Malatya Haber Conifers affected by drought, disease
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Conifers affected by drought, disease

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By Tracey Payton Miller

Horticulture Educator

If you have a conifer that is turning brown, you are not alone. Many homeowners have experienced problems with their pines, cedars, and spruce. Pines and other needled evergreens have definitely filled a niche; they are flexible with evergreen appeal and a delicate appearance, but they can also be used for windrows or privacy. However, most conifers can be stressed by the climate in Oklahoma. For example: Alberta spruce is native to Canada, Colorado blue spruce--Colorado. These trees cannot take the Oklahoma heat without suffering. In addition, plants weakened by environmental stressors are more susceptible to pest and disease problems. Recently, I've seen two major problems affecting conifers.

I know you're probably tired of hearing it, but the effects of heat and drought cannot be overstated. Extreme heat can be detrimental to pines, spruces, and true cedars. I've seen a ton of blue atlas cedars, deodar cedars, and various pines die in the past two years due to adverse environmental conditions. With these species, watering is very important. It is recommended you water established trees once a month during high heat, applying a slow running hose to the drip line for several hours. If your tree is in full, brutal 115 degree sun, you may still see damage. No amount of water can counteract that temperature. Check water levels weekly with newly planted trees. All plants need a period of drying out, but not to the point of wilting. More is not better, it is very easy to overwater and kill trees too. My recommendation for the future is to stop planting conifers. They are more trouble than they are worth, especially if attacked by insects or disease. Pruning and spraying a diseased tree is an expensive headache. Avoid it if you can.

The disease that most are worried about in Oklahoma is pine wilt. Pine wilt only affects true pines, not cedars, cypress, or spruce. Pine wilt is relatively new to Oklahoma; it was just confirmed in the late 1990s. Pine wilt is caused by the pinewood nematode that feeds in the resin canals of the tree, blocking the flow of water and nutrients. Hence, the needles turn brown, sometimes one branch at a time. There also tends to be no sap leakage, since the resin cells are blocked. How do these nematodes get into the tree? Female pine sawyer beetles feed on and also lay eggs in dead or dying pines. The feeding wound allows entry by the nematodes that are already present in the beetle. Now the tree is infected. Symptoms of pine wilt are brown, droopy needles that remain on the tree. The death of the tree is also very quick, typically less than one month. Unfortunately, there is no cure for pine wilt. There are some treatments, but they are ineffective and expensive. If you have a tree infected by pine wilt, it is recommended that you chip, bury, or burn the wood promptly and also grind the stump. Pinewood nematodes also feed on blue stain fungi. So, if you have a tree that you have recently taken out and think it might be pine wilt, the blue stain may be visible in the cut stump. If you are not sure that you have pine wilt, you can wait until April or Early May to take the tree out, as the beetles do not emerge until this time.

To be proactive against any disease, try to minimize stress to the trees and practice sanitation. Make sure the tree has adequate water and nutrients. We recommend you do a soil test every three to five years to measure the amount of nutrients present in the soil. Sanitation includes collecting fallen needles and disposing of them. Affected needles can harbor the disease and be a source of reinfection. Pruning is also a good method of sanitation, in cases where only a few limbs are affected. In pines, prune out completely dead limbs back to the main trunk and dispose of the wood. Be sure to sanitize shears or loppers after every cut to minimize the spread of the disease.

Date: 10/15/2012



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