Mites attack during hot dry weather. They can cause leaf drop and a rusty appearance to the avocado fruit. The fruit is still good. Try Safer's Insecticidal Soap spray for control. Use only organic products on edibles.
Systemic insecticides poison the entire plant including the fruit.
Safer Inc. offers a brochure that opens into a handy chart suitable for hanging. It covers many organic controls for weeds and insects that are safe and non-toxic. This should be very valuable for all gardeners concerned with the environment. Q. My avocado was planted from seed in 1994 and it blossomed this year. It didn't set any fruit.