Greenhouse and Nursery - More Mum Diseases and Control

The following are control recommendations for several common foliar disease problems in mums.

Alternaria, Botrytis and Septoria are common fungal diseases of mums that affect foliage and flowers. These diseases can be managed using thiophanate methyl (Cleary's 3336), iprodione (Sextant), chlorothalonil (Daconil Ultrex, Pathguard 6F), chlorothalonil & thiophanate methyl (Spectro 90 WDG) or fludioxonil (Medallion). As the plants grow rapidly in August and develop a dense canopy of leaves, treatments may be necessary.

Bacterial leaf spot, caused by Pseudomonas cichorii often occurs during hot humid weather in August. This disease tends to be problematic during years of heavy rains or where overhead watering is practiced. Plants with this disease have large black spots concentrated at the base of the plant. The spots often begin at the leaf margin but may also occur randomly. From the leaf, the bacterium can move through the petiole and into the stem resulting in a canker. The sepals of infected flower buds will become brown to black and up to several inches of pedicel may be killed. Copper hydroxide sprays such as Kocide 101 77 WP or Phyton 27 will help protect against this disease. These materials do not cure the disease, they limit spreading to uninfected plants. Also there are differences in cultivar susceptibility. Make notes when you see susceptible varieties and avoid growing them in the future.

Bacterial leaf spot and foliar diseases are spread by splashing water, which is why we see more of these diseases during rainy years. Drip irrigation helps to prevent foliar diseases. If overhead watering, foliage should always be dry before evening hours.

Information from "Garden Mums - Past Crop Problems and Production Tips" by Tina M. Smith, Extension Floriculture Program, UMASS.