Pecan Diseases

Anytime we observe significant limb dieback and buds sprouting along main limbs (Figure 3) we must suspect root damage of some type. This can result from construction injury, chemical misuse, watertable fluctuations or root knot nematodes (Figure 4 & 5). Nematode injury in addition may cause zinc deficiency symptoms (Figure 6) that cannot be corrected by zinc. Leaves will thicken, pucker on the edges and yellow. They may become curved or crescent shaped with necrotic spots. Trees will take on a rosetted appearance in the younger growth with a lot of dead branches (Figure 7). Shuck disease is one of the more common pecan problems and may appear in numerous forms. Stem end dieback or Botryosphaeria ribis (Figure 8) gets much of the blame. Although not uncommon, sticky shuck and premature nut drop is more commonly caused by moisture stress or physical damage (Figure 9) to the shuck. Either cause is responsible for much of what pecan producers refer to as August drop.

Chemical injury (Figure 10 & 11) is much too common. Improper rates, combinations and/or agitation are usually responsible. Marginal leaf necrosis (Figure 12) is usually blamed on Anthracnose and can be caused by several fungi; however, it is usually associated with stress of some type.

Shuck split (Figure 13) is sometimes a problem in late summer. This results when moisture is received following an extended drought. The shuck stops growing and when the nut tries to grow again, the shuck prematurely splits and the pecan embryo dies.

Vein spot Gnomonia nerviseda (Figure 14) and numerous other minor pecan diseases are often identified in pecan trees.

Chemical control of pecan diseases is often necessary. Kernel quality can be significantly increased (Figure 15) when pecan diseases as a whole are controlled.

Powdery mildew, Microsphaera alni (Figure 16) seldom if ever causes an economic problem to pecans. It is normally found in combination with pecan scab (Figure17) cause by (Cladosporium effusum). When pecan scab (Figure 18) & (Figure 19) is chemically controlled or the shucks and leaves, mildew and the other lesser diseases will also be controlled.

Control of pecan disease is affected more by coverage (Figure 23) than by the type of sprayer used. Large commercial sprayers (Figure 20), small air blowers (Figure 21), or aircraft Figure 22) can all do a good job depending on weather conditions. Adequate canopy coverage (Figure 23) is the important factor. If a part of the tree is not covered, it is not protected.

Kernel rots (Figure 24) are primarily a problem when pecans are left on the ground for an extended period prior to harvest. Rotting is also a problem when rain falls at or just prior to shuck split following a dry summer. This type of rot is often in the shucks when they fail to split. A good healthy canopy (Figure 25) is necessary to produce the kind of crop everyone desires. Good sanitation and proper pruning are necessary parts of a healthy canopy.