Diseases of Grapevine in Missouri
by Laszlo Kovacs

The pathogen that causes macrophoma rot is a common microorganism in Missouri. The disease used to be known as a fruit rot of muscadine grapes only, but more and more recent observations suggest that it also is an important problem in grape varieties grown in Missouri. In its early stages, the rot is difficult to identify and to differentiate from phomopsis fruit rot. The pathogen is able to grow in numerous woody plant species, causing such diverse diseases as white rot of apples and stem blight of blueberries. Because many other plants can serve as inoculum source, it is important to eliminate abandoned fruit trees from the vicinity of the vineyard. The pathogen appears to be difficult to control in other plant species, and nothing is known about its control in grapes in Missouri. If fruit rots present a perennial problem in the vineyard, the most promising solution may not come from the application of a novel fungicide, but from canopy management. The maintenance of an open canopy that dries up rapidly and that maintains low air humidity is the best way prevent fungal growth.