Grasshoppers are always worse in dry years. They tend to move from border vegetation or infield weed sources as they dry down (which occurs more readily in dry weather), or from cover crop after herbicide burn down. They will undergo several generations—we find hoppers in all sizes (nymphs and adults) almost any time during the season, especially as we move into late summer/fall. They will eat soybean leaves, but are also capable of feeding on young pods later in the year. Treatment this time of year has to be based on the extent of defoliation. Under normal growing conditions, soybeans are capable of withstanding a lot of defoliation (30-40%) in the vegetative growth stages because they are growing so rapidly constantly putting on new canopy. Of course under these dry conditions, they are standing still, almost. You have to gauge the need for treatment on this tough decision point and it is often a seat-of-the-pants call, as many of them are. If the defoliation is severe and hoppers are abundant, I think you need to consider a treatment. Treating field edges can be effective, especially if hoppers are still moving in from bordering weed sources. If we do not get rain enough to make a decent crop, control efforts and the $ spent will have been wasted—a hard call to make If treatments are made, our limited experience showed that products containing chlorpyrifos (Lorsban 4E at ½ to 1 pt/acre, or Cobalt at 7 to 13 oz/acre) were more effective than pyrethroids. All things considered, I would use the lowest labeled rate. Also, Lorsban 4E is pretty good for controlling twospotted spider mite, which may also be present, or at least a pending threat.

The dry weather has provided the perfect opportunity for spider mite flares. We have reports of infested soybean fields in Charles City County and some in the Suffolk/Southampton County area. Miticide options are limited in soybean to bifenthrin (Capture, Brigade, and others), dimethoate, and Lorsban 4E. Bifenthrin is a pyrethroid so products will provide knock down of adults and nymphs, but not control of eggs. If there are a lot of eggs present at the time of application, they will hatch and could require a second application within 5 days or so of the first. Dimethoate is a foliar systemic but must be absorbed and translocated by the leaf tissues to provide residual action; otherwise, it undergoes rapid photodecomposition from sunlight. This leaf absorption process is greatly reduced in drought-stressed plants that have “shut-down” physiologically. According to Dr. Whalen (Univ. of Del), another important factor that plays a role in the performance of dimethoate is the pH of the water used as the carrier. Many pesticides, especially dimethoate, are subject to breakdown by alkaline hydrolysis. In alkaline water (high pH), dimethoate break down can result in poorer than expected field performance. Dimethoate degradation is also accelerated by the mineral content of the water, especially the presence of iron. If a high pH situation exists, you can lower the alkalinity of the water in the spray tank by adding an acid-based buffer. The buffer must be added to the spray tank first, before the addition of dimethoate. Lorsban 4E is somewhat effective against mites and offers the advantage of also having good activity against grasshoppers and some other pests. The very best control for spider mites is rain. I wish I could ‘recommend’ that but I reckon my ‘connections’ are not quite that good, yet!