Plant Pathology Infobytes
September 09, 1996
Pecan Scab Severe On Susceptible Varieties
Many pecan trees over the state are carrying above average nut crops this season, but harvest quality may be reduced by pecan scab.
Scab is a fungus disease which attacks pecan trees during rainy weather, and most scab susceptible pecan varieties are now showing symptoms of the disease. On some trees scab has built up to damaging levels and is causing significant damage to the nut crop.
Scab isn't a new problem for pecan production. This disease has been around for years and is considered to be the most destructive disease of pecans in the South. The fungus that causes the disease starts early in the season by attacking young rapidly growing shoots, leaves, and developing nuts. Wet weather favors scab development and during such periods susceptible pecan varieties such as Schley, Success, and Stuart are attacked by the scab fungus. These and other susceptible varieties often produce poorly in years when scab is severe.
Scab infected leaves frequently fall in late summer, and this premature leaf shed deprives trees of a food supply needed for continued nut development. Heavily infected nuts take on a blackened appearance and drop prematurely. If you aren't sure whether you have a scab problem on your trees, bring several nut specimens by your county Extension office for examination and disease identification.
There's not much you can do about controlling scab on this year's crop. However, if you plan to install new trees in the fall or spring planting season, it's important to realize that the easiest and least expensive route to scab control is through planting recommended scab-resistant pecan varieties. For a listing, see MSU-ES publication 966 "Fruit and Nut Recommendations for Mississippi," available at the County Extension Office. Some of these varieties include Barton, Cheyenne, Davis, Elliott, and Owens.
Additionally, the following cultural practices should be part of a production program since vigorous growing trees are much less susceptible to scab and other diseases and insects:
* Collect a soil sample for nutrient analysis and apply recommended amounts of fertilizer before next season.
* Carry out sanitary measures to reduce the amount of scab fungus carryover into next year. Sanitation practices include removing old shucks and plant debris from around trees this fall and winter.
* Cut low hanging limbs. This will be important next season as a way of improving air circulation to speed drying of foliage and nuts following rainfall. The shorter the drying time, the better the chances for escaping infection by the scab fungus.
Many homeowners want to spray their trees as a means of preventing disease and insect problems. This is a difficult task since highly specialized application equipment is necessary to cover large trees. Also, several applications of fungicide are needed each season.
Homeowners with scab susceptible pecan varieties who wish to have their trees protected from scab should consider contacting a commercial pecan tree spraying firm. Such operators have the necessary equipment and spray "know-how." For a listing of licensed commercial operators, call your county Extension office.
Infobytes newsletter was written by the late Dr. Frank Killebrew, Extension Specialist.