Black Rot on Grapes - Solution Guide
Black Rot on Grapes
Black rot is the most widespread disease of grapes. This fungal disease often causes grapes to turn brown and shrivel. Most prevalent in warm, humid weather, this disease can cause a complete crop loss if proper precautions are not taken.
Symptoms
Black rot symptoms first appear on the leaves as small light tan spots with circular centers and darker tan margins.
- Fruit symptoms do not appear until the berries are half-grown. Then, berries turn brown and rapidly shrivel, becoming small, black, and hard. These dried, diseased grapes are referred to as mummies.
- Once black rot is discovered, very little can be done in that season to avoid fruit losses.
- Importantly, Black rot is a cumulative disease, starting the first season or two with little to no detection, or the grower often misdiagnoses it.
- It is essential to note that once fruit mummies are discovered on the vines, the disease has already been active there for a season or two, so it can take an equal number of years to suppress and control the disease.
Management & Control of Black Rot on Grapes
- Practice good sanitation. When black rot appears, begin sanitation cleanup immediately, writing off the current crop. Collect and destroy all fruit because any left behind will be a source of infection next year. Mummies can fall to the ground and be obscured by turf grass, so lawns under vines should also be carefully raked and cleaned up.
- In late winter, just before buds begin to break open, remove all the previous season's fruit-bearing stems, which likely still harbor disease, and start a spray program.
- Provide excellent air movement around & through the vines. Select a sunny open area and use proper row orientation. Perform annual dormant pruning.
- Use fungicides as soon as shoots emerge from the vine. During wet weather, applications should be at most seven days apart. Spray regularly until pre-fruit ripening, even during rain events, to maintain the schedule.
- Fungicides like Captan®, Sulfur, Liquid Copper, or Neem oil can all be used in rotation.
- Rotate applications of at least two different fungicide products during the season, paying attention to individual product application instructions since different products will have differing application intervals.
- Be sure to get sprays on the plant's interior where the disease is most present. Also, thin the foliage out for better ventilation.
Note: Generally, all organic fungicides currently listed for black rot have weak effectiveness. Copper has moderate efficacy if applied very regularly but the fungus may become more resistant after a while. If spraying with copper, rotate with Sulfur or Neem for the highest effectiveness.
**Always read and follow all product label instructions and safety warnings.
As with other fungal diseases, cultural practices, such as proper annual pruning, help open the canopy and promote quicker foliage drying. An open foliage canopy enhances fungicide spray coverage.
