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 while females protect themselves with a soft or hard "shell" body covering. Males can be Scales - over 200 species 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 coveting 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 up 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.
QUESTION: I have pear, apple, peach, nectarine, plum, apricot and cherry trees which have new leaves that are curling up around the edges and are deformed. Is this peach leaf curl?
ANSWER: Peach leaf curl is caused by a fungus and does not affect pear and apple trees. The problem at hand is caused by the western flower thrip or onion thrip. Thrips are small, l/25-l/50th inch long or so, and lay their eggs in flower or leaf buds or on very young leaf tissue. They feed with their rasping sucking mouth parts and cause irreversible damage to the plant tissue, flowers, and fruit. Five to 15 generations per year can be produced. To see if you have thrips, hold a piece of white paper under the damaged leaves and tap them sharply. Thrips will fall on the paper and start to walk around. They rarely fly because they are weak flyers but will hop. There have been vast numbers of thrips this year because of the good winter rains we had which caused cool season weeds, mustard particularly, to thrive. Thrip populations build up to high levels on these weeds and when they die down, due to warm weather, the thrips migrate to fruit trees, roses and other perennial flowers.
CONTROL: Thrips are hard to control once they are inside a bud because they are protected. Systemic pesticides do help with thrips on roses, peonies, and other perennial flowers. Hang up blue or yellow sticky traps to catch adults as they move into an area. Diatomaceous earth applied to the underside of the leaves may also be helpful. As a last resort sprays of insecticidal soap, rubbing alcohol or other insecticides may be helpful. The best thing to do is control weeds where thrips are living in the early spring. Annually check weeds on your property to see if thrips are there. Use the method described above. Generally plants will outgrow the damage caused by thrips by producing new leaves, but damaged leaves flowers and fruit will not be mended.
Source: Carr Anna et. al. Chemical-Free Yard and Gardening. 1991. Rodale Press, Inc., Emmaus, PA. pp. 242, 244.