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Corn+Soybean Digest

Ask The Experts

Q: Will bean leaf beetle be a problem in '03?

HARMS: It's difficult to predict what any insect infestation will be the next year, but there's no reason to believe they will go away. In some areas, we saw them start to build early in spring and expected to treat all of the early planted beans. However, because so many fields were planted at once, the population dispersed and we only had to treat a few fields.

This fall, the last generation built up in Illinois and we only treated a few fields. In Iowa, they built to economic thresholds early and we had to treat most fields.

As with most insects, the weather and environment play such big roles that the best approach is to monitor each field closely and make treatment decisions based on density and timing.

NAREM: The bean leaf beetle was a significant problem in my area for the first time. We don't know what -30°F will do to overwintering beetles if we lack snow cover. And, we don't know what percentage of our population is univoltine (single generation) and what is bivoltine (two generations). We probably have a mixture and will assume we have a potential problem (which complicated my job this past summer) until it's proved otherwise.

Q: Where did the soybean aphid go?

HARMS: I don't think anyone knows. This shows how much we know about some of these critters. All signs pointed to high infestations, but they never developed. Some researchers say this aphid, unlike most others, doesn't like hot, dry weather.

The dry summer kept the populations from building, but there are plenty this fall to be a threat next year. They can build rapidly since a new batch of young aphids can hatch every seven days.

The best monitoring tool is the ratio of ladybird beetles to aphids. If there's a good population of good guys feeding on them, they can be a good control.

NAREM: We saw our first soybean aphids in mid-July, waited for their populations to explode (as all aphids can) and then forgot about them as the beans filled. They did increase about Labor Day, but all recommendations indicated low impact on filling that late.

If our winter is kind to them, there are plenty around to try again next year. If not, aphids can literally “blow” a long way. We long for the days when the only significant soybean insect was the grasshopper.

Q: Is soybean rust a threat to my beans?

HARMS: Soybean rust is not in the U.S. yet, but it's only a matter of time. It's a wind-borne spore, so it can travel long distances and spread rapidly. The yield loss potential depends on the strain, but 80% losses have been reported.

Chemical treatments can be made, but the infection must be caught early and treated quickly to prevent it from spreading. Soybean rust has been found in South America, including Brazil. We could get it in the U.S. from wind (storms), seed grown in an infected area, or from people who travel to an infected area. Vigilance is the key to averting serious yield losses.

NAREM: Several articles about soybean rust caused alarm this past summer. We simply have no clue about its fitness under Corn Belt conditions, or the virulence of whatever strain(s) eventually establish a beachhead. Unfortunately, rust spores can theoretically blow many hundreds of miles, so dispersal from a southern location to the north is possible.

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