Pecan trees are large deciduous trees that produce deep brown edible nuts. Many factors can cause a crop loss or even kill a pecan tree, but it’s usually a combination of reasons. Problems including diseases, pests and water or nutrient deficiencies can affect pecans. Often it’s not easy determining the cause of a pecan tree problem, but once the problem is identified, a grower can either solve the problem or at least remove a tree.
Pecan scab is caused by a fungus that attacks young rapidly growing leaves and shoots that later develop into nuts. Pecan nuts that are seriously infected can result in an entire crop loss. Frequent precipitation and high humidity can cause leaves to fall off pecan trees early. This triggers a scab fungus to develop rapidly and spread. Common fungicides are used in treating the disease.
Powdery mildew, a fungal disease from the Microspaera alvi fungus, causes pecans to be covered with a powdery white material. The fungus starts on a shuck’s outside and feeds only on a plant cell’s outer layer. It’s mainly a cosmetic problem as no major loss comes from this disease, although it appears to look damaging. This fungus is activated by humid conditions and occurs during mid-summer. Affected foliage becomes somewhat distorted and is covered with a faint white powdery material. A scab fungicide program helps control the disease.
Water Stage Nut Drop
Water stage nut drop is a fungal infection caused by the fungus Botryosphaeria ribis and is linked with insect feeding. When this fungus attacks pecan nuts in late July and August, shucks turn black and drop quickly after being infected. Lesions from the fungus are shiny, black and sunken. Although losses from this fungus can be reduced, it’s impossible to completely eradicate the problem. Benomyl fungicides are used to treat this problem. Using a fungicide with a foliar spray, which increases nutrients for plants, can help control the problem.
Three different insects attack pecan nuts: the casebearer, the hickory shuckworm and the pecan weevil. The casebearer, the most damaging insect of pecans, is gray or black with dark scales. The insect’s larvae are olive-gray or jade green. The larvae of hickory shuckworms overwinter in shucks. Adults then begin emerging, laying their eggs on pecan nutlets, which causes nuts to drop. When this occurs after a shell hardens, the quality of nuts is reduced. Adult pecan weevils are brown and 3/4 inch long with snouts that are as long as their bodies, according to the Texas A&M AgriLife Extension website. Their larvae are legless and have creamy white bodies with reddish-brown heads.
Insufficient Water and Wind Damage
A lack of water can weaken pecan trees so the shucks can’t open, producing what’s called “stick tights.” Early freezes can cause the same problem, although pecans will still be well filled. Wind damage can cause shells to harden and nuts to drop. If wind damage occurs at the end of shell hardening, a pecan won’t drop or won’t fill, which causes it to produce empty nuts called "pops" that don’t contain meat inside.