Soybean Fungicide Seed Treatments - Do They Pay?

Fungicide seed treatments on corn and wheat are standard practice but the majority of soybeans planted in Ontario are not treated. Under ideal conditions soybeans do well without a seed treatment. However, cold wet spring conditions like those in 2002 have lead many producers to look more closely at soybean seed treatments.

Seed Rots & Seedling Blights

Seed rots and seedling blights are caused by a number of different fungi. In Ontario Pythium, Phytophthora, Phomopsis, Fusarium and Rhizoctonia are most often associated with early-season emergence and vigour problems. Seed infected by these organisms in the ground may rot or die shortly after germination. Seedlings that do emerge may be diseased suffering from delayed growth, wilting, or dieback. Although some fungi pathogens can be seed-borne, various fungi are already present to some degree in most Ontario soils. The extent of damage these diseases will cause depends on moisture, temperature, overall plant health, and soil type. Generally speaking cold wet soils make for the worst disease outbreaks.

Most Beneficial During Early Stress

Seed treatments are most beneficial when seedlings are stressed during the first couple of weeks after planting. Cold wet soils, crusting, heavy rains, compaction, and even postemergent herbicides can all cause stress. Seed treatments provide some protection to fight off pathogens during these stresses. Please see the following table to see which treatments are effective against various diseases.

Pioneer Trials

Nineteen side by side trials conducted by Pioneer in 2002 with Maxim/Apron showed a yield increases of 1.42 bushels per acre. A plant stand increase of 33% was also observed when using Maxim/Apron compared to the untreated check. Remember though that the spring of 2002 was cold and wet so we would expect more benefit from a seed treatment last year than we might see in an ideal spring.

RCAT Trials

Research results from soybean seed treatments are often not as clear-cut as the Pioneer data mentioned. Experiments conducted by Ridgetown College (University of Guelph) showed a significant yield advantage only one out of four years from 1998 to 2001 in the trials they conducted. During the other three years no significant yield advantage was evident. Why are research yield results often inconsistent? One of the main reasons is that environmental conditions have a tremendous influence on the extent of damage root rots can inflict on soybeans in any given year. Under ideal growing conditions a disease may never develop to any large extent but under cold wet conditions damage may be extensive.

When Recommended?

With the higher seed costs associated with the Roundup Ready production system the added plant stand protection provided by a good seed treatment is worth considering. It may also be possible to decrease seeding rates by 5 or 10% when using a seed treatment to help recoup some of the cost of the seed treatment. However, more research trials are needed in Ontario before decreasing seeding rates can be made as a general recommendation.

Seed treatments are highly recommended if the field has a history of disease, when planting early, or if the field is no till. No-till may increase the likelihood of cooler wetter soils early on, which may increase the risk of soil borne diseases. But even under "ideal" conditions a seed treatment should be considered. The weather may quickly turn for the worse.

Cheap Insurance Against Replants

Will soybean seed treatments pay every year? Probably not, but think of soybean seed treatments as having some cheap insurance against replants and re-sprays. Any possible yield advantage is a bonus on top of that. Try soybean seed treatments for yourself.

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