A ripe pecan nut (Carya illinoinensis) is ready to harvest in fall when the husk starts to split and the nut shell beneath the husk turns brown. Unfortunately, a number of things can interfere with proper nut formation and ripening, causing green nuts to drop from the tree. In most instances of fruit drop, the nut meat hasn't fully formed, so the nut isn't edible. For some insect pests, the nut meat has formed, but it is damaged or doesn't taste good. Pecan is hardy in U.S. Department of Agriculture plant hardiness zones 5 through 9.
Early Pecan Drop
Sometimes pecans fall from the tree early in the season while they're still small. This usually indicates poor pollination. Wind-pollinated pecans are dependent on good weather during the time when pecan catkins shed their pollen and the pollen grains land on the female flowers. Heavy rains can interfere with pollination, and male and female flowers can also bloom at different times, resulting in unfertilized fruits. It's also possible that there isn't a good pollinating tree for your variety of pecan nearby. If that's the case, these small fruits won't even have a nut forming inside the husk.
Drought-Related Pecan Drop
Pecans are a large nut and need plenty of water to fill out the nut meat. If water is short in late spring and early summer, the nuts won't be able to finish development, and small fruits fall off the tree, usually in July and August. These green pecans aren't usable because the nut meat hasn't fully formed. To prevent this type of loss, supplement natural rainfall with irrigation during dry periods. A tree may need a weekly deep watering of 1 to 2 inches during nut formation.
Nutrient deficiencies can occur at any time during nut formation, especially in trees that have a large load of developing nuts. Usually trees lack either nitrogen or zinc. Often fallen nuts will have a smaller-than-usual stem end that indicates a deficiency problem. These nuts are also not fully developed. To prevent this kind of nut drop, fertilize pecan trees in mid to late February with a 10-10-10 fertilizer containing 2 percent zinc. Apply 4 pounds of fertilizer for every 1 inch of trunk diameter, with the trunk measured 4 1/2 feet above the ground. Scatter the fertilizer evenly beneath the tree, going out to the drip line.
Stink Bug Damage
Green to brown shield-shaped stink bugs cause nut drop when they feed on pecans that have unhardened shells. The bugs insert their mouthparts into the pecan, inject a digestive saliva, and suck up the dissolved tissues. This results in black pit drop, where the developing nut meat is dissolved and turns black. When stink bugs feed on pecans with a hardened shell, circular discolored spots form on the kernel, which is bitter in these areas. The nut doesn't drop off the tree, and the damage is discovered when you crack open the nut. Control stink bugs by cutting down the stands of weeds they hide in.
- University of California Division of Agriculture and Natural Resources: Harvesting and Storing Your Home Orchard's Nut Crop
- Texas A&M University: AgriLife Extension: Watch out for Falling Pecans and Branches
- North Carolina State University Cooperative Extension: Wayne County Center: Pecans Falling Way Too Soon -- What to Do?
- Clemson University Cooperative Extension: Fertilize Pecan Trees to Encourage Nut Production
- Louisiana State AgCenter: Bug Biz: Stink Bugs and Leaffooted Bugs on Pecan
- Missouri Botanical Garden: Carya Illinoinensis
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