Answer: There are many potential answers to your question, but we'll concentrate on the two most likely causes of white infestations. First, your trees may have cottony scale. These insect pests attach themselves to stems and branches of all kinds of plants. Because they have hard outer shells, insecticides are virtually worthless against them, unless you catch them in the crawler stage. The best defense is to use a horticultural oil to smother the pests. Do this during the dormant season, when you would normally spray fruit trees with Bordeaux (lime-sulfur). The second possiblity is an insect called mealy bug. These are small pests covered with white, cottony fluff. They can occur in large clusters. Control is difficult, but you can try using horticultural oil during the dormant season. For a positive identification of the pests you might want to take a sample branch to your local Cooperative Extension office. You can contact University of Arizona, College of Agriculture, 301 Forbes Bldg., Tucson 85721. Phone (520) 621-7205.
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