Anyone who has a plum tree is familiar with fruit dropping off the tree and having black marks or cuts on the fallen fruit. Seeing this quickly deflates all expectations for a good crop of plums. The problem can be so bad that many people have given up on growing plum trees because few plums make it to the table.

The insect responsible for this damage is called a plum curculio which is actually a weevil. This weevil is a quarter-inch long, dark brown to black, with mottled gray markings, and of course has the weevil snout. Seeing them may be difficult because weevils will move to the opposite side of the limb to avoid being seen.

Curculio’s emerge or become active when the wild plum population reaches a stage called “shuck split.” Basically this means when the plum begins to grow and the flower splits. Another clue that curculios are active is signs of feeding. Adults will feed on the edges of the leaves and the small fruit.

Adults will feed a few days before the females begin to lay eggs. The usual pattern of egg-laying begins with plums on the perimeter of the tree. The female works her way down the limb depositing eggs on the small plums.

The weevils are probably active now. The females will make a small cut on plums that is shaped like a half moon. She then deposits an egg on the cut that hatches and burrows into the fruit. The newly hatched worm eats its way toward the pit of the fruit.

If the pit has hardened too much, the worm will tunnel around the pit. The damaged plums will turn reddish and fall off the tree. The worms emerge from the plum and pupate in the ground around the tree. In two months, a new weevil will emerge.

This second crop of weevils can damage additional fruit before harvest and these larvae may be undetected inside the fruit. This sounds nasty and is nasty because the worms are excreting “fecal matter” inside the plum.

If you have plums on your tree that have not been damaged, you need to treat your tree with an insecticide. Even if your plums have been damaged it may not be too late to salvage some fruit because the weevil’s first attempts at egg-laying often do not form larvae inside the fruit.

Homeowners have limited choices of insecticides to control these pests. According to our Georgia Pest Management Handbook, the fruit tree spray, Bonide Fruit Tree Spray, is the best available choice. Bonide spray contains the insecticides malathion and carbaryl plus a fungicide called captan.

This combination provides good control of curculios. The general rule for control is to make a foliar cover spray when the curculios emerge and repeat in 10 days to two weeks to kill any emergence after the first spray.

Many home orchard sprays available contain either malathion or permethrin. Alone, these provide only fair control, but applying Sevin (carbaryl) in addition to the other pesticides should increase effectiveness.

If you do not want to spray pesticides on your plums, the best option would be products containing kaolin clay which will give fair control. Plum curculios can also be easily detached from trees by wind or shaking trees. Placing a white sheet under the tree in the early morning and giving the tree some light shaking may dislodge the adults.

Do not forget about a second emergence of curculio’s which will be from mid-May to June. Treating your plums again at this late stage may prevent you from eating a few larvae with your plum.

Jake Price is University of Georgia extension agent/coordinator, Lowndes County, 2102 E. Hill Ave. More information, call (229) 333-5185, or email jprice@uga.edu.