QUESTION: My apple tree has branches that are dead or dying. Leaves are drying up and the bark is sunburned. What can I do to stop this?
ANSWER: What you are seeing are the symptoms of a problem in the root system of the apple tree. It could be a soil born fungus like phytophtera, but is more likely to be a ground dwelling insect pest called a wooly apple aphid (Erisoma lanigerum). Also pears are injured by the wooly pear aphid (Erisoma Pyricola). These aphids are native to the eastern United States and Canada, but is a worldwide pest that attack elm, mountain ash, and some species of hawthorn trees as alternate hosts. A fluffy white wooly covering over most of the insect's posterior end of their blue black bodies' accounts for its name. This cottony looking substance can be seen in small masses on branches and shoots where injuries or pruning cuts have been made, as well as on roots.
The life cycle of these insects is rather complicated. Females lay eggs on the bark of host or alternate host trees in the late summer or fall. These eggs overwinter and hatch in the spring as wingless parthenogenic (development from an unfertilized egg), females produce ovoviviparous (eggs hatch within the females' body), stem mothers which establish colonies on the terminal leaves. These leaves soon become curled and stunted from feeding. By early summer winged forms appear and fly to other apple trees or hosts to establish new colonies. Repeated generations are produced during the summer. Some of the individuals may crawl to the roots where they continue to reproduce indefinitely. In the fall, winged individuals develop again and fly to hosts and give birth to sexual forms which eventually mate and lay overwintering eggs. Not all aphids leave the apple trees, some wingless forms remain all winter, both above and below ground, thus maintaining a continuous infestation year around. On the roots, nodules are formed from the insects feeding. These nodules are rough and bumpy looking and restrict the flow of water and nutrients from the roots to the leaves. Small leaves form and eventually the bark becomes sunburned and dried out and limbs die over several growing seasons.
Control: When planting apple trees semi dwarfing and dwarfing rootstock with MM before the rootstock number should be used. Example: MM106 or MM111 are semi dwarfing rootstocks which are resistant to the wooly apple aphid. The MM stands for Malling-Merton which are agricultural research stations in England which developed these rootstocks. Currently chemical control is the only means available to control wooly apple aphid. However, BioLogic Company, a bio-engineering firm has developed a parasitic nematode (Steinernema carpocaposae) that has been 80% effective in controlling the ground dwelling form of this pest. They are not yet marketing the nematode. Chemical controls include dimethoate (Cygon), a systemic insecticide. Other organic and chemical based insecticides that control aphids will control the above ground generations of this insect when they are in the tree, though the ground dwelling forms will not be affected.
Source: Insect Pests of Farm, Garden, and Orchard, R. H. Davidson and W.F. Lyon. 1979. 7th Ed. pp. 392-393. John Wiley and Sons, New York.
QUESTION: My tomatoes have small water soaked areas that at first appear to be bruises, then turns into brown sunken leathery areas always on the blossom end of the fruit. Some of the sunken areas turn black. These diseased fruits usually ripen before the non-infected fruit. What disease do my tomatoes have?
ANSWER: This disease, called blossom-end rot, is caused by a localized deficiency of calcium in the fruits. Calcium is required in large quantities by growing cells like those in the blossom-end. When this rapidly growing tissue is deprived of the calcium needed for growth, especially cell-wall construction, tissues break down resulting in blackened, dry sunken spots or areas on the blossom-end of the fruit. Water stress usually creates this disorder because inconsistent watering will not allow the plant to translocate sufficient calcium. Also high levels of nitrogen can cause vigorous growth early in the season which with water stress can compound the problem. Blossom-end rot is also seen in chili and bell peppers and members of the squash and melon family.
Control: It is important to regulate soil moisture and maintain that moisture at a relatively constant level where possible. Plenty of organic matter in the soil and mulching plants will help maintain consistent soil moisture. Also avoid high applications of nitrogen to the plants. Some varieties of tomatoes are less susceptible to blossom-end rot. These include Early Girl, Floradel, Floradade, Tropic, and Jet Star. It has been demonstrated that foliar sprays of calcium chloride (1 lb./25 gallons of water), or calcium nitrate (2 lbs./25 gallons of water) can help reduce this problem. Applications must be made before calcium levels fall below critical levels and must be applied weekly for 3 to 4 weeks.
Source: Vegetable Diseases and Their Control. A.F. Sherf and A.A. MacNab. 1986. pp.689-691. John Wiley and Sons, New York.