- Fruits: cherries, general tree fruits
- Crop Production: application rate management, biological inoculants
- Education and Training: on-farm/ranch research
- Pest Management: biological control, cultural control
- Production Systems: general crop production
- Sustainable Communities: sustainability measures
A series of experiments to explore the impacts of temperature, inoculum load, and delayed inoculation on re-isolation of Pseudomonas syringae pv. syringae (PSS)from pruning wounds of sweet cherry. Report on progress of the repeatable infection system to test potential control products for infection of PSS. Temperatures 10ºC and 20ºC have no impact on pruning wound resistance development for at least 10 days after pruning. Recommended inoculum loads for a repeatable infection system are 105 and 103 cfu/mL. Preliminary report on potential efficacy of Kasumin as a PSS control.
Bacterial canker (caused by Pseudomonas syringae pv. syringae, PSS) can cause death of spurs, loss of limbs, decreased yields, and tree mortality. Once the bacteria enter the tree, the infection may become systemic making treatment impossible. The only way to overcome the disease is to prevent the initial infection. Late spring frosts, after a warm March in 2012, subjected many sweet cherry trees in Michigan to damage and subsequent bacterial canker infection which killed the infected spurs. Sweet cherry spurs bear fruit for several years, and the loss of these spurs will severely reduce yields for 2-3 years as the trees replace lost fruiting area with new growth. In a canopy training system trial that was infected with bacterial canker in Clarksville, Michigan, the number of dead meristems (which includes shoot and spur meristem death) ranged from 30 to 120 dead meristems per tree across all training systems (Lillrose & Lang, unpublished). Similar damage was seen throughout Michigan and has influenced grower yield in subsequent years. Damage is not limited to growing points; when spur infections migrate into the woody tissues, they create cankers that can girdle branches causing loss of limbs. These infections may become systemic, ultimately causing tree mortality. Young trees are more susceptible to bacterial canker, creating a concern for the establishment of new orchards because of the high investment cost of planting trees and the 3-4 years of orchard maintenance before marketable yields are attained.
The future uncertainties of climate change (i.e., an increasing incidence of temperature extremes) raise concerns that infections of this magnitude might become more prevalent and possibly cripple the sweet cherry industry. This problem is particularly important in the Midwest region where cool, wet weather in spring favors PSS inoculum growth. It is essential that we understand the factors contributing to PSS growth and infection of sweet cherry so growers can reduce inoculum during critical times when the tree is susceptible to infection.
Only using sprays (i.e., copper) to target bacteria when trees are most susceptible may help to slow the development of resistance in PSS, which can occur with overuse of pesticides. It can also reduce costs for growers and impacts on the environment.
Successful bacterial canker infections result from the convergence of three parameters: 1) a sufficient bacterial population, 2) an infectious environment, and 3) a susceptible host. Bacterial population sizes are influenced by many factors, including temperature and free moisture. Population sizes rise in response to rain events (Latorre et al., 1985). In controlled environments, free moisture increases infection when bacterial populations are low, but doesn’t impact infection under higher bacterial pressure. In the field, bacterial populations are under moisture and nutrient stress, and free water enables them to increase. Temperature increases infection rates for twigs up to 20?C (Latorre et al., 2002). In the lab, bacteria grow faster with increasing temperatures between 0-33?C, then growth slows at higher temperatures (Young et al., 1977). PSS have been isolated from tree cankers in the winter and early spring, but were undetectable during summer (Latorre et al., 1985). These higher seasonal populations were probably in response to the lower temperatures and the free moisture at that time of year.
Environment interacts with both the bacterial population size and tree susceptibility. It is hypothesized that wound healing rate is influenced by temperature (under investigation by Lillrose & Lang). Trees become susceptible through wounding events such as pruning, leaf scars in autumn, and freeze-damage of blossoms. More research is needed to understand the interactions of environment, inoculum load, and host susceptibility in bacterial canker infection.
Two SARE projects have relevance to this proposal. One examined the commercial viability of organic sweet cherry production using insect-exclusion netting (Project number LNE03-182). Success was limited by wind-caused branch abrasions that led to bacterial canker infections (Jentsch, 2007). This illustrates the importance of understanding the environmental and horticultural factors that make wounds susceptible to infection, so growers
can focus on strategies to reduce inoculum at those periods.
Another SARE project began in 2012 to study Pseudomonas syringae in blueberry (Project number FW12-074). This research examines the affect of wind turbines on frost-induced bacterial blight in blueberry, while monitoring environmental conditions (Uppal, 2012). Uppal’s research complements the proposed study because sweet cherry infections also occur from freeze damage. Data from the blueberry study could be applied to use of wind turbines in sweet cherry. Uppal’s study does not address woody tissue infections caused by pruning or leaf scar invasion, which is important for overcoming sweet cherry bacterial canker in the North Central Region.
It is essential to understand the environment’s influence on bacterial canker infections to help growers target the bacterium at crucial infection points. This will reduce spray use, save growers time and money, and reduce selection for resistance. The development of a repeatable infection system will enable rapid testing of potential control measures for bacterial canker that will increase sustainability for an expanding North Central (and Northeast) region sweet cherry industry.
Jentsch, P. 2007. Final report for: Determining the commercial viability of an exclusionary production system using disease-resistant columnar apple and sweet cherry cultivars. Available at:
Latorre, B., Gonzalez, J., Cox, J., and Vial, F. (1985). Isolation of Pseudomonas-syringae pv. syringae from cankers and effect of free moisture on its epiphytic populations on sweet cherry trees. PLANT DISEASE 69, 409–412.
Latorre, B., Lillo, C., and Rioja, M. (2002). Effects of temperature, free moisture duration and inoculum concentration on infection of sweet cherry by Pseudomonas syringae pv. syringae. PHYTOPARASITICA 30, 410–419.
Uppal, P. 2012. Proposal: Study and Control of Pseudomonas Syringae on Blueberry Plants. Available at:
Young, J., Luketina, R., and Marshall, A. (1977). Effects on temperature on growth in vitro of Pseudomonas syringae and Xanthamonas-pruni. JOURNAL OF APPLIED BACTERIOLOGY 42, 345–354.
Objective one: To develop a rapid repeatable infection system for leaf scar and pruning infections which will allow for rapid testing of new potential controls.
Objective two: To help determine the conditions that make sweet cherry more susceptible to bacterial canker infection to allow growers to try to prune when trees are less susceptible or spray to reduce leaf scar infection at key infectious periods.
Objective three: Test hypothesis from previous pruning experiments in the field to test pruning timing and effectiveness of a biocontrol for reducing infection.