Some producers have come to the realization that in the hectic pace of planting their Bt-RW corn that the soil insecticide for the 20 percent refuge was neglected. The good news is that a rescue treatment is possible, the bad news is that it requires another trip to the field.
Liquid insecticides such as Furadan and Lorsban can be applied at postemergence or cultivation-time, according to John Obermeyer, Purdue University Extension entomologist. "Hopefully the refuge is well marked to help locate the unprotected corn," says Obermeyer. "Shortly before or during rootworm egg-hatch, the end of May/early June, drop nozzles should be directed toward the base of the corn plants with the labeled rate of insecticide. Following-up with cultivation, if possible, will incorporate the insecticide and promote the establishment of brace roots. Weather is often a limiting factor in getting postemergence insecticides applied in a timely manner."
Liquid nitrogen can be included with this postemergence application, although Obermeyer warns applicators need to be cautious to keep the spray off the foliage in order to not burn the leaves. "In this day of high fuel prices, it would be tempting to combine the insecticide with a post-applied herbicide," he says. "This is unwise, as broadcasting the insecticide will result in poor rootworm control. Again, the insecticide needs to be concentrated near the base of the plant."