Friday, June 18, 2010
Brown spots on pear leaves
The brown spots on pear leaves are seldom the result of a fungus but due to an eight-legged eriophyid mite called the pearleaf blister mite. This mite is about one-quarter the size of a spider mite but you can see them with a 14 to 20X hand lens.
This pest feeds between the upper and lower tissue of the leaf. The spots are slightly raised and each has a tiny hole somewhere near its center. The mites enter these holes and feed on the soft tissue inside.
The photo shows several leaf blisters. The one in the upper left has an eriophyid mite emerging from a hole.
This mite also damages the fruit causing oval russet spots. Management includes the use of dormant or delayed dormant oil in the spring. The mite overwinters at the base of buds or under the outer bud scales. Apply the oil until it runs off the tree.
At this time of year, unless you are a commercial orchardist, I would suggest an insecticidal soap or a vigorous washing down of the tree with a hose. Make sure the water you use is cool or cold and not hot! Weekly washing would not hurt. Avoid the use of insecticidal soap and other insecticides during the heat of the day. Late evening or early morning treatments are more effective and cause less burning on foliage.