Question: We have a red oak tree that is infested with borers. The tree is about 75 feet tall, with a trunk circumference of about 9 feet. What is your suggestion on treating this tree to rid it of borers?
Answer: You may have a chance to save this tree, but when the beetle larvae are in the tree and eating, the damage has pretty much been done.
Borers usually attack sickly trees. Even if you soak the trunk with strong chemicals such as Dursban, lindane and the synthetic pyrethroids that some folks recommend, nothing will have been done to correct the conditions that attracted the pest.
You can kill the active borers by running a wire into the borer holes, applying beneficial nematodes to the holes or injecting orange oil or neem into the holes. My recipe for Tree Trunk Goop could help, too.
But to save the tree you must correct the condition that is causing stress. Severe stress can result from overfertilizing, using the wrong kind of fertilizer, providing too much or too little water, using herbicides or changing the soil grade around the tree.
Remove any added soil or planting beds from the root flare at the base of the tree. Make sure drainage is functioning properly and, if you have been watering around the tree, stop. The posies under the tree might need water, but the tree doesn't.
Question: I once heard you talk about one or more varieties of ash trees that are very good in Central and North Texas. You said that these do very well and are not junk trees like the Arizona ash. Can you tell us what variety of ash that is?
Answer: As opposed to Arizona ash and green ash, the native Texas ash (Fraxinus texensis) is a terrific tree. This is a subject that I discussed at length with the late Benny Simpson, who was a native plant expert at Texas A&M University. He taught me that the Texas ash and the white ash (F.
americana) are basically the same tree.
Others believe that Texas ash is a subspecies of white ash. It doesn't matter, they are both great, relatively fast growing, drought tolerant and have beautiful fall color that ranges from yellow to red. Texas ash will even grow in limestone outcroppings.
I have a photo of one of the North Texas specimens in my book "Howard Garrett's Texas Trees." You can see that tree in person just west of the intersection of Richmond Avenue and Alderson Street in East Dallas.
Question: How often should I water my trees this summer?
Answer: Well-established trees and correctly planted new trees need little additional water other than what is required to keep the plants around them growing.
Some trees, especially those with large leaves, will shed interior leaves to compensate for water lost through transpiration, but this is a cosmetic problem, not a life-threatening condition.