What's bugging you? Mar. 15, 2017
By Jim Leser
Published Thursday, March 16, 2017 8:16 am
Have you ever taken a big bite out of a crisp apple only to find a half wiggling worm sticking out of the remaining apple? If so, you have been the recipient of a codling moth infested apple, the bane of all growers of apples, pears and even crabapples.
If you have apple trees, now is the time to plan your management strategy for the dreaded codling moth. Without some kind of management program, expect to have a lot of "wormy" apples.
The codling moth (Cydia pomonella) in our area is a key pest of apples and in some districts it is mandatory to either spray to control this pest or spray a chemical at bloom time that removes most of the fruit. This is to protect our commercial apple industry.
In late summer or early fall, fully grown codling moth larvae spin a silken cocoon around them and pass the winter in protected places such as under tree trunk bark, garden refuse or infested, rotting apples. These larvae pupate in the early spring and transform into moths that emerge to lay the first generation eggs. Moths are rarely seen since they fly at night. They are about 1⁄2 inch long, buff colored with horizontal coppery bands on their wings.
Codling moths emerge looking for a sex partner. And once females are mated they can lay 30 to 70 single eggs. These eggs are generally laid on developing fruit in areas that afford some protection of small larvae including at the base of the stem, the calyx (bottom of the apple), where fruit touch each other or places where leaves contact fruit. Eggs hatch in about one to two weeks, depending upon temperatures.
Larvae go through five developmental stages or instars before they either exit the apple to pupate or are carried to the ground by damaged apples that are shed. There can be three generations of codling moths, each potentially more damaging than the last. By controlling the first generation, subsequent generation numbers will be greatly reduced, unless you get those unwelcomed immigrants from nearby untreated, infested trees. The most damaging generation is the second one.
While working for Extension in Texas, I developed a simplified homeowner codling moth management approach. I did use pheromone traps and a heat unit model to establish a spray schedule. The spray schedule I am outlining is the bare minimum you can get away with. You will still have some "wormy" apples but most of your fruit will be clean. First sprays should start about two weeks after petal fall with a second application two weeks later. This will take care of most of this first wave of activity. About six weeks later, the next attack will occur from the second generation. Again, two applications, two weeks apart will handle most of the activity.
Depending upon how late maturing your apple variety is, a fifth application may be necessary to target a smaller third generation. This would be in late August or early September. Use a spreader-sticker to enhance coverage of your application. Insecticides that can harm bees visiting blossoms but that are not used when trees are blooming include: phosmet (Imidan®), a pyrethroid such as one containing permethrin or fenvalerate, and acetamiprid (Assail®).
An insect growth regulator (IGR) such as Intrepid®, would work well, too, but would have to be applied 10 days earlier than conventional insecticides. IGRs are target specific and would not harm natural enemies or pollinators. Insecticides containing spinosid (organic approach) could work well but would need to be applied every seven days. Hence you would have to double the number of applications needed.
If you want to know of other trade name insecticide choices that are available, you could visit the CropwoRx store in Eckert or visit their website, Cropworx.net. While many of their pesticides are more expensive because of container size and/or percent of active ingredient, think in terms of cost sharing with a neighbor. They also write an informational newsletter and provide codling moth spray guidelines based on data from weather stations across the local area. If you decide to buy smaller quantities, you're likely to end up paying much more per application.
Last but not least there are a few cultural approaches to codling moth control that will help immensely but will not replace a good insecticide spray program. Thin fruit clusters since moths like to lay eggs where apples touch. Remove all fallen apples from the garden floor and even remove infested apples still on the tree. These will have "stings," minute holes where larvae entered, surrounded by a red halo. These same holes may have clumps of frass, insect poop, associated with them.
Good luck on achieving pristine, worm-free apples. Me, I prefer to buy mine from our local commercial orchards and forgo the fuss of trying to achieve worm-free apples. A few times in Texas I actually did succeed in growing 100 percent worm-free apples, but it took a lot of work!
Jim Leser retired to Cedaredge in 2007 after a career with Texas A&M University Extension in entomology. He is a member of the Cedaredge Tree Board and a Colorado Master Gardener.