Grape Black Rot. Leaf wetness duration-temperature combinations necessary for grape foliar infection by black rot. Lesions on canes from the previous season can also produce conidia for a period of at least one month starting at budbreak. Cane lesions are probably most important in mechanically pruned or hedged vineyards that have an abundance of canes in the canopy. All green tissues of the vine are susceptible to infection.
Leaves are susceptible for about one week after they reach full size.
Brown circular lesions develop on infected leaves about 9 to 11 days after infection. These conidia are spread by rain splash and can cause secondary infections of leaves and fruit throughout the growing season. Therefore, it is extremely important to control the early season primary infections caused by ascospores. Remember, infection by one ascospore can result in the development of millions of secondary conidia in the vineyard. The fruit infection phase of the disease can result in serious economic loss.