Pecan Hedge-pruning: A Sustainable Management Option for the Southeastern US

The studies proposed here will be conducted at the following locations:

            Experiment Site 1: Marshallville, GA where ~25-yr old hedge-pruned trees will be compared with non-hedged trees. Please refer to Fig. 7 for more details on the site and hedge-pruning program. The trees were hedge-pruned on alternate sides since 2013, and due to the relatively young age the tree height is still comparable between hedge-pruned and nonhedged trees (~35 ft); but overall tree canopy volume and row interference is contrasts (Fig 8).

            Experiment Site 2: Montezuma, GA where ~40-yr old hedged-pruned will be compared with non-hedged trees. Please refer to Fig. 9 for more details on the site and hedge-pruning program. Older trees were hedge-pruned on the sides and top, thus hedge-pruned trees are considerably shorter (~40ft) when compared to the nonhedged trees (~60ft).

            Experimental Site 3: Ray City, GA where ~30-yr old summer hedge-pruned trees will be compared with winter hedge-pruned trees. Please see Fig. 10 for more details on the site and the hedge-pruning program.

            All trees in the experiments (hedged and non-hedged) will be receiving the standard grower management including irrigation, spray inputs, fertilizer, etc.

            Across all comparisons, treatment blocks are replicated accordingly at each site. Data will be analyzed using standard statistical methods including, but not limited to analysis of variance and regression analysis (Steel and Torrie 1980, Cochran and Cox 1957).

            The following are the variables that will be collected, obtained and analyzed from the trees in orchards comparing the different hedge-pruning treatments as described above.

1. Assessment of production (nut quality and size), water and nutritional status. Methods to be followed will be based on that of Wells (2018). Midday stem water potential will be determined using a pump-up pressure chamber (PMS Instruments, Albany, OR) by measuring the water potential of leaflets located near the trunk or a main scaffold branch at mid-day. Soil moisture will be measured with a Field Scout TDR 300 Soil Moisture Meter (Spectrum Technologies, Aurora, IL) at 20 cm depth within the wetted zone of irrigation on each sampling date at the same time that stem water potential is measured for each tree. All plots will be mechanically harvested separately. In-shell nuts will be dried to 4.5% moisture with a commercial drier and processed in a commercial cleaning plant to remove all sticks, leaves, and debris. All cleaned nuts will be weighed by plot to obtain in-shell nut yield for each plot. A 50-nut sample will be obtained from each plot at harvest to determine nut size and quality (percent kernel). The effects of hedge-pruning on nutritional status of dormant and summer hedge pruned trees will be assessed through leaf and soil sampling of each plot. Samples of 50 pairs of leaflets will be collected randomly throughout each plot and analyzed for all macro and micro-nutrients. Temperature, light intensity and relative humidity in tree canopy will also be recorded. Cooperators: Wells, Jaros, Levi, Paulk
2. Assessment of incidence and severity of disease.

            2a. Assessing scab in trees. Methodologies will be the same in all experiments. Samples will be collected at up to four heights (in hedge-pruned trees only 3 heights). Ten compound leaves, fruit (mid and late season samples) and shoots (only late season) will be collected at each height on both row-sides of each sample tree using a hydraulic lift at approximately 5, 8, and 11 and 14+ m. Heights above ground will be measured using a laser rangefinder at the time of sample collection. Leaf and fruit samples will be assessed for severity of scab based on the percent area diseased by visual estimation on each leaflet and on each of the four valve faces. Assessments will be aided by previously developed standard area diagrams for leaflets and fruit. At the end of the season, the length of a sample of 10 shoots from each height in each tree will be measured and the number of scab lesions counted (scab lesions on shoots are considered a potential important source of inoculum for the following season’s epidemic). Methodology will be based on Bock et al 2017.

            2b. Assessing tree limb colonization by wood rot fungi. Trees in orchards at the Marshallville site which has been hedge-pruned since 2013 will be monitored for wood rot fungi. A total of 100 trees (50 hedge-pruned and 50 non-pruned) will be surveyed annually to determine incidence of wood rot colonization by visually assessing all limbs in the trees for evidence of fruiting bodies of common fungi (including but not limited to Trametes versicolor and Schizophyllum commune). Species identification will be based on morphology and, if available for the fungus, PCR diagnosis (Chen et al., 2015).

Cooperators: Bock, Jaros, Levi, Paulk

3. Assessment of insect pest populations, insect-related injury and beneficial insect populations.

            3a. Monitoring of insect pest populations and insect-related nut injuries. Across all studies, standard monitoring approaches for scouting pecan insect pests will be followed (Grantham et al 2002, Reid 2002). We will sample leaves for live aphids, parasitized aphids and mites at three distinct periods in the crop phenology coinciding with the grower management programs for these pests: post-pollination (mid-May), rapid nut sizing stage (July) and kernel filling stage (late August). A minimum of 100 leaf samples will be taken from the lower and upper canopies of trees for each treatment in each experiment at each sampling date. Leaf samples will be placed in Ziploc bags upon collection, and placed in coolers during transport to the lab where they will be examined for the target pests under the microscope.

