Pecans With Black Spots and Bitter Meat in Southern Nevada

Q. I had two pecan trees that are now 25 years old. One variety has round nuts and the other one has oblong nuts. This is the first year in 25 years they have produced nuts that have black spots and are bitter tasting but the outside of the nut looks normal. Any idea what the problem might be?

Pecan scab. Picture from Texas A and M University.

A. Pecan nut problems are hard to diagnose. The nuts themselves can be bitter if some of the husk is attached to the nut. But yours sounds like a disease issue to me. Perhaps it was our wet early summer and spring that created the problem.

The most common disease of pecans is scab. When it is a wet spring, after a rain, it is wise to spray the trees in March with a fungicide such as Bordeaux or copper sulfate. If it rains again, spray it again after the rain has stopped. The problem is spraying these trees top to bottom since there are no systemic fungicides that can be applied to the soil and taken up by the roots. The lesions on the outside surface of the shell this disease produces are difficult to see and does produce an “off flavor” once inside the meat.

I must guess a little bit, but the varieties popular about 25 years ago in the West were oblong nut varieties called “Western Schley”, “Mahan”, “Wichita”, “Mohawk”, and “Cheyenne”. The older and round nut varieties were either “Burkett” or possibly “Choctaw”. The reason I mention it is because there are probably well over a hundred varieties of pecan. The more recent hybrids are smaller, produce nuts sooner, less likely to bear nuts every other year (alternate bearing), and don’t need a pollinator tree. Also “Choctaw” and “Cheyenne” varieties were considered “resistant “to this disease.

Even though pecan trees can handle our summer heat and poor soils, I don't recommend them for our area because of their size and water use. Pecan trees can get big, growing 60 to 100 feet tall and 30 to 50 feet wide, and have no semi-dwarf or dwarf varieties that I know. Their size dictate they use a lot of water. They do have a sizeable tap root so they possibly could be used where there is shallow underground water.