Pecan Crop Load Management
Proper timing of fruit thinning is the key to achieving the desired results! In most
years, there is a window of only 10 – 14 days in which fruit thinning can be done
successfully. The calendar time varies with cultivar and orchard location. The time
is now in most of our Arkansas orchards.
Searcy, Ark. – August 9, 2022
Fruit Thinning Benefits
Through the process of photosynthesis, leaves convert water and carbon dioxide into carbohydrates needed by pecan trees for growth, flowering, and nut development. The more leaves the tree has for each nut, the greater the chance that adequate carbohydrates will be available for both tree growth and nut production. Research shows that at least 8 to 10 functional leaves are needed to adequately fill one nut. Large-fruited cultivars will require even more leaves per nut. Increased problems with over production and poor fruit quality as trees mature are related to a decrease in the number of leaves per fruit, especially in heavy crop years.
The apple and peach industries have long recognized the need to remove part of the crop to assure larger, higher quality fruit. The same principle applies to pecan. Research at Oklahoma State University and at Kansas State University demonstrated the benefits of fruit thinning in pecan. Thinning fruit from overloaded Mohawk and Shoshoni pecan trees increased nut size and percent kernel, plus improved kernel grade. Return bloom (flower production for next year’s crop) was increased in Shoshoni but not Mohawk.
Fruit thinning decreases total yield per tree for the current year, but in some cases increases marketable yield. The benefits of nut thinning are increased nut quality in terms of higher kernel percentage and kernel grade, as well as more stable yield and cash flow from year to year.
When should I thin pecans?
After the flower is pollinated and fertilized, the ovule (the tissue that becomes the kernel) begins to expand and lengthen from the nut tip toward the stem.
During June and July, the nut enlarges and reaches its final size as the ovule grows. As the ovule expands, the space is filled with liquid endosperm (a watery substance) until the ovule extends to the stem end of the nut. The nut shell begins to harden from the tip shortly after the nut reaches full size. After 100% ovule expansion is reached, the kernel begins to fill (kernel deposition) and nuts pass from the water stage to the dough stage.
The process of kernel deposition requires a large amount of readily available carbohydrates. During this process, each nut competes with other nuts for the carbohydrates manufactured by surrounding leaves or held in the wood of supporting branches.
Removing a portion of the crop (nut thinning) before nuts begin to actively compete for a fixed amount of carbohydrate reserve provides each remaining nut with a greater supply of carbohydrates from which to draw. It also provides the tree with enough reserves to support a flower crop for the following season.
Proper timing of fruit thinning is the key to achieving the desired results.
In most years, there is a window of only 10 – 14 days in which fruit thinning can be done successfully. Research has shown that nuts should be removed when the ovule is 50% to 100% expanded, but before the kernel enters the dough stage.
The calendar time varies with cultivar and orchard location.
The time is now in most of our Arkansas orchards. Thinning the nuts earlier, while they are too small, requires force that can damage the tree. Thinning too late, (after the nuts enter the dough stage) reduces thinning benefits on kernel quality, return bloom, and cold hardiness.
How do I determine nut development?
Determination of nut development is done by cutting nuts to expose the ovule. When a nut is pulled from the tree an oval shaped scar is left on the shuck. To obtain the proper view of the ovule, the nut should be cut lengthwise at a right angle to the long axis of the oval scar.
A straight cut at the length of the nut will expose the expanding ovule as well as the liquid endosperm within the nut. Thinning should be done when the ovule or kernel has extended more than 50% of the distance to the stem end of the nut but before the nut reaches the dough stage (Figure 1). Cultivars with large nuts should be thinned when 50% ovule expansion has occurred. Thinning can be delayed to near 100% ovule expansion on cultivars with small nuts.
How do I thin my pecans?
Nut thinning can be accomplished with a conventional tree shaker equipped with donut pads. Donut pads are essential in preventing injury to the tree trunk. As an additional precaution, apply a coating of grease between the rubber flap and the donut pad. This allows movement at that point and prevents movement of the bark during tree shaking.
How much should I thin?
The quantity of nuts to remove varies with a variety of factors, including nut size, cultivar, crop load, and environmental factors. Judging the tree’s crop load is another important factor in making the determination about whether or not a crop needs thinning. This is a practice that takes experience. The percentage of nut-bearing terminals can be developed by observing the number of fruiting terminals counted from an observation of 50-100 random terminals on a tree.
Trees with almost 100% of the shoots bearing fruit and a cluster size greater than three are overloaded and should benefit from thinning. Optimum crop load varies with cultivar and may range from 50-70% fruiting shoots. Varieties with small nut size can be thinned more lightly than those with large nut size. For example, optimum crop load on cultivars greater than 70 nuts per pound may be 60-70% fruiting shoots. Nuts in the size range of 50-70 nuts per pound, like Cape Fear or Stuart, have an optimum crop load of 50-60% fruiting shoots. While varieties with large nut size of less than 50 nuts per lb may have an optimum crop load of only 45-50% fruiting shoots.
The major mistake most growers make when attempting to fruit thin for the first time is that not enough nuts are removed. When shaking begins, don’t be alarmed by the number of nuts that fall. Trees should be shaken two to three seconds at a time, evaluated, and then shaken again if needed. This process should be repeated until the operator has a feel for how hard to shake to achieve the desired results.
Trees should be shaken in 2 to 3 second spurts until thinning is complete. The distribution of nut removal throughout the tree may be enhanced by shaking from two directions: a north/south orientation and an east/west orientation. This compensates for branch structure that can relay the force of shaking to various parts of the tree canopy. Shaking orientation may vary with the type of shaker used. Growers should try variations to determine the method that works best in each situation.
Will every tree need to be thinned? Does the cultivar matter?
Proper management of crop load requires the grower to be thoroughly familiar with the orchard. Not all cultivars or trees within a cultivar will require nut thinning in a single year.
Cultivars that have shown increased profitability potential in response to fruit thinning include:
- Mohawk, Maramec
- Cape Fear
- Kiowa, Barton
Elliot and Stuart showed no positive response to fruit thinning.
For those with no mechanical shakers, a PVC pipe hitting the limbs to remove nutlets or clusters has proven to be beneficial.
Thinning the pecan nut load in heavy crop years is beneficial. It increases nut quality as indicated by increased percentage of kernel, kernel grade, and nut weight. Increased quality is presumably reflected in greater value. Nut thinning improves return bloom of some cultivars, thus reducing crop variation from year to year, and has been shown to reduce the tree’s susceptibility to cold injury. Nut thinning can be accomplished with a conventional pecan shaker equipped with donut pads.
To make informed management decisions, the grower must be familiar with the concept and the technique. We encourage our homeowners or growers to test nut thinning in a portion of their orchards and personally evaluate the results.
*Information adapted from the University of Georgia and Oklahoma State University.
By Sherri Sanders
County Extension Agent - Agriculture
The Cooperative Extension Service
U of A System Division of Agriculture
Media Contact: Sherri Sanders
County Extension Agent - Agriculture
U of A Division of Agriculture
Cooperative Extension Service
2400 Old Searcy Landing Road Searcy AR 72143