Several questions have come to the Cooperative Extension Center recently about pecan trees. They cover nut production and damage, diseases, and general maintenance. While pecan trees can survive tough conditions such as prolonged drought, they require careful management to produce the bounty of sweet nuts we all hope for. This article will address some practices to follow to improve our chances of enjoying sweet pecans in pies, delights, and other dishes throughout the year.
Question: The husks on my pecan tree have black spots. What is wrong with them?
Pecan tree scab is a common disease that causes brown to black lesions or spots first on the underside of leaves, then on upper leaves and on husks. In some cases, the entire husk may become black. Scab is caused by a fungus and is more likely to occur in wet areas with poor air circulation. When severe, scab can damage the tree and reduce nut production in the subsequent year. The first preventative step is to choose tree varieties with resistance to the disease. Remove debris such as dead leaves, shells, and limbs during the fall and winter. Itis possible to control the disease with chemicals, however, this typically requires special equipment to apply and may not be feasible or economical for homeowners. Powdery mildew is another fungal disease that causes white powdery appearance on leaves. This does not damage nuts, but it can stress the tree. There are several other diseases that may occur on pecan trees, but they are not as common in this area.
Question: My pecan produced well but the nuts sometimes have black spots on them. What is causing the black spots? Are they safe to eat?
Stink bugs can pierce through shells and suck out nutrients from nuts, causing black, bitter spots on the nuts. These spots can be cut out, and the rest of the nut is safe to eat.
Question: My pecan tree has not produced much nuts in the last several years. We planted another pecan tree of a different variety close to the other and the new tree is bearing. Can we cut down the old tree?
Pecan trees require a different variety of pecan tree to be planted within about 200 feet of the first for the flowers to be properly pollinated and produce nuts. Not only does it need to be a different variety, but it also needs to be a different mating type that releases pollen at a time when they female flowers on the neighboring tree are receptive. Cutting down the older tree may cause the young tree to stop bearing.
The older tree may not bear because of environmental factors, variety, soil fertility, and insect damage. Late freezes during the pollination period can freeze flowers and reduce nut production. The foothills represent the cooler edge of where pecan trees will grow, so it is important to choose varieties that bloom later and to plant away from low-lying areas or frost pockets. It could be that later blooming varieties have been planted and will never bear in our climate. Some varieties are also “alternate-bearers”, meaning that they bear larger crops every other year. Fertilizing trees properly can reduce this phenomenon.
Summer droughts can lead to nuts dropping prematurely or lack of fill. A dry fall can also lead to low production the following year. Pecans are native to river valleys with well-drained soils that also provide plenty of water. It is critical to supply adequate water to pecans- a rule to go by is about 2” rain per week. Do not neglect watering pecan trees if you want them to keep them productive. Pecans require adequate light for nut production, so avoid planting them in crowded areas in the landscape.
Nutritional stresses or deficiencies can also lead to low nut production. It is a good practice to fertilize trees to support tree growth and nut production. Start with a soil test before planting or fertilizing any tree, but generally recommended rates for pecan trees are 1 lb. of 10-10-10 fertilizer per year of tree age, not to exceed 25 lb., for non-bearing trees, and 4 lb. per year per inch of trunk diameter, measured below the scaffold branches, for bearing trees. Evenly spread fertilizer under the tree canopy, in late winter or early spring. Do not fertilize young trees after June because new growth is especially susceptible to freeze damage. Zinc is a critical element for pecans, and pecan trees do not readily take up zinc from the soil. This can lead to distorted leaves or low nut production. Soil sampling around a pecan tree or before planting is a good way to tell if zinc is needed.
Insect pests can also damage nuts, perhaps the most common in North Carolina being the pecan weevil. The pecan weevil causes two types of damage on nuts. Adult weevils, which are beetles, emerge from the soil during August and September, typically after 1” rain has fallen, and feed on shells before they harden, causing nuts to cease developing. The females lay eggs in the developing shells and larvae will hatch inside the shell and feed on the nut. When the larvae mature, they drill a circular hole in the shell, exit the nut, and move to the soil, where they stay for one to two years, emerging during August as adults. If you suspect pecan weevil or another insect is damaging your pecans, there are simple monitoring measures you can take to catch the insect when it is active and take timely control measures to reduce damage.
There is an excellent publication on growing pecans in North Carolina that includes recommended varieties and more, accessible at: at: https://content.ces.ncsu.edu/growing-pecans-in-north-carolina. You can also pick one up at the Caldwell Cooperative Extension Center, 120 Hospital Ave NE, Lenoir NC. For specific questions about pecan trees or for other gardening information, contact Caldwell Cooperative Extension Center at 828-757-1290.