Why Does My Apple Tree Have Fire Blight?

Fire blight (Erwinia amylovora) is a highly destructive bacterial disease of apples, pears and related rosaceous plants, and it moves with devastating speed in warm, wet spring weather. The infected shoots wilt suddenly, the leaves and shoot tip turn brown and remain attached — giving the characteristic "burnt" or "scorched" appearance that gives the disease its name — and the shoot bends downward in a distinctive shepherd's crook. In a severe outbreak, multiple branches or the entire tree can be killed within a single season.

Identifying fire blight

Look for: shoots that wilt and die rapidly (days, not weeks), with dead leaves remaining attached rather than dropping; the shoot tip bent downward in a shepherd's crook shape; a reddish-brown discolouration visible if you cut the shoot — the discolouration extends in streaks into the healthy wood below the visible dead area; in humid conditions, a milky bacterial ooze may appear on infected bark surfaces. The spread through a branch happens rapidly, with the bacterial infection moving downward through the vascular system.

Emergency removal protocol

Remove infected shoots immediately. Cut at least 30–45 cm below the lowest visible sign of infection — the bacteria extend further into the wood than the visible dead area. After every single cut, disinfect the cutting tool by dipping in a solution of one part bleach to nine parts water, or 70% methylated spirits. Do not compost removed material — burn it or dispose of in household waste. Working on a dry day (rain spreads bacteria) and avoiding over-pruning of the remaining tree (which stimulates the soft growth most susceptible to infection) are both important.

Conditions that favour fire blight

Fire blight thrives in warm temperatures (24–29°C), high humidity and wet, windy conditions during flowering — the main infection window is at blossom time when the bacteria enter through open flowers. Avoid overhead irrigation during flowering, excess nitrogen fertiliser (which produces the soft, lush growth most susceptible to infection), and unnecessary wounding of the tree during the growing season.

Resistant varieties

Fire blight resistance varies enormously between varieties. Fiesta, Discovery and Greensleeves have some resistance; Cox is highly susceptible. In areas with high fire blight pressure, variety choice is one of the most important protective factors.