Take years off orchard development with these 5 facets of pecan culture
This photo shows another view of new 2018 plantings that stretch as far as one can see at Pancho Salopek Farms in La Mesa, New Mexico. (Photo by Catherine Clark)
The good news is that pecan trees can grow fast. Many fast-growing trees, like ash and mulberry, are weak-wooded and short-lived. But pecan, a hickory, is a fast-growing, hardwood tree species that also lives and can be fruitful for a very long time.
Yes, limb brittleness and breakage are a perpetual battle with pecan trees, but that doesn’t indict their longevity (unless their trunk or scaffolding is damaged by wind or ice).
So, why then do some orchards fail to get a first harvest on the short side of the non-productive phase? The answer is that a) pecan is stress-sensitive and some growers fail to manage those stresses properly, and b) pecan is input-responsive. When given in favorable growing conditions, management inputs of water, fertilizer, and weed control have a “compounding effect” on tree growth. Failure to provide all those inputs retards growth and canopy development, increasing the time required for abundant flowering.
Genetics matter
An experienced pecan grower in Alabama once told me, “‘Elliott’ is a young man’s pecan variety!” A comment borne of his experience with growing ‘Elliott,’ a variety known to be fast growing but slow to begin flowering.
Pecan varieties differ in “precocity,” their genetic tendency to branch out with short shoots despite the tree’s overall fast growth rate. Long, whip-like single branches are rarely flower-bearing due to their nitrogen to carbon ratio favoring nitrogen. High nitrogen levels translate into vegetative growth. When a given level of nitrogen is distributed over more branches, the carbon content is higher; resulting terminal shoots/branches are more likely to form spring flowers (nut clusters).
‘Elliott,’ ‘Desirable,’ and ‘Stuart’ are examples of varieties that are not precocious, while varieties like ‘Creek,’ ‘Shoshoni,’ ‘Lakota,’ and ‘Wichita’ are precocious. One of the most notable cases of precocity and early yields was obtained by Hal Berdoll in Bastrop County, Texas, who had fifth-year ‘Wichita’ trees produce 1,000 pounds per acre. Fourth-year yields are more difficult to obtain, and the most precocious varieties can bear 200 to 400 pounds per acre in the fourth year when stress is minimized and management inputs are maximized. Unprecocious varieties may not bear many nuts in the fourth or fifth years, so growers with cash flow challenges should consider the precocity of varieties that they plant in their financial planning.
Irregardless of precocity, a well-developed canopy is how you get flowers, nut clusters, and ultimately a crop to harvest. Management inputs are the key to shaving time off a pecan orchard’s unproductive establishment phase. Some new pecan orchard managers have unnecessarily added years to the non-productive phase of their young orchard by skimping on inputs. It may seem counterintuitive to the novice pecan grower to spend money while the orchard is not bearing, but such is the path to financial success in the pecan business—if money is spent wisely and the soil, site, and water quality are good. Obtaining a high growth rate throughout the growing season depends on five facets of pecan culture: irrigation, weed control, fertilizer, integrated pest management, and pruning. Failure to follow recommended guidelines in any of these five areas may add years of little or no income to a young orchard.
1. Irrigation
Water is the most critical component to rapid orchard development and our first component to pecan culture. It is a basic principle of horticulture science that water stress reduces growth. Annual tree rings, visible when studying a tree trunk in cross section, are narrower in years of drought (like in 2011) and wider in years of abundant rainfall (i.e., 2021). If a tree trunk doesn’t increase in diameter, we also find that limbs don’t increase in diameter and current season terminal shoots are shorter than normal. Stunted growth equals a loss in valuable development time.
A tree needs water moving from the roots to the leaves to cool itself in hot weather. The hotter and drier the air, the faster water must move in the transpiration stream to accomplish the hydro-cooling process. Tiny “feeder roots” are needed to withdraw the water from soil, and feeder roots are fragile organs found in the upper portion of the topsoil that don’t live long when dry. Thus, the pecan grower’s job is simple—never let feeder roots get too dry.
There is no single recipe for how often young pecan trees need to be watered because soils vary widely in water-holding capacity. Additional differences in humidity, rainfall, and wind velocity make it difficult to define a watering interval for every orchard. The key for proper irrigation is monitoring moisture depletion from the soil accurately, either by feel, soil moisture sensors, Class A pan evaporation, or combination thereof.
