COTTON ROOT ROT
Cotton root rot disease is caused by the fungus Phymatotrichum omnivorum (Shear) Dvgg., a soil-inhabiting pathogen that attacks a wide range of host plants including the pecan.
The roots of the pecan tree are invaded during the summer when growth of the fungus in the soil is most active. The infected roots are killed, disrupting the transportation of water to the leaves, [Figure 8]. Trees diseased by cotton root rot produce yellow foliage, and shedding of leaflets occurs during dry periods. Diseased trees usually die 1 to 3 years after becoming infected.
Figure 7. Spanish moss accumulation in pecan trees reduces vigor from excessive shading.
Figure 8. Cotton root infected with cotton root rot fungus. Note the splitting and general deterioration of the root.
Control.—An effective control for cotton root rot disease has not been developed.
New orchards should not be planted in soil having a history of cotton root rot disease.