Many pests and diseases affect plum tree. Plums are a stone fruit, and several diseases can be transferred between stone fruit trees. Here is some information on diseases to look out for as well as some pest control instructions to keep your crop healthier.
Bacterial spot can make stone fruit trees loose foliage and bear little fruit. It tends to form on trees in more humid areas. There is no cure for bacterial spot—you can only prevent it by treating with chemical sprays and trying to lower the humidity.
Black Knot is a fungal disease that attacks the wood of the tree. It will attack branches and the trunk, forming gnarled knotty growths of fungus around the stem. Treat with fungicide and cut the branch away at least 4 inches below the root knot. If possible, keep the infected tree away from other trees.
Brown rot is another fungal disease that covers the fruit in brown fungus-looking patches. It can invade a whole tree or orchard if not properly pruned or cleaned. Use fungicide to treat a tree and make it less susceptible to getting brown rot.
Crown gall is the collection of gall on the roots or base of the trunk. These are soft and spongy and cause more damage to new trees than old. There is no treatment if your plum tree develops this—only preventive measures to avoid and check for it on new crops.
Plum Pox Virus
Plum pox is a disease that can not be killed. Once it infects a tree or crop, the trees must be destroyed immediately. The disease is spread by aphids and can be carried pretty far away from the source. Prevent it by keeping aphids away from your trees.
Aphids feed on the foliage of your plum tree and they can indeed pose a problem in large quantities. To get rid of them, use a spray solution of soap and water to act as a pesticide. There are also commercial insecticide sprays that discourage aphid infestations.
Ants are attracted by rotting fruit and by aphid populations. If you keep your fruit cleaned and control aphids, an ant problem will likely go away on its own.
Japanese beetles will eat the leaves as well as all of the flowers and fruit if they are left to do so. There are pesticides that you can use as well as beetle traps that lure the bugs with pheromones.
Bees and Wasps
Bees and wasps are not an enemy to your plum tree. The bees are pollinating fruits and flowers, and the wasps are eating, too. Unless they become a huge problem, leave these insects alone.