Pecan trees occasionally suffer from stem-end blight, which is spread to its tissue through feeding insects. The symptoms of stem-end blight, or water stage nut drop as it is also commonly known, often appear up in July or August during the nuts' water stage. Once infected, the shucks develop black, sunken, shiny lesions. The shucks then quickly turn black, the liquid inside the kernel turns brown and the shucks drop from the tree. Once you have correctly identified stem-end blight, fix it by spraying the tree with fungicide and stopping the spread of the disease. However, this will only stop the fungus from spreading and may not save the entirety of this year's crop.
Make sure that you correctly identify stem-end leaf blight as the cause of your pecan tree's shuck drop. Many other causes can lead to fall drop in pecan trees. If you have any doubt, consult a professional. Or take a few pecans in to your local county extension office for testing. You should receive a report within two weeks.
Clear all leaf, branch and shuck litter and mulch from the bottom of the tree. The fungus that causes blight overwinters in this litter, and the insects that carry it thrive under this type of cover.
Spray the tree with a fungicide that contains benomyl when the pecans reach their water stage (between July and August). A pecan's water stage is the period when the green pecan grows rapidly, before the shell hardens and the kernel develops. Use a hose-end sprayer to apply enough spray so that the leaves and shucks of the plant are covered with fungicide but not dripping.
Spray the trees again in 10 days or at the frequency dictated by the manufacturer.
Look for insect activity in July and August. Insects such as stinkbugs, worms and aphids carry the fungus that causes pecan tree blight. Check for worm holes in the shucks or stinkbugs or aphids that may be crawling on or at the base of your pecan tree. Kill these insects with a pesticide prescribed for use on the specific insect in question and listed as safe to use on edible plants.