Wisconsin Corn Southern Rust Update – August 26, 2016

Damon L. Smith, Extension Field Crops Pathologist, University of Wisconsin-Madison

Corn Southern Rust positive confirmation map, by state county

Corn Southern Rust positive confirmation map, by state county

Southern rust of corn has been confirmed for the first time this season by the UW Plant Disease Diagnostic Clinic (PDDC) in Wisconsin. The positive sample was submitted from Rock Co. along the Wisconsin/Illinois state line and confirmed on August 25, 2016. As previously predicted, southern rust did make it to Wisconsin this year, however, its arrival is late enough that it should have minimal impact on yield. We published an article on WisContext about some reasons why this occurrence was expected in 2016, you can click here to learn more.

Most corn in Wisconsin is at least well into the milk stage (R3) or dough (R4). Once corn reaches the milk stage (R3), risk of yield loss from this and other foliar pathogens begins to quickly decline. Thus spraying fungicide at this time of the season is not recommended. If you would like to learn more about telling the difference between the two types of rusts that occur on corn, or management of southern rust specifically, see my previous article by CLICKING HERE.

If you need assistance in identifying rust on corn, leaf samples of corn plants can be sent in a sealed plastic bag with NO added moisture to the University of Wisconsin Plant Disease Diagnostic Clinic (PDDC). Information about the clinic and how to send samples can be found by CLICKING HERE.