in-row; WC, weed cover; ZHA, zone herbicide application.

Virginia buttonweed control in warm-season turfgrass species requires high application rates and/or repeated applications of herbicides (or both) with an auxin-type mode of action. These treatments often lead to unacceptable turfgrass injury. Diflufenzopyr functions as a synergist with auxin-type herbicides, and it has been suggested that it may do the same when combined with pyridine herbicides such as fluroxypyr. The objective of this field and laboratory research was to determine whether Virginia buttonweed control could be improved with admixtures of fluroxypyr and diflufenzopyr without unacceptable turf injury. Treatments consisted of fluroxypyr applied alone at 140 and 280 g ae/ha, diflufenzopyr alone at 70 and 140 g/ha, and all possible two-way admixtures. Treatments were applied to a hybrid bluegrass ‘Thermal blue’ infested with Virginia buttonweed. Sod of centipedegrass ‘common’, hybrid bermudagrass ‘Tifway’, hybrid zoysiagrass ‘Emerald’, and St. Augustinegrass ‘Raleigh’, which had been previously established in pots, were treated simultaneously and returned to a greenhouse. Fluroxypyr plus diflufenzopyr at 280 and 70 g/ha, respectively, controlled Virginia buttonweed nearly 40% more than fluroxypyr alone. Turfgrass injury was species-dependent, and was generally either equivalent to or less than that obtained with fluroxypyr alone. Radiotracer studies established that, depending upon the turfgrass species, fluroxypyr absorption was either not influenced or reduced by the addition of diflufenzopyr. Neither root nor foliar absorption of fluroxypyr by Virginia buttonweed was influenced by diflufenzopyr. Translocation of foliar-absorbed fluroxypyr was reduced, but translocation of root-absorbed fluroxypyr was increased by diflufenzopyr. The diflufenzopyr-induced synergism may indicate that a significant portion of the applied fluroxypyr was absorbed by roots or by other subsoil tissues, or both.

Nomenclature: Diflufenzopyr 2-(1-[([3,5-difluorophenylamino]carbonyl)-hydrazono]ethyl-3-pyridinecarboxylic acid; fluroxypyr; Virginia buttonweed, Diodia virginiana L. #³ DIQVI; hybrid bermudagrass, Cynodon dactylon Burtt-Davey X C. transvaalensis L. Pers. ‘Tifway’; centipedegrass, Eremochloa ophiuroides (Munro.) Hack. ‘Common’; hybrid zoysiagrass, Zoysia japonica Steud. X Z. tenuifolia Willd. Ex Trin ‘Emerald’; St. Augustinegrass, Stenotaphrum secundatum (Walt.) Kuntze. ‘Raleigh’; hybrid bluegrass, Poa pratensis X P. arachnifera Torr. ‘Thermal Blue’.

Additional index words: Auxin herbicides, ¹⁴C-fluroxypyr, herbicide translocation, herbicide synergist, pyridine herbicide, warm-season turfgrass.

Abbreviations: DAT, days after treatment; LSS, liquid scintillation spectrometry; WAT, weeks after treatment.

A laboratory study was conducted in 2003 at Louisiana State University in Baton Rouge, LA, to evaluate the interactive effects of bensulfuron or halosulfuron on clomazone in terms of rice foliar bleaching and chlorophyll content. Clomazone was applied alone at 0 and 1.227 μg/ml (672 g/ha) or in combination with bensulfuron at 0.0276 μg ai/ml (42 g ai/ha) or halosulfuron at 0.0345 μg ai/ml (53 g ai/ha) in a hydroponic solution. Bensulfuron and halosulfuron were also applied alone. Rice cultivars evaluated included short-grain ‘Pirogue’, medium-grain ‘Bengal’, and long-grain ‘Cocodrie’. Bensulfuron and halosulfuron, applied in a hydroponic solution, safened medium-grain Bengal, long-grain Cocodrie, and short-grain Pirogue at 21 d after treatment (DAT) from foliar bleaching caused by clomazone. Chlorophyll a and b and total chlorophyll content of all three rice cultivars decreased when treated with clomazone treatment. Only chlorophyll content of Cocodrie was increased by the addition of bensulfuron and halosulfuron compared with a single application of clomazone.

Nomenclature: Clomazone; bensulfuron; halosulfuron; rice, Oryza sativa L., ‘Cocodrie’, ‘Bengal’, and ‘Pirogue’.

Additional index words: antagonism, safening, synergism.

Abbreviations: ALS, acetolactate synthase; DAT, days after treatment.

