New EFB strains infecting resistant hazelnut varieties
By now you likely have heard about the new eastern filbert blight (EFB) situation. Several hazelnut orchards with the single dominant Gasaway gene for resistance have been found with extensive EFB cankers. We have seen small, poorly developed cankers on resistant trees before but not like this. Genetic analysis indicates these are new strains of the fungus that have developed here in the PNW. Research by Oregon State University faculty is ongoing but until we have more information ALL hazelnut growers need to take action this winter and spring.
Experienced (old timer) growers already know what to do. You can skip over the basics below but new timers who have not dealt with this disease should read it all. Even better yet, seek out those growers who have been through this before. They are a wealth of practical information. You can also study up on this disease by going to the EFB Help Page: https://bpp.oregonstate.edu/efb
New Research
Your hazelnut commission has continuously supported and funded EFB research at OSU for many decades. Recent genetic testing has shown that the strains of the EFB fungus from orchards in the PNW are distinctly different from strains found in the eastern United States. These fungi are more similar to the original strain that was introduced into the PNW than those found in New Jersey, North Dacoda, Illinois or Minnesota. More concerning is that although these PNW strains are closely related, they are different. Researchers believe that multiple strains of this fungus can and likely will emerge in different areas of the PNW.
These new fungal strains have been found on many hazelnut cultivars with the Gasaway gene for resistance. These trees include Dorris, Jefferson, McDonald, PollyO, Theta, Wepster and Yamhill. The infected orchards are located both in the north and south Willamette Valley. Also, new strains have been found near Chehalis and Salkum, Washington and in British Columbia.
The Woodburn strains found on Jefferson trees have been inoculated onto other trees. This research is still continuing but it appears that McDonald (with the Gasaway gene) and Sacajawea (with quantitative resistance) are highly susceptible. Stay tuned as there is likely more information to come from this aspect of the research.
A new area of fungicide research has been focused on drenching the ground instead of spraying the canopy. Initial results with a FRAC 3 chemical have been encouraging. Right now the chemical is labeled for foliar applications as well as through a drip or microsprinkler system. Specific chemical recommendations can be found in the handbook referenced below.
The OSU hazelnut breeding program is still quite active. The cultivar, Lagerstedt, was just approved for release and carries an EFB-resistant gene from the Spanish cultivar Ratoli. Lagerstedt is among several varieties now in the OSU breeding program pipeline with different genetic resistance to EFB than is conferred by the Gasaway gene. The Gasaway gene is from linkage group 6 while Lagerstedt, by comparison, uses a gene from LG7.
Another major emphasis of crosses is focused on quantitative resistance. Quantitative resistance generally results in fewer and smaller cankers. Different sources of resistance will be “pyramided” (bread) into new varieties. Trials with these other resistance sources are underway. New promising selections are close to development but many still rely on the Gasaway gene.
Summary
Bottom line: We know what it takes to manage EFB, a combination of scouting, pruning and fungicides. It has been fantastic to use resistant cultivars and not have to manage this disease as hard but that time has passed. The new cultivars already in the ground still have other useful horticultural characteristics, new ones are on the way and optimism still resides for the future of this industry.
Acknowledgement
The research discussed is ongoing and from many different laboratories including those led by Dr. Nik Wiman, Dr. Alexandra Weisberg, Dr. Jared LaBoldus, Dr. Alex Zaccaron, Dr. Tom Molnar and Dr. Gaurab Bhattarai.
Please note the following resources that can help you understand the biology of this unique disease and give management recommendations: