Remove leaf debris, check drainage to avoid diseases in black-eyed Susans

Backyard Q&A

August 08, 2004|By Jon Traunfeld & Ellen Nibali | Jon Traunfeld & Ellen Nibali,Special to the Sun

My black-eyed Susans for the second year have developed brown spotty leaves. Some leaves brown completely and dry out. This happens when they are about 8-10 inches tall before they bloom. It doesn't affect the blooms, which is what black-eyed Susans are all about, but the leaves ruin the effect of the flowers. They are in full sun and the soil is a clay-topsoil mix. Do you have any idea what may be causing this?

There are several possibilities. Rudbeckia are prone to many leaf spot diseases, with septoria leaf-spot fungus being the most prevalent. Septoria causes small dark brown lesions that enlarge from 1/8 inch to 1/4 inch, usually starting on bottom leaves and spreading upward. Anthracnose, a fungal disease rampant during wet years (last year and this), appears as dark colored spots or lesions that eventually run together and cause blighting of leaves and stems.

The first method of control is prevention. Unsuitable growing conditions aid disease. Rudbeckias require good drainage and will not like a soggy garden bed. Adding organic soil amendments will improve your clay soil's drainage. Pick up infected fallen leaves to prevent spores from spreading. A good fall cleanup helps, too. When plants are too close together, air circulation is reduced and a humid climate is created that is conducive to the spread of fungal disease. Copper fungicide can stop disease spread and protect new growth, too. Ideally, spray before the onset of symptoms or at sight of the first infected leaf.

Jon Traunfeld, regional specialist, and Ellen Nibali, horticulture consultant, work at the University of Maryland Cooperative Extension's Home and Garden Information Center. The center offers Maryland residents free gardening information and answers to plant and pest questions. Call its hot line at 800-342-2507 (Monday through Friday, 8 a.m.-1 p.m.) or e-mail questions to www.hgic.umd. edu. (You can also download or order publications and diagnose plant problems online.)

Checklist

1. Control yellow nutsedge by hand-pulling plants (as soon as they appear), or by applying a labeled herbicide containing MSMA.

2. Contact the animal control office in your county and learn the rules before live-trapping nuisance wildlife.

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