Friday, August 9, 2013

Powdery mildew on pecan shucks

Powdery Mildew on USDA 61-1-X
   White blotches growing of the surface of pecan shucks is the first sign of a fungal disease that can eventually spread to cover the entire surface of the nut. Powdery mildew (photo at right) is a disease that seems to attack only certain cultivars or individual native pecan trees.
    Powdery mildew is caused by the fungus, Microsphaera alni, which can actually infect both leaves and nuts.  Leaf infections are rare in our region but when they occur, cause no economic damage. If nuts are infected soon after pollination, powdery mildew can cause nut drop, reduce nut size or inhibit kernel fill. However, late season infections seem to have little or no impact on nut production. The pecans pictured in the photo were infected by powdery mildew in late July. They should grow to normal size and produce full kernels.
    Powdery mildew is often controlled by fungicide applications aimed at controlling pecan scab. In most cases, powdery mildew does not cause enough crop loss to justify the expense of additional fungicide applications specifically aimed at controlling this disease.