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Soybean seed quality a concernSoybean seed quality a concern

February 21, 2003

4 Min Read

Upper Southeast soybean farmers will need to run their hands through quite a few bags of seed this year, avoid saving seed, plant later-maturing varieties and look for tell-tale signs of poor seed quality following last year’s tough growing season. Other parts of the country are also experiencing seed quality issues from last year’s tough-growing season.

"In all my years of breeding soybeans, I’ve never seen seed quality as bad as this year," says Glenn Buss, retired Virginia Tech soybean breeder.

Phomopsis seed decay and purple stain are the main culprits, but other diseases and insects from last season’s early drought and late August and September rains stamped seed quality concerns across seed from the 2002 crop, says David Holshouser, Virginia Tech soybean specialist.

The practice of saving conventional seed will be extremely risky in 2003. He’s advising seed treatments where problems with purple stain exist, even though "seed treatment is no substitution for good seed quality." The seed quality issue is also giving him an opportunity to emphasize variety selection.

Early drought and continuous rains in the fall set up the problems farmers are now experiencing with seed quality.

The two main culprits, Phomopsis seed decay and purple seed stain, love moisture and warm weather. "If you had a chance to harvest this past season, it was going to rain tomorrow," Holshouser says.

Phomopsis is present in all Virginia soybean fields. It lies dormant until the crop begins to mature and first appears as tiny black specks, small fruiting bodies along the stem. As the stems dried down this past season, moisture and humidity moved the disease into the seeds, causing seed with a white, chalky and shriveled appearance. The seed may not germinate or may be delayed.

The problem was much more severe in full-season soybeans than in double-cropped soybeans. Early Maturity Group (MG) IIIs were much worse than Group IVs, which were worse than Group Vs and Group VIs. Virginia is a Group IV and Group V state. Some soybeans in 2002 were rejected on the Eastern Shore.

The other culprit is purple seed stain, which infects the plant earlier in the year. "It only becomes a problem during falls like we had," Holshouser says. Like Phomopsis seed decay, purple seed stain thrives in moisture and humidity. Its name implies its symptoms. The discolored area ranges from specks to large blotches. Usually purple seed stain infects only 2 percent to 3 percent of soybeans. This season, however, the incidence is running along the lines of 15 percent to 20 percent.

Both diseases result in germination problems, as well as low oil content. Seed decay can result in discounts at the elevator, Holshouser says.

"Both of these diseases will hurt germination and seed quality this year," Holshouser says. He’s been advising seed producers in Virginia and North Carolina to clean out wrinkled, light seed.

He’s also advising against saving conventional seed this year. It’s illegal to save Roundup Ready seed, but almost 25 percent of the soybean acreage in Virginia is planted to conventional varieties.

At the farmer level, "this is probably the first year I’ve not discouraged growers from using a seed treatment." Holshouser points out that a seed treatment is beneficial when planting seed with germination rates of less than 90 percent and when planting into cool, wet soils.

"Seed treatment is no substitution for good quality seed," Holshouser says. "Eighty percent germination with seed treatment is not as good as 90 percent germ."

He advises "trying to find out as much as you can about where the soybeans were grown in 2002." To help lessen the problem for next season, pick soybeans in the late Group 4s and Group 5s. You’re taking a risk growing Group IIIs and early Group IVs in southern and eastern Virginia. In the Virginia Piedmont, Group IIIs and early Group IVs, however, are a good fit. In peanut and cotton areas, the recommendation is Group V. Double-crop soybeans in general have less seed quality problems than full-season soybeans.

"When making variety decisions, farmers need to consider multiple year and multiple location data — not just one year," Holshouser says. "Base your variety decisions on multiple years and locations."

There is little you can do to prevent Phomopsis seed decay or purple seed stain in a year such as 2002. Rotating soybeans with corn will help, as will high-quality, later-maturing varieties under a double-crop system.

Foliar fungicide sprays during flowering and pod development will help avert the diseases, but are a preventative treatment. You may or may not have the disease develop later. Unless soybeans are being grown for seed, foliar applications are not usually economical. e-mail:[email protected]

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