Mechanical hedge pruning and topping of commercial pecan trees in the Southwest increases income potential for producers, according to University of Arizona (UA) Extension soil specialist James Walworth.

This common practice helps manage pecan tree size and improve orchard light penetration which can increase nut yields on the lower branches. Pecans are an alternate bearing crop with higher on-year yields and lower off-year yields.

“Hedging in the on-year reduces the amount of nut-bearing wood, fruit load, and is thought to increase nut quality,” Walworth said. “Hedging increases off-year yields and reduces alternate bearing,” Walworth said.

Walworth, along with Richard Heerema, New Mexico State University pecan specialist, discussed pecan tree hedging and topping with the nearly 600 pecan industry members at the 2012 Western Pecan Growers Association Conference in Las Cruces, N.M. held this spring.

Few studies have evaluated the impact of hedging on pecan crop production and quality, Walworth said. Each producer generally adapts a preferred hedging method since no textbook method really exists.

Walworth reported on a UA study conducted on a four-year hedging cycle implemented at the Farmer’s Investment Company’s (FICO) pecan operation located in south central Arizona on mature trees. The cycle included pruning every fourth row during every fourth year.

This program was adopted partly for practicality. Since the orchard covers almost 5,000 acres, it is impractical to prune more than one quarter of the orchard in any given year.

The farm’s Western Schley variety trees were planted in 1969 and are now on 60 x 60-foot spacing. The Wichita variety trees, planted in 1967, are spaced 30-feet apart in rows 60-feet apart. Both blocks are flood irrigated.

Walworth has monitored the pruned Wichita and Western Schley varieties to evaluate the impact of hedging since 2009.

In 2009 and 2010, nuts were collected from individual rows in the Western Schley and Wichita blocks with a self-propelled harvester for the study. A grocery bag-sized sample was collected from each harvested row and then cleaned.

The nuts were graded to separate marketable nuts, sticktights, and pre-germinated nuts. All three categories were weighed. A sub sample of good nuts was counted and weighed to measure the nut size, and then shelled to determine the percent marketable kernel.

Fertilization practices were not adjusted during the hedging cycle.

Here are the study results thus far.

Inshell yields

The Wichita tree yields rebounded faster from hedging and topping than the Western Schley variety. Wichita inshell yields in the first leaf averaged 45 percent. The second and third leaf were about 80 percent of the fourth-leaf yield.

Western Schley yields increased each year after hedging. First leaf yields were 24 percent, the second leaf at 50 percent, and the third leaf at an 80 percent yield of the fourth leaf.

“The Western Schley variety is less vigorous after hedging and topping; about a year slower compared to the Wichita,” Walworth said.

Kernel percentage

Based on the 2009-2010 crop years, the kernel percentage for both varieties was highest in the first leaf and then decreased over time.

The Wichita began kernel decline in the second leaf; in contrast with Western Schley which started decline at the third and fourth year. The overall decline was greater in Wichita (63.2 - 59.9 percent) than Western Schley (57.6 - 55.7 percent).

Nut size (weight)

The Wichita nut size declined in the second leaf after hedging. The Western Schley size declined in the third and fourth leaf. The Wichita nut size declined faster than the Western Schley.

Sticktights

Sticktight (meatless shell) numbers increased significantly in the Wichita; up from 1 percent to 3 percent over four years. Western Schley sticktights increased but the amount was not significantly higher four years after hedging.

Pre-germination

Nut numbers showing pre-germination, or vivipary, was varied but not related to hedging.

Alternate bearing

Pecan producers are very interested in the hedging impact on the alternate bearing crop cycle. Producers prefer fewer major yield swings during the on-off year cycles.

“Alternate bearing in the Western Schley and Wichita blocks appeared to decrease when hedging and topping were conducted,” Walworth said. “More hedging data is required to convincingly draw a firmer conclusion.”

Alternate bearing in FICO’s Western Schley block was basically “knocked out.” Studies conducted elsewhere support a reduction in alternate bearing from hedging, but not to the extent of the study at the FICO farm.    

Summary

Walworth says continued monitoring of yield and quality in the orchard blocks are required to gain a better understanding of the long-term impact of the four-year hedging program.

Initial results suggest multiple benefits from tree hedging and topping in Southwest pecan production. The study at FICO suggests hedging “knocked down” nut yields - more so in Wichita than Western Schley. Wichita rebounds surprisingly fast especially in the second year. The overall rebound in Western Schley occurs in the third year.

The kernel percentage in both varieties declined after hedging which is likely the case in all pecan varieties, Walworth says. The average nut size decreases as the fruit load increases which is normal. Sticktight numbers increase after hedging.

“Alternate bearing appears to be substantially tempered by this particular hedging program,” Walworth said. “The four years of results give a pretty good picture of how trees respond to hedging.”

Walworth was asked about the best tree height and age when hedging should first occur. Hedging decisions, he said, should be based on when trees begin to crowd each other.

The research was supported by the Arizona Pecan Growers Association and the Arizona Department of Agriculture specialty crops program.    

Richard Heerema, New Mexico State University (NMSU) pecan specialist, discussed the results from the first-five years of a planned 10-year study on mechanical hedging in pecans in the Mesilla Valley near Las Cruces.

Heerema discusses hedging and the New Mexico study results in a Western Farm Press video available here.