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Shot hole disease, also known as Coryneum blight, is a fungal disease that can commonly occur on fruit trees and can cause quite extensive damage.
WHAT IS SHOT HOLE DISEASE?
This is a type of fungal disease that spreads through the air from plant to plant, getting its name from the fact that it can create small holes to appear on your plant’s leaves. It especially affects fruit trees, but can also take hold on some other types of plants, such as flowering ornamental trees.
Like many fungal infections, shot hole disease thrives in wet conditions, and can arise after an extended wet period, such as spring rains. As such, it is typically most noticeable in spring (i.e. this is when the symptoms are often most clearly seen), but can occur anytime between fall and spring. Cases are often most severe following a wet winter. Additionally, the disease can be spread by splashing water, as rain spread fungal spores across leaf material. For this reason, it may be a good idea to avoid overhead watering during vulnerable times, to minimise the risk of your plant’s leaves being covered in water for a prolonged period of time.
Small purplish or reddish spots appear on the leaves. The damage can then progress as the spots get larger, leading to eventually create a characteristic hole
This can affect leaves, stems and fruits
Unfortunately, a consequence of this disease can be that the plant may lose a large part of its fruits
WHAT TO DO NOW
Unfortunately, it can be very tricky to treat Shot hole disease, so prevention is essential here. However, if you’d like to try and treat it, you can give the following a go:
Use a fixed copper fungicide
Apply a Bordeaux mixture (although note that this is usually intended to be used as a protectant rather than a treatment)
Alternatively, you can try a synthetic fungicide such as chlorothalonil
These treatments should be applied after leaf drop has started to occur
Bear in mind that the above fungicides are all quite harmful to the environment, and can be harsh on your plants too, so should only be used as a last resort if the infection is very severe and the plant is of high value.
It’s a better idea to try and protect uninfected plants from becoming affected instead.
HOW TO PREVENT THIS FROM HAPPENING AGAIN
Essentially, the key is to try and prevent your plant from being exposed to excessive moisture for extended periods of time. If your watering system tends to leave water sitting on the leaves, you may wish to consider changing it up a bit. If you water by hand, then try not to do it from overhead. Alternatively, if you use an irrigation system, try to only use low-volume sprinklers, drip irrigation, or make use of sprinkler deflectors to protect your plants from collecting water.
Keep an extra eye on your plants during wet periods to try and catch any symptoms early - as soon as you see them, remove and destroy any infected material. You can also try pruning lower branches to help prevent wetting of foliage.