unpublished).Įrwinia amylovora can also infect susceptible one- and two-year-old tissue directly through wounds (e.g. For example, in a Michigan study, fire blight bacteria moved an average of 6 cm per day in new growth and 4 cm per day in woody growth in five-year-old Gala, which equates to approximately 11 inches per week (Olive et al. Pathogen cells migrate inside the tree well ahead of visible symptoms where they can accumulate in other susceptible tissue such as one-year old shoot tips and susceptible rootstocks causing infections distant from the original infection (Bogs et al. It kills young host tissues as it progresses creating characteristic strikes and cankers. If the pathogen is successful in infecting the developing fruitlet, the disease spreads through the intercellular spaces and then the vascular system of the tree (xylem) (Momol et al. Insects and rain can move the pathogen to additional flowers (Johnson et al.
Once initial blossoms are infested, ooze droplets form with as many as a billion bacterial cells per droplet (Slack et al.
Bacterial cells can then be washed down the style into the floral cup by water (usually from rain or heavy dew) where they can invade flowers through the nectaries (Thomson 1986). Pathogen cells multiply quickly on nutrient rich floral stigma when temperatures are warm (70 to 80° F is optimal for the pathogen) (Ogawa and English 1991, Pusey and Curry 2004). Pathogen cells can also be moved from old cankers to flowers by splashed and wind-blown rain. This ooz.e is attractive to bees, flies and other insects who transfer the blight pathogen to flowers (Van Der Zwet and Keil 1979). 2022) and when humidity is high in the spring the pathogen ooz.es out of these cankers (Figure 5). In 7 to 62% of cankers active cells survive the winter (van der Zwet and Beer 1991, Santander et al. Signs and SymptomsĮrwinia amylovora overwinters in the living tissue around canker margins (Biggs 1994, Teviotdale 2011). amylovora has a wide host range within Rosacea and Rubus with reports on about 200 species including crab apple, hawthorn, mountain ash and Bradford pear (Momol and Aldwincklke 2000). Host RangeĬonsidered a problem for apple and pear, E. Above 95° F cell density on and in the plant can actually decline (Pusey and Curry 2004). At air temperatures above 70° F, the rate of cell division increases rapidly and is fastest at 80° F. Cell division is minimal below 50° F, and relatively slow at air temperatures between 50 to 70° F. The bacterium grows by splitting its cells and this rate of division is regulated by temperature. Casual Organismįire blight is caused by Erwinia amylovora, a gram-negative, rod-shaped bacterium. In Washington there have been minor outbreaks annually since 1991 and serious damage in about 5 to 10 percent of orchards in 1993, 1997, 1998, 2005, 2009, 2012, 2015, 2016, 20. Increased acreage of highly susceptible apple varieties on highly susceptible rootstocks has increased the danger that infected blocks will suffer significant damage.
Infections commonly occur during bloom or on late blooms during the three weeks following petal fall. Updated April 13, 2023.įire blight is an important disease affecting pear and apple. By Tianna DuPont, Associate Professor, Washington State University Tim Smith, Washington State University Tree Fruit Extension Specialist Emeritus Ken Johnson, Professor of Plant Pathology Oregon State University Youfu Zhao, Washington State University.
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