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Early Soybean Diseases Flaring Up -- Agronomists

So your soybean fields survived this week's cool snap? Unfortunately, you're far from out of the woods yet.

The spring conditions in a lot of areas have been generally cool and damp since most of the soybeans in the ground made their way there. Not exactly perfect for germinating seeds, but good for a lot of diseases. Just like with those acres that may be hampered by this week's frost, any bean fields coming up coming up in less-than-perfect conditions right now should get more of your attention than normal right now, agronomists say.

Stand issues are common around the Corn Belt, with farmers in eastern portions of the region facing mounting disease pressures due to the planting delays they've faced thus far this spring after a slow start to corn planting. Though the planting pace has caught up, the window for disease pressures has flown open, with rot and mold diseases thriving in near-perfect conditions for them, according to Ohio State University Extension soybean disease specialist Anne Dorrance.

"Some soybeans have been planted, and issues have already been reported. The most common symptom is spotty areas around the field with large skips or limited emergence," she says in a univerity report. "Take a garden trowel and dig up a few places, and try to find the seed that was placed there."

Any fields with weak stands can be in that condition for a number of reasons, Dorrance and fellow Ohio State Extension soybean speicalist Laura Lindsey say. There are three main categories of disease that are common in the eastern Corn Belt, at least. Depending on their severity and onset time, they may require replanting. Here's what to look for.

  • Pythium and Phytophthora root rots. These are most common in "poorly drained, high-clay soils," Dorrance says. She adds, "These pathogens love wet soil conditions. The few places in the state where saturated soil conditions have occurred are the very typical. Look for any shade of brown or tan on the seedling root or hypocotyl, the area right behind the deep green cotyledon."

  • Rhizoctonia. This pathogen thrives when soil and weather conditions fluctuate between wet and dry frequently during spring and early summer, and that's exactly what's happened in some parts of the Corn Belt so far this year. "This is a brick corky red color, close to a brick house on the lower stem, and the roots can range from light brown to dark brown in color," Dorrance says.

  • Fusarium graminearum. Fusarium has a pink or red tint to it and has a "fluffy" appearance, Dorrance says. This disease is most common in fields where there's a lot of last year's corn residue remaining.

"There are other pests that will feed on the seeds and seedlings. Seed corn maggot is one, slug damage is another. Missing plants or plants with holes in leaves, cotyledons will appear different than the sunken, rotting tissue of diseases," Dorrance adds.

Whether you have one of these diseases in your fields right now shouldn't affect how quickly you diagnose your overall soybean emergence and stands. It's still early in the growing season, Lindsey adds, and it's important to evaluate each field's stands based on specific soil and environmental characteristics before you make a replant or treatment decision.

"As soybeans are emerging, consider evaluating your stand this spring. Most are reporting good stands; however, there have been some reports of damping-off. To quickly estimate stand, count the number of plants in 69'8" of row for 7.5-inch row spacing, 34'10" for 15-inch row spacing, or 17'5" of row for 30-inch row spacing. These counts represent 1/1,000 of an acre. During the past 10 years, the AgCrops Team has conducted several seeding rate trials. When planting in May, soybean yield is maximized when there are at least 116,000 plants per acre at harvest," she says. "Keep in mind that soybean stand may look a little uneven, especially in areas of Ohio that are dry. If there are gaps where soybeans have not yet emerged, dig around in the area where there are no plants. If the seed healthy and germinated, but just not broken through, with moisture, the soybeans should continue to emerge."

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