Problem type: Insect
Name of problem: Plum and Apple Curculio
Plant name(s): Plum, apricot, cherry, apple, pear, gooseberry and chokecherry
Symptoms / Characteristics:
Symptoms of plum curculio damage include small irregular puncture wounds, semi-circular scars and crescent-shaped cuts on fruit, as well as misshapen fruit and premature fruit drop.
Plum curculio damage may be attributed to early season adult feeding, fruit injury during egg laying and summer adult feeding. The plum curculio is a snout beetle (Conotrachelus nenuphar), which overwinters in the adult stage under leaf debris and in piles of wood or brush near the host plant. Emergence occurs during spring flowering and lasts up to four weeks during which time the adult beetles feed on leaves, flowers and immature fruitlets. Early season fruit injury is characterized by small irregular puncture wounds and semi-circular scars. Following the emergence phase, the females lay eggs inside the fruit by making crescent-shaped cuts on the fruit surface. Multiple deposits can result in misshapen fruit if the injured fruit should remain on the tree until harvest. Once the eggs hatch, the larvae feed on the developing fruit resulting in premature fruit drop. Mature larvae drop to the ground to pupate and, after 2-3 weeks, emerge as summer feeding adults, which continue to feed on the fruit until early fall.
In the adult stage, the plum curculio is 4-6 mm long and is dark grey to brown in colour, with grey and white patches on the back. Other identifiable features include 4 bumps on the back and a long, curved snout. Depending on maturity, the grub-like larvae can range from 1-9 mm in length. They lack functional appendages and are greyish-white with a brown head.
Apple curculio (Anthonomus quadrigibbus) is very similar in both appearance and life cycle. Injury symptoms are similar to that of the plum curculio, with the exception of the crescent-shaped scar. Host plants include apple, crabapple, saskatoon and hawthorn.
Control / Preventions:
All susceptible fruit trees in the immediate area should be monitored before and during fruit set. Fruit should be inspected for semi-circular and crescent-shaped scars and insecticides may be applied once an injury is detected. Guthion may be used when populations of plum curculio are high, but should be handled with care due to its toxic properties. It should be substituted with Imidan when populations are low. Avoid summer adult infestations via regular collection and disposal of fallen fruit.