Bacterial spot on peach — symptoms and treatment

Severity: medium

What is Bacterial spot

Bacterial spot of peach is caused by Xanthomonas arboricola pv. pruni. It attacks leaves, fruit and twigs, which is what makes it more than cosmetic: the leaf phase thins the canopy, the twig phase carries the bacterium through winter, and the fruit phase ruins the crop. It rates medium severity — rarely fatal to an established tree, but persistent once it is in a garden, because no spray cures an infected tree.

Symptoms

The earliest sign is small, dark, water-soaked spots on the leaves, worst on foliage that stays wet longest. Held up to the light, young spots look greasy and translucent. As they age the dead centres turn brittle and drop out, leaving the shot-hole effect that gives the leaf a peppered, riddled look — the most recognisable symptom on peach. Heavily spotted leaves yellow and fall, and repeated defoliation weakens the tree. On fruit, small dark lesions deepen into cracked, corky pits as the peach expands beneath them. Twigs develop dark sunken lesions that harbour the bacterium.

• Early signs: small dark, water-soaked spots on leaves; dark specks on young fruit
• Advanced signs: shot-hole effect, leaf yellowing and drop, cracked corky fruit lesions, twig lesions
• Confusable with: fungal leaf spots and spray injury — water-soaked fresh spots plus corky, cracked fruit point to bacterial spot

Causes and conditions

The bacterium overwinters in twig lesions and buds, and each spring these start the new cycle. Bacteria ooze out in wet weather and reach leaves and fruit by rain splash and wind-driven rain, entering through natural pores and wounds. Warm, wet, windy weather is the driver: wind both spreads the bacteria and abrades the surfaces they land on, so exposed trees and rows facing the prevailing wind are hit hardest. Blowing sand makes it worse, and anything that keeps foliage wet — overhead irrigation, crowded canopies, long dews — increases infection. Young, expanding leaves and fruit are the most susceptible.

Treatment

Resistant varieties — cultural

Timing: at planting. Plant resistant peach varieties. Avoid overhead irrigation. Ensure good air circulation. Variety choice is the most effective decision you make with this disease, because it is taken before the tree is in the ground and cannot be undone afterwards.

Copper hydroxide — chemical

Timing: dormancy and early spring. Apply copper sprays during dormancy and early spring. Oxytetracycline during growing season. Sprays are protective — they reduce the bacterial population rather than cure infected tissue, so they must go on ahead of wet, windy weather. Repeated copper on foliage can injure peach leaves. Pre-harvest interval: 21 days. Pesticide registrations vary by country — check local approval before use.

Prevention

• Choose resistant varieties when planting — this outweighs everything you can do later
• Avoid overhead irrigation; water at the base so leaves and fruit dry quickly
• Prune to open the canopy for air circulation and faster drying
• Shelter exposed sites from prevailing wind, which spreads the bacteria and wounds the tissue
• Prune out twigs with lesions in dry weather to reduce overwintering sources

Frequently asked questions

Can I eat peaches with these spots? Yes. The lesions are on the skin and affected flesh can be cut away — the damage is to appearance and storage life, not safety. Cracked fruit spoils quickly, so use it promptly.

Will it spread to my other fruit trees? It spreads readily between peaches and to related stone fruit such as plums and apricots, which host the same bacterium. Unrelated trees like apples and pears are not affected.

Can I cure an infected tree? No. Nothing eliminates the bacterium once a tree has it — it survives in the twigs. Management means reducing it each year through variety choice, airflow, avoiding overhead water and protective sprays.