Phoma rot



Phoma rot (P. destructiva) is a plant pathogen of the genus Phoma which causes sunken spots on tomato fruit and lesions on stems and leaves.

Symptoms
In its earliest stages, Phoma rot of green fruit is marked by minute, slightly sunken spots. As these spots enlarge they develop brown or black borders with slightly lighter centers which become dotted with black pimple-like bodies (pycnidia) in which the seedlike bodies, or spores, of the fungus are borne.

On the plant; spots are seen on the leaves, leaf petioles, and the stems of the vines. (PI. I.) Spotted leaves dry out and are shed. In the early stages the spots on the leaves are mereiy small discolored areas, later turning brown or black, which are definite in outline. These spots enlarge, and often several merge into a large blotch. On petioles and stems the diseased areas appear as streaks or blotches.

Treatment
Spotted fruit, even though unsightly, is fit for food provided the diseased parts are cut away.

Chemical
A fungicide such as benomyl (Benlate), chlorothalonil (Bravo), copper, maneb (Manzate D or Dithane M-22 Special), mancozeb (Dithane M-45 or Manzate 200) or Dikar (Polyram) may be used to control the disease in the field. It is important to start the spray schedule as soon as the plants emerge and spray at 7-10 day intervals, covering all plant surfaces. High pressure (400 psi), high volume (100 gal/acre for a mature crop) spray equipment provides most effective coverage.

Prevention
Crop rotations with nonhost plants such as small grain, corn, of two or more years are effective in reducing the incidence if disease-free seed are used. Currently no varieties are resistant.