Pecan Tree Spots?

Allison C. sent this question about her 20-year-old pecan tree:

My tree has brown spots on the leaves, and pecans. I have not had this problem in the past. Do I need to fertilize the tree?


Observation of the leaves show brown spots. This is a fungal disease that attacks the pecan leaves, nuts, and stems. This will prevent the tree from making nutrients that are needed for healthy leaves, stems and pecans. At some point the tree could die from this disease.

The common name of this disease is Pecan Scab. Scientifically it is Fusicladium effusum a fungal plant pathogen that causes pecan scab. It is seen in North Texas around July and August. When Mother Nature provides a large amount of rain, the disease becomes more apparent. This year North Texas has had an abundance of rain and moist conditions. Fungus is more evident and has the capacity to kill plants and trees. Homeowners and Pecan growers are being affected by this disease.

What is a Fungus?

To define the term Fungi, it is a living organism that can cause over eighty percent of all plant diseases. Fungi are not photosynthetic, and they are not considered to be a plant. Plants that are photosynthetic can make their energy from water, nutrients and the sun. Fungi live off other organisms. Example you can acquire a fungal disease that lives off your skin. Commonly called Ringworm, (Tinea) it is a type of fungus that uses skin tissue for nutrients.  Not all fungus is harmful. We eat mushrooms and they are classified as a fungus.   In our environment we have both helpful and harmful fungus. Pecan scab is a disease and is harmful.

The common fungal infection on Pecan trees is scientifically called Cladosporium caryigenum. The disease is characterized by small, dark, circular, olive to black spots on foliage and nuts. As the disease progresses the blackened area become large spots that are highly visible. This fungal disease can destroy an entire field of Pecan trees if not treated.

How can you  prevent the disease? It is not possible, unless you have a tree that was genetically altered to prevent the disease. Individual trees can be sprayed, and it will possibly control the disease. If you had a pecan farm, the answer would be entirely different. Trees sprayed may have a secondary infection, which requires spraying repeatedly. For Pecan producers this is a very expensive procedure. If the weather continues to be rainy and wet your tree may have a secondary infection. This secondary infection could cause the tree to die.

The experts would recommend that you spray with a fungicide and the tree then recovers from the fungal infection. This is the best possible choice for protecting your tree for the future. The pecans for this year will need to be discarded. Hopefully the tree will have a better crop next year.


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