Manitoba Agriculture, Food and Rural Initiatives
Diseases of Trees - Fire Blight
DescriptionFire blight disease attacks a variety of trees in the rose family but is most common on apple, crabapple, and pear trees. Only trees and shrubs in the rose family are susceptible, including cotoneaster (Cotoneaster spp.), hawthorn, mountain-ashes (Sorbus spp.) and occasionally the saskatoon (Amelanchier spp.), spirea (Spirea spp.), rose and raspberry. Different species of trees are affected by Fire blight in varying degrees. SymptomsLeaves near the growing tips and the flowers suddenly wilt, turn reddish brown to black and may appear to have been scorched by fire. Infected new growth is often curled at the tip (shepherd's crook). A slimy bacterial ooze may be noticed on newly wilted shoots. The twigs and sometimes the larger branches are blighted. Cankers can develop on the trunk and branches. In some varieties of apple and crabapple, only the blossom spurs are affected.
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CauseFireblight is caused by the bacterial pathogen, Erwinia amylovora. It is spread from tree to tree by splashing rain, bees, flies, and other insects. Under favourable conditions, bacteria multiply rapidly contaminating hundreds of blossoms quickly. The bacteria penetrate and infect the blossoms, then continue down the fruit spurs, twigs and even branches, killing the tissue along the way. Even when disease has not been a problem in the past, the bacteria can be present in an orchard at low levels, causing significant losses. ControlBlighted twigs should be pruned at least 25 cm (10 inches) below the infected area and burned to eliminate most of the bacteria. Prune trees carefully to avoid infecting the healthy branch areas. Tools must be sterilized after each cut with a solution of 20% (regular) household laundry bleach (label should read 6% sodium hypochlorite) or use 70% ethyl alcohol or denatured alcohol. Preventative MeasuresOn ornamental crabapples, mountain ash, cotoneaster and hawthorn, a copper fungicide containing copper oxychloride can be applied as a preventative measure during the blossom period and summer when weather is warm (18oC). Fungicide activity continues for about 72 hours after application. If rain occurs during this period, reapply. Fireblight can be very severe following hailstorms particularly in May & June. There are currently no chemical controls registered for home use for fireblight management in saskatoons, apples, or pears in Manitoba. Additional treatment will be necessary to control the cankers developing on the trunks and branches of larger trees. Cankers should be removed by cutting into the healthy bark about 10 cm (4 inches) around the canker while the tree is dormant. Cut out the bark within the cut zone. Disinfect the resulting wound with a 20% hypochlorite solution (household bleach, one part solution to four parts water). Follow this with an application of wound dressing. This treatment works well on small cankers but is not recommended for larger cankers, extending around more than half of the affected branch. The best procedure for larger cankers is to completely remove the affected branch. All debris from pruning should be removed from the orchard and burned or buried immediately, leaving this material within the orchard, will only act as a source of bacteria for new disease outbreaks. NotesEffective control for fire blight is achieved only when the disease is detected and treated in the early stages. The pruning step is important in gaining control of fire blight. When copper oxychloride is applied as a preventative after pruning out of diseased branches, several sprays could be applied through the season especially after rains and during hot humid weather. Copper oxychloride is available under the names: Later's Copper Spray WP Fungicide (PCP# 16140) for domestic (home) use and as Copper Spray (PCP# 19146) for agricultural use. Please contact the following if you require further
assistance:
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For further information, contact your GO representative.
