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Soybean diseases: four risk factors to watch

Watch for these foliar diseases

Soybean farmers are familiar with plant disease, but not all diseases are created equal in terms of the damage they can bring. Some foliar diseases, such as bacterial blight and Septoria brown spots, can be found in almost every soybean field at some point in the growing season. Other diseases such as frogeye leaf spot and downy mildew are less frequent.

Foliar fungicides can be effective in controlling Septoria brown spot and frogeye leaf spot, but are generally ineffective when it comes to bacterial blight and downy mildew.

Know the risk factors

  1. Susceptibility of soybean variety –The USB Soybean Quality Toolbox is a useful tool for finding a variety’s resistance to disease. A variety’s susceptibility to frogeye leaf spot, in particular, can usually be obtained from the seed company, especially for maturity groups III and IV.
  2. Previous crop – Foliar pathogens survive in soybean stubble, increasing the risk of foliar diseases when soybeans are planted in back-to-back years.
  3. Weather – Rainy and humid weather fosters the development of foliar diseases, while hot and dry conditions suppress them. Cloudy days and moisture from dew, even without rain, can increase disease spread and severity.
  4. Soybean rust risk – For soybean rust to affect Illinois fields, the pathogen must blow up from the southern U.S. It hasn’t been reported in Illinois yet this year, though it appeared in four Illinois counties in 2013. This risk can be assessed through maps on the IMP PIPE website which show where soybean rust has been detected in the U.S., Mexico and Canada.

Take action

  1. Scouting for diseases– Once soybeans bloom, examine plants for symptoms in at least one area in a field for every 10 acres. Foliar diseases generally appear first in the lower part of the plant and areas protected from the wind and sun—like crops near trees and buildings. Once you spot symptoms, examine the leaves with a hand lens to identify the disease.
  2. Making a decision – When deciding whether to apply a fungicide, consider the four disease risk factors (listed above) and your scouting observations. You’re more likely to increase profits with a foliar fungicide if you use it for disease control rather than disease prevention. If you decide to apply a fungicide, choose the best product for the diseases present and the level of disease pressure.
  3. Applying foliar fungicides – The product will be most effective when applied with the best coverage. Select nozzle tips that deliver droplets between 200 to 300 microns in diameter. It’s also important to follow manufacturers’ recommendations for spray volume—generally a minimum of 15 gallons per acre and five gallons per acre are recommended for ground and aerial applications, respectively.

(Source – http://ilsoyadvisor.com/index.php/article/soybean-diseases-four-risk-factors-to-watch)

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