Wednesday, June 13, 2012

One Messed Up Mulberry

A gentleman brought in a Mulberry (Morus alba) shoot from a tree that was having problems. The new foliage was distorted and seemed to wilt over the course of one to two months. According to him the onset was sudden and no other nearby trees (this was the only mulberry) seemed to have the problem. We ruled out a gas leak and upon viewing the shoot under magnification no insects or insect debris were noted.
Distorted Mulberry Shoot
After ruling out insects and diseases the last thing left was to investigate physiological (nutrition, salt burn, etc.) causes and finally, herbicides. Going through the list the only description I found that matched the damage to the shoot was that for 'phenoxy' herbicides (the giveaway was the curly-queue stems). One of the most common scenarios where this type of herbicide damages trees and shrubs is when 'weed and feed' lawn fertilizer is applied to the lawn under the canopy of a sensitive tree. The owner of the damaged tree however did not apply any of this kind of fertilizer on the lawn under the tree. Another cause of this kind of damage is a disgruntled neighbor spaying an herbicide intentionally on the tree, but the tree owner denied having any tiffs or feuds with fellow neighbors. 

So the most likely cause of this damage to his tree was a neighbors spraying accident. 'Phenoxy' type herbicides (those containing 2-4 D and similar compounds) are notorious for causing damage to trees from spray drift caused by applicator error or applying the spray in windy, hot conditions. All it would take would be a neighbor spritzing weeds in his lawn with a hose end, pump, or hand pump sprayer in a light breeze; and to top it off Mulberries are notoriously sensitive to these types of herbicides. 

The treatment? If the accidental dose is not to great the tree should grow out of the damage either before the summer or next spring when the tree re-leafs after its winter dormant period.

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