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Gardening advice on stressed out palo verde trees

Author: Cathy Cromell
Issue: March, 2013, Page 145


Q - My large palo verde tree dried out on top and has brown liquid dripping from the trunk where two branches arise. A landscaper said that it has slime flux disease. His expensive treatment plan includes applying insecticide to kill the bugs, a “bio-feed” treatment to kill the bacteria and furnish needed nutrients, and pruning. Is this appropriate?

A - Slime flux is a bacterial disease that causes dark, watery sap to drip from wounds, pruning cuts or branch unions, explains Certified Arborist Cathy Rymer. Insects do not cause this disease, so the insecticide treatment recommended by your landscaper is useless. Since our native palo verde trees are legumes, they are able to “make” nitrogen on their roots and seldom need fertilizer. Because your tree is most likely in stress, it would not be a good idea to fertilize now. “Forcing” it to grow will increase stress. Also, fertilizer will not kill bacteria. And because bacteria cause slime flux, it can be easily transmitted by pruning tools.

The best treatment is deep, infrequent watering and minimal pruning. Always water to a depth of 3 feet and apply water at the drip line and not next to the trunk. If your tree is on a drip system, let your system run for several hours to deliver the correct amount of water to soak 3 feet deep. You may need to add more emitters to apply enough water. If your tree has been in the ground for at least 4 to 5 years, you can shut off the drip system and water with a slow trickle from the hose during extremely dry periods. Rymer says she seldom waters her mature palo verde from December through February and waters only monthly in the summertime.
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