Ash rust detection and control |

Ash rust detection and control

David Lott
Horticulture Extension Educator
North Platte, Neb.

Each season, a handful of insect or disease related problems arrive in higher concentrations than in the past. This week, I would like to discuss more about ash rust that has infested ash tree species in western Nebraska.

Ash rust is found periodically in Nebraska when wet and humid conditions provide a favorable environment for the fungus Puccinia sparganioides to grow and thrive on green, white and black ash species. Ash rust is also known to live on and survive the winter in cordgrass and marsh grass.

Infestations are usually found on leaves, but it has been found on the leaf stems this year in western Nebraska. Yellow or orange spots are first noticed. After two weeks, bright orange lesions can be found on the leaves, leaf stems, and the underside of leaves. Concentrated infestations can cause early leaf defoliation. Current year shoots can become deformed, or possibly die in severe cases.

Homeowners can spray trees with an appropriate fungicide at bud break stage until the foliage is fully developed. Fungicides available for sale to homeowners include products containing chlorothalonil or propiconazole on the active ingredient label. Systemic fungicides containing thiophanate-methyl can also be applied, reducing the number of applications. Please read and follow all application and safety precautions when applying these products.

Supplemental deep trickle water can also be applied to reduce the stress on the host tree if the host tree is not in an area providing irrigation in the landscape. The important thing is to watch for infestations, defoliation of leaves, and sanitation in the landscape.

If you have any questions about ash rust, please contact me at, by calling (308) 532-2683, or by contacting your local University of Nebraska-Lincoln Extension Office.

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