What is fire blight?
Fire blight is the most devastating bacterial disease of apples, pears and crabapples. It is caused by a gram negative bacteria called “Erwinia amylovora“. The bacteria can enter into the host plant from natural flower openings or injuries due to rain, hail storm, insect damage, or farm machinery. Blossoms, shoots, and rootstock infections are called ‘blossom blight’, ‘shoot blight’, and ‘rootstock blight‘, respectively.
What does fire blight look like?
The name “fire blight” comes from the fire-scorched appearance of infected organs. Infected blossoms appear water-soaked, wilt, turn dark brown and remain attached to the tree. Infected leaves wilt, darken, and remain attached to the tree. Infected twigs and young branches darken and their tips usually bend to form a “shepherd’s crook.” During warm and moist conditions, infected tissue may exude bacterial ooze in droplets. Fire blight cankers on stems appear as slightly sunken, dark discolored areas with a narrow callus ridge. The inner bark of the infected stem turns from green to brown. The visual symptoms may slightly vary depending on weather conditions and plant variety.
Where does fire blight come from?
Bacteria overwinters in old cankers and in early spring insects, bees and farm management tools, rain splashes move it to natural openings of the plant or injured parts. Alternative hosts of the fire blight bacteria are many other plants from the Rose family, including serviceberry (Amelanchier spp.), cotoneasters (Cotoneaster spp.), hawthorn (Crataegus spp.), quince (Cydonia spp.), blackberries (Rubus spp.), raspberries (Rubus spp.), and mountain ashes (Sorbus spp.).
How do I prevent and control fire blight?
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- Plant resistant scion varieties and rootstocks
- Use clean orchard management tools
- Use clean plant material for grafting and rootstocks
- Prune infected plant parts and dispose of appropriately
- Use antibiotics and biocontrol during high risk periods in combination with disease forecasting models