Margaret Lauterbach

Margaret Lauterbach: Beware of codling moths; they are harmful to fruit trees

Now is the season to start control of codling moths. If you have apple, pear or even peach trees, in whose fruit you’ve found pinkish-white “worms” with dark heads, those are offspring of codling moths.

Right now, the 2015 class of codling moths are reposing in pupas or cocoons in soil or under bark, waiting to emerge at a time when they can mate and lay eggs on some fruit that will feed those larvae when they hatch. Their tastes favor apples, pears, English walnuts and my white peaches. They emerge at different times, an inconvenience to gardeners and orchard growers.

I think it’s now too late in spring to use beneficial nematodes, but they could control codling moths in pupas or cocoons in soil in other years. Steinernema carpocapsae and Steinernema feltiae are the types of nematodes used to destroy dormant codling moths in soil or lawns.

Do not even think of using a systemic pesticide on any plant that produces parts to be eaten by humans. “Systemic” means throughout the system, from the tiniest roots to the tips of twigs, flowers and seeds. All pesticides are toxic, at least to some degree, and systemics’ extruding into flowers is one of the reasons I’m opposed to year-round control of insects on trees and shrubs, using neonicotinoids. They kill bees.

How do we control these moths once they emerge without destroying bees? Codling moth traps are used to tell us when the moths have emerged, so we can plan to spray. They’re about a half-inch long, with bands of gray and white stripes on their wings, the ends of their wings copper-colored.

The traps can’t catch enough to make a significant difference in your fruit results, so control is up to us. The moths are active only a few hours per day, a few hours before and after sunset. They mate when sunset temperatures are above 62 degrees F.

Then what do we spray and when?

Some home orchard growers claim “Last Call” works. Last Call’s active ingredient is Spinosad, a soil bacterium that’s safe for pets and most others. It may kill on contact, but is more effective if the target insect feeds on it. It is toxic for bees for three hours after spraying, so do not spray blossoms where bees may be feeding or when they may be feeding. Evening spraying of this product is safest.

The label indicates six applications may be required, halting applications seven days before harvest. If you have a large tree, do not use the ready-to-use spray bottle, but instead look for a concentrate, and use a different sprayer, such as a trombone sprayer.

Another spray you could use is a wettable powder, called Surround. Surround is powdered kaolin clay, and it will leave a powdery coat on fruit and leaves. It reportedly does not interfere with the leaves’ chlorophyll function, but it does deter codling moth larvae and other pests.

Follow label directions. This product may be applied until the day of harvest. The whitish film will easily wash off, but ingesting it wouldn’t hurt you. Kaolin clay is the same ingredient as in Kaopectate, a medicine used to treat human stomach upsets. If we have heavy rain, you may have to re-apply Surround. The film residue may deter egg laying (females can lay 30 to 70 eggs in a season), or just appear not attractive to the moths.

North End Organic Nursery (NEON) carries Surround, and perhaps other garden centers carry it too. Mail order sources sell 40- or 50-pound bags, adding shipping costs to the cost of the product. NEON sells in much smaller amounts and no shipping charge.

My late friend Ross Hadfield used to spray his sweet cherries with dissolved baking soda that dried to a white haze, discouraging children from poaching his fruit. “Oh, I just sprayed,” and would-be poachers could see the result. That may have deterred cherry fruit flies from laying eggs too.

Sevin, applied at exactly the right time, will kill codling moth larvae and the moths, but it will also kill bees and other beneficial insects. Products containing Permethrin as the active ingredient may also control codling moth larvae, but the time of application of any substance is crucial, and insecticides with this ingredient may not be safe for bees either.

Pheromone disrupters used for control in commercial orchards are quite effective, and ecologically sound, but too costly for home use. A new product, called CYD-X is a virus that is specific to codling moths. It is very costly, but I’m trying it this season.

There are other beneficial insects that attack these small moths, too. Assassin bugs, green lacewing larvae, minute pirate bugs and Trichogramma wasps attack them or their eggs, too. The latter are expensive from insectaries, and require several releases per season for effectiveness. None exist in sufficiently large numbers to make a significant difference in codling moths.

Another way to cut down on the codling moth population is through the use of banding the trunks of target trees with cardboard or burlap. After emerging from a fruit, the larvae crawl down the trunk or lower themselves on silk strands to soil or debris under the tree. Do not put any Tree Tanglefoot or other substance directly on tree bark, but on a bark-protective wrap.

We used to have an old crab apple tree that was home to many codling moth larvae, judging from the number of silk strands one had to brush off to walk under the tree. Nobody sprays crab apple trees for codling moths in the city, but landscapers plant a lot of them.

If you band a tree with cardboard or burlap, and catch a number of the larvae, then it’s fairly easy to destroy them, dumping them into a bucket of hot, soapy water.