   Interesting Insects and Diseases of Summer 2000 - July 12, 2000 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County In many ways, this summer is not unlike other summers. Horticultural inquiries to the Cottonwood Cooperative Extension office have resulted in the normal diagnoses of Texas Root Rot (Cotton Root Rot), cicada damage to ornamental trees and shrubs, fungal diseases in vegetables and turf, and other pest and disease problems common to the Verde Valley. The summer of 2000 has also brought us a few unique and interesting plant insects and diseases that are detailed below. When we have a dry winter and spring, cypress bark beetles (Phloeosinus arizonicus) cause damage to Arizona cypress, Leyland cypress, and sometimes one-seed junipers. Watch for branch tips to die back and/or break off. Upon close inspection you will see a small tunnel in the center of the branch at the point where the twig died. This is where the cypress bark beetle entered the twig and fed. If the tree is still stressed, the beetle's next step will be to attack the trunk. This usually results in death of the tree. There are no known insecticides to effectively treat this pest. The best defense against cypress bark beetle is deep irrigation about every one to two weeks during the dry period until we have sufficient monsoon rains. When irrigating, remember, tree roots are not concentrated near the trunk, but near the drip-line and beyond. Black rubber soaker hoses work nicely. A rust fungus has infected many of the catclaw plants throughout the Verde Valley. The rust fungus is called Ravenelia pringlei. It is noticeable where it causes a distorted growth pattern commonly called a "witches broom". There is no known treatment for this disease. It is likely a cyclic disease acting as a natural population control on its host the Acacia. If you have it in an intensely managed area of your landscape, let it run its course over the summer and prune it out next winter discarding or burning the trimmings. Red Rocks State Park Manager, John Schreiber, told me about a localized Tussock Moth (Orgyia sp.) infestation in Arizona sycamore and Arizona alder along the park's reach of Oak Creek. This light colored, hairy, caterpillar has completely defoliated a few sycamores near the park's bridge. John said when they most numerous you could hear them feeding and fecal pellets were raining from the canopy. Again, this is likely a cyclic phenomenon and should not pose a serious threat to these native tree populations. Bob Celaya, Arizona State Land Department Forest Health Specialist, will be visiting the park to assess the infestation and I look forward to his assessment of the situation. Although not unique to this year, I have seen some cases of Oleander gall. This is a bacterial infection that causes prominent lesions on the stems, leaves, and flowers of Oleanders. Pseudomonas syringae is the bacteria responsible for this disease. Inspect any new plants for symptoms before purchase. Oleander gall spreads rapidly under moist conditions and with overhead irrigation. To manage, stop watering, prune out affected stems several inches below the point of infection, and treat cut surfaces with a 10% bleach solution. Disinfect pruning tools with this solution after each cut and destroy the trimmings. Heavy infestations sometimes require complete removal. If you need help with any other insects or plant diseases, call The University of Arizona Cooperative Extension, Yavapai County. We have publications and information on a range of horticultural topics. Master Gardener volunteers are available to assist you in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. The Yavapai County Cooperative Extension web site is http://ag.arizona.edu/yavapai/. |