Verticillium Wilt (fungus – Verticillium albo-atrum): This is the major disease of ornamental catalpas. Trees wilt suddenly, defoliate, and have a brownish discoloration of the outer sapwood. There is no control. Heavy fertilization sometimes enables infected trees to put a new ring of summerwood and springwood outside the infected area, stopping the radial spread of the fungus. Some trees may then recover.
Leaf Spot (fungi – Cercospora sp., Phyllosticta sp.): Round to irregular brown to black spots appear during prolonged periods of damp weather. Center of spots may fall out, leaving a “shot hole” appearance. Collect and burn fallen leaves. Chemical control usually not necessary. Spray valuable trees as leaves unfurl, when half-grown, and again when full grown.
Powdery Mildew (fungus – Microsphaera alni, Phyllactinia corylea): White to gray powdery mold on both leaf surfaces, usually late in the season on younger leaves. Leaves may be deformed or curled. Spray as needed with a powdery mildew control fungicide.
Trunk Rots (fungi – Collybia velutipes, Polyporus versicolor, and Polyporus catalpae): These tree fungi are heartwood rotters of catalpa that enter through wounds. Avoid wounding and keep the tree in good condition by fertilizing and watering.
Rosette: (See section on Pecan Diseases.)
Leaf Scorch: Usually caused by heat or drought.
Cotton Root Rot (fungus – Phymatotrichum omnivorum): Catalpa is rated intermediate in susceptibility to Phymatotrichum omnivorum.
Crown Gall: (See section on Crown Gall)
Nematodes: (See section on Root Knot Nematodes)
Wood Rot: (See section on Wood Rot)