Bollworm Treatments Starting In Later Planted MS Soybeans

The bulk of our soybeans are going to outrun the current bollworm flight. Over the last 5-7 days we are getting reports of above threshold numbers of bollworms in soybeans. This is pretty much restricted to the soybeans that are R2-R4. We have had reports of people finding very high numbers of bollworm eggs in R5 plus soybeans in the terminals. Bollworms are not going to be a problem until they get 1/2″ long or longer. If you are finding eggs in the terminals, I would not get to excited until they actually hatch and survival is documented. There is tremendous mortality of bollworm eggs in soybean at these later growth stages. I have seen R5 stage beans with 2-5 eggs on every plant that never developed into anything. Basically you have another week before you have to worry about damage so you can reevaluate the situation on your next scouting interval to see if the eggs materialized. Most often time they do not.

Remember we have a new dynamic threshold for bollworms in soybeans. This was used extensively last year with success.  In the table below it is important to remember that the control cost must have the application cost included with the cost of the insecticide. An example would be if you were getting $12 for your soybeans and applying a $10 insecticide + $5 application cost = $15, the threshold would be 5.5 larvae/25 sweeps. You may notice that we removed all pyrethroids from our control guide for bollworms in cotton and soybean. This is due to widespread tolerance and very inconsistent and poor performance over the last several years.

What to treat with? You may remember a time when bollworms were very easy to control with a low rate of a pyrethroid insecticide in soybeans. In fact, many of the pyrethroid labels still  include extremely low rates for control of bollworm in soybean. Over the last 5 years we have seen the level of control with straight pyrethroids fall off dramatically. Because of the high number of control failures or less than acceptable control, we no longer recommend pyrethroids for control of bollworm in soybean. This does not mean you will get zero control with a pyrethroid but 7 out of 10 pyrethroid sprays targeting a bollworm in the Delta region of the state in recent years resulted in poor control or outright failures.

Preferred treatments are the diamide class of chemistry or Intrepid Edge. Diamides include Prevathon by Dupont (use rates of 14-20 oz.), and Besiege by Syngenta (use rates of 7-10 oz.) or Intrepid Edge by Dow (use rates of 4-6.4 oz.). These materials are very good on caterpillar pests and have long residuals.