Garden mum growers who are encountering rainy, humid weather should be regularly checking their plants for root rot problems. Univ. of Md. extension specialists advise growers to regularly check the growing medium soluble salts level. If a controlled-release fertilizer was applied make sure it did not release all of the nutrients during warm weather periods. During hot humid weather roots can be injured making them more susceptible to root rots.
Maryland growers also submitted garden mums for plant damage that was identified as feeding by Pyrallid caterpillars on the inner growth of the plants. Control sprays of Bacillus thuringiensis, Conserve, Pylon (greenhouse only) and Acephate need to penetrate into the interior of the plants in order to be effective.
Saltmarsh caterpillars and yellow-striped armyworms have also been feeding on mums. Early instar saltmarsh caterpillars do not feed through the leaf. Look for thin, brown areas on the leaves. Later stages of this caterpillar eat holes in the leaves.
Grasshoppers are also feeding on mums and other ornamental plants. Look for chewing damage on the leaves.

Pictured: Saltmarsh caterpillar damage on mums
Photo by Shannon Wadkins, Univ. of Md.