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 are a worldwide pest that attack elm, mountain ash, and some species of hawthorn trees as alternate hosts. It is the fluffy white wooly covering over most of the insect's posterior end of their blue-black bodies that account 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 producing 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. Winter soil temperatures in the Southwest are not cold enough and normally do not freeze deeply, therefore the wooly apple aphids do not remain in check.
Control: When planting apple trees semi-dwarfing and dwarfing rootstocks 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, but not immune. 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, although 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: Are there any garden vegetables that I can plant for a fall harvest in Cochise County?
Answer: Many of the cool-season crops, those that can withstand freezing temperatures, do very well in Cochise County during the fall. In fact, the fall in Cochise County is better generally than the spring to raise cool-season crops. These vegetables include the cabbage family, i.e. broccoli, cauliflower, kale and cabbage among others. Also, spinach, small beets, peas-both snap and edible pod-turnips, radishes, lettuces of all kinds, mustard greens and other greens may be planted. The onion family does best when planted in the fall and then over-wintered and harvested in early summer. Members include garlic, onions and chives. Prepare and plant during the last week in August or first two weeks in September. I have had broccoli, cabbage, cauliflower, and onions growing the whole winter long during mild winters, pulling the plants out in May to make way for warm season crops. Robert E. Call Extension Agent, Hori