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Attack Plant Bugs Early And Often


Before cotton was even in the ground this year, Jeff Gore was seeing indications this will be another bad year for plant bugs and mapping out the strategies needed to control them.

Broadleaf weeds along the roadsides and field edges have been supporting large numbers of plant bugs since February. In April, producers began planting a lot of early-season soybeans. Both mean trouble for cotton.

Early season soybeans that flower over a longer period of time provide another host crop for plant bugs feeding before they move into the cotton fields a little later, notes Gore, entomologist with Mississippi State University’s Delta Research and Extension Center in Stoneville.

The increase in corn acres in recent years provided more food and habitat for plant bugs, but these insects will utilize soybeans just as well. In fact, there isn’t a corner of the country where plant bugs aren’t happy. You might think they wouldn’t like cacti much, except that California and Arizona have almost as big a problem with plant bugs as the Delta.

And then there’s the resistance issue. With organophosphates and pyrethroids losing ground to resistant plant bugs year after year, the insecticide choices have narrowed. Mid-South entomologists have teamed up to look for the Best Management Practices to help cotton producers make it through the challenge.

Their recommendations are anchor-ed by neonicotinoids (Centric, Trimax Pro and Intruder), novaluron insect growth regulator (Diamond 0.83 EC) and flonicamid (Carbine) in various timings, rotations and combinations. Organophosphates (Bidrin, acephate) and pyrethroids remain in the program but are usually not standalones.

Avoiding Resistance

There does not appear to be plant bug resistance developing to Diamond. When stewardship and marketing of this insecticide was acquired by MANA last year, Mid-South entomologists were asked to take a fresh look at its fit in plant bug Best Management Practices. It is considered a strong Integrated Pest Management partner with a unique mode of action.

The product provides control of a wide range of insect larvae and nymphs over an extended period by sabotaging their development so they can’t molt. It also controls fleahoppers, several worms including fall armyworm, and stink bugs, a major problem in the Southeast where plant bugs don’t seem to find the mix of crops and environment as inviting.

Good Control

“Diamond has some characteristics that are good for plant bug control,” says Gus Lorenz, University of Arkansas Extension entomologist.

“Nymph control with this product is extremely good, and maybe the best thing is that it stays out in the cotton. The residual control with this product is really the key to keeping those plant bug populations back below economic thresholds. It also has control of other pests like fall armyworm.

“Diamond quickly became our standard for fall armyworm in the Mid-South. It’s a good plant bug material and very effective for fall armyworms, which give us a bad outbreak every two or three years. If you use Diamond for plant bugs in mid- to late-season, you’re not going to have a fall armyworm issue.”

Timing Is Everything

Lorenz says the insecticide’s mode of action requires that a producer know when to apply it during the season.

“Diamond has some positive attributes, but you need to understand the best timing for applications,” he says. “It is not a knockdown like the organophosphates. What we begin to see now is that it reduces egg laying and the hatching of nymphs.”

The key with Diamond is starting early to maintain control of those populations before they get out of hand. At the same time, Lorenz recommends not making six to eight applications of other insecticides with the same mode of action. That will lead to resistance.

Use a sensible rotation and switch between modes of action. Orthene and Bidrin are organophosphates, so if they are in the rotation, a producer needs a neonicotinoid such as Trimax Pro or Centric in there as well as Diamond.

“Before adults start attacking cotton, if we can get some Diamond in the system we may be able to reduce the overall population over time, but it can be problematic to us,” says Lorenz. “Often what you see is that a grower gets behind with plant bug control, and then it’s really hard to catch up once the canopy closes.”

In Search Of Thresholds

Lorenz says Mid-South entomologists have arrived at a common economic threshold to begin spraying:

• Pre-bloom: Nine to 12 plant bugs per 100 sweeps

• After bloom: Three plant bugs per five feet of row.

Gore says the best chance for nearly 100 percent control is a spray interval of five days. At six days, control slips to 70 percent and drops to 20 percent on seven-day intervals. In the Delta, producers averaged 5.5 plant bug applications, though in the plant bug-intensive counties around Stoneville, farms often had more than 10 applications in each of the past two years.

“Right now, organophosphates are still important in the rotation primarily because they’re the cheapest options,” says Gore. “But the majority of those applications need to be tank mixed with something. We’ve even seen synergism with pyrethroids and organophosphates. It gets the control up to where it’s acceptable.”

Spray Program For Plant Bugs

A typical recommended spray program for plant bugs would be:

• Nothing for plant bugs before the first square.

• Between first square and first flower, use a neonicotinoid alone or Carbine alone.

• Between first flower and peak flower, use an organophosphate tank mixed with Diamond or a pyrethroid, and an organophosphate alone.

• Between peak flower and cutout, use a neonicotinoid alone or mixed with a pyrethroid, Carbine plus pyre-throid, and an organophosphate tank mixed with a pyrethroid or Diamond.

“We recommend that for at least one of those applications Diamond should be used, and preferably more than one,” says Gore. “Right now the recommended timing with the research we have is for the first application after first flower to be Diamond, but we’ll test other timings this year.

“Right now it’s during flower, and if there are two Diamond applications they would be 10 days to two weeks apart to get the later nymphs.”

With many organophosphates and pyrethroids fading fast under the pressure of resistant plant bugs, Lorenz says rotation is essential.

“I’d like to see new chemistry come out, and there are some on the horizon,” he says. “But in the meantime we have to make the best control with what we have.

“We need to save our standards like Orthene and Bidrin for late in the season to avoid further resistance. Unfortunately, you can see a lot of producers go out at pinhead square or right before and throw some insecticide for plant bugs in with the glyphosate or a plant growth regulator. They don’t need the insecticide then, and it’s a recipe for resistance.

“We’ve even seen data that a little plant bug pressure is helpful to cotton if it knocks off a square here and there. It keeps the plant from loading too fast too soon and cutting out. The best yields aren’t with 100 percent square set, but 80-85 percent. So wait for the economic threshold, then spray.”

MANA contributed information for this article.

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