Identification and Control Methods of Rhododendron Flower Rot

Symptoms Rhododendron flower rot only harms the flowers, causing the flowering period to shorten, flowers to droop, and early withering and dropping. After the petals are infected, the diseased parts lose their luster, become water-soaked, soft and discolored, and finally turn brown, rot and blacken; when humid, a gray mold layer grows on the surface, affecting ornamental value.

Pathogen and disease pattern This disease is caused by a fungus of the class Hyphomycetes, subphylum Deuteromycotina. The pathogen forms sclerotia on rotten flowers, and the sclerotia fall into the soil with the spent flowers to overwinter. In the flowering period of the following year, conidia are produced, spread by wind and rain or air currents, and invade the host tissue when the flowers sprout, forming lesions. The disease is generally severe in the spring rain season. The disease symptoms on the petals of red varieties are dirty white to brown spots, and on the petals of white varieties are light brown spots. Later, black irregular flat sclerotia are produced on the rotten flowers. They fall into the soil with the flowers to overwinter.

Control methods

1. After the rhododendron flowers fade, promptly dispose of diseased residual plants, flowers and fallen leaves, and burn them in a centralized manner to reduce the source of infection.

2. Mix 1 part of 50% benomyl wettable powder with 50 parts of plant ash, stir well, and scatter it on the surface soil of flower beds and flower pots. Starting from before flowering in early spring, spray 1000- to 1500-fold thiophanate-methyl solution 1 to 3 times every 7 to 10 days, which can control the disease.

3. When the disease occurs, spray 120- to 160-fold equal-amount Bordeaux mixture or 800- to 1000-fold 50% amobam solution.