Cedar-Apple Rust Active


Many people in southern Kansas have noticed the large, bright orange, jelly-like, tendril covered balls on the cedar trees since the rains started last week. These cedar-apple rust galls release millions of spores that can infect apples and crabapples with the rust disease. There is a related disease named cedar-quince rust that infects hawthorn trees. Unprotected, susceptible apples, crabapples and hawthorns are likely infected. Though not yet visible, we can’t cure what is already there. But many of the newer crabapples are naturally resistant. Though they may show signs of the disease, they won’t defoliate like susceptible varieties. Even susceptible varieties that defoliate will throw out a new set of leaves if they were healthy before infection. Significant damage to crabapples is rare. But fruiting apples pour a great deal of energy into the fruit and may be stressed more severely. It will be important to pamper them this summer by keeping them watered. It is also recommended to prevent further infections by applying fungicides through Memorial Day. Several fungicides, including Banner, Systhane, Rubigan, Funginex and Bayleton, applied on a 14- to 21- day interval are very effective in controlling rust. However, most of these products are only available to commercial applicators. Homeowners may use triadimefon (Green Light Fung Away), propiconazole (Fertilome Liquid Systemic Fungicide) or myclobutanil sold as Immunox (same active ingredient as Systhane). Chlorothalonil is also labeled for rust, but it is not as effective as the other products listed and cannot be used on apples. Only myclobutanil can be used on fruiting apples. Fungicide applications to the leaves of hawthorn, apple and crabapple must continue as long as cedar galls remain active (jelly-like). If you don’t want to mess with fungicide applications, use flowering crabapple or apple varieties that are resistant and avoid the use of any hawthorns in areas where cedar-quince rust has been a problem.

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