Trunk Injection

Experience with trunk injections of zinc has been disappointing in all cases despite rumors of success. It would seem logical that placement of any form of zinc in the secondary xylem of an actively transpiring tree would utilize the xylem vessels to rapidly transport the zinc to the actively growing meristems. However, many researchers including Millikan and Hanger (35,36) have proven that zinc transport is more complex than injecting zinc in any form into tree trunks. Millikan and Hanger (36) reported that ⁶⁵Zn moved from the injection point only when zinc was injected into the bark of 2-year-old apple trees. Supplying ethylenediaminetetraacetic acid (EDTA) enhanced ⁶⁵Zn movement in an acropetal (upward) direction only. The ⁶⁵Zn was distributed to spurs and laterals on the distal side of the injection point. Millikan and Hanger (36) also reported that ⁶⁵Zn accumulated at the nodes on lateral branches and in the petioles, midrib, and major veins of the leaves.

Wadsworth (37) reported no significant effect of ZnEDTA applied via injection into the secondary xylem of mature 'Western' or 'Burkett' pecan tree leaves on nut quality or yield. He suggested that the volume of zinc was inadequate to influence such a large tree. The possibility of home owners using this means of applying zinc to their large pecan landscape trees, which would otherwise require large spray machines, was discounted by the danger of small children pulling them out of the trunks and inserting them in their mouths. The direct application of zinc chelates to the secondary xylem via injection was unsuccessful primarily because of the small volume of zinc injected (37).