Q. Why do my plums shrivel on the tree?
The cause may be a weevil named plum curculio. Plum curculio (Conotrachelus nenuphar), a native of North America, is widely distributed east of the Rocky Mountains. The name is somewhat misleading because this insect attacks not only plums, but also apples, peaches, pears, cherries, quince, and other wild and cultivated fruits. It can be very destructive if no control measures are applied. The fruit is injured in four stages: the spring feeding of adult beetles, then punctures by the female when laying eggs in the fruit, followed by larvae feeding within the fruit, and finally early fall feeding of adult beetles.
One method of nontoxic mechanical control is shaking and beating the sluggish beetles from trees in the morning and capturing them on sheets or tarps spread under the tree. While an old control method, it can still be practical today on a small scale. Insects that fall on the sheet should be removed and crushed.
Another nontoxic control tool is kaolin clay. The clay forms a thin clay barrier around the fruit that repels adults and prevents them from depositing eggs in the fruit. Researchers sprayed kaolin clay on the trees when the flower petals fell and continued applications until one week before harvest. This study found that a heavy, consistent coating provided the highest level of control, best for an orchard of fruit trees.
Natural control of the curculio results from winter mortality, attacks by birds and other predators and from parasites. You can also pick up fallen fruit two to three times a week, put it in a plastic bag, tie it tightly, and place it in the trash can. This will help keep larvae in fallen fruit from developing in the soil and, if done regularly, should lessen the damage done by this insect.
For tips on a variety of gardening topics, see our Plant Information Guides.
- Courtesy of NYBG Plant Information Service