During the moderate spring and fall months, soil moisture should be monitored once or twice per week in most soils. During the hot summer months, soil moisture should be monitored every 1 to 3 days so that irrigation can be applied and feeder root health maintained. With experience, growers can better understand how quickly soil dries under normal conditions and may reduce the frequency of close inspection and monitoring.
Automatic irrigation controllers and soil moisture sensing equipment can lower the potential for human error in maintaining an irrigation schedule. While growth of above-ground woody tissues ceases in the winter, feeder roots must continue to be maintained with occasional winter irrigation when rainfall is lacking.
2. Weed control
Weeds, both grasses and broadleaf species, are a challenge in every orchard. Populations and densities of weeds vary by region and field, but one fact is universal: weeds growing around young pecan trees are bad for tree growth.
Weeds not only compete with trees by withdrawing water and nutrients but also have demonstrated allelopathic effects in studies on pecan tree growth (Smith et al., 2001). Allelopathy is a form of biochemical warfare among plants where excretions from living and dying roots have a growth stunting effect on neighboring plants.
Allelopathy means that very low numbers of weeds can be detrimental, and thus to maximize growth, it is important to strive for a totally weed-free area around the tree. The weed-free area should also be maintained throughout the year, including the dormant season in winter. “Weeds” here means all plants, including clovers and other legumes planted in some orchards to deliver organic nitrogen.
How much weed-free area around a young tree is needed for maximum growth? A study in Alabama demonstrated that a small, 3-by-3-foot weed-free area was no different than letting weeds grow, but expanding the weed-free zone to a size of 7-by-7 feet significantly increased growth and early yield (Faircloth et al., 2002).
Post-emergence herbicides are essential tools for maintaining a weed-free area around a young pecan tree each growing season. Non-selective synthetic product options include glufosinate, paraquat, and glyphosate. Comparable organic products include d-limonene, clove oil, eugenol, vinegar, and others. I’m a proponent of anything that will keep weeds in check and not injure the tree. Protecting the tree trunk with tree sleeves, aluminum foil, or latex paint is also advisable. Preemergence herbicides may also be used to prevent new weed emergence if proper products are used for the soil type, tree age, and applied with a calibrated sprayer.
Mulch should be part of the orchard floor management program for any grower wanting to maximize young pecan tree growth and development. Two important studies (Foshee et al., 1996; Smith et al., 2000) demonstrated impressive improvements where mulch was used around pecan trees compared to weed-free bare soil alone. The mulch in these studies was from a natural material (chipped limbs, etc.). Weed barrier fabrics can give similar effects. Mulch lowers root temperature during the summer months, slows soil moisture evaporation, and suppresses weeds. Thus I consider it a win-win-win for young tree growth promotion.
3. Fertilizer
Nutrient deficiencies must be avoided if rapid growth and development is expected. There are 6 essential macronutrients and 11 essential micronutrients, and the manager’s goal should be to prevent deficiencies of all of them. This goal brings us to the third facet of pecan culture—fertilizer.
Unnecessary fertilization of a nutrient is wasteful and potentially harmful; thus, it is better to monitor nutrient levels by soil and leaf testing and fertilize accordingly. Soil analysis should be performed prior to planting and every 1 to 3 years thereafter. Leaf analysis should be performed annually in July.
Young pecan trees should normally be fertilized with nitrogen (N) each growing season, due to the transient nature of nitrogen in soil. Heavy rain or regular irrigation leaches nitrogen away from tree roots, and most horticulturists today recommend multiple doses of an N-carrying fertilizer during each growing season. Injection through a drip irrigation system is a sound approach.
Nitrogen is best applied in late winter, spring, and summer. Fall applications of nitrogen are largely not recommended for young trees because they may reduce the trees’ ability to withstand winter freezes.
Again, soil type, the amount of organic matter in the soil, and precipitation levels all affect the amount of nitrogen needed for each application. Recommended rates vary from 0.17 to 0.50 pounds actual N/tree per year for the first year, and 0.5 to 1.0 pounds actual N the second year. Growers should follow Extension recommendations developed in their own state for best results.
Young trees also require annual zinc fertilization. Pecans take up zinc very slowly on some soils and not at all on others; therefore, foliar sprays are needed if good growth is desired.
Zinc is needed for leaf expansion. Zinc-deficient leaves will be small and borne on short, bunchy shoots. Leaves that are growing need zinc, and leaves that have stopped growing don’t need it. With this principle in mind, growers should spray zinc to coincide with new flushes of growth and active growth periods.
