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Aphid populations excessive in parts of Minnesota, Iowa Thursday, August 14, 2008
WORTHINGTON (McClatchy Newspapers) -- Rural Round Lake farmer Tom Wiese pointed out a winged aphid on the underside of a leaf in his soybean field Wednesday morning, as crops specialist Liz Stahl, of the Regional Extension Center in Worthington, looked on.
Aphid populations across southwest Minnesota and northwest Iowa have been excessive in recent weeks, forcing many farmers to not only apply insecticide, but continue monitoring their fields just in case there's a second explosion of the yield-robbing pests.
Wiese, who sprayed his bean field two to three weeks ago, found high numbers of aphids again on Sunday, but without applying a second treatment, the numbers had dropped considerably by Wednesday morning. The drop, said Stahl, may mean a second treatment isn't needed.
"We've really been encouraging people to go back out and check (their fields), because there's been so much movement," said Stahl. "You've got to worry about what's reproducing in your own field and also what's producing in other fields. There's been a lot of migration -- moving around of aphids -- this year."
Early predictions called for a mild aphid population this growing season, but with temperatures consistently in the 80-degree range for the past several weeks, conditions have been ripe for aphid reproduction and conducive to longer aphid lifespan.
"The big question is, where are they all coming from?" said Stahl of the calls she's received from area farmers. The answer, however, is more difficult to pinpoint.
"Not everybody sprays their fields at the same time -- that's impossible," she said.
Further north, Stahl said farmers began seeing aphid treatment levels -- 250 aphids per plant on at least 80 percent of plants -- already in early- to mid-July.
"The earlier they were treated, the more likely they needed to be treated a second time this year," she added. In addition, farmers who treated for aphids before the threshold was reached may also see a resurgence in pest numbers.
"Some of these fields that might have been treated at sub-threshold levels, (the farmer) might have wiped out all of the beneficial insects too -- then those (aphid) populations can take right off again."
It's too early to tell what kind of damage was caused by the increased number of aphids this year. Stahl said they won't know for sure the impact until the fields are harvested.
"With the narrow price of beans, we have a more narrow window to get out there and treat," said Stahl. "If you see a treatable population out there, get on it right away."
If there is a bright spot in the aphid situation, it's that the soybean plants are nearing full seed development.
"At that point, we've made all our yield," Stahl said.
A series of days with cooler temperatures and rain could also help curb the aphid population, as wet weather is conducive to fungi, which attack aphids.
"If that happens in the field, populations can crash dramatically," said Stahl.
Aside from the aphid infestation, Stahl said area crops are about two weeks behind in development compared to the average.
"We've certainly been catching up in growing degree days," she said. "There's a good-looking crop out there. We just want to get it finished off.
"We don't ask for much -- timely rains, 86-degree days, warm and not too hot, a late frost -- and no bad weather," Stahl said with a laugh. |
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