Organic pest management: Codling moth in apples
Codling moth Cydia pomonella is the most common pest in our area (Intermountain West of United States) of apples and pears. If someone is complaining of "wormy apples", it is likely codling moth larva causing the damage. We deal with codling moth in our apple and pear trees, and we've tried a lot of organic control methods. Here is a bit about our experience of what we have tried.
Larvae drop with fruit, well fed, in the fall and hide under leaves, soil, apple containers, or in the bark grooves on tree trunks where they overwinter. Larvae pupate in the spring, and emerge as adult moths. Adult moths are nocturnal, and begin flying at night when the temperatures are consistently above 60 degrees. Moths mate and females each lay 30-70 eggs on or near developing fruit. Eggs look like tiny transparent spots of glue on apple surfaces, and turn brown as the egg develops. Larva hatch out and begin tunneling in the the apples. Here in southern Idaho, there are about 3 generations of codling moth a year.
Signs and symptoms:
Being nocturnal and quite small, codling moth will rarely be seen in its adult stage. When scouting for codling moths and damage, first look for the small "stings" of a larva bite on the surface of the apple:
Larva travel through the apple flesh to feed on the apple seed, leaving brown tunnels and frass in their wake. If you have codling moth you will find:
Codling moths themselves are easy to spot inside an apple, they have a dark head and white body, and will be busy making their way through your lovely apple:
Once codling moth eat the seed the apple, the fruit itself will fall to the ground, so premature fruit drop is another sign you might have codling moth.
Organic control methods:
The only way to prevent codling moth damage is to somehow prevent the larva from entering the fruit. This is either done through excluding female moths from laying eggs on the fruit, preventing moths from mating, reducing moth population through overwintering habitat reduction, or through killing moths and eggs with well timed organic sprays.
Plastic bag covers on fruit:
This solution involves sealing plastic sandwich baggies over tiny developing fruit prior to female egg lay. We have tried this on the two large trees near our house. It's a solution best suited for yards with just a few trees, and while its labor intensive, grab a friend and the two of you can do it in a few pleasant hours.
To make the bags, I watched this very helpful video. Just make sure you don't cut the corners too large, as moths can fly right into those. We have dry summers, and I've never had a problem with too much moisture being trapped in the bags with the fruit, so don't worry about cutting those corners a little smaller.
I do worry about using all this plastic, but if you treat them nicely, you can use these bags for a number of years. We will be on year three this year.
In my experience, this solution can be quite effective but you have to be sure you get the timing right!!! It can be difficult, but you need to get the bags on when the fruit are large enough to hold the bag without the bag bringing down the fruit, but before egg-laying female moths are flying. This is about early June for us, and if Father's Day comes around I know it's too late. That's why this solution is best used in conjunction with a pheromone trap (see below) which you can check every day to see when adult moths are flying.
Corrugated cardboard around trunks: In conjunction with other control methods, placing corrugated cardboard around the tree trunk is an excellent way to reduce the adult moth population. Adult moths hide on the tree trunks during the day, where they are very well camouflaged. When they encounter the corrugated cardboard, they think, what an amazing hiding place in these corrugations!! Cardboard can be periodically gathered during the day and destroyed to kill the moths hiding inside. Replace cardboard and repeat.
Molasses traps are another way to reduce the adult moth population and should be used in conjunction with above treatments. The idea is to attract adult moths to the sweet smell of rotting fruits, where they drown. Watch this video to learn how to make molasses traps to hang from your tree, and to see the cardboard trunk trap in action.
Apple and leaf sanitation:
Clean up all fallen fruit and rake leaves in the fall. Because larva tunnel out of fallen fruit and into their overwintering sites, disposing of all fallen fruit immediately can be an excellent way to reduce the population. We give fallen fruit to our chickens, who live in an area very separate from our orchard, and are confident the chickens eat the larva out of the fruit. While we try to compost all garden and yard waste, we make exceptions for plant parts infected by pests and diseases. When we can give it to chickens or cows, we throw it into the garbage to get it off the property. That type of prevention is a huge part of being able to farm organically.
At the end of the season, rake leaf litter to reduce overwintering sites under and around the tree. We compost the leaf litter away from the orchard.
Pheromone traps work best as a method of population reduction and eradication in larger apple orchard plantings, with studies saying that the apple stand must be at least 4 contiguous acres to be effective. If that's your situation, pheromone traps are an excellent means of organic control. They basically work using pheromone lure placed on a sticky trap that hangs from the tree. The pheromone released is a female pheromone, which the male moths are attracted to and then trapped in the sticky. This limits mating and egg laying not only because it reduces the number of males, but because the female pheromone is how males find females, and with so much of it wafting around the orchard the males have a tremendously hard time navigating. Which is why is works best at larger 4+ acre scales.
While it can't be counted on to fully eliminate codling moth damage in smaller plantings, pheromone traps can be used to monitor the activity of moths. Simply place them in the tree in late spring when moths are expected to be active, and monitor daily to determine when other treatments should be used. Pheromone lures need to be changed every week or two to remain effective.
Organic spraying regime:
If you decide to use an organic spraying regime to control codling moth, know that you will be applying quite frequently due to the frequency of generations and the short residual of organic products. Some options for this include Entrust, a bacterial product which must be reapplied every 7 days. Dipel, Crymax Bt, and Javelin can also be used. These products are very specific to caterpillars (larval stage) and should be applied when the larva are expected to be active in early summer and weekly through harvest. Surround (kaolin clay) acts as a suppressant to codling moth and must be applied before adult moths emerge in and reapplied every week or two. Pyrethrin (Pyganic) is produced from African chrysanthemum flowers and also has a short residual of protection, 5-7 days. Horticultural mineral oil, which is highly refined oil, can be used on trees during the growing season. Horticultural oil suffocates codling moth eggs, and when applied at the beginning of each generation can help suppress egg hatch.