POTENTIAL OF IMAZAQUIN SEED TREATMENT FOR CONTROL OF STRIGA-GESNERIOIDES AND ALECTRA-VOGELII IN COWPEA (VIGNA-UNGUICULATA)

The herbicide imazaquin was tested for efficacy in Striga gesnerioides and Alectra vogelii control when applied as a cowpea (Vigna unguiculata) seed treatment. Four sets of experiments were conducted in the laboratory and screenhouse. Two cowpea cultivars, three geographical isolates of S. gesnerioides from two hosts, and two geographical isolates of A. vogelii from two hosts were used. Preliminary experiments indicated cowpea seed treatments of 5-min duration in aqueous solutions of the ammonium salt of imazaquin, ranging from 1.8 to 7.2 mg a.i./ml, fit our test criteria of 50% germination and observable radicle growth inhibition. Treated cowpea seeds were dried and planted in soil-filled pots infested with 3,000 germinable S. gesnerioides or A. vogelii seeds. All experiments showed imazaquin seed treatments to significantly reduce numbers of attached (emerged and unemerged) parasites. Imazaquin seed treatments resulted in increased total cowpea dry weight in S. gesnerioides-infested pots in all experiments. Increases were significant at P < 0.05 in two experiments. Observations in vitro, combined with screenhouse data, showed apparently normal parasite germination and attachment, indicating postattachment demise of both parasites. Increasing imazaquin rates led to delays in cowpea flowering; and increased soak times, at 3.6 mg a.i./ml and higher concentrations, led to reductions in cowpea seedling emergence. By prolonging seed soak times at an imazaquin concentration of 1.8 mg/ml, good parasite control was obtained. The lower rates at longer soak durations would provide both economical ($2.31 to $3.85 per hectare) control and the flexibility in treatment necessary for implementation on African farms. Field trials on farmer fields are under way to tailor specific seed treatment recommendations.