Agronomic Crop Insect Scouting

David Owens, Extension Entomologist,

There have been recent reports of fungal infected spider mites, and with recent storm events, I wouldn’t be surprised if spider mite populations in field crops crashed in the next week or so. Dead mites are going to appear brown and fuzzy. Now that soybean is entering reproductive stages, defoliation thresholds decrease to 15 – 20% new defoliation with defoliators present. Begin scouting for corn earworm, among other pod-damaging insects like stink bug and bean leaf beetle. Corn earworm moths are particularly attracted to flowering, drought stressed, open canopy soybean fields. Pyrethroids have in recent years been inconsistent in efficacy. Last year some trials resulted in good efficacy while others resulted in poor. There is an excellent threshold calculator for determining whether or not to treat, based upon sampling method, cost of an application (product + application), value of soybean, and row spacing:

Now is the time to be checking for earworms in heads. The best sampling method is the beat bucket. Shake sorghum heads hard into a 2.5 to 5-gallon bucket and count caterpillars. Open headed sorghum varieties tend to sustain less damage than closed-headed types. In general, pyrethroids offer only 50 – 75% control. If a pyrethroid is used, use the highest label rate, and do not target anything larger than a medium sized worm. A good threshold calculator for earworm can be found here: Sorghum webworm is present in low numbers; thresholds are approximately double those of the other headworms.

Also be sure to flip a few leaves over to check for white sugarcane aphid. Last year we found our first around August 8. This is definitely not a critter to miss. By September, their populations were astronomical. More information can be found here:

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