Pecan tree management after ice storm damage
Ice damage is typically more severe in pecan orchards than in other orchard crops as the pecan’s height, long limbs, and large leaf areas accumulate ice, the weight of which causes breakage. The damage is especially severe in trees without hedging. Pecan trees usually take 3 to 5 years to recover productivity, but improper management may extend that time period. One management scheme to avoid is the application of high levels of nitrogen to encourage growth and redevelop the tree canopies. This management technique causes trees to become vegetative and develop long, weak shoots that can not support the nut load’s weight when the trees do finally produce a large crop.
When severe breakage of limbs occurs, adventitious buds will arise at the broken/cut end of a limb, which will develop into epicormic shoots. Figure 1 (c) shows abundant epicormic shoots developing beneath a cut of the broken limbs from trees damaged in the October 2020 ice storm in the OSU experimental orchard near Perkins, Oklahoma.
As these epicormic shoots develop, growers may question what to do about them. Do we need to thin epicormic shoots? The management of epicormic shoots in damaged pecan hasn’t received much attention. According to a 2020 presentation from Dr. Charles Rohla with the Noble Research Institute, an over-abundance of epicormic shoots could reduce the vigor of single shoots and weaken limb structure in the future. Additionally, in an article published in HortScience in 1991, Dr. Ray E. Worley indicated sprout removal was required to reduce the number of epicormic shoots around the pruning wound.
Or is it unnecessary to prune epicormic shoots? Some pecan specialists believe so. In a 2011 blog post titled “Ice storm recovery update,” Dr. William Reid argued that the competition for sunlight among these epicormic shoots will eventually lead to natural thinning, with the least heavily shaded limbs becoming dominant and growing into fruiting wood. The reason makes sense. But obviously, waiting for natural competition also means a waste of carbohydrates, and the broken part might not be able to rebuild strong limbs to bear nuts.
We have initiated a long-term study to evaluate the management of epicormic shoot regrowth and selective removal to encourage a return to productivity in this orchard. As part of this study, we have begun trials to explore epicormic shoot removal levels on the carbohydrate status in trees to understand and promote quicker return bloom and to help construct a clear-cut recovery strategy. Two OSU graduate students, Niranjan Pokhrel and Rashmi Kumari, who started their Master’s program this Spring, are focusing on damaged tree pruning and fertilization.
This year we have thinned epicormic shoots on damaged tree branches at three levels: 1-2 remaining (about 75-95% shoot removal), 4-5 remaining (about 60-75% shoot removal), and a control without removal. Figure 2 demonstrates before and after epicormic shoot removal at the cut end of damaged trees.
To explore the optimum amount of nitrogen application used in damaged trees, we adjusted the amount of urea. The study tests these three application rates: applying full amount (70 lbs/acre nitrogen), half amount (35 lbs/acre nitrogen), and none (0 lbs/acre nitrogen) to trees at 25%, 50%, and 75% canopy loss. We will continue to observe epicormic shoot growth (length and diameter), compare the difference in carbohydrate allocation, and eventually time to re-fruiting between epicormic shoot removal levels and nitrogen treatments.
The success of this experiment could help us develop management recommendations for pecan tree recovery after limb breakage from adverse weather events, like ice storms. Although this research is focused on ice storm recovery, it will be of use for canopy recovery from other types of weather damage, such as tornadoes and hurricanes. We will provide an update with our research results in future issues of Pecan South.