Monday, May 21, 2018
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Pests, disease bedevil apple trees, but there are solutions


The three major insect pests of apples are apple maggot, plum curculio, and codling moth.

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With more forethought, Adam might not have bitten the apple and I might not have planted apple trees. But he did, and I did, and we each must deal with the consequences.

For my part, I hadn’t realized that apple trees had so many pest and disease problems until I planted 25 dwarfs.

Sure, those problems can be fought with repeated sprays of pesticides. But with a little research and planning, an acceptable crop of high quality apples can be harvested using little or no pesticide.

Insect thugs

The three major insect pests for apples are the apple maggot, plum curculio, and codling moth. Apple maggots are the worst of the lot, dimpling fruits and riddling them with brown trails of burrowing larvae. Given free rein, they make almost every fruit too damaged to eat.

Thankfully, the apple maggot has an Achilles heel. When this insect emerges as a fly about six weeks after the trees have bloomed, the females search around for the biggest, reddest apples in which to lay eggs.

Ms. Maggot can be hoodwinked with fake apples: red spheres coated with a sticky material called Tangletrap.

Or with sacrificial real apples: Buy the firmest, reddest Red Delicious you can find, force a stiff wire through the core to hang the apple, and coat the fruit with Tangletrap. (Traps of real apples eventually rot, so usually need to be replaced once or twice a season.) One trap per dwarf tree, hung at head height in clear view, or four traps per full-size apple tree, should provide an irresistible enticement to the egg-laying apple maggot.

Plum curculio, which is active during the six weeks immediately following bloom, can cause fruit to drop early. The traditional way to thwart it, effective if done diligently, is to spread an old sheet or dropcloth beneath each tree each morning, then give the tree or branches a sharp whack with a padded mallet. Curculios drop from the tree and play dead, at which point they can be gathered up and destroyed. Letting chickens forage beneath apple trees also offers some control.

Spraying is another way to control curculio, but instead of the usual chemical pesticide sprays, use a spray derived from nothing more than kaolin clay. The material, marketed under the name Surround, leaves a white coating on the fruit. Build up a good, powdery base with three sprays just before trees bloom, then spray every seven to 10 days, or after heavy rains.

The clay spray also thwarts codling moth, with its signature big, fat worm. This pest is active for much of the season, but even unchecked, affects only 25 percent of fruits.


The three worst diseases afflicting apple trees are fire blight, cedar-apple rust, and scab. A combination of strategies keeps damage within reasonable bounds.

Fire blight disease blackens leaves as if they had been singed by fire. The ends of young stems curl over in a characteristic shepherd’s crook.

Cedar-apple rust defaces leaves, and sometimes fruits, with rusty-colored lesions. Certain pesticides control cedar apple rust, but spraying must begin before blossoms open. For myself, I choose to accept a certain amount of damage rather than suit up for an additional spray session.

Apple scab results in corky brown lesions on fruits and leaves. Defense against scab begins in fall; smother fallen apple leaves — the source of next year’s infections — beneath a thick mulch of wood chips. You also can defuse leaves that fall on nearby grass by mowing thoroughly. Chopped, the leaves decompose quickly and are rendered harmless.

Although apple insects have cosmopolitan tastes, disease organisms are finicky. So another way to control diseases is to plant one of the many disease-resistant varieties. One that I grow, Liberty, is resistant to all the major apple diseases.

Even without paying particular attention to planting disease-resistant varieties, you can harvest a reasonably good yield of reasonably clean fruit using a combination of cleanup, limited spraying, and traps. This is especially true in Western states, where some of these pest problems are less severe.

Cosmetically, my fruits put on a poor show compared with the perfect apples you see in markets. But mine are pesticide-free, and the Macouns, Jonagolds, Spitzenbergs, and other select varieties that I grow are simply scrumptious picked at their peaks of perfection.

I hope Adam’s apple was as good.

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