GARDEN HOTLINE | What’s bugging my fruit tree?

There is nothing like the taste of a freshly picked apple off a tree in your own backyard. Growing fruit in your yard can be very rewarding, as well as delicious. It is also a way to ensure that the fruit you eat is not sprayed with pesticides.

Yes, there are some pests in the Pacific Northwest that make fruit-growing a bit more challenging, but creative fruit growers have come up with innovative ways to help reduce pest attacks.

Apples wearing nylons?

The apple maggot fly (Rhagoletis pomonella) is a fruit-loving pest that came from Europe, where they fed on hawthorn fruit. They first appeared in Oregon in 1979 but have now spread throughout Washington state. These flies will attack other fruits but have been primarily a threat to apples, crab apples and haws.

Natural processes and abandoned orchards account for some of the spread, but according to the Washington State Department of Agriculture, the primary source has been the transport of infested fruit from backyard apple trees into non-infested areas.

The adult apple maggot fly is 1/4-inch in size, with white bands on the body and wings. When the soil warms up in late May or June, the adult flies emerge.

After mating, the female looks for apples upon which to lay her eggs. She can lay as many as 500 under the skin of the fruit.
When the larvae hatch about a week later, they begin feeding and create tunnels throughout the flesh of the fruit.

The mature larvae exit the fruit when it falls to the ground, where they may stay for the winter or longer and then repeat the cycle.

Fruit-bagging tips

It is important for home fruit growers to try to control the apple maggot because it poses a huge threat to the commercial apple industry. Putting socks or bags over each apple is too labor-intensive for large orchards but is an option for someone with a small number of trees.

Some folks prefer to use paper or plastic bags as an alternative to footies, which may run and split. Bagging fruit will not prevent the fruit from dropping off the tree prematurely, which is important to clean up.

If you want to try apple maggot barriers, here are a few things to keep in mind:

•Thin the fruit at the same time or before you bag — Washington State University recommends leaving one fruit per 6 inches of branch. Remove the smaller apples, those with spots or defects and those that hang close to the ground or are shaded.

This will also improve the quality of the remaining fruit.

•Bag the apples when they are about the size of a dime.

•In late summer or fall, harvest the infected fruit before the mature larvae make their exit.

•Pick up and destroy fruit that has fallen on the ground — Adding fallen fruit to commercial compost is acceptable.

Other pest-control strategies

Apple maggot barriers won’t deter the codling moth, another pest that lays its eggs in apples. Kaolin clay (sold as SurroundWP) can help prevent codling moth. The clay is mixed with water and sprayed on the leaves, stems and fruit, coating them with a powdery, white film that agitates the moths.
Repeated sprayings must be made to be effective.

Kaolin clay is an edible product that is often used as an anti-caking agent and found in toothpaste. SurroundWP is the only kaolin clay registered for horticultural use.

Traps can also help reduce the number of apple pests. Many styles exist, though most are coated with a sticky substance (Tanglefoot) that captures the fly. This horticultural “glue” can also be banded around the trunk of the tree to prevent the female codling moths from crawling up from the ground.
Pheromone traps mainly lure males codling moths, but new pheromone traps on the market can attract male and female flies. Some pheromone traps (“mating disruptors”) are only effective in large orchards and not recommended for home use.

Beneficial nematodes that target apple maggot and codling moth larvae are another option. Nematodes are microscopic organisms that live in the soil. They are watered into the soil and do not attack other beneficial insects.

Healthy trees are better able to withstand attack from pests and disease in the first place. Maintaining a diverse yard will help reduce pest attacks by offering plenty of food for natural predators. Chickadees, lacewings, black shiny beetles and parasitic wasps will eat insects, including apple maggots and codling moths.

Chickens and ducks will also eat larvae, so throw a garden party and invite your friends who raise urban fowl — just make sure they don’t get into your vegetable beds!

There are a number of good resources and organizations available to help you grow healthy fruit trees:

•Seattle Tree Fruit Society: seattletreefruitsociety.com

•City Fruit: cityfruit.org

•Home Orchard Society: homeorchardsociety.org

Buy apple maggot barriers online from Seattle Tree Fruit Society or Home Orchard Society, or look for them at your local nursery.

To learn more about growing healthy fruits and other plants, contact the Garden Hotline at (206) 633-0224 or www.gardenhotline.org.

SUE HARTMAN is an environmental educator for the Garden Hotline at Seattle Tilth (seattletilth.org).