Diseases of Grapevine in Missouri
by Laszlo Kovacs

This disease rarely causes serious damage in Missouri because the weather tends to be too hot and wet for the development of the pathogen. Nevertheless, mild and humid weather may facilitate the development of the disease in susceptible cultivars. Care should be taken when the disease is controlled with sulfur sprays, because many of the hybrid and American grape varieties grown in the state are sensitive to sulfur. Should the disease become a problem, a dormant lime sulfur spray applied shortly before budbreak provides excellent control for the following growing season. Lime sulfur applied during dormancy does not present a danger to sulfur-sensitive varieties. Powdery mildew infection frequently develops on the leaves of most varieties in September and October in Missouri. If the variety is susceptible to the disease, it is advisable to control the pathogen at this stage to prevent a heavy inoculum pressure in the following season.