Insect Pests: What To Expect

Three regional experts offer their thoughts.

By Amanda Huber

 
Troublesome Pests in 2008
 

By Ron Weeks

Three insect pests have become troublesome to growers. Though not widespread problems each year, growers have seen damage and significant economic losses. Drought, tillage changes and different cultivars are factors that may be impacting the increase in these pests.

The first insect pest is the granulate cutworm. It is considered a foliage-feeding pest that hides in soil-surface debris during the day and crawls up on plants to feed at night. Late afternoon or night applications of recommended insecticides are most effective for control.

Use foliage damage as an indicator for treatment, in addition to the number of “worms” per row foot. Not all the cutworms on the soil surface are actively feeding. If they are not feeding, you probably won’t see good results with sprays. Only newer insecticides, such as Tracer or Steward, have provided consistent control in high population situations.

TCAH Treatment Threshold Elusive
The second pest is the three-cornered alfalfa hopper (TCAH). Although there are efforts to develop treatment thresholds for these pests, so far results have not provided a useful tool. These insects can be found in just about every field in the Southeast. As a result, we have seen a tendency for multiple insecticide sprays. A few of these applications were warranted, but only a few. In addition to cost, these sprays kill beneficial insects and set growers up for serious problems with spider mites and foliage-feeding worms. Evaluate damage, as well as populations, of TCAH before spraying. Also, I like to see immatures in the field before a recommendation to spray.

Burrowing Into Profits
The third pest is the burrower bug, a cousin of stinkbugs. It is shiny black with piercing mouthparts and legs adapted for digging. During pod develop, they burrow down around the pod and “sting” the seed. Damage is not evident until shelled out and the skin is removed, then damage can be easily seen.

The majority of damage occurs in strip-tilled peanuts or where organic matter is high in the topsoil. Granular insecticide applications at pod development have been effective in reducing damage, but not always enough to prevent grade losses. Changes in tillage practices and eliminating high residue situations are the best way to reduce burrower bug damage.

Each season is different. Scouting fields on a regular basis throughout the season is the surest way to identify what insect pests are present and when they reach treatable levels.

Ron Weeks, now retired, is a Professor Emeritus of Entomology/Plant Pathology at Auburn University.

Will it be a bad year for insect pest pressure? Three area experts offer their thoughts on insect pest issues this growing season.

Rick Brandenburg, Extension entomologist at North Carolina State University, says that growers in his area are concerned about the hot and dry-weather pests such as beet armyworm, spider mites and lesser cornstalk borers, likely in response to serious problems they had with these pests in 2007.

Expect Hot, Dry Weather Pests
“Last year was, hopefully, a once-in-one hundred-year event, with the hottest and driest summer on record, and these three pests are always most severe under those conditions.

“Lesser cornstalk borer are rarely a problem in our region, and I have no reason to believe they will be in 2008,” Brandenburg says. “The same applies for beet armyworms.”

However, he says to keep in mind that spider mites can be a problem during even short, dry spells.

“The use of the leaf spot advisory to spray only when necessary and using thresholds to treat for worms has really reduced the threat from spider mites in recent years,” Brandenburg says. “Spider mites are a problem when it is hot and dry and we use other products that reduce their natural enemies.”

Something Brandenburg is a little more concerned about is the threat from tomato spotted wilt virus, and he urges growers to be wary of it, too.

“We’ve seen a few more western flower thrips than normal, and the last time we had a serious problem with the disease, we observed the same thing,” he says.

“Growers have been using practices that help reduce the incidence of the disease, but since it has not been a problem for five years, some have relaxed a little on using the best options to minimize tomato spotted wilt virus.”

Watch For Grasshoppers In Texas
While there is not as much insect pressure in the West Texas production, Scott Russell, Extension and Integrated Pest Management agent for Terry and Yoakum Counties, says there are pests growers should be alert for.

“With the dry winter conditions we have had, we are already seeing numerous grasshopper nymphs in wheat fields, and I am anticipating significant grasshopper problems,” Russell says. “As wheat is terminated for planting or dries naturally, nymphs will migrate to greener fields.”

He says peanuts can tolerate significant defoliation. However, in seedling development, try to minimize stress and work to insure rapid development.

Russell says to scout peanut fields weekly for grasshoppers, take note of the insects’ sizes (nymphs are small and without fully developed wings) and note the distance into the field they have moved.

“A chemical application should be considered if grasshoppers are consuming foliage faster than it is replaced by new growth,” he says. “There are several pyrethroids labeled for grasshoppers in peanut, and Orthene 75S and Sevin 80S are also labeled options.”

Russell says, like most insects, grasshoppers are easily controlled as nymphs but more difficult to kill as adults.

Mites Might Be A Problem
Another pest, Russell says, they have seen in higher numbers are spider mites.

“Again with dry winter and planting conditions, I would not be surprised to see large numbers of spider mites late in the season,” he says. “Typically, spider mites are held in check by beneficial organisms, but when we treat for other pests, or some environmental factor goes to their favor, they increase rapidly in peanut fields.”

Russell says to scout peanuts closely for the tiny mites throughout the season. “A 10X to 12X hand lens comes in handy when checking for spider mites.

“If chemical control becomes necessary, Danitol, Omite and Comite II are labeled for spider mite control in peanut.”

Russell reminds growers to be sure to read and follow all label directions and observe the pre-harvest interval.

PG