Using insecticide as add-on impacts ROI: study

BLOOMINGTON, Ill. — A common practice of adding an insecticide with a fungicide application at R3 is likely missing its mark with no return-on-investment, according to researchers.

Nick Seiter, University of Illinois entomologist, just completed a second yield of field trials funding by the soybean checkoff to investigate if insecticides pay off.

“We’re not often necessarily responding to insect densities in the field for a variety of reasons. We’re looking at some of those approaches, tying the insect data into it,” Seiter said at U of I Extension’s Farm Assets Conference.

“What we found over the last couple of years is that when we don’t have an insect population, and we’ve done this trial 15 times now and 13 times we’ve had useful yield data, we haven’t exceeded an economic threshold for insects in any of those trials. We haven’t lost fields to insects in any of those trials.

“With minimal pest activity, it makes sense that insecticides didn’t improve yield.”

Seiter, a conference panelist along with Stephanie Porter, Illinois Soybean Association outreach agronomist, was asked what his research has shown in terms of a return-on-investment when applying an insecticide with fungicide during the growing season.

“With an insecticide what we’re trying to do is kill an insect. That’s our goal. One thing that we find, they get tossed in because they’re cheap, obviously. They’re, in many cases, quite cheap, like a generic Warrior is like $1.15 acre, something like that. So, it doesn’t cost that much, and you’re going across the field with a fungicide anyway,” Seiter said.

“If you think about weeds, for instance, we know in any given field, any year, if you do nothing for weed control, you will fail. They’ll get you. We also know that we have to do something for weeds early before the canopy closes.

“Insects aren’t like that. We don’t see yield reduction from insects in every field in Illinois. It never exceeds 10% of the acres where we do, and 10% is probably a dramatic overestimate, particularly for soybeans.”

Timing Critical

The challenge with insects is they are active at different times of the year, and for a viable level of insect control, an insecticide is typically effective for seven to 10 days after application.

“So, to put these out as a preventative, it better be going on something that’s there in the next seven to 10 days to have the effect. We’re applying insecticide at R3 which is the typical fungicide timing,” Seiter said.

“We’ve pretty much never seen anything of any sort of consequence at all with insects at R3.

“In those plots where we have sprayed at R3, we often get bean leaf beetle late all the time in east-central Illinois. Do you know how much impact that R3 insecticide has on bean leaf beetles? Zero. Timing is everything when it comes to insecticides.

“The reality is, what we see in a lot of cases, we had an insecticide, we didn’t see an insect infestation. Great, we must have done something. The reality is most of our fields do not have insect infestation, not an economical one.

“When we do that as a prophylactic, fine, it might prevent something, but only if it’s going to happen in the next seven days, and for us, at R3 in Illinois, and usually most of the time it doesn’t happen.”

Damage Thresholds

An insecticide application is not recommended until damage thresholds assessed.

“Scouting soybeans is hard. Scouting any of these crops is hard. It’s difficult to do. But when we do the automatic application, we’re sort of throwing a dart at a board. Most of the time in Illinois, that board is empty and we’re not throwing into anything with insects,” Seiter said.

“It’s obviously different with disease. I’m not pathologist, but typically you can usually predict disease based on weather conditions. You can’t do that with insects very effectively, most of the time. Weeds, you can predict it based on the fact that it’s a bare field that you planted a seed. That’s going to happen every time. It’s a different situation.”