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Q: I have this apple tree, around 20 years old. I have been very patient with it, but since it started giving me a decent size of fruit, it has been infested with bugs - that is, worms - which cause rot at the core. I want to share the fruit, but I can’t offer friends wormy apples. I have tried spinosad, and all the “low-octane,” healthy, not-ruthless-to-the-environment sprays, but to no avail. I have reached the end of my rope this year, and the ax is ready unless you can recommend something that will produce fruits I can give away to friends without an asterisk.
A: Your apples are surely infested with codling moth. This pest, common in Bay Area locations with warm to hot summers, can render apples, pears and walnuts unappetizing, if not inedible. No pesticide alone, environmentally ruthless or not, will be the magic wand that will make your apples welcome gifts, but by combining several tactics, you can save most of your fruit. After several seasons, these tactics can reduce damage to only 10 to 20 percent of the crop.
In winter, remove loose bark from your tree and clean up any remaining fallen fruit and leaves, to remove overwintering pupae. As fruit develops, thin it to one at a site, since the moths especially like to lay eggs between two fruits. Continue to pick up fallen fruit through the season. (In fact, if you feel you have lost the battle at any point, and find most of your fruit is infested, consider removing and destroying the entire crop for one year to reduce the number of insects in your garden.)
A pesticide, if applied correctly, will kill many of the worms. Timing of the first spray is important, because pesticides only work in the short time after the eggs hatch and before the worms enter a fruit. Farmers use a combination of pheromone (scent) traps and temperature calculations to calculate the first egg hatch. Home gardeners can approximate the correct timing by spraying when they see the first “stings” where caterpillars have entered fruit, usually in April or May. Because the insect continues to lay eggs all summer, any pesticide needs to be sprayed repeatedly, following package directions.
Spinosad is a relatively environmentally friendly choice, but can kill bees. A new biological pesticide, codling moth granulosis virus, kills only codling moth. You can order it from Peaceful Valley Farm Supply (groworganic.com, (888) 784-1722).
Pheromone or other traps can be used to catch a significant number of moths. To trap male moths, preventing mating, place one to two purchased codling-moth-specific pheromone traps in a small tree, two to four in a large tree, away from the trunk, near the tree top. Start hanging traps in mid-March. Or try homemade traps that catch both males and females. Make a round, 2-inch hole in the side opposite the handle of a half-gallon plastic milk carton. Mix 1 cup cider vinegar, 1/3 cup dark molasses, 1/8 teaspoon ammonia and enough water to make 1 1/2 quarts. Add 1/4 cup bait to each jug, put on the lid and hang two to four jugs per tree at chest height. Empty weekly.
Remember you will need to combine several tactics to succeed. For a fuller discussion of codling moth management, and more management tips, see the UC Davis IPM site at bit.ly/tapl7D.
Two readers respond to my Jan. 20 column on mysterious sunflower leaf raiders:
I have watched lesser goldfinch go through my sunflowers in the summer. I’ve sat and watched them eat the leaf until there’s nothing left but the veins. I have several bird feeders, but they like their salad too. It’s usually the jays that plant my sunflowers so guess I can’t complain about something I didn’t even plant. Birds sure do damage to the plants, though. And then the squirrels eat the seeds.
I just had to write regarding your article about sunflower leaves. Last year I planted ‘Lemon Queen’ sunflowers, as part of my participation in the Great Sunflower Project. I noticed many of my leaves becoming skeletons and initially blamed the resident insects and snails. However, one day when I was out doing my bee count, I noticed some of the finches abandoning their seed-filled sock to rapidly peck away the sunflower leaves! By the end of the season, I had only skeletons for leaves - although I did have hugely beautiful flowers too.
Aha! So birds are indeed sunflower leaf raiders! I suggested using Mylar streamers to frighten birds away. (Also, see greatsunflower.org for more on growing sunflowers for that citizen bee count project.)