The use of seed treatments for early season insect and disease management

By Dusty Sonnenberg, CCA, Field Leader, a project of the Ohio Soybean Council and soybean check-off.

Planting progress continues across Ohio going into the fourth week of May. As crops are emerging, stand evaluation is taking place. It is also the time to be on the lookout for early season insect and disease pressure.

The environment a crop is planted into can contribute to both insect and disease pressure on the newly established crop. “When it comes to seed corn maggot, the biggest risk factor for having a seed corn maggot problem in the first place is for farmers who disk in any type of organic matter into the soil before planting. That would include a cover crop, or previous alfalfa field, or disking in manure,” said Dr. Kelley Tilmon, OSU Extension Entomologist. “If planting occurs within a week to 10 days after that organic matter is incorporated into the soil, flies that lay the eggs for seed corn maggots are attracted to the rotting smell and that is where they will lay their eggs.”

“Fortunately, the seed corn maggots don’t set up permanent populations in fields. They are opportunistic,” said Tilmon. “They will come in each year and lay their eggs in the fields they are attracted to. A strategy to avoid seed corn maggots is to avoid the practices that would attract them to the field. If you do use practices that incorporate organic matter into the soil prior to planting, then use a moderate to high rate of insecticidal seed treatment to protect that seed.”

For early soybean disease management, a similar approach should be taken. “First we need to know what disease problems or pathogens are present in the field,” said Dr. Horacio Lopez-Nicora, OSU Extension Soybean Pathologist and Nematologist. “Many times, there may be multiple pathogens present, attacking the seedlings in the early stages. It is important to know what you are concerned with because the products that are effective against the water molds, the oomycetes such as phytophthora and pythium, will absolutely have no effect on the other true fungi, like fusarium, rhizoctonia, and other early season pathogens. There is genetic resistance available, and most of the time it will be listed on the seed information for the variety you are selecting to plant. Some may be in the form of genes that confer resistance to a specific pathotype or race. Others may be a quantitative resistance that is more broad in the sense that they can protect against several races of a specific pathogen (such as phytophthora).”

A strategy is to avoid planting into a seed environment that favors the pathogens and gives them an advantage over the seed.  “If a farmer can wait to plant when soils are warmer and if fields are well drained, and not plant into cool wet conditions then it will help the seed get a better start,” said Lopez-Nicora. “Unfortunately, there are times when it cannot be avoided. This past April, farmers planted when the weather and soil conditions were beautiful, and then we experienced a week of rain and cold temperatures, and those conditions came after the seed was already in the ground.”

“The past several years we have experienced similar extreme weather changes, so it is a good practice to take advantage of seed treatments, knowing what pathogens may be present, and also to protect the seed by selecting varieties with the best resistance,” said Lopez-Nicroa. “These are great ways to prevent stand reduction and yield losses.”

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