Question: Recently many twigs with new leaves on them have started falling from my desert willow tree. I have seen leaves fall after winds in the late spring, but this is twigs falling with the leaves attached. What is wrong with my trees, does it have a disease?

Answer: If you will remember we had a cold spell with frost which occurred after leaves were on the trees. Looking at the sample you sent it appears that the new twigs were damaged by the frost. This damage affected the outer layers of the twig, the phloem and cambium, but not the xylem. The xylem carries water from the roots to the leaves, the phloem carries the food produced by the leaves to the rest of the tree, including the roots. The cambium is the layer which produces new xylem and phloem cells. When the phloem and cambium are damaged and the xylem not injured, the water and nutrients needed by the leaves can proceed from the roots to the leaves normally, the leaves look normal and are healthy. Because of the injury to the tissues at the base of the twig, however, the twig has been weakened and easily blows off in our spring winds.

I have observed this in a number of trees and in the absence of symptoms of disease, don't consider this a problem about which to be overly concerned. You may notice that some branches have considerable dieback and that more dieback and other weak growth appears as the summer progresses. It is a good idea to remove the dead and dying branches as they appear. As long as the majority of the tree appears healthy it should survive. Be sure to provide adequate water through the summer as the heat and dry winds will increase the stress on the trees.

Question: There are hundreds of thousands, perhaps even millions of insects that are long and black with grey spots that look like beetles have been swarming onto our property. They have been stripping our trees and vegetable garden with their voracious appetites. What are these insects? We have sprayed them and they die quite easily. What can we do about them?

Answer: What you have experienced are blister beetles. In particular the spotted blister beetle, Epicauta maculata, according to my reference books. There are other types of blister beetles that have stripes or are solid black in color and even a metallic Arizona blister beetle. Blister beetles are elongated beetles 3/8" to 1 1/8" long. Their broad head is usually wider than their prothorax and connected by a narrow "neck." The wings and body are soft and frequently the tip of the abdomen is exposed. Eggs clusters of up to 100 are laid in holes in the soil and hatch in 10 to 21 days. Larvae burrow in search of grasshopper eggs, pupate in 2 weeks, and overwinter in the soil. Larvae are beneficial. One larvae can destroy 30 or more grasshopper eggs, which is the total laid by a single grasshopper. The active parasitic larvae can gain access to bee nests by attaching themselves to foraging bees. Adults of the several species have similar habits. They appear in the late spring through summer. The entire population will emerge in a very short period and forage on many different host plants. They feed on foliage, usually in large numbers, and after defoliating a plant will migrate to others. Usually only one generation is produced each year. All species contain a blistering substance, cantharadin. This material is extracted from a species in southern Europe, the Spanishfly, and used as a drug. Some species will secrete blistering materials or oily substances as a defensive action. Sometimes alfalfa hay that is bailed will have large populations in it and when eaten by livestock can cause blisters in the mouth and on the tongue, causing sores that will cause animals to stop eating because of the pain. Sources: How to Know the Insects. 1978. Roger G. Bland and H.E. Jaques. Page 223. Insect Pests of Farm, Garden, and Orchard, 7th Edition. 1979. Ralph H. Davidson and William F. Lyon. Pages 265-266.