Bacterial spot on bell pepper — symptoms and treatment

Severity: medium

What is Bacterial spot

Bacterial spot of pepper is caused by Xanthomonas species. It causes leaf spots and fruit blemishes, and although rated medium severity it is one of the most frustrating diseases a pepper grower meets: no spray cures an infected plant, the bacteria arrive hidden on seed or on bought transplants, and by the time spots are obvious the population is established throughout the planting. Much of the damage is indirect — defoliation strips the canopy that shades the fruit, and exposed peppers scald.

Symptoms

On leaves the disease starts as small dark spots that are raised and slightly rough — run a finger over an affected leaf and it feels scabby rather than smooth, the quickest field check. Young spots often look water-soaked and greasy against the light, sometimes ringed by a yellow halo. As they multiply the leaves yellow and drop, stripping a plant from the bottom up until the peppers hang on bare stems. On fruit, lesions begin as water-soaked areas that develop into raised, roughened, scabby patches. These break the surface and let soft-rot organisms in, so affected peppers often rot rather than simply looking marked.

• Early signs: small dark, slightly raised spots on leaves, water-soaked when young; a scabby feel to the leaf
• Advanced signs: yellowing and premature leaf drop, bare stems, scabby raised fruit lesions, sun-scalded peppers
• Confusable with: fungal leaf spots — the raised, rough texture and water-soaked margins point to the bacterial disease

Causes and conditions

The bacteria come into a garden two ways above all: on contaminated seed, and on infected transplants that look healthy when bought. They also survive on crop residue in the soil and on volunteers and related weeds. Once present, they spread by rain splash, overhead irrigation and on the hands and tools of anyone working among wet plants. Warm, wet, humid weather drives it hard, and the bacteria enter through natural pores and wounds, so anything that injures the tissue helps them: wind, blowing sand, insect feeding. Crowded plantings that dry slowly suffer most.

Treatment

Seed treatment and rotation — cultural

Timing: pre-planting. Use certified disease-free seed. Rotate with non-solanaceous crops for 2-3 years. Both attack the sources rather than the symptoms: clean seed and clean transplants keep the bacteria out of the planting, and rotating away from peppers, tomatoes, aubergines and potatoes lets infected residue break down first.

Copper + Mancozeb — chemical

Timing: transplanting through harvest. Apply copper-based bactericide mixed with mancozeb as preventive spray every 7-10 days. These sprays are preventive — they protect tissue that is not yet infected and reduce the bacterial population on the plant surface, but cannot cure a plant that already has the disease, so they must begin at transplanting rather than at the first spot. Pre-harvest interval: 14 days. Pesticide registrations vary by country — check local approval before use.

Prevention

• Start with certified disease-free seed and inspect bought transplants
• Rotate with non-solanaceous crops for 2-3 years and control solanaceous weeds and volunteers
• Water at the base — overhead irrigation splashes bacteria through the row
• Space plants for airflow, stay out of the planting while leaves are wet, clean tools between plants

Frequently asked questions

Can I eat peppers with these spots? Sound fruit is fine. Cut away small scabby lesions, but discard peppers that have started to rot — broken skin lets soft-rot organisms in. Observe the pre-harvest interval after spraying.

Will it spread to my tomatoes? Yes. The same bacteria affect tomatoes and other solanaceous plants, which is exactly why rotation must be to non-solanaceous crops and why an infected pepper bed beside tomatoes is a risk.

Can I cure infected plants? No. Copper-based sprays are preventive only, and infected plants stay infected — the payoff comes from clean seed, rotation, and starting protective sprays before symptoms appear.