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Pod feeders start food fight with soybean growers

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Written Friday, September 02, 2005  

The soybean aphid may be on the downturn from high summer populations, but their lower numbers don't necessarily mean an end to scouting fields.

Ron Hammond, an Ohio State University research entomologist, said that defoliators are giving way to pod feeders as fall approaches.

"Things have finally started calming down with the soybean aphids. But we need to remind growers that we aren't out of the woods yet," Hammond said.

"This reminder is important for a number of reasons. One is that although growers may be tired of scouting fields, they need to realize that there's still something out there that can cause of a lot of damage. And secondly, unlike defoliators, which cause a lot of indirect damage, pod feeders can cause direct damage to the crop and impact yields and quality."

The bean leaf beetle is the most problematic of the pod feeders. The insect, heading into its third production of adults before overwintering, is present throughout soybean fields and likely will increase in number over the next several weeks.

Adult bean leaf beetles not only chew on the leaves and stems, but also feed on soybean pods, increasing the chances for secondary pathogens to attack the seed and cause reductions in quality.

"If growers have noticed a lot of bean leaf beetles throughout the season from earlier generations, then they need to be out in their fields scouting for plant damage and bean leaf beetle populations," Hammond said.

Hammond recommends that growers examine plants for damage by pulling 20-30 plants, counting the number of pods and determining the percentage of scarring, the most obvious damage from feeding. Growers also should sweep their fields and count the number of bean leaf beetles in any given area.

"If numbers are small -- say, 10-20 beetles per 10 sweeps -- the population may be low enough where treatment is not warranted," Hammond said. "But if you have fresh scars and high beetle populations -- 30-50 beetles per 10 sweeps -- then a grower needs to put a stop to it."

Grasshoppers are another pod feeder that can cause significant damage if present in high enough numbers. Hammond said grasshoppers tend to feed heavier along the edge of fields, but if grasshoppers are present in large numbers 50-100 feet into a field, then treatment may be necessary.

"There are issues that we remind growers about every year," Hammond said. "They tend to just want to be done with summer, but there are insect problems that need to be followed until the plant reaches maturity and the pods start to brown up and are no longer being fed upon by these insects."

According to the Ohio Agricultural Statistics Service, Ohio's soybean crop already has set pods, outpacing last year's crop development and 10 percent ahead of the five-year average.

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