Problem Identifier Unit Screen//v.w/ RR Template

Problem Identifier Unit Screen//v.w/ RR Template Rust

Problem
Yellow or orange spots appear on the upper surfaces of the leaves in the early spring. Grayish brown pustules develop on the undersides of the leaves and possibly on the stems. These pustules may turn dark brown to black as the growing season progresses. Severely infected leaves shrivel, turn gray or tan, and hang down.

Analysis
This fungus (Puccinia malvacearum) causes the most serious and widespread disease of hollyhock. The fungus spends the winter as spores on living plant tissue and plant debris. Infection starts in the early spring as soon as conditions are favorable for plant growth. The spores are spread to healthy plants by splashing water and air currents. A number of weeds known as cheeseweeds or mallows (Malva species) are frequently infected with rust, and are a source of spores. Rust is also favored by wet conditions.

Solution
Spray with a fungicide containing chlorothalonil in the spring as soon as the first signs of infection are noticed. Spray the foliage thoroughly, being sure to cover both the upper and lower surfaces of the leaves. This fungicide protects the new, healthy foliage but will not eradicate the fungus on diseased leaves. Spray once every 7 to 10 days, or as often as necessary to protect new growth until the end of the growing season. Remove and destroy all infected foliage and any nearby cheese-weeds in the fall when the plant has stopped growing, and again in early spring. Pick off and destroy infected plant parts during the growing season. Water early in the day so that foliage will dry thoroughly.

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