Long-season labels and late blight updates impacting Michigan potato production

Jaime Willbur<willbur1@msu.edu>, Michigan State University Extension, Department of Plant, Soil and Microbial Sciences - July 23, 2025

Three special local needs labels for Bravo and Echo products cancelled and withdrawn following an EPA Interim Decision for active ingredient chlorothalonil.

Composite image showing symptoms of potato late blight. The top image displays an entire infected plant. The bottom left shows water-soaked lesions with light green borders on the upper leaf surface. The bottom right shows fuzzy, gray-white growth along lesion margins on the underside of a leaf. — Figure 1. Examples of potato late blight on whole plant (top) with typical water-soaked lesions on forward (bottom left) and reverse (bottom right) sides of leaves. Light green border sometimes present around lesions. Faint gray-white, fuzzy growth observed at margins of lesions on the underside of leaves, apparent in humid conditions. Photo by Jaime Willbur, MSU.

Three special local needs (SLN) labels for Bravo and Echo products are cancelled and withdrawn following an Environmental Protection Agency (EPA) Interim Decision for the active ingredient chlorothalonil.

In Michigan potatoes, chlorothalonil-containing products are a critical backbone in preventative early and late blight fungicide programs. Current maximum use rates for these products are 11.25 pounds of active ingredient per acre per year. Due to persistent risk and extended growing season length in Michigan, the Federal Insecticide, Fungicide, and Rodenticide Act Section 24(c) SLN labels allowed for increased maximum use rates of 16 pounds of active ingredient per acre per year “for control of diseases on full-season potatoes grown under irrigation.”

After a mandatory 15-year registration review process that began in March 2012, “EPA identified dietary risks of concern and ecological risks of concern for chlorothalonil and identified necessary rate reductions to reduce the amount of chlorothalonil entering drinking water, thus reducing dietary exposure and risk in vulnerable soils.”

"Vulnerable soils" are:

Sand, loamy sand or sandy loam soil, as defined by the U.S. Department of Agriculture’s soil classification system without a restrictive layer that impedes the movement of water through soil.
Less than 2% organic matter content.
Where the water table is 30 feet or less from the surface.

Soils that do not meet all three of these criteria are considered “non-vulnerable.”

The EPA Interim Decision (December 2024) identified maximum annual rate reductions across many crops and agricultural use sites. In potato, new seasonal use limits have been reduced to 8.0 pounds of active ingredient per acre per year in non-vulnerable soils. However, much of potato production is conducted on sandy soils, therefore this rate will further be reduced to 6.5 pounds of active ingredient per acre per year in vulnerable soils. These label changes are expected to take effect in 2026.

Despite initial efforts and intentions to renew SLN labels, 24(c) labels for Echo 720 (EPA Reg. No. 60063-7; SLN No. MI 180004) and Echo 90DF (EPA Reg. No. 60063-10; SLN No. MI-180003) were cancelled and for Bravo Weather Stik (EPA Reg. No. 66222-276; SLN No. MI-190002) withdrawn and not renewed. Previous labels expired Dec. 31, 2024.

The single remaining 24(c) SLN label for Bravo ZN (EPA Reg. No. 66222-278; SLN No. MI-180006) “For Control of Disease on Potatoes” will remain valid until the cancellation process is completed this year. This label is currently valid until Dec. 31, 2025 and will be available at Michigan Department of Agriculture and Rural Development (MDARD) 24(c) Special Local Needs Pesticide Labels until its cancellation. For additional details, information and questions, contact Kevin Kern, MDARD pesticide registration specialist, at kernk@michigan.gov or 989-239-7637.

On July 17, potato late blight was reported in Dufferin County in Ontario. Additional details available in the article “Late Blight Update – July 17th, 2025” from ONvegetables. Testing of the genotype for the Phytophthora infestans pathogen is in progress. However, previous year detections were typically US-23, which is still considered sensitive to phenylamide fungicides including mefenoxam and metalaxyl (Ridomil). No additional recent late blight detections have been reported and current season risk maps are available through the USABlight Current Outbreak Map. Michigan State University Extension strongly recommends preventative foliar programs for late blight (Table 1) and early blight (Table 2) and diligent crop monitoring.

The current late blight risk in Michigan is generally medium, however, areas in southwest Michigan may have experienced more favorable conditions in the past several weeks due to frequent rain events. Late blight forecasting tools for Michigan State University (MSU) Enviroweather are in development this season and will be available soon. In the meantime, tools for the Upper Midwest are available through the UW-Madison Vegetable Disease & Insect Forecasting Network.

