Grape plants are popular for their fruit and their decorative qualities, but they are susceptible to a variety of different diseases and infections. As a result, you can quickly lose an entire harvest or even an entire set of plants if you do not halt an infection in time. Knowing the signs and symptoms of grape plant diseases will help you keep your grape plants healthy and happy and yielding.
Grape Black Rot
Grape black rot can destroy entire clusters and crops of grapes in short order. It first manifests as small, yellowish brown spots on leaves. As the infection progresses, the spots will develop a dark border and black fungal fruiting bodies will appear inside the spots. When the fruits are about half-grown, the brownish spots will appear on them as well, eventually rotting the fruits away entirely and leaving small, grape "mummies" on the vine. You must use sterile pruning to remove all affected foliage and fruit immediately. Burn the debris or dispose of it in airtight bags. The next growing season, apply black rot fungicides to the vine before the plant blooms to prevent the growth of any remaining spores that you did not get rid of the season before.
Downy mildew grows on grapes that are growing in an environment that is too moist and humid. It can be hard to spot at first since the initial infections are a very pale yellow and hard to see. However, as the infection spreads it will develop a dense, cottony growth that can cover leaves and the fruits of the plant as well. To control the infection, make sure that your plants are getting plenty of sun, and water using a drip hose to keep the leaves dry. Remove all dead leaves and dropped leaves from the area on a daily basis. Control weeds and tall grasses to improve air circulation. You can control downy mildew with fungicides, but you must consult local regulations before selecting one.
Grape Leafroll Virus
Grape leafroll is also called red leaf disease and white emperor disease. It causes the lower foliage of grape plants to redden or yellow in September or October, and is associated with depressed yields. It delays foliation and also may stunt fruit growth. Since leafroll is a virus, you must control the vectors associated with the virus to stop the infection. Eradicating mealybugs, sterile pruning and destruction of affected areas of the plant and removal of debris in the planting area are all essential elements of controlling the virus. If you cannot get rid of the virus, you may have to quarantine the area and plant something other than grapes for a few years until you are sure it is gone.