Pecan Management Problem

Many decisions can go into establishing and managing a pecan orchard.
First, you’ll need to choose the tree cultivars that will work for your plans, or identify the ones you have in your orchard.
Not all management issues are pest issues. Management issues can result from nutrient or physiological issues as well.
Credits: Dr. Charles Rohla, Noble Research Institute; Becky Carroll, Oklahoma State University; Dr. Eric Stafne, Mississippi State University

Name Secondary Name Source Description
Zinc Deficency Rosette Zinc deficiencies often become visible when leaf Zn is less than 40 ppm. Zinc availability is reduced on alkaline soils. Even under ideal conditions, uptake of zinc is slow, thus foliar zinc sprays are the fastest method of supplying zinc to the tree. Leaf absorption of zinc is not efficient after leaves harden off. Properly timed sprays are required to eliminate any deficiency problems. Rosette begins as chlorosis and curling or twisting of young leaflets. The condition is first visible in the the terminal leaflets. As the problem progresses, further chlorosis and wavy leaf margins develop including narrowing leaflets, interveinal necrosis, and terminal dieback. Affected trees may appear rusty brown or yellow-green, especially near the tops of the trees.
Squirrel Damage Southern flying squirrels create shelters to raise their young or as a daytime refuge. They store food within their nests which are commonly made of bark. These nests are usually made in already existing tree cavities in dead or live trees where a broken limb or fungal decay has created an empty compartment. Flying squirrels are social creatures that do not hibernate so they are active year-round. They sometimes have aggregate nests where up to 50 squirrels live together, but usually the number is between 10 and 20. Studies have shown that one flying squirrel could store as many as 15,000 nuts in one season. The diet of a Southern flying squirrel includes pecans as well as acorns and other nuts, insects, spiders, slugs, snails, tree buds, flowers, berries, fungi, eggs, bark cambium, and tree sap. They can damage trees and limbs causing decreased yields and tree death. The squirrels may hoard large quantities of nuts in tree cavities. They open nuts with their incisors and the damage has smooth edges and oval in shape.
Water Split Longitudinal splitting during the water stage is driven by internal turgor pressure within the developing kernel from mid-August to early September. This is most likely to occur when trees bear a heavy crop load and soils are dry before a sudden influx of water via rainfall or irrigation. Most water-stage split occurs within 24 hours of a thunderstorm. Fruit will drop from the tree approximately seven days after splitting occurs. High relative humidity and low solar radiation can also induce minor splitting before the major episode occurs. Splitting usually occurs in the pre-dawn hours and is most common in the upper 1/3 of the tree canopy. Manage water-stage split by maintaining adequate soil moisture for at least 2-3 weeks prior to shell hardening and mechanical fruit thinning. When internal splitting occurs, a brown discoloration extends through the shuck along the split area. Later, any portion of the shuck may be discolored, and the nut falls from the tree about 7 days after rupturing occurs. The splitting occurs internally, and a split or crack in the shuck may or may not be visible. Over 30 percent of the crop on a particular tree may exhibit nut drop caused by water-stage fruit split.
Sunscald Direct sunlight on unprotected nut clusters, typically on clusters that began their development in shade. Drought conditions often worsen the effects. Discoloration on shucks, which may be brown, cracked, or shriveled
Frost Injury When temperatures dip below freezing for a significant period of time, usually in the spring or fall. Actively growing green tissues may be destroyed. Buds may be damaged if sufficiently cold. Green tissue will shrivel and turn brown. Shoots generally emerge from secondary buds to compensate for injury in spring. Shucks may be damaged and rendered unmarketable when early frosts occur in the fall.
Herbicide Injury Usually occurs from accidental drift from applications within the orchard or nearby. Aerial applications tend to drift farther and may be more destructive. Phenoxy herbicides in the ester form are more volatile and therefore are more likely to create damage on unintended targets. Leaves become yellow and small, sometimes cupped or extremely misshapen. Symptoms vary by herbicide and amount. Young trees may be permanently damaged, older trees often recover.
Fall and Winter cold damage Typically seen on dormant buds, but may also affect woody parts of the tree. Uninjured buds will be green, whereas dead buds will be brown or black. Uninjured woody tissue will also be green, whereas damaged cambial tissues become brown. Injured cambium may recover. Severely injured trees may begin to grow in the spring but collapse late spring or summer.
Overcropping Improper management that allows too much crop to be left on the tree during “on” years. Some cultivars are more prone to excess crop load than others. Limbs may weep or break under stress of overloading. Effects of overcropping include limb breakage, reduced winter cold hardiness, reduced return bloom, and overall tree stress. Overcropping is a significant reason why alternate bearing occurs in some pecans.
Drought When insufficient water is available to the tree. Drought stress occurs in very dry years, usually in non-irrigated, improved-cultivar orchards. It may also arise when trees have heavy crop loads during hot, dry summers. Drought stress can be manifested in a variety of different ways. One way is the cessation of shoot growth. A stoppage of shoot growth is often noticeable due to the lack of light green foliage. A further indication is tip-burning on leaves and leaflets. This is when permanent damage is done to plant tissues from lack of sufficient water. A clear indication of drought stress is poor nut fill, when the kernel does not fill the entire nut or is wafer-like.
Vivipary Vivipary occurs when two conditions are met; the development of high humidity between the shell and shuck and high temperatures during ripening. The incidence of vivipary varies with crop load, irrigation, tree crowding, soil depth, and length of the growing season. When green shucks fail to open and the kernel develops, there is often an increase in the number of nuts which germinate and sprout on the tree. The longer the fruit remains on the tree, the greater the degree of vivipary. Pecan trees growing in southern Oklahoma will be more susceptible to vivipary than those in northern Oklahoma.
Sooty Mold A secondary infection that occurs after heavy aphid populations. A black fungus that forms on the honeydew left behind by feeding aphids. A heavy infestation may inhibit photosynthesis thereby reducing tree productivity and cold hardiness.
Kernel Necrosis Unknown cause but may be due to poor tree nutrition. End of nut is necrotic and dark colored. Kernel necrosis occurs in some cultivars more than others.
Yellow-bellied sapsucker Sphyrapicus The Yellow-bellied sapsucker is a type of woodpecker that drills rows of sap wells into a tree. It then eats the insect attracted to the sap. It has a vertical white strip on the shoulder and Adult males show a red cap and throat with females having a red cap and white throat. Juveniles are brownish gray all over. It is known to nest in cavities. Yellow-bellied sapsuckers will generally not cause economic damage in an Orchard. However, they can cause damage to the bark of the tree that can then allow insect or disease to enter the tree. In younger trees they can drill enough sap wells around a tree or branch to girdle the tree or limb causing death of the tree.