Color-coded map showing late blight risk levels across the upper Midwest. Risk levels range from very low (green) to very high (red). Most of Michigan shows low to medium risk, with some very low and isolated high-risk zones. Surrounding areas in Wisconsin, Illinois, and Indiana display mostly low to medium risk. Major cities are labeled, including Detroit, Chicago, Milwaukee, and Grand Rapids. — Figure 2. July 22, 2025 late blight risk as reported by the UW-Madison Vegetable Disease & Insect Forecasting Network. Green = very low, light green = low, yellow = medium, orange = high, and red = very high.

Table 1. Registered products for control of potato late blight listed in the 2024 Midwest Vegetable Production Guide.

Products	Active Ingredient	FRAC Group	Rate (per A)	PHI (days)
Bravo, Echo, and Equus, Initiate	Chlorothalonil	M5	Various	7
Curzate 60DF	Cymoxanil	27	3.2 oz	14
Gavel 75DF	Mancozeb + Zoxamide	M3, 22	1.5-2.0 lbs	14 (3 MI)
Dithane, Manzate and Penncozeb, etc.	Mancozeb	M3	Various	14 (3 MI)
Orondis Opti (Premix)	Chlorothalonil + Oxathiapiprolin	M5, U15	1.75-2.5 pts	7
Orondis Ultra (Premix)	Oxathiapiprolin + Mandipropamid	U15, 40	5.5-8.0 fl oz	14
Omega 500F	Fluazinam	29	5.5 fl oz	14
Previcur Flex	Propamocarb hydrochloride	28	0.7-1.2 pts	14
Ranman 400SC	Cyazofamid	21	1.4-2.75 fl oz	7
Revus Top 2.08SC	Mandipropamid + Difenoconazole	3, 40	5.5-7 fl oz	14
Tanos 50 WDG	Cymoxanil + Famoxadone	27, 11	6.0-8.0 oz	14
Zampro	Ametoctradin + Dimethomorph	45, 40	11-14 fl oz	4
Zing!	Zoxamide + Chlorothalonil	22, M5	30-34 fl oz	7

Table 2. Registered products and active ingredients for control of potato early blight listed in the 2024 Midwest Vegetable Production Guide.

Products*	Active Ingredient	FRAC Group	Rate (per A)	PHI (days)
Azteroid (FC), Quadris (SC)	Azoxystrobin	11	Various	14
Bravo, Echo, Equus, Initiate	Chlorothalonil	M5	Various	7
Dithane, Manzate and Penncozeb, etc.	Mancozeb	M3	Various	14
Endura (WG)	Boscalid	7	3.5-4.5 oz	10
Endura Pro	Boscalid + Mefentrifluconazole	7, 3	18.5-20 fl oz	10
Gavel 75DF	Mancozeb + Zoxamide	M3, 22	1.5-2.0 lbs	14 (3 MI)
Headline (SC)	Pyraclostrobin	11	6-9 fl oz	3
Luna Pro	Fluopyram + Prothioconazole	7, 3	10 fl oz	14
Luna Tranquility (SC)	Fluopyram + Pyrimethanil	7	8-11.2 fl oz	7
Miravis Prime (SC)	Pydiflumetofen + Fludioxonil	7, 12	9.2-11.4 fl oz	14
Quadris Opti (SC)	Chlorothalonil + Azoxystrobin	M5, 11	1.6 pt	14
Quadris Top	Azoxystrobin + Difenoconazole	11, 3	8-14 fl oz	14
Revus Top 2.08SC	Mandipropamid + Difenoconazole	3, 40	5.5-7 fl oz	14
Rovral	Iprodione	2	1-2 pt	14
Scala (SC)	Pyrimethanil	9	7 fl oz	7
Tanos 50 WDG	Cymoxanil + Famoxadone	27, 11	6.0-8.0 oz	14
Velum Prime (SC)	Fluopyram	7	6.5-6.84 fl oz	7
Zing!	Zoxamide + Chlorothalonil	22, M5	30-34 fl oz	7
Velum Prime (SC)	Fluopyram	7	6.5-6.84 fl oz	7
Zing!	Zoxamide + Chlorothalonil	22, M5	30-34 fl oz	7

Contact MSU Potato and Sugar Beet Pathology at willbur1@msu.edu or 517-355-4754 or MSU Plant & Pest Diagnostics at pestid@msu.edu or 517-355-4536 to report potential late blight detections or visit our websites for more information.

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).