Every year, weather permitting, farmers seem to be planting corn and soybeans earlier- especially beans. This early planting is one of the most important of several factors that may lead a farmer to consider using seed treatments.

"Not to jinx us, but if the favorable weather holds, bean planting could start in the April window," says Clarke McGrath, Iowa State University Extension crop specialist. "That would make seed treatment information especially pertinent."

Probably, the most common soybean disease problems in Iowa are seedling damping off and seed rot caused by several fungi. Early season damping off and root rots are often followed by premature death, which in many instances may be attributed to fungal infections earlier in the season.

Sometimes large areas of a field or even entire fields need to be replanted due to early season fungal problems. This is especially true when cool, wet weather early in the growing season creates favorable conditions for infection by certain soilborne pathogens that attack developing soybean plants.

Beware of cool, wet weather early

"Several pathogens are involved in damping off seedling diseases, with our most common being species of Fusarium, Phytophthora, Pythium, and Rhizoctonia," he says. "All four are capable of killing soybean seedlings or at least causing sufficient damage so that the plant cannot achieve its full yield potential."

Seed treatment fungicides are available in a variety of formulations. Some products are labeled for commercial use in slurry- and mist-type seed treaters. "This is the most common type many local seed dealers apply," says McGrath. "I tend to favor these, as the coverage is generally good, seed is handled gently, we have access to most of the top products, and we can make the decision to treat/not treat by assessing soil and weather conditions close to planting time."

Other products are labeled for on-farm application, commonly referred to as hopper-box or planter-box treatments. "Good seed coverage is required for maximum benefit, and there are several good products in this line as well--if you don't mind treating your own beans," says McGrath. "Talk with your local seed or chemical dealer for specific information on types of treatments and availability. "

Considerations to help you decide

McGrath lists some factors to help you make up your mind if you are deciding when to use a seed treatment:

"It may take more than one of these factors to lead to problems with plant health, as disease problems are hard to predict," he points out.

Research in southwest Iowa by McGrath and seed suppliers in the area indicate that when conditions meet several of these criteria, the probability of getting a yield response to using a fungicide seed treatment is good. "But we don't have enough years of data yet in our trials to say much more than that," he adds.

A quick rundown of the various types of seed treatments and what they control is at www.extension.agron.iastate.edu/soybean/seedfungtmt.html. "I recommend a broad spectrum treatment if you choose to use a treatment, for protection against the widest range of pathogens. Each brand name may not be listed, but I think every active ingredient in the combination products should be on the list," he says.