I have some peony bushes that had buds on them, but didn't open.
They were black and hard. I have been told to use
|Peonies have few pests or problems. The most frequently occurring pests are botrytis blight and leaf blotch, both fungal diseases. Especially prevalent during wet springs, botrytis affects leaves, stems and flowers. Spots appear on leaves, stems soften and decay, and flowers either rot or buds blacken and fail to open.
Sanitary measures offer the most effective means of control. Start with a thorough cleanup of old, infected stems and leaves and other plant debris in the fall. This reduces the overwintering site for the fungus. Pull the soil away from the crown, without injuring the buds.
In the spring, remove and destroy any wilted or rotted shoots as soon as you detect them. If mulch or another covering is used for winter protection, remove it in the spring before the new shoots emerge from the soil.
Improving air circulation and penetration of sunlight to peony plants often solves the problem. Sometimes, however, chemical control is necessary. If so, spray with a fungicide labeled for botrytis blight, when new shoots appear in the spring. Follow 2 weeks later with another application and every 14 days thereafter until mid-June. Pesticides registered for use include copper fungicides, captan, Daconil, mancozeb, maneb, sulfur, and thiophanate methyl (Cleary 3336). Fungicides must be applied in advance of the disease as a protectant. Be sure to follow label instructions.
Ferti-lome Halt Systemic Fungicide is a broad-spectrum fungicide but, as you've discovered, can be rather expensive. Best wishes with your peonies.