Inland Northwest Gardening

Its spring and the fruit trees are about to bloom. It’s time to start planning how to reduce the chance that you will have to share your apples with codling moths and apple maggots. As it finally warms up, apple trees will soon be blooming. With the blooms will come the battle with the apple maggot and coding moths to see who gets the fruit on the tree. A little planning and preparation will help you get more than they do.

Apple Maggots

Apple maggots are a fairly new but serious pest of apples in the Northwest. They were first detected in Portland in 1979 and have since spread to all the counties in Western Washington and Spokane, Kittitas, Klickitat and Yakima counties on the east side. Their presence in commercial orchards can have serious impact on an important element of the state’s economy. Because of this, homegrown fruit technically can’t be moved out of the area.

The maggots are a creamy white worm about a quarter of an inch long that tunnels through the flesh of the fruit. They are the larvae of the apple maggot fruit fly; a housefly-sized insect with a black body, large dark red eyes, a black and creamy-white abdomen with a distinctive white spot. The transparent wings are banded with black.

The adults emerge from the ground in late June and are active until October. They lay single eggs under the skin of the fruit and will lay about 300 eggs in a 30-day period. The eggs hatch in three to seven days and begin tunneling through the fruit. The fruit subsequently rots and falls from the tree. The larvae then burrow into the soil to pupate over the winter. Each fly has only one generation a year. The apple maggot is only open to control at the adult stage. Once the eggs are laid in the fruit, they and the larvae are out of reach of any control method.

The flies are detected by using yellow or red sticky traps baited with an attractant. The yellow traps are flat and resemble apple leaves while the red traps are round to mimic apples. They are hung at head height amongst the foliage and fruit so the flies can see them. Traps should be hung by early June using one for small trees and up to three for large trees. Once they are detected, a control program needs to be started immediately.

There are no biological or organic controls readily available to the home grower. Traps can be used to catch adults but they aren’t going to get them all. All fallen apples must to be picked up immediately to keep larvae from crawling from the apple into the soil. Damaged apples should be thrown in the trash and not composted. Seemingly undamaged fruit needs to be monitored as eggs continue to hatch. The best way to control the fly may be to just remove the tree completely if you aren’t using the fruit. For conventional home growers, Malathion needs to be applied at about 10-day intervals through the rest of the apple season.

A specially processed non-toxic kaolin clay (Surround at Home) can sprayed on the fruit and trees. The clay covers the tree with a white powder that camouflages them to the fly. It is easily washed off but does leave the tree looking a bit ghostly. It may be hard to find locally.

For more information and pictures of apple maggot contact the WSU Spokane County Master Gardeners at  509 477-2181 or go to: http://cru.cahe.wsu.edu/CEPublications/eb1928/EB1928.pdf.

Codling Moths

Adult coding moths are about half to three quarters of an inch long with mottled gray wings tipped with coppery brown. They start appearing two to three weeks after the tree reaches full bloom. Each moth lays about 50 to 60 eggs on leaves, branches and fruit. After the eggs hatch, the larvae feed on the tree for a short period before burrowing to the core of young fruit. The larvae are pinkish white with brown heads and leave a frass-filled hole on the outside of the fruit. The larvae feed for three weeks and then leave the fruit to pupate for two weeks. We can get several generations a year making control necessary throughout the fruit season. The larvae over winter in cocoons under loose bark or in debris on the ground.

Good control starts with cleanliness. Rake up all old fruit and leaves in the fall to remove hiding places and over wintering cocoons. Gently remove bark scales from trees to further reduce over wintering places.

Because the moths and larvae are only exposed to the open air for very short periods of time, any controls have to be timed to be on the tree before they enter the fruit or pupate. Pheromone traps hung in the trees are the most accurate way to tell if adult moths are present. 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. Once they start showing up, its time to get the rest of the control program underway. Traps are readily available at garden centers and should be hung fairly high in the tree near fruit areas.

Check the traps every couple of days for the presence of moths. Once they are present, begin a regular spray program every ten days. If no moths show up in the traps, you probably can skip spraying until they do. Malathion is the conventional spray for codling moth. A relatively new one is Spinosad, a new type of pesticide that is OMRI listed for use on organic production. It has to be ingested by the insect to be effective which makes it less likely to harm non-target 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, non-toxic coating. The tiny particles don’t kill the larvae but camouflage the fruit so it looks less like a meal and irritate the insects’ skin so they don’t hang around. This treatment may be hard to find locally. Always use and store pesticides according to the label directions.