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Spider mites found in soybeans
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By The Associated Press
| 08/31/2009 |
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South Dakota Cooperative Extension Service agronomy educators have found spider mites in soybean fields in several counties, and suggest producers keep scouting their fields for this pest.
Chuck Langner, an Extension agronomy educator in Codington County, said weather predictions of higher temperatures in the next few weeks could lead to rapid increases in spider mite numbers.
"We have found spider mites in soybeans in Codington, Deuel, and Roberts counties," Langner said. "When temperatures increase into the 90s, that will accelerate the rate at which they reproduce. Even fields with low numbers could see some threats as the weather gets warmer."
Elsewhere in South Dakota, spider mites have not yet appeared in soybeans. Tim Berndt, a crop consultant with Northern Plains Consulting, said Brown County areas that suffered from spider mites last year are currently clear of the pest.
"So far, so good, but this next week or two is going to be crucial," Berndt said. "We have been fortunate. Areas that were hard hit last year are not showing any mites so far this year, but this is the time to be on the lookout, and to be prepared."
South Dakota Cooperative Extension Entomologist Mike Catangui said that the current spider mite infestation on soybean appears to be localized in a few northern counties in South Dakota and not as widespread as the 2006 and 2007 spider mite outbreaks.
"According to our data, soybean growers who treated for spider mites on soybean during the outbreak years may have increased their yields by up to eight bushels per acre over untreated soybean," Catangui said. "The two-spotted spider mite is the main species that affects South Dakota soybeans. Spider mites are almost microscopic in size and are best scouted using a hand lens or a microscope."
Despite their size, Catangui said spider mite soybean damage is easy to see.
"The injuries caused by spider mites are seen on the leaves in the form of tiny white spots or `stipples,' and they can be clearly seen even with the naked eye," Catangui said.
Typically, spider mites infestations are concentrated on field margins. Soybean damage by mites first appears as small white "stipples," and as feeding activity increases, leaves become yellow, bronzed, brown, and eventually drop off the plant.
Pods from infested plants may also become more prone to early shattering before harvest.
Catangui recommended that spider mites be controlled if one out of 10, or 10 percent, of the soybean leaves are heavily infested with spider mites and the leaves are starting to turn brown, during the R3 (beginning pod) through R6 (full seed) soybean growth stages.
This recommendation assumes that 10 percent defoliation will cause 2.5 percent yield loss on $9 per bushel soybeans, with a $10-per-acre chemical-plus-application control cost, and 45-bushel-per-acre yield potential.
Because spider mites are not insects but arachnids, only a few insecticides are also effective miticides. In South Dakota, insecticides also labeled for use against spider mites on soybean are Brigade, Cobalt, Dimate, Hero, Lorsban 4E, Nufos 4E, and Tundra. Catangui reminded producers to always read and follow label directions.
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©Madison Daily Leader 2009
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