Bacterial leaf spot
Bacterial leaf spot, caused by Xanthomonas campestris, is a common disease affecting a wide range of plants. It manifests as small, water-soaked spots on leaves that eventually turn brown or black, often surrounded by a yellow halo. While it can cause significant cosmetic damage, it is generally manageable with proper cultural practices.
About this problem
Bacterial leaf spot is a disease caused by the bacterium Xanthomonas campestris, which affects a variety of plants, including vegetables, ornamentals, and fruit trees. The bacterium enters the plant through natural openings or wounds and thrives in warm, wet conditions. Over time, the initial water-soaked spots on the leaves enlarge and darken, potentially leading to leaf drop if the infection is severe. The disease is often confused with fungal leaf spots, but bacterial spots typically have a more angular appearance and lack the fuzzy growth associated with fungi. Managing the disease involves improving air circulation, avoiding overhead watering, and removing infected plant debris.
Symptoms
- Small water-soaked spots on leaves
- Spots turn brown or black
- Yellow halo around spots
- Leaf drop in severe cases
Cause
Bacterial leaf spot is caused by Xanthomonas campestris. The bacterium thrives in warm, humid conditions and spreads through splashing water, contaminated tools, and infected plant material.
Conditions that favour it
- Warm temperatures
- High humidity
- Overhead watering
- Poor air circulation
- Presence of infected plant debris
Lifecycle and spread
Xanthomonas campestris overwinters in plant debris and seeds. It spreads through water splashes, wind-driven rain, and contaminated tools. The cycle can be broken by removing infected debris, rotating crops, and using disease-free seeds.
Plants most affected
- Tomato
- Pepper
- Lettuce
- Cabbage
- Broccoli
- Cauliflower
- Radish
- Bean
- Ornamental plants
Treatment
Educational information only, and not a substitute for professional diagnosis. Identify the problem before treating it, and check that any product is registered for this plant and this use where you live.
Cultural control
- Improve air circulation by proper spacing
- Avoid overhead watering
- Remove and destroy infected plant debris
- Practice crop rotation
- Use disease-free seeds
Organic options
- Copper-based fungicides
- Neem oil
- Bacillus subtilis
Chemical options
- Copper hydroxide Used to manage bacterial leaf spot
Read and follow the product label. The label is the legally binding instruction. Confirm the product is registered for this plant and for this use in your area before applying it.
Prevention
- Ensure good air circulation
- Water plants at the base
- Sanitize tools regularly
- Remove plant debris promptly
- Use resistant plant varieties