Progress made on the management of Anisogramma anomala in USA
As recalled by Johnson et al. (1996) in their review, Anisogramma anomala (EPPO A1 quarantine pest) causes an insignificant and endemic disease of American hazel (Corylus americana), but induces a very serious canker on European hazelnut (Corylus avellana). In the past, the fungus was essentially present in the north-east of USA (where it has prevented the production of C. avellana) but was absent from the main hazelnut-producing regions situated in the West. 98 % of the North American production of C. avellana are situated in Oregon. Despite quarantine measures applied to avoid movement of plants from infected areas to the west of the Rocky Mountains, A. anomala was reported for the first time in the Lewis county (south-west Washington state) in 1973. In 1976, it was established in several orchards and by 1994 most of the Lewis county orchards were destroyed. In 1986, the disease was found in Willamette Valley (Oregon), the main production site. The disease moved southward at an average rate of 2 to 3 km per year. It is estimated that 30-40 % of the Oregon hazelnut trees are diseased or situated within a few km from a diseased orchard. ;Most orchards situated near the initial detection sites have been destroyed. In the face of such a serious disease, research programmes have been initiated to understand the biology of the fungus and its dispersal, to develop cultural and chemical control methods and to initiate breeding programmes for resistant cultivars.
Research has shown that A. anomala is an obligate parasite which cannot survive in dead hazelnut branches, that external symptoms appeared only after a 12 to 16 month period, and that infection occurred only through immature tissues near the apical meristem of growing shoots in spring. Several methods are being applied in Oregon to slow down the spread of the disease. Fungicide treatments (chlorothalonil, copper hydroxide, fenarimol, propiconazole) can provide protection when applied in spring, and 3-5 applications are needed at 8-17 day intervals. Disease scouting and pruning of diseased branches (generally in winter) which are then destroyed can reduce the inoculum. Removal and replacement of susceptible pollinizer cultivars is gradually performed. Elimination of volunteer and non-managed hazel trees is also recommended. The development of resistant cultivars is under study. A source of resistance has been found in an obsolete pollinizer cultivar (Gasaway) and may offer some good perspectives. In addition, Coyne et al. (1996) have developed an indirect ELISA method which allows a rapid detection and screening of potentially resistant cultivars.
Coyne, C.J.; Mehlenbacher, S.A.; Hampton, R.O., Pinkerton, J.N., Johnson, K.B. (1996) Use of ELISA to rapidly screen hazelnut for resistance of Eastern Filbert Blight.
Plant Disease, 80(12), 1327-1330.
Johnson, K.B., Mehlenbacher, S.A.; Stone, J.K.; Pscheidt, J.W., Pinkerton, J.N. (1996) Eastern Filbert Blight of European hazelnut - It's becoming a manageable disease.
Plant Disease, 80(12), 1308-1315.