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.
[Illustration: Figure 7. Spanish moss accumulation in pecan trees
reduces vigor from excessive shading.]
[Illustration: 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.
_Pecan Insects and Their Control_