Plant Health

Claims continue to be made that fungicide applications made in the absence of Asian soybean rust or secondary disease can improve soybean yields and a producer’s bottom line. Until more evidence offers proof of the “plant health” claims, growers are encouraged to follow Integrated Pest Management principles when determining whether to apply fungicide.

Marty Draper, plant pathologist at South Dakota Statue University, evaluated 65 trials conducted across the North Central region of the United States. The report showed that strobilurin fungicide sprays made absent of soybean rust only provided economic return about one-third of the
time.¹

One-third of the trials actually resulted in a yield loss where strobilurin fungicides were applied. Another third showed yield gains that did not provide a return on investment.

Only in the southern United States has fungicide use proven to provide economical control of late-season diseases, such as frogeye leafspot and Septoria brown spot.

“Greening effect” is the physiological effect associated with the concept of plant health. This effect is thought to be associated with an overall increase in stress tolerance by the plant. However, the drawback of this treatment approach may include delayed harvest due to longer time needed for plant dry down, increased pod shatter as a result of delayed harvest and increased potential for volunteer soybeans as a result of shattering.

Until more is known about the soybean plant’s response to fungicides absent of soybean rust, inconsistent yield response makes their use economically risky.¹