Agronomic Crop Insects – July 6, 2012

Alfalfa
With the recent weather, leafhopper populations have significantly increased so be sure to keep a close watch for adults and nymphs. We are seeing economic levels in fields throughout the state and in a number of cases yellowing has already occurred. Remember, the nymphs can quickly cause damage and once yellowing is present significant damage has already occurred both in season as well as to the long term health of the stand. With the hot, dry weather, you should consider reducing treatment thresholds by at least one-third.

Field Corn
We are starting to see an increase in Japanese beetle and have found the first rootworm beetles feeding on corn silks. Although beetles feeding on silks can potentially interfere with pollination, research indicates that silk feeding does not reduce pollination if they cut the corn silks after pollination has already taken place. As a general guideline, an insecticide treatment may be needed if two or more Japanese beetles and/or corn rootworm beetles are present per ear and silks are clipped to less than ½ inch prior to pollen shed.

Soybeans
We continue to see a wide variety of defoliators present in full season soybeans including Japanese beetles, yellow striped armyworm, green cloverworm and grasshoppers. The best way to make a treatment decision in full season soybeans is to estimate defoliation. Before bloom, the defoliation threshold is 30%. As full season beans enter the reproductive stages, the threshold drops to 15% defoliation. Remember that double crop soybeans can not tolerate as much defoliation as full season beans so be sure to watch newly emerged fields carefully.

Continue to scout for spider mites in full season and double crop soybeans. Economic levels can be found in fields throughout Kent and Sussex Counties. With the current hot, dry weather, economic populations are being found field wide so be sure to scout the entire field because edge treatments may not be effective. At this time of year any rains we receive will allow beans to grow and then allow treatments to be more effective. If egg populations are high at the time of application, a second application will mostly likely be needed. Labeled materials include dimethoate, Lorsban (chlorpyrifos), Hero (zeta-cypermethrin + bifenthrin) as well as a number of stand-alone bifenthrin products. All of these products need to be applied before mites explode. Be sure to read all labels before making an application since there are restrictions on the total number of applications allowed, rotation between materials as well as the minimum number of days needed between applications.

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