Cotton and Soybean Insect Update

Author: Scott Stewart, IPM Extension Specialist Comments Off on Cotton and Soybean Insect Update

Cotton: Much of our cotton is within 7-10 days of when insect controls can be terminated, and it looks like this cotton may outrun the bollworm moth flight in many areas. Most the bollworm action appears to be pretty moderate and still primarily concentrated along the Mississippi River and south of I-40. Having said that, we are some seeing bollworm larvae slip through on Bollgard 2, WideStrike, and TwinLink varieties. It’s a numbers game. Moderate or sustained pressure will likely result in a need for an insecticide application on these technologies, and the insecticides of choice will be Prevathon or Besiege. There may be some opportunity to sneak by on earlier maturing cotton, if the pressure is not too high, with an application of a pyrethroid (full labeled rate) tank mixed with 0.75 lb of acephate. I would ONLY consider this if you within a week of terminating insecticide applications (i.e., NAWF5 + 350 DD60s). That typically occurs once a field is averaging less than 3 nodes above white flower.

I’m also getting more and more comments about spider mites, and this also includes some issues on soybean. We’ve been spraying a lot of Acephate, Diamond and other insecticides that can flare spider mites. Also, since we’ve started using less Liberty and more Dicamba, we are seeing that there was some benefit from Liberty in suppressing spider mites. FYI – Liberty is known to provide reasonably good control of spider mites.

Almost always, fields relatively free of spider mites are good to “cut loose” at NAWF5 + 350 DD60s because there is not much time for mites to build up and cause much defoliation before it’s too late to matter. However, it’s a different ball game if spider mites are well established in a field at NAWF5 + 350 DD60s. Treatment for spider mites requires a little judgment, but it should be made anytime they threaten to cause substantial defoliation prior to NAWF5 + 600 DD60s (typically about when the first bolls start opening in a field). Abamectin products such as Abba, Agri-Mek, Reaper, and Zoro are typically used for control, primarily because they are affordable but also because they work pretty well. The use rates have gone up as the price has gone down. I suggest 8-10 oz/acre with the original formulations including Agri-Mek, but if you are using the more concentrated Agri-Mek SC formulation, a 1.5-2 oz/acre is a roughly equivalent. These miticides are also labeled for use in soybean.

Soybean: There are some reports on bollworm (corn earworm) moths and larvae showing up in late planted soybeans in the Mississippi River Bottom. Fields that are flowering, and particularly those having a relatively open canopy, need to be scouted closely for  larvae. Remember that the threshold is based on the cost of control and the value of the soybean (table below). Don’t be a victim of fake news. The mention of a moth flight is not a reason to spray. I’ve discussed treatment options in a previous article.

Green cloverworm and bean leaf beetle continue to generate some concern, with bean leaf beetles being mostly concentrated in the early maturing fields and especially in the river bottom. Generally, the best approach is to base treatment on defoliation. Treatment is recommended from R1 to R6 if 20% defoliation or more has occurred. Stink bug populations are spotty but building, so don’t forget the treatment threshold is 9 stink bugs/ 25 sweeps.

Reminder: There is good information and scouting and managing insect pests in soybean at http://guide.utcrops.com/soybean/soybean-insect-guide/.

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