INTERACTION OF PLANTING TIMES FOLLOWING THE INCORPORATION OF A LIVING, GREEN COVER CROP AND CONTROL MEASURES ON SEEDCORN MAGGOT POPULATIONSIN SOYBEAN

The impact of delaying soybean [Glycine max (L.) Merr.] planting follo wing the incorporation of a living, green cover crop and using various insecticide management practices on seedcorn maggot [Delia platura (M eigen)] populations was evaluated. Phorate soil insecticide in a 15.8 cm band and Agrox D-L Plus seed treatment [a mixture of diazinon (0.33 % w/w), lindane (15.0% w/w), and captan (14.67% w/w)] were applied at planting immediately after, and 1.5 or 3 weeks after, cover crop incor poration that occurred in early May. Seedcorn maggots were sampled wit h adult emergence traps, and subsequent soybean injury to plumules was estimated. The number of days following tillage that soybean was plan ted had little effect on maggot numbers collected, but injury was lowe st on soybean planted 3.5 weeks after incorporation of the cover crop. Thermal unit accumulations indicated that seedcorn maggot oviposition occurred at the time of tillage, and that the majority of insects wer e nearing or entering the non-feeding pupal stage at the time of the l ast planting, resulting in less plant injury. Phorate treatments provi ded the largest reduction of maggot numbers. Plant injury was least, h owever, when soybean was protected by an Agrox seed treatment, especia lly when the seed and the Agrox were mixed in a bucket before use. The se reductions were observed at all three planting times, although the percentage reduction from the control differed among the three plantin g dates. When spring tillage incorporates a green, living organic matt er into the soil in the spring, plant injury can be reduced if a growe r waits for 2.5-3 weeks after tillage until planting, when approximate ly 250 thermal units (base of 3.9-degrees-C) are accumulated and the m ajority of insects are in the pupal stage. If planting is done immedia tely or shortly after tillage, it is recommended that soybean seed be protected with a seed treatment, preferably one that ensures complete coverage of the seed.