Grapes are a sweet and juicy snack, especially if they are grown from your own home vineyard. When growing grapes, however, it is important to keep a close eye not only on the fruit itself, but on the leaves surrounding the little clusters of grapes. Finding discolouration of the leaves, roots or stems could indicate a problem with the entire crop and should be dealt with as soon as possible.
Rusty brown spots on grape leaves could be an indication of several problems. One common problem is referred to as bird's eye rot and presents as small holes in the leaves. These holes have a greyish centre with brown and black discolouration around them. The area around the holes is raised and wrinkled, with a brittle texture and the edges of the leaves are similarly coloured and dried out.
The grapes themselves begin to rot as well, with a small reddish spot that is sunken in and surrounded by brown discolouration.
The second common type of brown spots on grape leaves is botrytis, which is characterised by large, reddish-brown patches. This may be accompanied by moulding on the grapes themselves, which looks like a heavy grey fuzz surrounding each grape.
The grapes may be extremely soft and watery.
Diagnosing the Problem
It is easy to tell which one of the two problems your grape leaves have because botrytis presents with big patches, while bird's eye rot has small holes. Examine your leaves to see which of the two problems your brown spots look more like to make the official diagnosis. Once you know the problem, you will be able to take the proper steps to eliminate the disease and save your crop.
Common Times to Occur
When the weather is especially wet and rainy, it is much more likely that your crop will be affected by mould or rotting, especially with bird's eye rot. This is because the water accumulates on and around the plant, causing disease and bacteria to flourish. If you are experiencing a very rainy year, you should take extra measures to examine your plants. Keep them properly watered, but not overly wet. You might want to refrain from watering them altogether if there is rain falling frequently on your vineyard.
Ridding Plants of Disease
The best plan of attack is to remove the infected plants from your crop and keep the area as clean and free of bacteria as possible. When you see the first signs of brown spots on your leaves, immediately remove those leaves and check the surrounding grapes as well. If any of the plants contain fuzz, mould or circular rotten spots, remove that particular plant so you can keep the disease from spreading.
Keep your vineyard clean and neat year round to prevent disease from cropping up in the first place and spray with liquid lime sulphur in the early spring when the first buds appear.