Field studies were conducted in 2002 and 2003 in New Jersey to determine the length of time after a bispyribac-sodium application at which creeping bentgrass, Kentucky bluegrass, and perennial ryegrass can be safely reseeded. Bispyribac at 148 or 296 g ai/ha was applied 6, 4, 2, or 1 week before seeding (WBS). Bispyribac at 148 g/ha applied 1 WBS reduced ground cover of creeping bentgrass and Kentucky bluegrass at 3 weeks after seeding (WAS) by 30 and 42% as compared to the nontreated check, respectively. Reductions in Kentucky bluegrass and creeping bentgrass ground cover from bispyribac at 296 g/ha applied 1 WBS were evident at 28 WAS, whereas perennial ryegrass recovered from initial reductions in ground cover by this time. Applications made 6 to 2 weeks before seeding did not adversely affect ground cover of any species at any evaluation date as compared to the nontreated check. These studies suggest creeping bentgrass, Kentucky bluegrass, and perennial ryegrass can be safely reseeded 2 weeks after a bispyribac application. However, ground cover may be reduced by bispyribac applied 1 WBS.

Nomenclature: Bispyribac-sodium; creeping bentgrass, Agrostis stolonifera L. ‘L-93’; Kentucky bluegrass, Poa pratensis L. ‘Kenblue’; perennial ryegrass, Lolium perenne L. ‘Pizzazz.’

Abbreviations: ALS, acetolactate synthase (EC 2.2.1.6); SE, standard error; WAS, weeks after seeding; WBS, weeks before seeding.

A laboratory bioassay was conducted to describe the effects of cold stratification and solid matrix priming (SMP®) on the germination response of common lambsquarters and Pennsylvania smartweed seeds. Treating seeds of common lambsquarters with a combination of cold stratification and SMP resulted in 78% germination compared with 13% in control seeds. Analogous treatments of Pennsylvania smartweed seeds resulted in 22% germination compared with 1% for control. Improved germination of common lambsquarters and Pennsylvania smartweed seeds suggested that the combination of cold stratification and SMP treatments have potential for improving seed germination in other weed species that exhibit high levels of seed dormancy.

Nomenclature: Common lambsquarters, Chenopodium album L. #³ CHEAL; Pennsylvania smartweed, Polygonum pensylvanicum L. # POLPY.

Additional index words: Seeds, scarification, stratification, sulfuric acid, potassium hydroxide.

Abbreviations: H₂SO₄, sulfuric acid; KOH, potassium hydroxide; SMP, solid matrix priming.

Prescribed burning has primarily been used as a tool for the control of invasive late-season annual broadleaf and grass species, particularly yellow starthistle, medusahead, barb goatgrass, and several bromes. However, timely burning of a few invasive biennial broadleaves (e.g., sweetclover and garlic mustard), perennial grasses (e.g., bluegrasses and smooth brome), and woody species (e.g., brooms and Chinese tallow tree) also has been successful. In many cases, the effectiveness of prescribed burning can be enhanced when incorporated into an integrated vegetation management program. Although there are some excellent examples of successful use of prescribed burning for the control of invasive species, a limited number of species have been evaluated. In addition, few studies have measured the impact of prescribed burning on the long-term changes in plant communities, impacts to endangered plant species, effects on wildlife and insect populations, and alterations in soil biology, including nutrition, mycorrhizae, and hydrology. In this review, we evaluate the current state of knowledge on prescribed burning as a tool for invasive weed management.

Nomenclature: Barb goatgrass, Aegilops triuncialis L. #³ AEGTR; Canada bluegrass, Poa compressa L. # POACO; Chinese tallow tree, Sapium sebiferum (L.) Roxb. # SAQSE; downy brome, Bromus tectorum L. # BROTE; French broom, Genista monspessulana (L.) L. Johnson # TLNMO; garlic mustard, Alliaria petiolata Andrz. # ALAPE; Kentucky bluegrass, Poa pratensis L. # POAPR; medusahead, Taeniatherum caput-medusae (L.) Nevski; red brome, Bromus madritensis L. ssp. rubens (L.) Husnot # BRORU; ripgut brome, Bromus diandrus Roth # BRODI; Scotch broom, Cytisus scoparius (L.) Link # SAOSC; smooth brome, Bromus inermis Leysser # BROIN; sweetclover, Melilotus spp.; yellow starthistle, Centaurea solstitialis L. # CENSO.

Additional index words: Fire, integrated vegetation management, rangelands, wildlands.