For some reason, the apple blooms seem to be particularly abundant this year. Even the old farm trees I see along Chester Creek seem to be full of blooms. Unfortunately, between the beauty of the blossom now and a ripe apple in the fall is codling moth – the critter that makes an otherwise great apple full of holes.
Codling moth adults are about half to three-quarters of an inch long, with mottled gray wings tipped with coppery brown, that will start appearing two to three weeks after the tree reaches full bloom. That means around Memorial Day the moths will appear and begin laying about 50 to 60 eggs on apple tree leaves, branches and fruit. The larvae are pinkish white with brown heads and after hatching will feed on the tree for a short period; they then move to the new fruit and burrow to its core, leaving a frass-filled hole on the outside of the fruit. The larvae feed on the protein-rich seeds for three weeks and then leave the fruit to pupate on the tree or ground for two weeks before beginning the cycle again. Here in the Northwest we can get two to three generations a year, which makes control necessary throughout the fruit season.
Good integrated pest management starts with cleanliness. Rake up all old fruit and leaves in the fall to remove hiding places and overwintering cocoons. Gently remove bark scales from trees to further reduce overwintering places. This doesn’t hurt the trees.
Because the moths and larvae are only exposed to the open air, and thus to control, for very short periods of time, timing is everything. Once the larvae are in the fruit they are immune to control.
To determine when the moths are present, pheromone traps can be hung in the trees to catch adult moths. The traps are sticky pieces of cardboard baited with the scent of the female moth. The male moths, thinking they have found their true love, get stuck on the trap. Check the traps every couple of days for moths. If the moths are present, so are their larvae. Once they are present, begin a regular spray program every ten days. This offsets their lifecycle.
Malathion is the conventional spray for the codling moth. A relatively new organic control is spinosad, a soil bacteria-based spray that is OMRI listed for use in organic production. The larvae ingest the bacteria and it kills them internally, which makes it less likely to harm nontarget predatory insects.
A last method is the use of highly processed kaolin clay called Surround WP. This food-grade clay is mixed with water and sprayed on the tree and fruit, leaving a white, nontoxic coating. The tiny particles don’t kill the larvae but camouflage the fruit so it looks less like a meal and irritates the insects’ skin so they don’t hang around. The clay slowly washes off over the summer.
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