Answer: The worms are plum curculio larvae. When nighttime temperatures reach 55F, adults begin emerging and the females lay eggs on the undersides of developing fruit. Usually the hatching larvae cause the fruit to drop. However, a second generation in August can cause deformities and scarring of developing fruit. The telltale sign of plum curculio damage is a small, crescent shaped cut on the fruit where the female inserts the egg. You can check for plum curculio by placing a sheet under your plum tree and shaking the limbs. The small, dark, lethargic beetle will fall onto the sheet. The plum curculio is hard to control without using chemicals. One spray of Imidan after petal drop and another in mid August should do it. There are no effective biological controls available yet, and cultural controls give limited results.
Q&A Library Searching Tips