What is in this article?:
- Soybeans: need for insect scouting great
- Let natural enemies work
- Soybean insects pests were continual and multiple applications were necessary in 2010.
- This insect activity in soybeans points out the importance of a good scouting program.
- Integrated pest management works in soybeans.
- Unneeded applications lend themselves to developing insecticide resistance issues.
- Tolerance to pyrethroids is being documented for bollworms in the Southeast and, possibly, in Louisiana.
- With the high costs of production and a decent price for soybeans, the need for good scouting has never been greater.
Let natural enemies work
Let me tell you, soybeans are not cotton! That may sound obvious, but let me explain. Rarely do you want to treat soybeans before they at least get close to threshold. There are a lot of natural enemies out there in soybeans that help us keep those pest populations in check.
A good example is the looper virus that hit many looper populations across the state and controlled this pest far better than any insecticide application.
We see it every year in our work — we put out a bollworm trial in soybeans and come back in four days only to see that the untreated check actually has fewer bollworms than the insecticide treatments.
Notice that in our thresholds we say “treat when population of larvae is one-half-inch or larger.” That’s to give the natural enemies time to do their job and references the fact that until the larvae get that big they really don’t cause that much damage.
In many cases for larval pests, 90-plus percent of what a larva consumes in its time as a caterpillar is right before it pupates and no longer feeds, at all. Another reason is that unlike cotton, insect pests have nowhere to hide in soybeans; there is no square and boll for them to burrow in to get away from the application. In almost every case you don’t need as high a rate to control a pest in soybean as you do in cotton.
With the recent declines in cotton acreage, we have a bunch of cotton consultants out there scouting soybean. They need to recognize the obvious differences between these crops when it comes to insect pest management.
Integrated pest management works in soybeans. This year, many growers found that out when they just had to throw in a pyrethroid with their fungicide application at R3. They didn’t have any insect pests close to threshold, but they were going across the field, so “why not throw it in the tank?” Then, they had to come back in 10 days or less and spray another insecticide application for loopers or bollworms (or both), not realizing that the pyrethroid killed the natural enemy complex and opened the door for the caterpillar pests.
These unneeded applications also lend themselves to developing insecticide resistance issues. We saw multiple examples of control failures this year with pyrethroids for bollworm control. Many of those failures are probably the result of poor application or higher-than-normal numbers of budworms we saw in beans this year.
But I suspect more may be going on than these factors. Currently, tolerance to pyrethroids is being documented for bollworms in the Southeast and, possibly, in Louisiana. Time will tell, but to say we are concerned would be an understatement of the situation.
We also had failures with pyrethroids on bean leaf beetles, which were recently found to have tolerance. Loss of the pyrethroids will only result in higher control costs for growers.
With the high costs of production and a decent price for beans, the need for good scouting has never been greater. Growers can ill afford to have a crop failure because of insects.
If a grower cannot afford the time to devote to scouting his crop on a regular basis, he needs to seek out and find a competent individual who can properly sample, identify, and recommend the right product for control. Also, that professional may help you in deciding when not to spray, save you some money, and help keep the insecticides we have viable for the future.
In most cases, the cost for someone to check your beans is around the price of a bushel of beans or maybe about the cost of one insecticide application and could make the difference in making a profit or losing the crop. When you think of it in those terms, soybean scouting is pretty cost-effective.