A promising approach for the control of parasitic weeds is herbicide seed priming, which consists of soaking crop seeds in a herbicide solution such that the herbicide is later present in the crop seedling to inhibit growth of attaching parasites. This technique is effective where selectivity exists between crop and parasite; for example, varieties of imidazolinone-resistant maize. However, seed priming has not been reported for sorghum or pearl millet, two crops that are greatly affected by purple witchweed. Research was initiated to evaluate herbicides for potential use as seed priming agents in these crops. Auxin-mimic and acetolactate synthase-inhibitor class herbicides were evaluated; specifically, clopyralid, 2,4-DB, dicamba, picloram, and prosulfuron. For sorghum, immersion of seed in 0.5% (w/v) ae 2,4-DB for 5 min 1 d before planting reduced purple witchweed densities to levels 20 to 50% of nontreated controls. However, this concentration was at the threshold of crop toxicity and reduced sorghum yields in some experiments. None of the herbicides tested consistently reduced purple witchweed on pearl millet. This research illustrates both the potential and limitations of adapting seed priming technology for sorghum and pearl millet.
Nomenclature: clopyralid; 2,4-DB; dicamba; picloram; prosulfuron; purple witchweed, Striga hermonthica (Del.) Benth, #3 STRHE; pearl millet, Pennisetum glaucum L.; sorghum, Sorghum bicolor (L.) Moench.
Additional index words: Herbicide seed treatment, parasitic weed, seed priming.
Abbreviations: ALS, acetolactate synthase; DAP, days after planting.
