Q: I have two mature palo verde trees in the enclosed portion of our backyard (many more in the desert).Β They are next to each other surrounding a rock outcropping. There was a nasty shrub in the rock outcropping that I kept trimming back, but it always returned. So I bought a small container of poison ivy killer (only shrub killer I could find) and sprayed the contents on the shrub. Good news is shrub appears dead. Bad news is one of the two palo verde trees dropped the leaves off of the branches growing from one of the three main trunks. The main branches are still green, but the small leaf bearing branches have turned brown, though still pliable. The other two main trunks of that tree and the other palo verde are unaffected. Will the tree survive and regrow its leaves?
A:Β It is hard to know how much herbicide your tree absorbed. The roots of mature trees extend two or three times the diameter of the crown. The best thing you can do for the trees is taking good care of them. That means deep watering once every two weeks down to about 24 to 36 inches. Make sure the water is going to the absorbing roots that are out around the drip line (the edge of the crown) of the tree. These trees need that much water anyway and flushing out the root zone may help wash out the herbicide. Time will tell if the tree got a strong enough dose to do it in.
Herbicides can be used in situations where plants are in close proximity by painting them on the offending plant rather than spraying or drenching the soil. Often this is done soon after making a basal pruning cut. This should reduce exposure to nearby desirable plants.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email: plwarren@cals. arizona.edu
