Prepared by Dr. Robert L. Wick, Department of Plant Pathology, Fernald Hall, University of Massachusetts Amherst, MA 01003. Tel. (413) 545-1045 Fax. (413)545 2532

Revised September 24, 1991 V3

Bacterial spot is caused by Xanthomonas campestris pv. vesicatoria. In general, Xanthomonas pathovars have very narrow host ranges. Xcv has several strains which vary in their pathogenicity to tomato, pepper and nightshade.

The bacterium is seed-borne and can overwinter on diseased plant debris for at least one year. Plant to plant spread occurs during rainy periods and by humans and farm machinery, particularly when plants are wet.

All above-ground parts of tomatoes and peppers are susceptible. Spots on leaves are irregular and water soaked or greasy in appearance. The dead tissue often dries and cracks. Severely spotted leaves will appear scorched and defoliation may occur. Foliar symptoms on pepper are similar to those on tomato. Only green tomato fruit is susceptible to infection and the lesions are quite distinct. Young spots often have a halo around them and may resemble the birds-eye spot caused by Clavibacter michiganense (the bacterial canker organism). Well-developed lesions loose the halo and are l/8 to l/4 inch in diameter, raised and scab-like. Lesions on pepper fruit may be scab-like or sunken and may occur on ripe fruit.

Bacterial speck occurs on tomato but not pepper. The bacterium, Pseudomonas syringae pv. tomato, causes a fruit spot and blight of the foliage. On the foliage, small black spots develop resulting in chlorosis. On green fruit, small (1/16 inch) spots develop. Bacterial speck can usually be distinguished from bacterial spot by the size of the lesions; however, in some cases, the symptoms can look similar.

These two unrelated bacteria are similar in their life history therefore management practices for both are similar. Buy certified seed from a reputable source. Transplants purchased from southern states should be certified and inspected carefully when they arrive. Practice crop rotation. Streptomycin can be used on transplants but can not be used once the plants are in the field. In general, bacterial diseases of field crops are difficult to control with pesticides; however, copper/mancozeb solutions are most effective. When a significant amount of disease occurs, pesticides are usually not effectvie. Avoid working in fields when bacterial diseases are present and plants are wet.

Chemical recommendations:

streptomycin (Agrimycin®, Agristrep®): 1 lb./100 gal. when the first true leaves appear; continue every 4 to 5 days until transplanted. Streptomycin cannot be used after transplanting.