Fire Blight

Plant disease · Erwinia amylovora (causal bacterium)

Description

Fire blight is a bacterial disease of plants in the rose family, especially apple, pear, quince, and some ornamental relatives. It can kill blossoms and young shoots, form cankers on branches, and, in severe cases, kill an entire tree. The bacterium survives in cankers and becomes active in spring. Warm, wet weather favors its spread, particularly during bloom, when insects and splashing rain can carry bacteria to flowers. It can also enter through wounds caused by hail, wind, or pruning. Infected shoots often wilt and darken rapidly, giving the plant a scorched appearance. Leaves may remain attached after they die. Under humid conditions, infected tissue can produce droplets of bacterial ooze that spread the disease further. Young, vigorously growing plants are especially vulnerable. Fire blight affects aboveground growth; it is not a root disease. Its severity varies with the host variety, weather, and the amount of infection already present nearby.

Symptoms

• Wilting
• Bleached or scorched patches
• Flowers or buds dropping
• Rotting fruit
• Leaves dropping

How to Identify

Look for blossoms that turn brown or black, followed by shoots that wilt, darken, and often bend at the tip into a characteristic “shepherd’s crook.” Dead leaves commonly cling to the shoot. Branches may develop sunken cankers, and sticky, pale-to-amber bacterial ooze may appear in warm, humid weather. Young fruit can shrivel and darken. Drought and heat scorch can also brown leaves, but they usually lack blossom blight, hooked shoots, and cankers. Frost can blacken blossoms suddenly, but does not typically produce spreading shoot dieback or ooze. If the pattern is unclear, ask a local extension service about laboratory diagnosis.

Prevention

Choose fire-blight-resistant varieties where available, particularly for pears and apples. Plant in a site with good air movement, and space and prune trees so foliage dries readily. Avoid excessive nitrogen fertilizer and heavy pruning that stimulate susceptible, tender shoots. Do not irrigate over the canopy during bloom if another method is practical. Inspect trees regularly in spring and remove overwintered cankers during dormancy, cutting back into healthy wood. Clean pruning tools when moving between infected and healthy material. Avoid working on trees while they are wet, and protect bark from avoidable injury. Remove nearby abandoned or heavily infected host plants when feasible. In places with a history of fire blight, local bloom-time risk forecasts can help growers time preventive measures.

Treatment

There is no cure for infected tissue. On a dry day, promptly prune out affected shoots, cutting at least 8–12 inches (20–30 cm) below visible symptoms into healthy wood; larger cankers are best removed during dormancy. Discard cuttings rather than leaving them beneath the tree, and clean tools between cuts, especially before working on healthy branches. Check the tree again for new symptoms. Avoid heavy fertilization or pruning afterward, since vigorous new growth is susceptible. If the infection reaches the trunk or main framework, removal of the tree may be necessary. Preventive products cannot repair damaged branches. Where fire blight recurs, a copper product labeled for the host may help reduce bacteria when applied at its specified dormant or early-season timing, but copper can damage foliage or russet fruit if mistimed. Other bloom-time controls, including biological products or antibiotics, depend on local availability and regulations; follow local extension guidance and the product label.

Plants Affected

Apple, Chaenomeles, Cotoneaster, Crabapple, Mountain Ash, Photinia, Quince, Serviceberry, Spirea

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