Pecan Trees.
This is the most destructive disease of pecans in the South. The fungus overwinters on infected leaves, twigs, and shucks, both on the ground and on the tree. In spring, wind and rain carry the spores to young, rapidly growing shoots, leaves, and developing nuts. Only growing tissue is susceptible, and the fungus causes infection only if there is adequate moisture. Mature foliage and nuts are immune to scab. The disease is most prevalent in areas with frequent rainfall and high humidity.
The disease is characterized by small, dark, circular, olive to black spots on foliage and nuts. These spots may fuse to form large blackened areas. If the disease is not controlled, entire crops from most cultivars (varieties) and some native and seedling trees may be lost during periods of frequent rains or extended dew. The pink mold fungus, Cephalothecium roseum, invades old scab lesions on nut shucks. If it invades the nut kernel, it can cause off flavors and pink rot. The shells of infected nuts may have an oily appearance.
Pecan scab is readily controlled with properly applied sprays of effective recommended fungicides, in conjunction with strict adherence to recommended sanitary practices, or by use of resistant cultivars.