Ask a Master Gardener: What is attacking my apple trees?

COURTESY TO THE BELLINGHAM HERALDAugust 15, 2013 

Question: Something is making the apples on my four trees look awful. Can you help me know what's happening and what I can do to stop it?

Answer: Three things make an apple grower's heart stop: codling moth, apple maggot and apple scab.

Codling moth is the universal insect pest of apples. Don't read any further if you've got a weak stomach and love apples. Female coddling moths lay eggs on the leaves or the fruit. The larvae will dine on the apple core and seeds.

If you cut into a moth-infected apple, it will appear dirty brown and rotted in the center, and you'll see the culprits: pinkish white, 3/4-inch long, with black heads. They tunnel out of the apple, making cocoons under the bark or at the base of the tree. There they overwinter and pupate, emerging as adults in the spring. Sadly, there can be two generations a year.

So what can you do?

1. Bag fruit, as long as the bags are placed before adult moths emerge in the spring. Bag the fruit when it's about the size of a dime. Use paper lunch bags or wax paper bags. You can remove them in late spring to improve fruit color, but know that the second-generation moths in mid-July to early September might attack your fruit.

2. Pheromone-baited traps reduce the populations of male moths.

3. Remove brush and debris from the orchard.

4. Remove loose bark to reduce hiding places for cocoons.

5. Use cardboard to wrap the apple trunk, trapping migrating larvae; destroy them with vigor.

Apple maggots are equally harmful to apples. Adult maggots are small black flies with white marks on the back and black markings on their clear wings. After the female lays her eggs by puncturing the apple's skin, the voracious cream-colored larvae tunnel throughout the fruit, rendering them inedible. When mature, the maggots drop to the ground, only to re-emerge and continue their damage the next summer. To prevent them, bag the fruit as described above.

Apple scab is a fungus. It first infects the tree during the cold, wet spring. Tiny, pale, water-soaked spots occur, followed by darkening, distortion and puckering of the infected leaves. They may drop, sometimes causing defoliation of trees. Sadly, the fungus also can damage fruit, resulting in misshapen or scab spots while in storage. The disease overwinters in infected plant debris.

Here's what to do:

1. Avoid watering overhead.

2. Plant apple trees in full sun.

3. Plant scab-resistant varieties.

4. Rake and put in the garbage all fallen leaves.

5. Make sure the tree has good air circulation.

Q: A beautiful evening to garden, I thought. Then, when digging, I was practically knocked down by the vomitus smell of a gelatinous-looking white/yellow/gray blob on the bottom of my raised bed. What is it and where did it come from? I'm afraid to venture near it.

A: What you discovered is slime mold. Yup, the stuff that inspired the movie "The Blob."

Slime mold is not a plant, not an animal and not a fungus. It's an amoeba, a brainless, footless, single-celled organism. It comes in every color of the rainbow except true green. Slime mold organizes itself into strange, wild and sophisticated shapes -honeycomb, blackberries, dog vomit, to name just a few of thousands.

For something with no legs or feet, it gets around. Not fast, travelling a glacially slow 1 millimeter per hour, but researchers found a slime mold in New Zealand that is genetically identical to one in the U.S. How it traveled here, no one knows.

Gardeners don't need to worry. It may look alarming, it may smell horrible, but it's harmless. It eats bacteria and decaying organic matter, and never touches living plants. It typically occurs in warm, wet conditions, and will disappear in dry weather.

If you find it unsightly, use a broom or hose, though in most cases it will turn black and disappear on its own. People who see slime mold have most likely spread wood or bark mulch.

One last thing about slime mold. It is providing invaluable assistance to scientists studying cancer and computing algorithms. It provides scientists with career-long material to study.

And consider this: Some slime mold spores survive in the dormant stage for 75 years before they germinate. Doesn't that seem to hold some research promise?

Master Gardener Kathleen Bander is a resident of Bellingham and a lifelong gardener. For more information on Whatcom County Master Gardeners, go online to whatcom.wsu.edu/ch/mg.html.

Ask a Master Gardener will appear in The Bellingham Herald weekly through the summer growing season. If you have a gardening question you'd like answered in the column, please email it to newsroom@bellinghamherald.com.

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