Cercospora leaf spot identified in Michigan sugarbeets

David Wishowski<wishowsk@msu.edu>, Michigan State University Extension - July 02, 2025

Updated from an original article written by Steven Poindexter.

Identifying Cercospora leaf spot is key to managing fungicide application timing.

A sugarbeet leaf with black spots on it caused by Cercospora leaf spot. — Cercospora infection at this level is well beyond the economic threshold. Photo by Jaime Willbur, MSU.

Cercospora leaf spot is the most serious foliar disease in Michigan sugarbeets. If not managed properly, leaf spot will reduce both tonnage and sugar content. Research trials conducted by the Michigan Sugar Company have shown reductions in net revenue of $120 per acre or more if left uncontrolled. Progress has been made in controlling Cercospora in Michigan with the introduction of fungicides, CR+ technology and utilizing the BEETcast prediction model.

The single most important Cercospora leaf spot fungicide spray is the first application. Research indicates the best timing of fungicide for control and net revenue occurs just prior to the first spot being found. Timing of the first and subsequent fungicide applications should be applied according to the fungicide label coupled with the BEETcast disease severity values (DSV) for your management zone and variety tolerance. You can access the BEETcast model and spray recommendations at MichiganBeets.com. The timing of the first spray should never be delayed beyond the first spot being found in the field.

Even though the BEETcast model is currently showing low to moderate DSVs, Cercospora leaf spot was found in two fields as of July 1, 2025. These fields are in what is referred to as a “Red” zone and often where Cercospora is found first in the growing season.

Remember, fungicides classes should always be rotated. To reduce the chance of Cercospora developing further fungicide resistance, fungicides can be tank-mixed with unrelated types of compounds such as EDBC or copper. Always scout fields in conjunction with the BEETcast spray model. Follow labeled directions for application and pre-harvest intervals.

For additional information, visit the Michigan State University Extension Sugarbeets website.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).