Question: I have a pear tree that has some bumps the leaves. Over time the bumps turn into brown spots. Is this zinc deficiency?
Answer: No, you do not have a zinc deficiency. The damage you see is caused by mites, most likely the pear leaf blister mites (Pytoptus pyri Pagenstecher). This mite was introduced from Europe, probably before 1900. It is a pest of most pear growing areas of the world. Feeding by these mites causes damage on leaves and fruit. Blister mites overwinter as mature females at the base of buds or under outer bud scales. Adults are light to amber yellow in color and cylindrical, tapered sharply at the posterior end, and resemble a short worm. In spring, when buds begin to swell, overwintering females penetrate deeper into the buds and lay eggs on live tissues. Development from egg to adult requires 20-30 days during spring. Feeding of females and their offspring causes blisters on developing leaves. Blisters are green or red at first, but turn light brown to black as affected tissue dies. As the blisters form, leaf cells near the center of the blisters die and pull apart as surrounding cells enlarge, creating a hole. Blisters vary in size, with the largest about 1/8 inch in diameter. Mites do not live in the blisters on the fruit, but the fruit will be scarred. Mites of the first spring generation enter blisters through these holes and feed on soft leaf tissue inside. Several generations develop within the blisters during a growing season. Summer generations require only 10 to 12 days to develop. When blisters become crowded or leaves become heavily damaged, mites may migrate to growing terminals where their feeding produces new blisters. Fruit damage is caused by injury to buds before bloom. Severe damage to foliage can cause leaf drop and reduce shoot growth. Look at young leaves before bloom early in the spring just as leaves are unrolling. Noticeable light green to light red rough areas where mites have been feeding will be seen. This damage becomes more noticeable as the growing season progresses.
Control: Blister mites are not normally controlled by natural enemies. Predatory mites will feed on blister mites when they are exposed. Blister mites often attack weak, neglected or abandoned trees. If a pesticide is used to control blister mites the best timing is after harvest when mites migrate from leaf blisters to terminal and fruit buds. They are exposed on those sites until buds swell in the spring. Pre-bloom treatments can prevent fruit damage that occurs just before and during bloom.
Source: Orchard Pest Management. 1993. Edited by: Elizabeth H. Beers, et al. Good Fruit Grower Publications, Yakima, WA Pages 151-153.
Question: My mesquite trees have brown round bumps on many of the limbs. In fact some of the branches have ooze dripping from them. Is this scale?
Answer: Yes, the problem is scale, soft brown scale in fact. Scale are a "super family" of over 200 insects that feed on plant sap. Females protect themselves with a soft or hard "shell" body covering. Males can be winged. Scale produce young by eggs or by bearing live young. The young, called crawlers, may crawl out from under mother's covering and move to another location, usually close by, and then set up "housekeeping." One to five generations will be produced each year, depending on the species and environmental conditions. Scale are protected by the covering they make for themselves and it is very hard to penetrate with pesticides.
Control: Physical removal by spraying a hard stream of water may work, however many times they are stuck on the plant very tightly. Even rubbing off the scale with a stiff brush can be effective. Using systemic insecticides can help control scale, but many times does not work very well. Suffocating or penetrating their "shell" are methods also used to kill this pest. Dormant oil sprays are used when plant leaves are no longer than a half inch in early spring. If used later leaf damage may occur. Rubbing alcohol applied to scale will penetrate their waxy shell covering and kill them. Use 70% isopropyl (rubbing) alcohol, mixing 1 to 2 cups of alcohol per quart of water. Since alcohol can damage some plants first test spray on a small area. Wait for a day or two to see if damage occurred. If not it is safe to spray, you can mix insecticidal soap according to the label directions but substitute rubbing alcohol for half of the water. A recipe that has proven effective in the past for scale control and other insects is made by mixing one cup cooking oil plus 1 tablespoon of dish detergent (non-citrus). Mix one to two teaspoons of this solution with one cup of water. Spray mixture on the infected plant until it drips off. It is best to spray a few leaves and then check for leaf burn the next day before spraying the entire plant. With many of these treatments the scale will not drop off of the plant but will remain attached even though they are dead. Pry some off several days after treatment to determine if the scale are dead. If not treat again.