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Peony Blights

Source: NDSU Extension Horticulturists

Springtime in North Dakota often brings about two distinct peony diseases: a fungus, Phytophthora, and a mold, Botrytis. Symptoms are very similar and control measures are somewhat alike. Distinguishing the two diseases is not always easy, but control is basically the same.

Look for common symptoms of the fungal disease on the foliage and stem. Dark brown or black leathery diseased areas may occur on any part of ~he above-ground plant tissue: the young shoots, leaves, buds and sometimes more mature stems. When the disease attacks the lower stem, black lesions several inches long appear and the shoots then collapse. In severe cases, the disease may invade the entire crown of the plant. The disease is usually more severe in cool springs, but very wet conditions are even more favorable.

The fungus organism overwinters in the plant debris from the previous year and in the surrounding soil.

The symptom of Botrytis is a gray or brown growth. Botrytis can attack the foliage, producing symptoms like Phytophthora. The main damage occurs to the bud. The buds turn brown and die, and the stalk rots.

To control both diseases, start with sanitation. Carefully clean up plant debris at the end of the season. Remove diseased plant parts as soon as they appear. Replace the top 2 inches of soil around diseased plants with fresh soil. Cover with sand or pebbles to prevent the disease from spreading from splashing rains.

Both diseases are seldom serious except when spring weather is wet. Peony beds with a history of disease can be sprayed with Benlate several times at 5 to 10 day intervals. Begin a spray program when new shoots emerge. Benlate can be used to control Botrytis only. Read and follow all label directions.

For future reference, you may want a copy of Extension bulletin H-281, entitled "Peonies," which is available free of charge at your county Extension office.

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