MACROPHOMA ROT
Description
Symptoms
Disease Cycle
Control

Description:
Macrophoma rot affects both bunch grapes and muscadine grapes in the Southeast, but the disease is most destructive on muscadine grapes.

Symptoms:
Early-season infections remain latent and there are no visible symptoms until the fruit begin to mature. When fruit begin ripening, lesions develop that are black, circular and flat, or slightly sunken (Fig.1). The centers of the lesions develop a tan color and become embedded with scattered fruiting bodies called pycnidia. As the lesion expands (Fig. 2) the entire grape may develop a soft watery rot. Fruit eventually drop from the vine, becoming shriveled, hollow, and covered with pycnidia.

Disease cycle:
The causal fungus, Botryosphaeria dothidea, overwinters as pycnidia on infected stems and fruit. Conidia are released from the pycnidia throughout the growing season, and are dispersed to shoots and fruit by wind and rain.

Control:
Cultural - To successfully manage macrophoma rot, begin by reducing the amount of over-wintered inoculum left on the trellis and ground from the previous season. Infected stems and fruit are the major source of primary inoculum for infections, and should be removed from the vine and vineyard floor before spring arrives. Practice good canopy management for control of macrophoma rot. Shoot thinning, leaf removal, pruning, cluster thinning, and shoot positioning are all cultural practices that open the vine canopy to air and light, reducing the amount of moisture trapped within the canopy, and allowing better penetration and spray coverage (Table 1).

Chemical - Refer to the Winegrape Spray Program in the North Carolina Agricultural Chemicals Manual for current recommendations for macrophoma rot control on bunch grapes (http://ipm.ncsu.edu/agchem/chptr7/706.PDF) and muscadine grapes (http://ipm.ncsu.edu/agchem/chptr7/707.PDF). Fungicide applications to control macrophoma rot should begin after bloom and continue throughout the fruit ripening period.