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?
This is not an uncommon scenario that can happen to large, crowded, older pecan trees on a calm summer day. Factors that can contribute to limb breakage in pecans (and sweetgums, too), are a heavy crop of pecans (or sweetgum fruit), lots of new spring growth from abundant rains, and very long limbs. Crowded and older trees often have major limbs reaching out for more sunlight. Eventually, physics takes over and limbs break.
There’s really not much that can be done to prevent this problem. An AgriLife Extension pecan specialist in College Station once told me pecan orchard managers deal with the same problem as homeowners. 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.
Every year, usually in August, we also hear another sad story – it’s raining pecans! What can start out as a bumper crop might look like it will all end up on the ground months before harvest time. A certain amount of premature nut drop is unavoidable. Here are some of the reasons why pecan trees shed their crop early.
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. Pecans require a very large amount of soil moisture to mature satisfactory crops of nuts. A shortage of water in the late spring or summer will result in small pecans that will shed in large numbers in July and August. This is probably the number one reason pecans fall at that time. Soil saturation from excess rain can also cause stress symptoms and related nut drops.
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.
Pest-related Damage. There are several insects and diseases that can cause nut drop. The pecan nut casebearer is a tiny worm that bores into the base of the nut and hollows it out. The major attack is in late May or early June, but later generations in July and August can also cause nut drop, but to a much lesser extent.
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.
Bottom Line. What I always come back to is the fact that it is not an easy task to bring a good crop of pecans to maturity. It takes a lot of water and regular spraying to keep the crop clean and healthy. So, I figure let the commercial folks grow the pecans for me and I’ll buy them in the store for a lot less time and money than I could raise them. Enjoy your pecan trees for the great shade they provide (watch out for falling branches) and be thankful for the years you do get a bumper crop.