Fire Blight

Infected blossoms wilt and blacken, and young shoots die back from the tip, often curling into a distinctive shepherd's-crook shape. Cankers on branches or the trunk can appear sunken and discoloured, and in humid conditions may ooze bacterial exudate.

Bacteria overwinter at the margins of existing cankers and become active in spring, producing ooze that is carried to open blossoms by rain splash, wind, and insects, including pollinators. Bacteria multiply on the stigma surface before entering through natural openings or wounds, then can move systemically into shoots and branches.

• Existing untreated cankers are a key source of bacteria at the start of the bloom period
• Hail or wind damage can create additional wounds allowing bacterial entry
• Vigorous, succulent shoot growth is more susceptible to systemic spread

Apple is a major host of fire blight among pome fruits. Closely related pome-fruit species and some ornamental relatives are also susceptible in many regions.

• Warm, wet, or humid weather coinciding with bloom
• Existing cankers providing a source of bacteria nearby
• Hail or wind damage creating wounds during susceptible periods
• Vigorous, succulent shoot growth from high nitrogen supply

Because fire blight can spread rapidly during a favourable bloom period, management combines reducing existing inoculum, limiting susceptible growth, and monitoring bloom-time weather.

• Plant resistant or tolerant varieties and rootstocks where available
• Prune out and destroy cankers and blighted shoots well below visible symptoms, during dry weather
• Avoid excess nitrogen that promotes susceptible, succulent growth
• Monitor bloom-period weather-based risk information where available