Smith County Horticulturist
It was a beautiful, sunny afternoon — not a cloud in the sky. The air was still, almost stifling, when suddenly, “Craaack! Wham! Thud!” You look around and there is a very large pecan limb lying (hopefully) in the middle of the lawn. A close inspection of the broken ends reveals no clues as to what happened to make this large branch unexpectedly break and fall. The break was right in the middle of the branch, and there is no sign of insects, borers or decay. What happened?
About all one could do is to selectively remove or thin out smaller, crowded branches attached to long branches to lighten the overall weight of the limbs. Even removing a few secondary branches can significantly lighten the load on a branch. Long branches can also be shortened, but do not stub them back indiscriminately. Cut back to another branch.
Shortage of Nutrients. This can cause pecans to drop at any time during their development, but most of these drops occur in August and early September as the nuts are rapidly growing and filling. Drops due to a shortage of nutrients will always be greatest on heavily loaded trees. In many cases, the nutrient-deficient nuts that drop will be abnormally small on the basal or stem end. Nitrogen and zinc are the most commonly deficient nutrients in pecans. Good fertilization practices starting in early spring are needed to avoid this problem.
Soil Moisture Stress
Regular, soaking irrigations (preferably weekly) are needed to avoid stress-related drops. Apply at least 1 to 2 inches per watering when using a sprinkler (measure with a rain gauge, tin can etc.) or water for 8 to 10 hours per application with a drip system. Remember that the tree's root system extends out to and well beyond the ends of the branches. This is where the active roots are — not near the base of the trunk.
Nuts of certain tightly filled varieties, like Wichita and Cherokee, will split and drop in August and September if stressed excessively between irrigations. Also, very large varieties, like Mahan and Mohawk, are notoriously difficult to fill and poor nut quality often results in dry years when irrigation has been insufficient in August and September.
Stink bugs and their relatives suck sap from the nuts. They can be a continual problem throughout the summer. Damage prior to shelling hardening (mid-August) causes the nut to blacken internally and drop. Nuts injured after shell hardening mature with blackened, bitter tasting spots on the kernels.
Pecan scab is fungal disease that causes dark spots or lesions on leaves, twigs and the shuck of pecans. A severe infection can cause premature nut shed, particularly in August and September.
If all that weren't enough, at the end you still have to fight off the squirrels and crows for the maturing crop.
Keith Hansen is Smith County Horticulturist with the Texas AgriLife Extension Service. His web page is EastTexasGardening.tamu.edu His Blog is agrilife.org/etg Texas AgriLife Extension Service educational programs are open to all individuals without regard to race, color, sex, disability, religion, age or national origin.