Bacterial leafspot is a severe disease of peppers and tomatoes in North Carolina. It is more prevalent during wet seasons. Damage to the plants includes leaf and fruit spots which result in reduced yields, defoliation, and sun scalded fruit.

Symptoms

Bacterial spot of peppers and tomatoes can be recognized by numerous angular spots on the leaves. Initially, the spots are water-soaked. Leaves infected at an early stage become deformed. Often, the margins of affected leaves are rimmed with a narrow band of necrotic tissue. Infected pepper leaves drop prematurely; this exposes fruit to sun and may result in sun scald, secondary fruit rots, and reduced yields. Bacterial spots on the fruit are at first small, blister-like and irregular, and later turn brown and develop a warty appearance.

Cause

The disease is caused by the bacterium Xanthomonas campestris pv. vesicatoria (proposed names, X. vesicatoria and X. axonopodis pv. vesicatoria). The bacteria are microscopic and occur in enormous numbers in affected areas. They are rod-shaped and have a long whip-like tail that propels them in water; this helps them invade wet leaves and cause infection.

Source of Infection

The disease is widespread in tomatoes and peppers in the southeastern United States. Bacteria may overwinter in infested plant debris one year. The most important means of overwintering, however, is in seed. In North Carolina, most disease outbreaks can be traced to the use of infected seed or diseased transplants. Lesions may be observed on cotyledons of seedlings. Once initial infections take place, it can spread rapidly throughout the entire field during rainy weather from a few infected plants. Spread in plant beds/greenhouses and during planting operations is especially serious.

Field Spread

Any water movement from one leaf or plant to another, such as splashing rain drops, overhead irrigation, and touching or handling wet plants, may spread the bacteria from diseased to healthy plants. Bacteria then enter the leaf through stomates, hydathodes at leaf margins, and damaged epidermal cells and cause new spots. The longer the plants are wet, the greater is the opportunity for infection to occur. If a protective film of copper fungicide is on plant surfaces, most bacterial cells will be killed before gaining entry into the leaf or fruit -- hence, the importance of applying sprays before and during rainy periods. Sprays are not effective against bacteria inside the tissue.

Control

Control is based on preventive steps taken during the entire season. Once the disease has started in a field, control is very difficult, especially during wet weather.

A. Obtain seed that has been grown in regions without overhead irrigation and is certified free from the disease-causing bacteria. This is by far the most important step. Seed may be treated by washing 40 minutes with continuous agitation in 2 parts Clorox Liquid Bleach (5.25% sodium hypochlorite) plus 8 parts water (e.g. 2 pints Clorox plus 8 pints water). Use 1 gallon of this solution for each pound of seed. Prepare fresh solution for each batch of seed treated. Rinse seed in clean water immediately after removal from the Clorox solution and promptly allow to dry prior to storing or treating with other chemicals. This treatment will likely reduce seed germination. Thus before attempting to treat an entire seed lot, perform a test using 50-100 seed and check for the effect on germination.

B. Produce plants in sterilized soil or commercially prepared mixes.

C. Avoid fields that have been planted to peppers or tomatoes within one year, especially if they had bacterial spot.

D. Do not plant diseased plants. Inspect plants very carefully and reject infected lots -- including your own! Use certified plants.

E. Prevent bacterial leafspot in the plant beds:

1. keep the greenhouse as dry as possible and avoid splashing water;
2. spray with a fixed copper (Tribasic Copper Sulfate 4 lb, Copper-Count N, or Citcop 4E 2 to 3 qt, or Kocide 101 1.0 to 1.5 lb per 100 gal water). The addition of 200 ppm streptomycin (Agri-mycin 17-1.0 lb in 100 gal of the copper spray with a spreader-sticker) will improve the effectiveness of the spray program. Make applications on a 7- to 10-day schedule if spots appear, and one day before pulling plants.

F. In the field start spray schedule when the disease first appears. However, do not use streptomycin in the field.

1. Mix fixed copper (see E above for amount) and 1.5 lbs of mancozeb (Manzate 200DF or Dithane M-45) or maneb (Maneb 80WP, Maneb 75DF, Manex) in 100 gal of water. Do not use mancozeb on tomatoes within 5 days of harvest. Mancozeb is not registered for use on peppers; use maneb.
2. Adjust sprayer and speed of tractor to obtain complete coverage of all plant surfaces. Spray pressure of 200-400 psi is recommended and the use of at least three nozzles per row for pepper and 5 drop nozzles per row for tomato. Depending on plant size, use 50-150 gal/A of finished spray.
3. Adjust spray schedules according to the weather and presence of disease:
   (a) Spray one week after plants are set; (b) spray every 5 to 7 days during rainy periods; spray on 10-day intervals during drier weather; (c) spray before rain is forecast but allow time for spray to dry.

For the latest information on chemical recommendations, see the North Carolina Agricultural Chemicals Manual.

Cautions

A. Cercospora leafspot of pepper may resemble bacterial spot and can be serious during dry weather. The above procedures will also control this disease. For accurate diagnosis, contact your county agent to send diseased leaves to the Plant Disease and Insect Clinic, N. C. State University.

B. Always follow directions on the label of agricultural chemicals. Federal and State registrations change periodically. Observe safety directions on the label of the container, and dispose of excess material and empty containers in a safe manner.

Other Resources

Back to Vegetable Disease Notes
Plant Disease Information Notes Home Page
HIL-21 Pepper Production (Bell, Small Fruit and Pimento) or PDF version of HIL-21
Horticulture Information Leaflets Home Page
North Carolina Insect Notes
North Carolina Agricultural Chemicals Manual
NCCES Educational Resources

Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact your county North Carolina Cooperative Extension Service agent.

Published by the North Carolina Cooperative Extension Service Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability.

Last update to information: May 1996
Last checked by author: June 1996
Web page last updated on Dec. 2000 by A.V. Lemay.