Resistance of the frogeye leaf spot fungus (Cercospora sojina) to strobilurin fungicides (FRAC code 11; Headline, Quadris, Evito, and Approach) has been reported from the Mississippi Delta and other areas in the past several years.
Most finds of resistant fungus strains have been confined to the Mississippi River Valley as far north as Illinois.
Some growers are reporting that management of frogeye leaf spot with fungicides in North Carolina has been poor this year. This may be a result of: 1) applications made in an untimely manner, 2) applications of a less than labeled rate, and (or) resistance of the fungus to the fungicides used.
If an application of a strobilurin type fungicide has been made, then a traizole fungicide (FRAC code 3) should be used if a second application is necessary.
For additional information on this development and control recommendations, visit http://www.nccrops.com/ .
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