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Paynesville Press - August 20, 2003

Soybean aphids, drought pose threat

By Bonnie Jo Hanson

aphidsCausing crop damage that has been exasperated by drought conditions, soybean aphids moved into area fields earlier than experts expected and their numbers have been higher than anyone anticipated, said Dave Schwartz, Meeker County extension educator.

Soybean aphids - insects relatively new to Minnesota - found their way into area fields and by the end of July and their populations exploded in area fields and in fields in surrounding counties, said Schwartz.

The insects are native to Asia and it is believed that they found their way into this country along with Asian soybeans in 2000. Because they are still a relatively new nusance in this country, not a lot is known yet about the insects, said Schwartz.

Soybean aphids attach themselves to healthy soybean plants and suck fluids from it, essentially dehydrating the plant leaving behind a sticky residue.

During the current stage of soybean development, when pods are forming and beans are developing, plants respond to the loss of nutrients by either forming smaller than usual beans or aborting pods before beans can form.

Female aphids are born pregnant and can double their population in two to three days, said John Vanderbeek of the Paynesville Farmers Union. Because they are new to area fields, natural peredators like ladybugs haven't established themselves in the fields in large enough numbers to help fight the aphid's growing populations.

In many cases, spraying to kill the aphid is the only viable alternative. Determining when to spray for the the insects is difficult, said Vanderbeek. According to the University of Minnesota, to be economically feasible, spraying should be done when there are 200-250 insects on each plant, while the University of Wisconsin determined that spraying should be done when the population reaches 100 insects per plant. Counting aphids on a soybean plant can be difficult because they are tiny, roughly the size of a pinhead, said Schwartz, but counting is important in determining if there is a need for insecticides.

According to Vanderbeek, spraying can be expensive, between $10-$12 per acre, and farmers need to carefully weigh the economic impact before determining whether or not to spray. Vanderbeek added that his company has already sprayed over 14,000 acres of soybeans in the Paynesville area.

Just because fields have been sprayed doesn't mean they are out of danger from soybean aphids. According to Schwartz, the insects are likely to reappear within a few weeks of spraying. These fields will likely have to be sprayed a second time. Paynesville area farmers are just beginning ther second round of spraying, said Vanderbeek.

Vanderbeek pointed out that the insects prefer green, healthy fields. At least one soybean field he pointed had no aphids because the plants had already succumbed to the lack of water.

Even though his fields are infected with soybean aphids, Jim Hartman -╩who farms near Paynesville with his brother, Bub - elected not to have his fields sprayed. Hartman believes his beans could be burned up by heat and drought conditions before aphids destroy them.

According to Glen Young, a Meeker County weather forecaster, there hasn't been significant rainfall in the area in over five weeks. Also concerned about dry conditions, Schwartz believes that if rain doesn't come by the end of August, farmers could face significant yield losses in soybeans and corn.

In an effort to conserve moisture, corn that is stressed by drought will begin to have furled leaves and soybean plants will respond by furling and turning their leaves, both of which have already begun to happen in some local fields. Corn responds to drought by producing short kernels, said Schwartz and soybean plants, which are more suited to dry conditions, will tend to produce smaller beans if they are stressed.

According to Schwartz, plants in heavy soil might be saved from the drought, but plants in sandy soils, including many fields surrounding Paynesville, have already begun to show signs of stress from the lack of moisture.

To make matters worse, soybeans and corn were just setting roots in June when the area had heavy rains. As a result, many plants didn't set deep roots, which would have made it easier to survive drought conditions now.

Statewide, according to the U.S. Department of Agriculture, farmers report 11 percent of fields were very short of moisture and 42 percent were short moisture.

The amount of corn and soybean acreage rated as excellent has also dropped in August: from 75 percent to 69 percent of corn and from 72 percent to 66 percent for soybeans.

Although some damage has already been done, according to Schwartz, a significant rainfall within the next week could save area farmers from a catastrophic loss. Rain has been forecasted for mid-week.



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