Q: Last year most of the fruit on my apple trees had worm damage. Can I do something now to prevent this problem? - Lisa Tirado, SLO
A: The damage was probably caused by larvae of the codling moth, a common pest of apples. Moths lay eggs in spring on fruit, leaves, and spurs; the worm-like larvae that hatch beginning in May or June are whitish or pink with brown heads. They bore into fruit and eat up to 90 percent of the apple as they mature, leaving behind a trail of red-brown crumbly droppings called frass. When mature, they leave the apple and search for a place to pupate, forming cocoons in soil or debris under the tree or in crevasses of the bark.
The moths that hatch from the cocoon repeat the cycle; there may be two to four generations a year. Moths are ½ to ¾ of an inch long with mottled gray wings that blend well with tree bark. Codling moth wings are edged with a dark coppery-brown band.
Control is difficult for home gardeners. Several non-chemical ways of controlling the population may keep it within acceptable bounds. To reduce pupating sites, good sanitation around trees is primary, other non-chemical methods of control include banding trunks, trapping of moths, and bagging fruit (on small trees.)
It may take several years to reduce a serious infestation to acceptable amounts using these non-chemical means. Insecticidal sprays and summer oil spray are available for home garden use against codling moth, but they need to be repeated during the spring and summer. Some insecticidal sprays damage beneficial insects and bees. Sprays recommended are best applied just as moths are hatching — trapping the moths in pheromone traps helps determine this period.
Master gardeners can give more information on codling moth control or go to: http://www.ipm.ucdavis.edu/ Click on “Insects, mites, mollusks, and nematodes" and choose “codling moth."