Black rot of grape is an important fungal disease of American origin that was probably spread to the Old World through the importation of phylloxera resistant rootstock. Primary infection usually arises from infected fruit from the previous season and all green tissue of the grapevine is susceptible to infection. Brown circular lesions appear on infected leaves and within a few days, black fruiting bodies are formed within the lesions. These leaf lesions then become the primary source of infection to developing
fruit clusters. An infected berry first appears light brown, soon the entire berry turns dark brown, and black pycnidia develop on its surface. Infected berries shrivel, turn hard and black and are called mummies. The black rot organism overwinters in mummified fruit on the vine and on the ground. Spring rains trigger the release of airborne ascospores from mummies and subsequent infection of susceptible tissue takes place if temperature and duration of leaf wetness are conducive.
Pycnidia form within lesions and produce pycnidiospores that are spread by rainfall. Leaf lesions are capable of producing spores and causing secondary infection approximately five to seven days after they first appear. Control of black rot is based on properly timed applications of fungicides.
Black Rot Infection Chart
*R.A. Spotts, Ohio State University
*Note that at 55’F, it takes 12 hours of leaf wetness for infection to occur, but only 6 hours at 80’F. Most fungicides are protectants and must be applied before an infection period to provide effective control. Fungicides that provide “reach-back” properties must be applied within a specific time period after the infection period starts. Site selection, row orientation and canopy management techniques that increase airflow and decrease canopy-drying time can be beneficial in a black rot management program.
See the Fungicide Efficacy Table for comparisons of various labelled fungicides.