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Corn+Soybean Digest

Coming Soon To A Field Near You: Soybean Insects and Diseases



A light winter. Warm March temperatures. Early planting. The welcome scene has been set. The next shot opens to giant aphids and bean leaf beetles raging through your flourishing soybean fields, chewing up what's left of the leaves that haven't been attacked by soybean cyst nematodes (SCN), white mold or sudden death syndrome (SDS).

Sounds like a shot from a Hollywood horror flick, but these are just some of the soybean insects and diseases you need to watch for after a mild winter.

A warmer-than-average winter in Iowa (and many other states) left the winter kill numbers of bean leaf beetles lower than usual, says Erin Hodgson, entomologist at Iowa State University.

"Overwintering adults are strongly attracted to soybean and will move into fields with newly emerging plants," she says. "Early planted fields should be monitored closely this year, given the predicted likelihood of adult overwintering survival.

"Sampling early in the season requires you to be sneaky to estimate actual densities. Although overwintering bean leaf beetles rarely cause economic damage, their presence may be an indicator of building first and second generations later in the season," Hodgson says.

Mike Gray entomologist and crop sciences Extension coordinator at University of Illinois and Christian Krupke entomology associate professor at Purdue University also caution growers in their respective states to watch for the beetles, among other pests.

"Growers should walk bean fields after emergence and look for cotyledon feeding by bean leaf beetles or other pests," says Krupke, who notes that slugs should also be watched for this year.

Slugs are also on the radar for Ron Hammond, Ohio State University Entomologist.

"Slugs can cause significant damage in soybeans grown using no-till practices," he says.  "We expect the warmer winter and spring to allow slugs to hatch and become a greater threat earlier this spring.  Slugs can begin feeding on the cotyledons and growing point as the plant emerges from the soil, and for this spring, requires more monitoring and scouting than in previous years."

As farmers get into fields early, it's also important to remember that early planted fields are more susceptible to soybean aphids, says Gray, who reminds growers that weather will also play a key role during the growing season.

"Spring precipitation patterns and how they affect planting dates of soybeans are critical influences on the densities of many insect pests. A summer drought may lead to a two-spotted spider mite outbreak, whereas a mild to moderate summer can help intensify soybean aphid problems," he says.

Gabe Sciumbato, pathologist at Mississippi State University, echoes the weather concerns.

"They are predicting a drought for this year (in our area). If so, charcoal rot could become severe," he says. "Charcoal rot is the No. 1 disease in Mississippi year in and year out, and the severity of disease depends on stress."

Sciumbato also says frogeye leaf spot could be problematic if the weather is right and resistance issues persist, along with a variety of nematodes and Phomopsis.

And let’s not forget everyone's favorite villain, SCN.

"A survey we are completing on SCN indicates that up to 20% of Kansas soybean fields are currently infested," says Doug Jardine, Kansas State University plant pathologist. "A few fields have levels off the charts. With the spread of SCN, SDS should continue to spread as well, especially in irrigated fields or when rainfall is above normal."

Minnesota could also see SDS, along with white mold, Phytophthora or brown stem rot (BSR), says Dean Malvick, University of Minnesota plant pathologist.

"SDS, BSR, pod and stem blight, SCN, Phytopthora rot, Fusarium root rot, white mold and seedling diseases continue to cause problems in Minnesota, and I suspect they will be problems that should be watched for in many fields again in 2012. SDS is still limited mostly to the southern half of Minnesota to our knowledge, but could be spreading," he says.

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