The pecan tree and its popular, sweet, and nutritious nuts are native to North America. The tree is susceptible to more than 20 fungal diseases, two of which can cause the pecan nut to rot on the branch.
Phytophthora shuck and kernel rot is a fungal disease that attacks many types of trees, particularly the pecan tree. When it infects a pecan tree, it tends to attack the shuck (the hard, green shell around an immature nut) and the nut kernel. The infected nuts tend to turn black and spongy. The disease is caused by the fungus phytophtora cactorum. The disease usually spreads with rain in the humid climate of the Southeastern United States. It's a relatively new disease, discovered in the late 1980s.
Pecan scab, consider the pecan tree's most virulent disease, is another fungus that causes the pecan to rot on the tree. Caused by cladosporium caryigenum, this fungus infection attacks the shuck, twigs and leaves of the tree. Scab is a common problem for pecan grows all over the continent. It was discovered in 1888.
Fighting Pecan Disease
The most common way to fight these rotting diseases is by spraying orchards with fungicide. Pecan scab requires that farmers spray their crops about nine to eleven times per growing season, starting when the leaves first bud on the trees in April, all the way through the end of the harvest. It is extremely expensive for farmers to spray this often. Scientists are researching ways to reduce costs associated with fighting the disease. Phytophthora begins infecting pecan trees in September, so it requires fewer fungicide treatments through the year.