Have a Game Plan Ready for Plant Bugs
April 12, 2011 As cotton prices hover above the $1 mark, many growers in the Mid-South will be dipping their toes back into cotton production for the first time in several years this season. Unfortunately for them, they may be facing a few new obstacles they don’t recall from just a few years ago.
Growers are no doubt aware that glyphosate-resistant weeds have crept into cotton fields all over the Delta region. Perhaps even more problematic, and less publicized, is the threat of plant-bug pressure that has proved capable of costing upwards of $65 an acre for growers in Arkansas, Louisiana and Mississippi.
For these reasons, most growers in the Mid-South will be more than familiar with crop protection products from MANA in 2011. In late February, MANA hosted cotton consultants from across the region in Tunica, MS. Extension cotton experts from Louisiana, Mississippi, Tennessee and Arkansas laid out the best production practices to combat these problems.
“There’s not one single thing you’re going to do that’s going to allow you to control plant bugs,” said Dr. Fred Musser, of Mississippi State University’s Department of Entomology and Plant Pathology.
“Some things that we need to keep in our toolbox are minimizing corn and cotton interfaces, and planting shorter season varieties and getting that crop out early. We need to keep in mind our chemical controls. We’ve talked about resistance. Chemical rotation is a way to minimize that resistance.”
Research suggests that plant bugs tend to migrate heavily into cotton by mid- to late-season once corn fields begin to dry down. By putting some distance between fields of the two crops, growers can reduce the chance that plant bug migration will have a heavy impact on their cotton crop.
Musser wasn’t the only entomologist on hand who encouraged growers to plant shorter season varieties as another method to avoid heavy late season plant bug pressure. According to Dr. Jeff Gore of the Mississippi State University Delta Research and Extension Center, limiting the length of the growing season gives the bugs less time to reproduce.
“Where we used an early season variety, we were able to eliminate anywhere between one to three plant bug applications, because the breeding time on that early maturing variety was a lot shorter than the later variety,” Gore said.
Gore noted that an added bonus to eliminating late-season plant bug sprays is that often, plant bugs will develop resistance to certain insecticides over the course of a single season. So by reducing the late-season sprays, growers are more than likely eliminating their least effective applications.
“When you have to spray at the end of the season when those bugs are more resistant, they’re just a lot more difficult to control. Like we’ve mentioned, the later we planted and harvested, the lower our overall yields were,” said Gore, referencing a series of tests the Extension entomologists conducted.
Diamond in the Rough
Of course, one of the best ways to eliminate the threat of insecticide resistance is to rotate chemistries. This makes MANA’s Diamond insecticide especially effective in fields where plant bug pressure is heavy, because of its unique mode of action.
Musser remarked that the conventional wisdom on Diamond was that it is a very effective chemistry when directed at nymphs, but that it did little to nothing to control adult plant bugs. He also noted that it is commonly thought that Diamond has much longer residual effects than other comparable insecticides.
Extension research supported Diamond’s reputation as a longer lasting insecticide, but served to change the thinking on exactly why Diamond was so effective against nymphs, and ultimately, adult tarnished plant bugs. Musser presented some research conducted by Mississippi State entomologists to the crowd of consultants in Tunica.
“You can see that five days after the first treatment, Diamond is one of the best products. It is right there with Orthene and Bidrin. If we take it out further, 13 days after that treatment, you can see that Diamond is working better than everything else,” says Musser.
“So that’s where we get the idea that is has a long residual.”
Because Diamond is an insect growth regulator (IGR), it has no impact on the lifespan of an insect. Adults live just as long whether they feed on a steady dose of Diamond or whether they had a clean diet. Musser’s research suggested that Diamond did have a profound impact on tarnished plant bugs, however.
When feeding on Diamond, the eggs laid per females dropped by as much as 50% in some of Musser’s tests. Perhaps more telling was the percentage of those eggs that actually hatched.
“The most important part of this is the percentage of eggs hatched. In the control (untreated) population, roughly half of the eggs hatch. Among treated females, the hatch rate went down to 10%, and in same cases down to 1%,” says Musser.
“So even though they were laying eggs, we weren’t getting any nymphs out of it.”
All of Musser’s research suggests that Diamond serves to effectively sterilize the adult tarnished plant bug population. This runs against the commonly accepted idea that Diamond is most effective by killing active nymphs.
“In every case, the highest yields we got were from plots sprayed the third week of squaring. In the third week of squaring we had virtually no nymphs in the field. So we weren’t getting any direct control in the nymphs,” Musser says.
“My contention, based on the lab data I have there, is that Diamond’s primary control is sterilizing those adults. They had recently migrated into the field, and they hadn’t laid most of their eggs yet. They were sterilized, so he was able to get better control of those plant bugs throughout the season by spraying early on them.
Musser’s research suggested that the earlier a Diamond application could be made, the better, so that plant bugs are treated before they are able to lay eggs.
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