Farm Progress

• Combine the higher than usual populations of plant bugs, with usually high stink bug populations, lower than expected corn earworm populations, early fall armyworms and kudzu bugs and growers found more and more problems getting the right insecticide on at the right time to take care of different combinations of these pests.

Roy Roberson 2

October 10, 2013

7 Min Read
<p> MULTIPLE INSECT pests in late-season crops was a &lsquo;mess&rsquo; said Virginia Tech Entomologist Ames Herbert.</p>

This year’s excessive rainfall in much of the Southeast created delays from planting all the way through to harvest and caused some unusual combinations of insect problems that veteran entomologists in the region haven’t seen often, and in some cases ever.

Typically, plant bugs, for example, are a problem on less than 5 percent of cotton acreage. This year the wet, extended cool weather provided an ideal environment that amped up the plant bug pressure throughout the Carolinas and Virginia.

Combine the higher than usual populations of plant bugs, with usually high stink bug populations, lower than expected corn earworm populations, early fall armyworms and kudzu bugs and growers found more and more problems getting the right insecticide on at the right time to take care of different combinations of these pests.

And, the unusual weather extended into the late summer months, which continued to challenge entomologists and growers alike.

For example, soybean aphids were reported in several areas in late August. It is typically a cool season pest, which doesn’t often happen in August in the Southeast, but cool weather this year even brought this pest into play as harvest approached.

In Virginia, Virginia Tech Entomologist and IPM Leader Ames Herbert said, “some unlucky growers were faced with a heretofore undocumented pest mixture that could include soybean aphid, brown marmorated stink bug and other stink bug species, kudzu bug, corn earworm, green cloverworm and armyworm species. What a mess.”

Likewise, plant bugs, when they appear in cotton in the Carolinas and Virginia, are usually gone fairly early in the season, but not this year. Using a black drop cloth and shaking cotton plants in a 2.5 foot area on both sides of the row, North Carolina State University Entomologist Dominic Reisig said he continued finding plant bugs in damaging numbers well into August.

Reising sasid many cotton growers aren’t familiar with plant bugs and if they sample, they often try sampling with the wrong equipment. “It’s like choosing a crescent wrench to work on your car and finding you need a socket wrench instead — it just won’t work,” he said.

The North Carolina State researcher said a black drop cloth works best for plant bugs. These tiny insects have distinct green color that seems to pop out on a black background, he adds.

Plant bugs often over-looked

Plant bugs are often over-looked because the adult of the species can move from place to place very rapidly.

Unlike many pests of cotton, both plant bug adults and nymphs can damage the crop and when the final yield and quality assessments are in, it’s likely there will be much more damage from plant bugs than in most years.

Because of their rapid movements in and out of cotton fields, and subsequently of adjacent grain fields, and the difficulty in sampling for these insects, some growers tried preventative applications of neonicotinoid insecticides to take out plant bugs and the first generation of stink bugs.

Applied in mid- to late-June in Virginia and northern areas of North Carolina, the treatment was successful and economical at about $3 per acre when using low rates of insecticide.

Herbert said spraying for an insect that may not be in the field is not a good idea for at least two reasons.

“First, the grower in most years will be paying for something he or she doesn’t need. This year, the conditions were good for plant bug populations to thrive, but in most years we are much more prone to drought and heat than to rain and cool, cloudy weather,” he said.

Perhaps more importantly, the Virginia IPM leader said there are distinct indications that resistance to neonicotinoid insecticides is building in several pests for which these sprays are used.

When there is a sample and thresholds are there, then growers need to use these insecticides, Herbert said.

Reisig adds, “For example, Centric is a popular neonicotinoid insecticide that provides very good aphid control. As a result, it is widely used in many cotton growing areas of the Southeast.

“In tests using Centric and another neonicotinoid insecticide, Belay, Reisig said they are already seeing reduced control with Centric.”

He added that both Centric and Belay, combined with a pyrethroid like Swagger and Endigo provided good control of plant bugs and stink bugs.

“Transform is a new material that is similar in mode of action to the neonicotinoid insecticides, but has a different active ingredient and does not pose a threat to increasing neonicotinoid resistance.

“When growers are sampling for most insects, plant bugs in particular, they need to remember the differences between adults and nymphs. The nymphs will sit in the field and feed for extended periods of time, but the adults can move in and out of a cotton or corn field very quickly,” Reisig said.

Plant bugs disappeared quickly

For example, the North Carolina State researcher said a sweep net sample of plots at the Blacklands Farm Managers Tour site in Terra Ceia in eastern North Carolina this year showed 35 adult plant bugs per 100 cotton plants sampled.

When he came back to spray two days later, his research team could find no adult plant bugs.

“In this case, the test plots were surrounded by corn and the plant bugs moved that quickly out of cotton into corn,” Reisig said.

“It’s important for growers to remember, however, that plant bugs can move back into cotton from corn or other crops just as rapidly,” he added.

Herbert says some late planted crops may be attacked by three formidable pests simultaneously. “We had a situation in Virginia, and other parts of the Southeast I suspect, that we’ve never seen before because of the pushback on planting dates created by excessive rainfall,” Herbert said.

“For example, we had late-planted soybeans that had kudzu bugs, stink bugs and corn earworms in the same field. How infestations of these insects lines up should determine how they are managed.

“In some fields one well-timed insecticide may do the job, but in others a separate spray for each insect may be needed.

“If you spray kudzu bugs with a pyrethroid and corn earworms are building, the risk is high you will create a bigger corn earworm problem.

“We have decent triggers for when to spray each insect, but we’ve rarely had all three in fields at one time, so we don’t really know how taking out one insect might create problems for another,” Herbert said.

The products to manage each insect are available. The trick is to pick the right active ingredient and apply it at the right time. Otherwise, the result can be the same as Reisig’s analogy about trying to use the wrong size crescent wrench — it just won’t work.

In the Upper Southeast a lot more grain sorghum was planted this year and a good part of it was planted in a double-crop with wheat. Rain significantly slowed down wheat harvest and pushed back planting date for double-crop sorghum and soybeans.

Prone to build up late

“We know fall armyworms are prone to build up late in the growing season in grain sorghum. This year there will be sorghum out there later than usual, so fall armyworms could be a bigger problem,” Herbert says.

“On the other hand, in early August, our fall armyworm counts were running below 20 per sample. At this time of year, 30 is more normal and 50 isn’t unusual in a droughty year,” he said.

These insects, he said, typically aren’t as big a problem in cool, wet years.

Cotton planting date was delayed and maturity was delayed after that, because of the continuous wet weather in the Upper Southeast. Late-planted, late-maturing cotton was at risk from insects that usually aren’t a problem because cotton is mature and/or picked.

Herbert and Reisig agree the biggest insect problem for late cotton is usually stink bugs.

In Virginia, Herbert says the wild card among insects in soybeans is now the kudzu bug. “We went from zero counties with kudzu bugs on soybeans to having 33 of 48 soybean producing counties infested with these bugs,” he said.

“Based on research in Georgia and South Carolina, we shouldn’t get but two generations of kudzu bugs, but this is a new pest and in much different cropping conditions than we’ve ever seen it before,” Herbert says.

Much the same level of uncertainty is the case with many crops in the Virginia-Carolinas area, Historic rainfall throughout the planting and growing season forced growers to manage crops at times of the year when they are typically mature.

What impact the late planting had on pest management and final yield and quality of these crops is in large part unknown and in larger part to be determined by harvest time weather.

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