Notes on Raspberry Diseases: Fire blight
Primocane tips and laterals of infected raspberry canes develop blackened tissue around the veins and frequently wilt or curve down in the form of a shepherd's-crook. Infected fruit or flower clusters appear water-soaked and eventually turn black. Droplets of white or amber bacterial ooze may be excreted from the lesions of infected tissue. Infected berries become hard, dry, brown and remain attached to the pedicel. The disease is caused by bacteria, similar but not identical to, the bacteria that causes fire blight on apples and pears.
Period of Activity
Fire blight infection shows up on susceptible varieties between bloom and harvest. Symptoms on primocanes and laterals may develop soon after high winds, driving rains or hail. These conditions create small wounds, which allow bacteria to infect.
Fire blight on raspberry is not common in Ontario. Occasionally it causes severe damage to the variety K81-6 and it has also been observed on Boyne. Watch for symptoms after periods of hail or severe weather.
- To avoid fire blight, do not plant susceptible varieties such as Boyne and K81-6. See Table 1. Relative Resistance of Raspberry Cultivars to Fire Blight Infection.
- Avoid overhead irrigation on susceptible varieties. Overhead irrigation can create wounds in plant tissue and favours infection through the spread of bacteria to healthy plants.
- Prune-out infected canes and remove from the planting as soon as observed. Remove infected canes on a dry day to prevent the bacteria from spreading to other canes.
- Insects such as tarnished plant bugs, earwigs and ants can spread the fire blight bacteria and encourage infection. Monitor for these insects and control them if necessary.
|Cultivar1||Lesion length (cm)|
1 Cultivars are ranked from most resistant to least
2 Plants were inoculated with three isolate of Erwinia amylovora. Lesion length was measured 17 days after inoculation.
Source: G. Braun, A. Jamieson, and P. Hildebrand Resistance of raspberry cultivars to fire blight, Hort Science 39(6) 1189-1192 2004.
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