Potential new aggressive EFB strain infecting resistant hazelnut varieties
This alert is intended to inform the Oregon and PNW hazelnut industry about some disturbing observations of eastern filbert blight (EFB) on resistant hazelnut varieties. Infections have been examined by OSU, members of the Oregon Hazelnut Commission (OHC), the Nut Growers Society (NGS), the Industry Office, and experienced growers. Research is ongoing, but all have expressed a high level of concern and alarm about the severity of these infections. These EFB Infections are characterized by very aggressive cankers with fully developed stromata and production of ascospores indicating the pathogen is actively reproducing on resistant plant material (Fig 1.). These symptoms are comparable to infections that are familiar from highly susceptible varieties like Ennis. Varieties where we have seen these new severe EFB symptoms include Jefferson, Theta, Dorris, Yamhill, McDonald, and Wepster, all of which have the Gasaway gene for resistance to EFB. Significant numbers of spores have already been released over a period of years from some of the infected orchards of concern.
Currently, it appears that the most immediate threat from this more aggressive EFB is geographically restricted to the northern Willamette Valley from west of Woodburn and north to Donald and Hubbard, where we have concentrated initial survey efforts. However, we know that EFB historically made big jumps between orchards and it is very difficult to predict the spread of this disease. Our survey efforts are limited at this time, but we are confident we are seeing spread between adjacent plantings, particularly northward with prevailing winds. We cannot rule out the possibility that the infections could have originated with planting stock from elsewhere in the Valley, or that the problem began somewhere else entirely. As a result, we cannot say that we know the full extent of the issue at this time.
We need your help. All growers, field consultants and agronomists should be aware of this situation and should be scouting for EFB in resistant hazelnut varieties. Winter is the best time to scout for cankers. Please report finds of aggressive EFB infections in resistant varieties. Include contact information, location, variety, age of planting and estimated percentage of trees infected. We are specifically focused on EFB symptoms on resistant varieties that are showing black stromata, possible flagging of leaves, and evidence of aggressive canker growth (Fig. 1).
Growers in the vicinity of the focus area described above should plan on implementing a full EFB management program including pruning of diseased wood, destroying infected wood by burning or chipping, and implementing a fungicide spray program commencing between budswell and budbreak. Growers with orchards outside the initial focus region may also wish to implement a management program. Remember, there is no visual indication of disease until the second season after infection, so there is likely more disease present than is immediately evident. Growers with mature plantings of susceptible varieties are encouraged to maintain a strong EFB management plan as susceptible varieties could also host a more aggressive pathogen without any apparent changes in symptoms.Fortunately, we have a solid understanding of EFB biology and effective management strategy.Many growers are successfully managing EFB on susceptible varieties through pruning and spraying. Please note the following resources that can help you understand the biology of this unique disease and give management recommendations:
- The PNW Plant Disease Management Handbook
- 2023 Hazelnut Pest Management Guide
- The Eastern Filbert Blight Help Page
The PNW hazelnut industry has made a huge comeback from the devastating impacts of eastern filbert blight (EFB) with resistant varieties from the OSU Hazelnut Breeding Program. However, important threats from EFB remain, including further accidental introductions of the causal pathogen Anisogramma anomala from the Midwest and the mid-Atlantic US, where there are additional strains of the pathogen that cause devastating EFB on OSU varieties with Gasaway gene resistance. While a control order protects Oregon from importation of infected hazelnut material from outside the state, it is hard to detect violations and thus difficult to enforce.
Another threat from EFB comes from within. We have put great pressure on our resistant varieties, challenging them to resist the pathogen when interplanted in orchards with susceptible varieties, or planted adjacent to diseased orchards where there are tremendous inoculum loads. This pressure increases the likelihood that a new strain could emerge. Often, we have not sprayed new varieties against EFB even in the presence of high levels of inoculum, giving a potential foothold to new variants of the pathogen.
For years, occasional EFB infections on varieties with single gene Gasaway resistance have been observed. Often, these infections occur when trees are very young, and symptoms of the disease fade with maturation. Sometimes perennial EFB cankers take hold in trunks, which can kill the tree, or in branches. However, the difference is that the EFB infections we are used to seeing do not produce fully developed stromata (Fig 1), which are the raised, football-shaped bumps that erupt through the bark. The stromata produce the ascospores that become airborne and initiate new infections on growing shoots during wet periods in spring. The absence of fully developed black stromata on EFB cankers indicates active resistance. Such infections are not the concern and need not be reported. Example photos of this non-spreading form of EFB infection are in PNW Plant Disease Management Handbook.
Contact: Nik Wiman, OSU Extension Orchard Specialist, Jay Pscheidt, OSU Extension Plant Pathologist, or Colleen Nihen, Executive Director, Hazelnut Industry Office for questions or to report severe EFB symptoms with fully developed stromata (Fig. 1) on hazelnut varieties with genetic resistance to EFB: Jefferson, McDonald, Wepster, Dorris, Yamhill, PollyO and pollinizers.