Zinc sulfate wettable powder at rates of 0.25 to 1.0 pounds per 100 gallons of water will prevent zinc deficiency. “Mouse-ear syndrome” is sometimes a problem on young pecan trees, especially those that were grown in the nursery in soilless potting media. Foliar sprays that contain the essential element Nickel (Ni+) correct mouse-ear very effectively.
4. Foliage protection
Leaves are the “engines” that drive the pecan tree’s growth process. If you envision each leaflet on a tree as a working solar panel, capable of generating photosynthetic energy, then you may also understand the importance of protecting those leaflets from damage and infection from insects and diseases. Thus, foliage protection serves as the fourth facet of pecan culture.
Scab and Leaf Dieback may need to be prevented with fungicide sprays if susceptible varieties have been planted. Growers also must be vigilant for several different arthropod pests that feed on pecan foliage, branches and trunks. Minor insects in mature orchards, like May beetles (June Bugs) and grasshoppers, can be major problems in young orchards. It is important to know the economic injury level for these pests, as well as beneficial insects that may control them.
Deer or other foliage-grazing animals can be similarly limiting to pecan tree growth. Feral hogs don’t eat foliage but destroy roots or even uproot trees, which is also counter to tree growth and development. Fencing is usually the surest way to end those problems.
5. Training and Pruning
Young pecan trees that are given the management inputs described above, but don’t also have some training along the way will be multi-trunk in shape and have narrow-crotch scaffold limbs that are susceptible to breaking out when production begins. Long-term production can be undermined by the resulting poor structure. While maximum growth is desirable, the goal should also be to train the tree as it grows, so that energy expended by the tree goes to forming one central leader trunk, scaffold branches with wide angles, and an abundance of terminal branches. The “cut-back and select” training method, described in the Texas Pecan Handbook (available from Texas Pecan Growers Association) should be followed during the first four years after planting.
Tip pruning can be beneficial to canopy development and early production. Nut clusters are borne on terminal branch tip ends. Tip pruning is simply removing the tip ends of long, whip-like terminal branches to encourage lateral bud breaking and the occurrence of more forked branches in the canopy. By turning one branch into two, two into four, four into eight, it stands to reason that greater amounts of nut production are being facilitated.
The best training and pruning cuts are those made with hand pruners rather than limb loppers or saws. Most tree training and pruning of young trees should happen during the growing season, especially prior to August. Pruning in September and October may stimulate late growth that can be injured by freezing temperatures in the winter. Growers who wait to “fix” their pecan trees once a year during dormancy will prune off too much limb and branch weight; those arising from narrow crotches, etc. These net carbon losses could have been avoided with lighter snips made when the growth was first observed in the summer, which then allows the tree to redirect that vegetation into desirable locations in the canopy.
Putting it all together
I can’t stress enough the need for pecan orchard establishment to hit on all five cylinders! I’ve seen it happen often that an orchard took great care of their trees with zinc, fertilizer, and weed control, but the irrigation system had problems. Or someone else had a fabulous irrigation system but couldn’t keep the weeds under control.
Five years is a very long time to wait to get a first harvest. Adding two to three years on top of that because one of these five management areas went neglected should not be an option! Growth fuels more growth. It’s like compound interest in a thriving investment portfolio. Pecan trees have an amazing capacity to respond to management inputs with impressive gains in growth and development. Water, weed control, fertilizer, foliage protection, and training all contribute to a new pecan orchard enterprise that is financially healthy and ahead of schedule.
Literature Cited
Faircloth, W.H., M.G. Patterson, M.L. Nesbitt, W.G. Foshee, and W.D. Goff. 2002. Width of weed-free strip required for young pecan (Carya illinoiensis) trees. Proc. South. Weed Sci. Soc. 55:72.
Foshee, W.G., W.D. Goff, K.M. Tilt, J.D. Williams, J.S. Bannon and J.B. Witt. 1996. Organic Mulches Increase Growth of Young Pecan Trees. HortScience 31(5):811–812.
Smith, M.W., B.L. Carroll and B.S. Cheary. 2000. Mulch improves pecan tree growth during establishment. HortScience 35(2):192-195.
Smith, M.W., M.S. Wolf, B.S. Cheary, and B.L. Carroll. 2001. Allelopathy of Bermudagrass, Tall Fescue, Redroot Pigweed, and Cutleaf Evening Primrose on Pecan. HortScience 36(6):1047–1048. 2001.
The first version of this article appeared in Pecan South’s February 2012 magazine. This article has been updated.
