Apple growers require effective disease control to protect both their individual crops and the long-term health of their orchards. One of the most damaging diseases affecting apple trees that must be controlled is fire blight. This disease, and the pathogen Erwinia amylovora, is a major focus area of research from Dr. George Sundin, Michigan State University.
For more than 12 years, we have worked on short-term goals for fire blight control, including studying and optimizing the best disease-control materials under field conditions and documenting the occurrence and spread of streptomycin resistance in the pathogen E. amylovora. We also have worked on long-term goals for fire blight, such as studying the disease interaction between the pathogen and host with hopes to either develop host resistance against fire blight or target pathogen virulence traits for disease control.
Additionally, research by my team at Michigan State University explores disease management of fungal tree fruit diseases and genetics and mechanisms of fungicide resistance. Over the years, we’ve seen gaps in knowledge, but the goal remains clear: a full understanding of what the bacterium does to take over plants and how horticulturalists and researchers — and, ultimately, growers — can control it.
One aspect our research team studies in depth about fire blight is the “ooze,” which is the output of approximately one-third of the cells from a tree as the E. amylovora spreads. Ooze contains pathogen cells and sugars and facilitates the spread of the fire blight pathogen between trees. Cells can be spread from ooze by rain and wind; also, insects such as flies are attracted to ooze and can spread pathogen cells on their bodies to apple flowers and shoots. Our studies have shown the critical nature of ooze to the spread of fire blight as well as how a reduction in ooze formation is an important part of reducing fire blight.
With that, two major reasons arise for controlling fire blight:
- Fire blight can kill trees. Growers want and need orchards to last 20 to 30 years or more, so when trees die and are removed due to fire blight, that has a major impact on orchard blocks.
- Heavy infections spread extremely quickly. Blossom blight (which spreads through the apples’ flowers) can be costly as severe blossom infection can initiate fire blight epidemics.
Specifically, throughout Michigan, apple growers have seen an increase in resistance to streptomycin, which for many years has been the most effective control of fire blight. Since 2006, we’ve worked with many commercial products, including KASUMIN® Bactericide, to explore more ways to assist in controlling fire blight. We determined that the efficacy of KASUMIN is similar to streptomycin, and this product controls streptomycin-resistant strains. Another important point is there are no uses of KASUMIN outside of plant agriculture, which reduces concerns of the Environmental Protection Agency (EPA) and the general public about resistance.
KASUMIN was registered and became available to pome fruit growers in the states of Michigan, New York and Washington in fall 2014, and California registration was granted in 2018. We have used KASUMIN in Michigan for several years, and the control it provides has given New York and Washington growers another tool to fight fire blight. Additionally, growers should remember that kasugamycin, the active ingredient in KASUMIN, is most effective when it is incorporated in a rotation program, as well as when it is applied preventively.
ABOUT THE AUTHOR
George Sundin received his bachelor’s degree in biology at Pennsylvania State University and credits William Merrill with stimulating his interest in plant pathology. Dr. Sundin also earned a master’s degree in plant pathology from Michigan State University and his Ph.D. in plant pathology from Oklahoma State University. Sundin started his faculty career in the Department of Plant Pathology and Microbiology at Texas A&M University with a research emphasis in phytobacteriology. In 2002, Sundin joined the Department of Plant Pathology at Michigan State, where he is currently a professor and extension specialist with responsibilities in tree fruit disease management.
