Almost from the time soybeans emerged this year — and all the way until harvest — it seemed there were problems with soybean insect pests.
Early in the season we had outbreaks of fall and yellow-striped armyworms, garden webworms, bollworms and grey loopers, followed by saltmarsh caterpillars, bean leaf beetles and then, once again, bollworms (and some budworms) as bad as we have seen in many years.
Then, the looper complex, soybean and cabbage looper, hit us — not just in the southern half of Arkansas where they usually cause problems, but across the entire soybean-growing region. This resulted in a very significant portion of the acreage across the state having to be sprayed.
All this and I haven’t mentioned the three-cornered alfalfa hoppers, grasshoppers, lesser cornstalk borers, spider mites, and whiteflies that I had countless calls about.
In many locations, pests were continual and multiple applications were necessary because of the overwhelming numbers, pest complexes, or sometimes because the applications just were not effective.
This lack of effectiveness stemmed from application issues (such as not enough volume or spraying in the middle of a 110-degree day with 2 gallons per acre by air), to tolerance, to downright insecticide resistance.
Then, at the end of the season we had stink bugs. One of the positive things about this season, compared to the last several, was lower than average numbers of stink bugs. However, there were still enough that a significant amount of acreage had to be treated.
And when they hit fields in conjunction with loopers it became very expensive to control both pests.
All this insect activity in soybeans once again points out the importance of a good scouting program. I really don’t understand why we still have growers who do not believe in — or are not willing to pay for — good scouting.
Let’s be clear that “good scouting” refers to scouting all fields, at a minimum, of once per week by someone who is adequately trained to sample, identify, and recommend the proper insecticide to control the pests that are present. Scouting on an “as needed” or “whenever I get around to it or think about it” basis will only get you in trouble.
I can’t tell you how many times I had calls this season from people who sprayed pyrethroids for looper control and couldn’t understand why they did not get control.
One person called to ask me what to spray for Mexican bean beetles. We don’t even have this pest in Arkansas, that I am aware of anyway, and certainly not at treatment levels.
Inevitably, when pests are flaring in some areas, I get the call about what to spray for “worms.” When I ask the caller what worm it is, many times they don’t know and can’t even tell me how many worms they have. They just want to spray.
How many applications were made this year “after the fact?” That is, an application made after the damage was done? This is what we call a “revenge treatment” and rarely has any positive impact on yield. It may make you feel better, but it certainly isn’t helping the bottom line. In my opinion, we have too many of those situations.
The flip side is where we are spraying in advance of pest populations reaching threshold. I hear: “I knew they would get to treatment level, so I went ahead and treated.”
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.