            Periodic collection of nut samples to assess for insect-related injury will be conducted in late May for pecan nut casebearer injury, in late June for shuckworm and nut curculio infestation, and at harvest for pecan weevil, shuckworm and stinkbug attacks. Samples will be taken from the lower and upper sections of the trees, placed in Ziploc bags and will be taken to the lab for examination. A minimum of 100 nut samples will be collected from each treatment in each experimental site per sampling date.

            3b. Investigation of the natural enemy populations. We will be deploying yellow sticky cards in the lower and upper canopy of trees for one week during distinct periods in the season: post-pollination, rapid nut sizing and kernel filling stages. A minimum of 10 yellow sticky cards will be deployed per treatment at each experimental site per trapping period. We decided to use yellow sticky cards as these were proven to be effective in monitoring for pecan aphid parasitoid, Aphelinus perpallidus (Fig. 10). The parasitized aphids collected during the leaf sampling, as described above, will be separated and reared until parasitoid emergence for assessment of parasitism rates. Another sampling methodology (e.g., using small pyramid traps deployed in the lower and upper canopy of trees for a week) may be explored to survey other generalist predators such as coccinellids and spiders (Paulsen et al 2011, Fig. 10).

Cooperators: Acebes, Schmidt, Jaros, Levi, Paulk

4. Assessment of belowground entomopathogens. Methods to determine persistence of entomopathogens will be based on those described by Shapiro-Ilan et al. (2003, 2017b). Six soil cores will be taken 1 meter from the trunk and another six cores will be taken from the 1 m distance from the trunk to just inside the dripline (approximately 3 meters) of a hedge-pruned and nonhedged pecan tree. It is important that the longer distance remain inside the herbicide strip (not into the grass beyond the strip). Samples will be pooled from within each distance (so each tree has three pooled samples, one from each distance). Soil will be brought back to the lab (in a cooler) and will be exposed to bait insects (greater wax moth, Galleria mellonella). Koch’s postulates will be conducted to verify the presence of entomopathogenic nematodes and fungi. Identification of entomopathogens will be conducted by Shapiro-Ilan and if additional verification is needed by the USDA-ARS collection curators (Shapiro-Ilan holds an International Collection of entomopathogenic nematodes and is versed in identification of entomopathogenic fungi as well). Mortality in bait insects due to entomopathogenic fungi nematodes and overall mortality will be compared among treatments using standard statistical approaches (Steel and Torrie 1980). Samples will be taken bi-weekly during April to October. Cooperators: Shapiro-Ilan, Jaros, Levi, Paulk
5. Economic analysis, Extension and Outreach.

            5a. Economic analysis. In conjunction with the various field trials, an economic analysis will be conducted to assess the economic costs and benefits of pecan hedge-pruning strategies relative to non-hedged orchards and the timing of when hedge-pruning is conducted. This is a critical component not only to evaluate the efficacy of pecan hedge-pruning, but to also deliver clear recommendations to growers as part of the larger extension and outreach program, and help guide future orchard-level research on pecan hedge-pruning. The economic analysis will synthesize the findings of the various orchard trials with input and output price data. Using standard statistical and extension budging methods, estimates of the relative profitability of hedge-pruning vs. nonhedging and summer vs. dormant hedge-pruning will be evaluated by incorporating the orchard trial results on tree health (e.g. disease and pest rates), production measures (e.g., nut size, yield, and quality), input costs (e.g., labor rates, equipment, water usage), and market price data into a grower-level economic analysis and enterprise budget. Further, sensitivity analysis including multivariate econometric modeling, inclusion of temporal considerations, and production practice transition costs (Lima et al., 2013) will be conducted.

            Overall, the economic feasibility assessment and sensitivity analysis will yield estimates (with confidence intervals) of the expected costs and benefits of pecan hedge-pruning relative to not hedging. However, as revealed in previous research, non-monetary considerations such as grower risk perceptions, subjective beliefs of new production practices, and information and experience have been found to influence risk management and technology adoption decisions (Menapace, Colson, and Raffaelli, 2013; 2015). Hence, to complement the economic analysis and aid in the development and refinement of the extension and outreach materials and programs, grower surveys will be administered to assess grower perceptions and knowledge of hedging strategies for pecans. The surveys will be administered in conjunction with the planned extension and outreach grower meetings and field days. 

            5b. Extension and Outreach Programs. Extension and Outreach programs will be conducted including demonstration trials, grower, industry and scientific meetings. Results will be published via print (magazines, spray guides, fact sheets) and online resources (blogs, apps, websites). Please see the detailed description of our Extension and Outreach programs in the “Information Dissemination and Outreach Plan” section. Drs. Acebes, Schmidt, Hudson and Wells have Extension responsibilities in the southeastern US.

Cooperators: Colson, Acebes, Schmidt, Hudson, Shapiro-Ilan, Bock and Wells