Disease Management

Tomato Clavibacter Pseudo Xanthomonas

BACTERIAL SPOT AND BACTERIAL SPECK OF TOMATO AND PEPPER

The Plant Disease Diagnostic Laboratory

Prepared by M. Bess Dicklow, UMass Extension, Fernald Hall, University of Massachusetts, Amherst, MA 01003-9320. Tel 413-577-1827 Fax 413-545-2115. mbdicklo@umext.umass.edu.

Revised July 29, 2005 V4

Bacterial Spot of Tomato and Pepper

Bacterial spot caused by Xanthomonas campestris pv. vesicatora (Xcv) is present wherever tomato and peppers are grown. In general, Xanthomonas pathovars have narrow host ranges. Xcv consists of different strains that vary in their pathogenicity to tomato, pepper, and nightshade.

The bacterium is able to survive on tomato volunteers and can overwinter in diseased plant debris. Seed is an important mechanism for survival and dissemination of  Xcv. Disease development is favored by temperatures between 80˚ and 90˚ F and by heavy rainfall. The bacterium is spread by wind-driven rain, workers, farm machinery, and aerosols. It penetrates through stomates and wounds created by insects, wind-driven sand, and tools.

Xcv affects all aboveground plant parts. On leaves, the spots are generally brown, circular, and water-soaked. Bacterial spot lesions do not have concentric zones or a prominent halo. When conditions are optimal for disease development, spots can coalesce to form long, dark streaks. A general yellowing may appear on foliage with many lesions giving the plants a scorched appearance, and the plants may exhibit severe epinasty. Only green tomato fruit is susceptible to infection and lesions are quite distinct, beginning as minute, slightly raised blisters with a halo that resemble the birds-eye spot caused by Clavibacter michiganense (bacterial canker). As lesions enlarge, they loose their halo and become brown, raised, and scab-like. Lesions on  ripe pepper fruit may be scab-like or sunken.

Bacterial Speck of Tomato

Bacterial speck occurs on tomato not pepper. It is a cosmopolitan disease, generally of minor concern, favored by low temperatures and high moisture. The bacterium Pseudomonas syringae pv tomato causes a fruit spot and foliage blight. This bacterium is also seedborne, spreads within fields in the same manner as bacterial spot, and may persist in weed species. Lesions on leaves are round and dark  brown to black with a halo that develops with time. Spots may coalesce, killing large areas of tissue. On fruit, small (1/16 inch), dark spots or specks develop with the tissue around them often more  intensely green than unaffected areas.

Management of Bacterial Spot and Bacterial Speck

Although the two bacteria are unrelated, their life histories and management strategies are similar.

1. Buy certified seed from a reputable source or use seed treatments to reduce transmission.
2. Produce disease-free transplants by raising transplants in an area where production does not occur. Inspect all purchased transplants carefully and if  transplants originate in southern states they should be certified.
3. Rotate fields to avoid carry-over on volunteers or crop residue.
4. Keep fields free from volunteers, weeds, and cull piles.
5. Avoid working in fields when bacterial diseases are present and the fields are wet.
6. Apply appropriate bactericides or combination pesticides.

In general, bacterial diseases of field crops are difficult to control with pesticides; copper/mancozeb solutions are most effective When a significant amount of disease is present, pesticides are usually not effective.

Chemical recommendations:

acibenzolar-S-methyl (Actigard 50 WG): 0.3 to 0.75 oz/A (14 dh, REI 12 h).Do not apply more than six times per crop season or on less than a 7 day schedule. Under certain conditions, this product, when used on tomatoes, may lead to reductions in yield.

copper hydroxide (Chanp, Champion WP): 4 tbs/1000 sq ft ( 0 dh, REI 24 h). Greenhouse and Shade house crops .Begin applications when disease first threatens and repeat at 7-10 day intervals as needed. Do not apply in a spray solution with pH less than 6.0 or phytotoxicity can occur.

copper hydroxide (Kocide 2000, KOP-Hydroxide):  1.5 to 3.0 lb/A (0 dh, REI 24 h). Begin applications when disease first threatens and repeat at 5-10 day intervals. Use higher rates when conditions favor disease development.

copper salts of fatty acids (Tenn-Cop 5E): 3 pts/A. (0 dh, REI 12 h). Apply at the first sign of disease and repeat at 7-10 day intervals. Enhanced control obtained by tank mixing with Manzate 75 DF. Avoid spray solution with pH of less than 6.5 as phytotoxicity may occur.

copper sulfate monohydrate, tribasic (Basicop): 2-4 lb/A ( 0 dh, REI 24 h). Begin when disease normally appears and repeat at 7-10 day intervals. Use higher rate when disease pressure is heavy.

ethylene bisdithiocarbamate plus manganese plus zinc (Manzate 75 DF): 0.75-1.5 lb/A (5 dh, REI 24 h). Start applications at transplant. Repeat at 3-7 day intervals throughout season. Do not apply more than 22.4 lbs per acre per crop.

mancozeb plus copper hydroxide (ManKocide): 2.5 to 5.0 lb/A (5 dh, REI 24 h). Begin applications when disease threatens and repeat at 7-10 day intervals as needed. Use higher rates and 3-7 days when disease pressure is severe.

streptomycin sulfate (Agri-mycin 17): 200 ppm (REI 12 h). Use only up to transplant.