TRUNK INJECTED ETHEPHON: A POTENTIAL HARVEST AID MECHANISM FOR PECANS

Manipulation and control of pecan harvest is a goal of growers due to problems associated with harvesting. Ethephon has had limited success as a harvest aid chemical in field trials in Texas. Due to limited success from foliar applications of ethephon, ethephon was trunk injected into the secondary xylem of the tree in an attempt to promote early shuck opening without adverse effects on the tree or nuts.

Trunk injected ethephon at College Station and Hondo, Texas significantly increased shuck opening in 1983. Leaf drop was 35% at 10 ppm (based on the estimated tree water volume) up to total defoliation at 100 ppm. The ethephon injections advanced the maturity of the nuts by three weeks without a subsequent loss in quality.

High concentrations of ethylene releasing compounds in 1984 showed that pecans would respond to spray applications even before the shuck from nut separation stage. However, this was not true for limb injections. Rather injections made prior to this time resulted in dried up shucks with no shuck opening. Shuck opening was advanced in all trunk injections made at the critical shuck from nut separation stage where good uptake of the chemical was obtained. However, severe leaf drop also occurred in all cases where good uptake occurred which drastically reduced crop set in 1985. Since the concentrations used in 1984 were based on the volume of water injected rather than the estimated volume of water in the trees as in 1983, higher concentrations were injected. In concentration experiments in 1984 using 50, 100, 500, & 1000 ppm in similar volumes of water, good opening was obtained at all concentrations. More importantly, the subsequent leaf drop was proportionate to the concentration used and the 50 and 100 ppm rates subsequently set a crop comparable to the control trees in 1985.

Based on these results, lower concentrations were injected in 1985 at the critical shuck from nut separation stage. In these experiments, 100 ppm significantly advanced the harvest date over the non-treated trees by two weeks. These trees also set a crop comparable to the control trees in 1986.