Bacterial Spot

  • Symptoms

  • Trigger

  • Biological Control

  • Chemical Control

  • Preventive Measures

Bacterial Spot

Xanthomonas spp.

Bacteria


In a Nutshell

  • Small, yellow-green lesions appear on young leaves.
  • Leaves are deformed and twisted.
  • Dark, water-soaked lesions on older foliage.

Hosts

Capsicum & Chili

Tomato

Symptoms

The first symptoms are small, yellow-green lesions on young leaves, which usually appear deformed and twisted. On older foliage, lesions are rather angular, dark-green, and greasy in appearance, often surrounded by yellow circles. They are often more numerous on leaf margins or tips. Eventually, the spots look like shot holes because the center dries up and disintegrates. Fruit spots (up to 0.5 cm) start off as pale-green, water-soaked areas, which eventually roughen, becoming brown and scabbed.

Trigger

Bacterial spot occurs worldwide and is one of the most devastating diseases on pepper and tomatoes grown in warm, moist environments. The pathogen can survive in association with seed, either externally or internally as well as on specific weeds and later spreads through rain or overhead irrigation. It enters the plant through leaf pores and wounds. Optimum temperatures range from 25 to 30°C. Once the crop is infected, the disease is very difficult to control and can lead to total crop losses.

Biological Control

Bacterial Spot is very difficult and expensive to treat - if the disease occurs early in the season, consider destroying the entire crop. Copper-containing bactericides provide a protective cover on foliage and fruit. Bacterial viruses (bacteriophages) that specifically kill the bacteria are available. Submerge seeds for one minute in 1.3% sodium hypochlorite or in hot water (50°C) for 25 minutes.

Chemical Control

Always consider an integrated approach with preventive measures together with biological treatments if available. Copper-containing bactericides can be used as protectant and give partial disease control. Application at first sign of disease and then at 10- to 14-day intervals when warm, moist conditions prevail. The active ingredient copper and mancozeb give a better protection.

Preventive Measures

Plant certified disease-free seeds.,Use resistant varieties.,Inspect, remove and burn any seedling with leaf spots.,Remove weeds in and around the field.,Mulch around plants helps to avoid soil to plant contamination.,Crop rotation of 2-3 years is recommended.,Avoid overhead irrigation and working in fields when foliage is wet.,Plow in or remove plant debris after harvest.,Clean tools and equipment.