Bacterial leaf spot 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.
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.
The disease is caused by four species of Xanthomonas--X. euvesicatoria, X. perforans, X. gardneri, and X. vesicatoria. X. perforans is the most predominant species causing bacterial spot in North Carolina. 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.
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.
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 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 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 transplants:
- Keep the greenhouse as dry as possible and avoid splashing water;
- Spray with a copper-based product or streptomycin or both in the greenhouse. Mancozeb may be added to copper to improve efficacy. Make applications on a 7- to 10-day schedule if spots appear, and one day before pulling plants.
F. In the field, start the spray schedule when the disease first appears. DO NOT use streptomycin in the field.
- Mix fixed copper and mancozeb in 100 gal of water. Do not use mancozeb on tomatoes within 5 days of harvest. Note: Copper tolerance is prevalent in this pathogen in North Carolina.
- To increase efficacy, apply an SAR (e.g., Actigard, Lifegard) every 14 days starting with the first spray. Do not use Actigard within 14 d of harvest.
- 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.
- 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.
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, NC 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.
- Plant Disease Factsheets
- Vegetable and Herbs Disease Notes
- Horticulture Information Leaflets
- North Carolina Agricultural Chemicals Manual
For assistance with a specific problem, contact your local North Carolina Cooperative Extension personnel.
Publication date: Dec. 6, 2017
Recommendations for the use of agricultural 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 North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural 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 regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension agent.
North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.