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Corn and Soybean Disease Scouting Challenges This Year

This growing season has had some unusual weather. And it may be affecting what you should be looking for when scouting your fields.

“Weather has been a big factor this year. So be aware of that and how it’s interactive with some of the diseases,” says Laura Sweets, University of Missouri plant pathologist.

Scouting corn

“July is usually the time we start to see foliage diseases on corn,” says Sweets. “We’re seeing a little bit, but the grey leaf spot, common rust, and southern rust really like warmer conditions. Those are the ones that the cold snap slowed down.”

The cool weather may have only slowed them down. There’s still potential for them to establish in Missouri cornfields.

“If we move into a warm and wet spell, then the grey leaf spot and rusts have potential of taking off again,” says Sweets.

Yet there’s good news: As we move along in growth stages, the potential for yield loss drops off. The later in the season the diseases become established, the less likely you are to have yield loss, says Sweets.

Scouting shouldn’t stop just because diseases have had delays in establishing themselves. Other diseases are showing up in areas where they aren’t typically an issue, and it’s important to be aware of those.

“Northern corn leaf blight is a disease we don’t normally see a lot of in Missouri, but with the cooler temperatures, that might be one that’s showing up,” says Sweets.

“Later in the season, stalk rots and ear kernel rots start showing up,” says Sweets. “We’ll start scouting for them more toward the end of August and the beginning of September.”

Scouting soybeans

“Soybeans also got off to a rough start,” says Sweets. “We had such fluctuation in soil temperatures and moisture.”

Sweets saw Phytophthora as seedling blight earlier this year, and says you may also see Phytophthora taking out larger plants this time of year. Generally the whole plant turns color – gray, green, or yellow, and it wilts and dies. It could be showing up in varieties that don’t have good resistance or field tolerance.

This is also the time when you start to see some of the leaf spot diseases on soybeans. “We’re starting to see some of those diseases, but they aren’t real severe or widespread yet. Part of that is cool temperatures aren’t going to favor them as much,” says Sweets.

Sudden death syndrome (SDS), caused by a soil fungus, is causing some concern for Sweets. It enters the roots on the seedlings, and then you see symptom expression as the plants are moving from the vegetative to reproductive growth stages.

“Usually, it’s August when we really start to see symptoms,” says Sweets. “But I have found a few plants with symptoms of SDS. Symptom expression tends to be more severe when you have cool weather conditions.”

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