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Beginner

Scientific Name: Erwinia amylovora

Identification

• Tips and laterals of infected canes develop blackened tissue around the veins and wilt or curve down.
• Infected fruit or flower clusters appear water-soaked and turn black.
• Lesions may excrete white or amber coloured bacterial ooze.
• Infected berries become hard, dry, brown and remain attached.

Often Confused With
Raspberry cane borer  
Botrytis grey mould

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.

Scouting Notes
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, Encore and some fall-fruiting varieties. Watch for symptoms after periods of hail or severe weather.

Thresholds
None established.  

 

Advanced

Scientific Name: Erwinia amylovora

Identification
Fire blight is a bacterial disease which causes symptoms on leaves, canes, blossoms and fruit. The disease is caused by bacteria, similar but not identical to, the bacteria that causes fire blight on apples and pears.

Early symptoms include blackened veins at the base of new leaves. Black patches develop around the veins and progress to the entire leaf.  Infected shoot tips may droop or wilt downwards 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 infected tissue, especially in humid conditions.  Infected berries become hard, dry, and brown and remain attached to the pedicel.
Raspberry cultivars vary in response to fire blight. Table 1 ranks selected raspberry cultivars by relative resistance to fire blight infection in the lab. 

Table 1. Relative Resistance of Raspberry Cultivars to Fire Blight Infection

Cultivar1	Lesion length (cm)2
Royalty	2.6
Nova	3.2
Polana	3.9
Caroline	4.0
Heritage	5.2
Autumn Britten	4.9
Reveille	5.8
Killarney	6.1
Lauren	5.6
Latham	5.8
Canby	5.7
Algonquin	6.6
Boyne	6.5
Prelude	6.4
K81-6	7.5
Encore	7.5

¹ Cultivars are ranked from most resistant to least resistant.
² Plants were inoculated with three isolates 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.

Often Confused With

Raspberry cane borer  
Both fire blight infection and raspberry cane borer injury cause the tip of primocanes to bend over and wilt.Raspberry cane borer injury is distinguished by two zipper-like girdles above and below the point where the female lays an egg. Characteristics of recent fire blight infections include amber coloured ooze and blackened leaf veins.  

Botrytis Grey Mould
Both diseases can cause dry, hard, mummified fruit. In the case of fire blight, previously healthy leaf and cane tissue may be affected as well. Initially, fire blight infections exude an amber or milky ooze in humid conditions. It is important to identify fire blight infections soon after they occur because symptoms are indistinguishable from old botrytis infections later in the season. Also, Botrytis eventually colonizes tissue that was initially killed by fire blight.

Biology
E. amylovora causes severe infections on apple and pear trees while raspberry and blackberry plants are only infected sporadically and the disease remains localized. The bacterium will only spread from one bramble plant to another. Strains found on pears or apples will not cross-contaminate raspberry plants.

The pathogen overwinters in cankers on old fruiting canes. In the spring, the bacteria in these cankers rapidly multiply and serve as the initial source of inoculum. Wind, rainstorms and insects, such as tarnished plant bugs, earwigs, ants and aphids, spread the bacteria to nearby, uninfected plants. Warm, wet conditions increase the rate of infection. Once the bacteria have entered the plant, they multiply inside the vascular tissue, restricting the flow of nutrients and water.

Infections usually begin at the tip of primocanes and spread down up to 20cm. However, flowers, fruit clusters and lateral shoot buds may also become infected. Initially, these plant parts may take on a water-soaked appearance but will blacken and dry out with time. Once infected, berries become hard, dry and dark.   

Period of Activity
Fire blight infections develop 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.

Scouting Notes
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, Encore and some fall-fruiting varieties. Watch for symptoms after periods of hail or severe weather.  

Thresholds
None established.  

Management Notes

• 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 infected canes and remove from the planting as soon as fire blight is 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.
• See OMAFRA Publication 360: Fruit Crop Protection Guide (Chapter 3 Berry Crops), for information on registered products for fire blight control or suppression.