Broad-spectrum weed control options for pea are limited. Field experiments conducted from 1998 to 2000 evaluated reduced rates of imazethapyr for selective control of grass and broadleaf weed species in pea. Imazethapyr was applied preemergence (PRE) and postemergence (POST) at 20, 40, 60, 80, and 100% of the PRE rate of 75 g ai/ha currently labeled in Ontario. A rate of 45 g/ha or greater was required to maintain consistent control of common lambsquarters and wild mustard when imazethapyr was applied PRE. Green foxtail and redroot pigweed control was excellent at all PRE rates 56 d after treatment. The 75-g/ha rate was required to maintain effective and consistent control of common ragweed. No injury or yield reductions were observed for any of the PRE application rates of imazethapyr. Reduced rates as low as 30 g/ha of imazethapyr applied POST maintained high levels of weed control. Pea tolerance to low rates of imazethapyr applied POST was acceptable except when applied in a year of low rainfall when peas experienced moisture stress.
Nomenclature: Imazethapyr; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; green foxtail, Setaria viridis (L.) Beauv. # SETVI; redroot pigweed, Amaranthus retroflexus L. # AMARE; wild mustard, Sinapsis arvensis L. # SINAR; pea, Pisum sativum L. ‘Bolero’, ‘Sanchos’.
Additional index words: Herbicide efficacy, pea yields, reduced herbicide rates.
Abbreviations: DAT, days after treatment; OCHU, Ontario corn heat units; POST, postemergence; PRE, preemergence.
