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

The impact of delaying soybean [Glycine max (L.) Merr.] planting following the incorporation of a living, green cover crop and using various insecticide management practices on seedcorn maggot [Delia platura (Meigen)] 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 incorporation that occurred in early May. Seedcorn maggots were sampled with adult emergence traps, and subsequent soybean injury to plumules was estimated. The number of days following tillage that soybean was planted had little effect on maggot numbers collected, but injury was lowest 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 were nearing or entering the non-feeding pupal stage at the time of the last planting, resulting in less plant injury. Phorate treatments provided the largest reduction of maggot numbers. Plant injury was least, however, when soybean was protected by an Agrox seed treatment, especially when the seed and the Agrox were mixed in a bucket before use. These reductions were observed at all three planting times, although the percentage reduction from the control differed among the three planting dates. When spring tillage incorporates a green, living organic matter into the soil in the spring, plant injury can be reduced if a grower waits for 2.5-3 weeks after tillage until planting, when approximately 250 thermal units (base of 3.9-degrees-C) are accumulated and the majority of insects are in the pupal stage. If planting is done immediately 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.