Cause Xanthomonas arboricola pv. corylina (formerly Xanthomonas campestris pv. corylina), a bacterium that attacks buds, leaves, branches, and trunks. Occasionally it attacks nuts but seldom invades roots. Tree mortality due to this disease is commonly found in orchards the first few years after planting. The most serious phase of the disease is trunk girdling and killing of trees up to 8 or 10 years old where generally only 1- and 2-year-old twigs are attacked and killed. Rain splash or the movement of infected nursery stock spreads the bacteria. Seedborne transmission has been reported but no data is presented to support the claim. Infections are indirect, through wounds or by bacterial invasion of blighted buds and shoots of current-season growth. The disease has been associated with high stress sites and dryland production.
In Italy, higher disease incidence was found in regions with higher rainfall and a greater difference between high and low temperatures during frost events. They also found higher disease incidence for soils with higher nitrogen levels.
Symptoms Small, angular or round, yellowish green, water-soaked spots develop on leaves, later turning reddish brown. Buds may turn brown and fail to leaf out. Shoots may develop but are infected. The first infections on current-season stems consist of dark green water-soaked areas on bark, which turn reddish brown. Lesions may girdle stems and kill them. Dead leaves often cling to girdled stems a long time. Lesions or cankers may extend into the main scaffold or trunk. Use a pocket knife to determine the extent of canker development. Lesions may be wet and ooze in spring. Can be confused initially with flathead borer damage.
- Plant pathogen-free nursery stock in early winter. Do not let roots dry out.
- Prune out infected twigs and branches. Make cuts 2 to 3 ft below affected branches. Soak pruning tools between cuts with shellac thinner (70% ethyl alcohol), 10% Clorox (which is corrosive), Lysol, ZeroTol, Oxidate, or X3. Disinfestants work better on clean equipment with long contact times. Use the two pruners method: having one soaking in the solution of choice while using the other; then switch pruners, leaving the one you just used to soak, and the one that had been soaking, to continue pruning. If used as a soak, change solutions every 2 to 3 hours.
- Control sunburn during summer using shields or white paint on trunks.
- Mulch around the base of newly planted trees with chipped, composed tree debris to reduce moisture stress.
- Irrigate during the first 3 summers after planting to reduce moisture stress.
- Apply nitrogen fertilizer in the spring based on leaf tissue analysis the prior August.
- A hot water soak of nursery stock for 45 min at 108°F was effective to reduce bacterial populations.
Chemical control Apply sprays in late August or early September before the first heavy rains. If fall rains are heavy, apply another spray when 75% of the leaves have dropped. Note that most copper products do not allow use until after harvest. Spring applications do not improve disease control over fall applications alone and spring applications alone helped a little in 2 out of 5 trials. Copper-resistant bacteria were not found among isolates collected in 2018-19 but minimize copper use so resistant bacteria do not develop.
- Badge X2 at 7 to 20 lb/A. Oregon and Washington only. Can be used past harvest. Group M1 fungicide. 48-hr reentry. O
- Basic Copper 53 at 8 to 11.3 lb/A plus 1 pint superior-type oil/100 gal water as a postharvest spray. 48-hr reentry. O
- Bordeaux 6-3-100. Group M1 fungicide. O
- ChampION ++ at 7 to 10.5 lb/A Can be used only after harvest. Oregon and Washington only. Group M1 fungicide. 48-hr reentry. O
- C-O-C-S WDG at 11.6 lb/A plus 1 pint superior-type oil/100 gal water. Can be used only after harvest. Group M1 fungicide. 48-hr reentry.
- Copper-Count-N at 8 to 12 quarts/A. Can be used only after harvest. Group M1 fungicide. 48-hr reentry.
- CS 2005 at 64 to 128 oz/A. Group M1 fungicide. 48-hr reentry. O
- Cueva at 0.5 to 2 gal/A after harvest. Oregon and Washington only. Group M1 fungicide. 4-hr reentry. O
- Cuprofix Ultra 40 Disperss at 10 to 15 lb/A. Oregon and Washington only. Group M1 fungicide. 48-hr reentry.
- Kocide 3000-O at 7 to 10.5 lb/A plus 1 pint superior-type oil/100 gal water. Can be used only after harvest. Group M1 fungicide. 48-hr reentry. O
- Monterey Liqui-Cop at 1 to 2 Tbsp/gal water. H
- Nordox 75 WG at 8 to 13 lb/A. Can be used only after harvest. Group M1 fungicide. 12-hr reentry. O
- Nu-Cop 50 DF at 8 to 12 lb/A with 1 pint superior-type oil/100 gal water. Can be used only after harvest. Group M1 fungicide. 48-hr reentry. O
- Previsto at 2 to 4 quarts/A after harvest only. Group M1 fungicide. 48-hr reentry. O
- Aviv (Bacillus subtilis strain IAB/BS03) at 10 to 30 fl oz/100 gal water. Unknown efficacy. Preharvest interval not specified. 4-hr reentry. O
References Moore, L.W., Lagerstedt, H.B., and Hartmann, N. 1974. Stress predisposes young filbert trees to bacterial blight. Phytopathology 64:1537-1540.
Lamichhane, J.R., Fabi, A., Ridolfi, R., and Varvaro. L. 2013. Epidemiological Study of Hazelnut Bacterial Blight in Central Italy by Using Laboratory Analysis and Geostatistics. PloS one 8:e56298.