Fire Blight
Erwinia amylovora is a highly destructive bacterial disease that spreads rapidly in warm, wet conditions during flowering. The bacteria enter through flowers, young shoots, and wounds, and move through the vascular tissue. Infected shoots take on a characteristic burnt, scorched appearance and bend into a distinctive "shepherd's crook" at their tips. A severe outbreak can destroy a significant portion of a tree's canopy in a single season.
Symptoms to Look For
- Shoot tips wilting and bending into a tight shepherd's crook shape, as if scorched
- Leaves on infected shoots turning brown or black and remaining attached to the branch rather than falling
- Brown, water-soaked, or sunken lesions extending down branches from an infected shoot tip
- White or amber bacterial ooze appearing on bark lesions in warm, humid conditions
- Cankers on older wood with a reddish-brown discolouration visible when bark is cut away
Affected Plants
Organic Solutions
Prune Out Infected Wood Immediately
Cut infected shoots at least 30 cm below any visible discolouration, cutting into healthy wood with a clear white interior. Disinfect cutting tools with 70% alcohol or a 10% bleach solution between every cut. Remove all prunings from the site and burn or bag them - do not compost infected material.
Copper-Based Spray at Dormancy
Apply a copper hydroxide or copper sulphate spray during full dormancy in late winter, before any bud movement. Copper at dormancy kills overwintering bacterial cankers on the bark surface and reduces the amount of inoculum available for the following spring. Follow label rates carefully.
Copper Spray at Bloom
Apply dilute copper sprays every 3 - 5 days during bloom in warm, humid, or rainy weather when infection risk is highest. Cover all flower clusters thoroughly. Limit bloom-period copper to the minimum rate that is effective to avoid fruit russet, which copper can cause at higher rates.
Avoid Stimulating Soft Growth
Fire blight is far more severe on trees with an abundance of soft, rapidly growing shoots. Avoid high-nitrogen fertilisers and heavy pruning in spring, both of which stimulate the susceptible succulent growth that is preferentially infected. A steady, moderate growth rate produces more resistant tissue.
Prevention
- Plant fire blight-resistant varieties wherever possible - Enterprise, Goldrush, Liberty, and Pristine in apples, and Moonglow, Harrow Sweet, and Harrow Delight in pears have strong genetic resistance
- Prune out all known cankers in late winter during dry weather before the disease becomes active - do not leave any infected wood on the tree through the growing season
- Apply a dilute copper spray every 3 - 5 days during bloom in warm, rainy springs - the flower is the primary infection site and the most critical period to cover
- Avoid sprinkler or overhead irrigation that wets foliage and flowers during bloom and summer growth periods - fire blight bacteria spread rapidly in surface moisture films
- Disinfect all cutting tools with alcohol between every cut during the growing season - cutting tools carry bacteria between trees and between cuts on the same tree
Garden, by Willowbottom recommends only organic, wildlife-friendly solutions. No synthetic pesticides, no harmful chemicals - ever.