Pests in Gardens and Landscapes: Quick Tips
Codling moth larva in fruit.
Newly hatched larva and eggs.
Sting on fruit indicates where codling moth larva has entered.
Codling moth, the infamous “worm” in the apple, is difficult to manage in the home orchard. Soon after hatching, caterpillars bore into apples, pears, or walnuts and feed, leaving reddish-brown droppings (frass). Early-maturing fruit varieties are less likely to suffer damage. Use an integrated pest management (IPM) approach that combines several of the methods described below. Trees heavily infested every year require carefully timed sprays.
Codling moth life cycle:
- Mature larvae overwinter under bark in cocoons and pupate in spring.
- Adult moths emerge in mid-March to April and mate after sunset temperatures exceed 62°F.
- Tiny disc-shaped eggs are laid on fruit or leaves.
- Hatching larvae immediately bore into fruit.
- Larvae feed within fruit until mature then drop to the ground to pupate in soil or debris or under tree bark.
- Two to four generations occur per year in California.
Reduce codling moths with sanitation practices.
- Promptly remove infested fruit from trees. Look for worm entry points (“stings”) marked by tiny mounds of reddish-brown frass.
- Rake up and destroy dropped fruit as soon as it falls, especially in May and June.
- Sanitation alone won’t control the pest.
Bagging protects fruit without chemical sprays, even when infestations are severe.
- Bag when fruit is 1⁄2 to 1 inch in diameter, four to six weeks after bloom.
- Cut a 2-inch slit in the bottom of a standard lunch bag, thin fruit to one per cluster, slip the fruit through the slit, and staple the bag shut.
- Remove bags just as fruit begins ripening.
Use insecticides when infestations are severe.
- Codling moth granulosis virus (sold as Cyd-X) is a safe biological pesticide that won’t harm beneficials or bees. Add 1% horticultural oil to increase effectiveness. Apply every seven days after eggs hatch, at least three or four times per generation.
- Spinosad is a low-toxicity pesticide made more effective by adding 1% horticultural oil. Apply every 10 days after eggs hatch, or about three times per generation.
- Carbaryl is effective when properly timed at 14- to 21-day intervals but is very toxic to natural enemies, honey bees, and other nontargets and can cause water quality problems.
- Combining low-toxicity insecticides with nonchemical methods is the most environmentally sound approach.
Insecticides are effective only when sprays are precisely timed to kill caterpillars just as they hatch.
- Hang a pheromone trap in your tree in March, and check it every few days for moths.
- Once moths are found and sunset temperatures exceed 62°F, start calculating degree-days following the instructions in Pest Notes: Codling Moth. Degree-days will help you determine when eggs will hatch or when to start looking for “stings” on fruit that indicate larvae have hatched and are entering fruit.
- Start applying insecticides as soon as degree-day calculations indicate eggs are hatching (250-300 degree-days after moths are caught in traps) or as soon as you see stings.
- Use new stings or degree-day calculations to initiate sprays for second and third generations.
Minimize the use of pesticides that pollute our waterways. Use nonchemical alternatives or less toxic pesticide products whenever possible. Read product labels carefully and follow instructions on proper use, storage, and disposal.