Prevention Is the Cure
The big news in pear growing is kaolin clay, a superfine organic spray sold as Surround that coats pear trees in a thin, white protective barrier. The pear psylla, a small sucking insect much like an aphid, is the primary insect scourge of pears, largely because the honeydew left by the pests encourages the growth of sooty mold. Psylla adults simply won't lay eggs on trees sprayed with kaolin, and the kaolin residue irritates psylla nymphs. Your trees will look like they're dusty, but the stuff is harmless. It is so effective, says John Dunley, Ph.D., an associate professor of entomology at the Washington State University Tree Fruit Research and Extension Center in Wenatchee, that even the big nonorganic growers in his area are using it. Cover your trees through bloom, and ideally keep them covered across the growing season, Dr. Dunley says.
Codling moths affect pears less than they do apples, but they can be a problem in some areas. You can control them with nothing more complicated than religiously picking off damaged fruit and disposing of it, with the larvae still inside, thus disrupting the insect's life cycle, says Bill Denevan, a commercial organic pear grower in Santa Cruz, California. Be sure to put it in the refuse pile, not your compost heap.
Fire blight is a bacteria that thrives especially in warm, rainy spring weather. Stella Otto follows the "65/65" rule of thumb: If the temperature is above 65°F and the humidity is above 65 percent, fire blight can develop. The bacteria typically enter the plant via the blossoms, as well as through breaks and damage. The tips of affected branches curl in the shape of a shepherd's crook, and pustules that form on the tree may ooze infectious orange-brown liquid.
It bears repeating that the first line of defense is choosing blight-resistant varieties. Conventional wisdom advises you to prune off infected branches a good 8 to 12 inches below visible damage when you see it and then in winter cut off the cankers that house overwintering bacteria. Stella Otto recommends waiting until winter to cut out damaged branches; you'll be less likely to miss the full extent of the damage and less likely to spread the infection. It's also a good idea to pinch off the extraneous blooms that appear after the tree's primary bloom. Which is why you'll see old pear growers pinch off stray blooms whenever they walk an orchard, as a matter of habit.