Tuesday, July 23, 2013

Hollyhock with rust

Hollyhock leaf covered with rust
Hollyhocks get a fungal disease called rust, which produces reddish colored pustules (spots) on the upper and lower surfaces of leaves, stems, and green flower parts and causes early leaf drop. Hollyhock rust attacks only hollyhocks and other members of the hollyhock family (Malvaeceae), including albutilon, hibiscus, lavatera, and malva. 

You can take a few easy steps to prevent the disease from recurring and spreading. Rust, like most fungi, needs water to germinate and grow. So it's important to keep your hollyhocks' foliage and flowers as dry as possible, though this can be difficult in very humid climates. Hand water at the base of the plants, or use soaker hoses to keep leaves dry when watering. Space plants farther apart to ensure good air circulation, and avoid working around plants when they are wet. Don't plant hollyhocks by other susceptible host plants, and be sure to pull any weeds in the mallow family.

If your plants do become infected, remove affected leaves immediately and burn or dispose of them in the garbage. Don't place affected plants in your compost pile. Spores overwinter in infected leaves and stems. Most hollyhocks are biennial, which means that once they produce seed, they die. In late summer, when you see the rosettes of foliage that will provide next year's display, promptly pull up any finished stalks and dispose of them. At the end of the season, be sure to remove any dead plant matter remaining in the bed, because it harbors rust spores and perpetuates the problem. In spring, mulch around the base of the hollyhocks.

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Yellow hollyhock
Hollyhock plant with rust

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