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188 M. G. Maw
Recommendations
Literature Cited
bination, however, may not be as important as once thought. New races appear first in the
main north-south rust population, and only later become established in populations
cycling on buckthorn. (Simmons M.D. personal communication 1983).
Infections of rust due to buckthorn are usually very local but can result in complete
loss of the crop near buckthorn. Infection levels usually decline linearly with distance
from the buckthorn (Harder 1975) and a few hundred meters from the source is
sufficient to make a significant difference in infection incidence. Growers must either
avoid planting oats near buckthorn or eradicate it from their farms. Buckthorn is so
widespread and persistent that complete eradication is not feasible.
Biological control of buckthorn appears to be the only course to lessen the impact
of crown rust on oat production. It is not expected that introduced bi;:'logical agents
will eradicate buckthorn, but they might add to the stress of climate and soil type to
slow the spread of the shrub. Also, it is expected that any reduction in leaf surface will
aid in diminishing rust inoculum early in the season when the greatest injury is caused
to the oat crop. Not many insects find buckthorn an attractive food source because of
the feeding deterrent chemical, emodin (Trial & Dimond 1979). The original sources of
the North American populations of buckthorn are not known and there could be
different biotypes containing varying amounts of emodin. This may make selection of
effective biological control agents difficult.
Surveys for phytophagous insects in Europe found no species specific to R.
eathartiea, although the Lepidoptera Seotosia vetulata and Thecla spini exhibit a
degree of specificity to Rhamnaceae.
Thus when attempting to control buckthorn biologically, one has to consider that
species other than R. eathartiea will be attacked. The degree to which these other
species will be damaged must be determined in the screening tests, and decisions made
as to whether damage and possible loss of other species of Rhamnaceae can be
tolerated.
Even though R. eathartiea is the source of early infection of oats by crown rust and is the
site of the aecial stage of the rust, its complete eradication would at best result in only a
reduced incidence of the disease and the appearance of new rust races. Therefore. it is
recommended that biological control work on R. cathartiea be discontinued.
Bassett. 1.1. (1958) A sUlVey of the European buckthorn and common barberry in southern Manitoba. Science Service, Division of Botany
and Plant Pathology, Canadian Department of Agriculture Ottawa, 22 pp.
Dietz, S.M. (1926) The alternate hosts of crown rust, PucciniD corofUlta Corda. Jounuzl 0/ Agricultural Research 33, 953-970.
Fernald. M.L. (1950) Gray's manual of botany. American Book Corp., New York, 1632 pp.
fleischmann. G. (1963) Crown rust of oats in Canada in 1963. ConodiDn Plant Disease Survey 43,168-172.
fleischmann, G. (1968) Crown rust of oats in Canada in 1968. CatuldiDn Plant Disease Survey 48,99·101.
fleischmann, G. (1969) Crown rust of oats in Canada in 1969. Canadian Plant Disease Survey 49,91-94.
fleischmann. G.; Samborski, D.l.; Peturson, B. (1963) The distribution and frequency of occurrence of physiologic races of Puccinia
coronata Corda. f. sp. avenae Erikas. in Canada. CanaditJn Journal of Botany 41, 481-487.
Godwin, H. (1943) Rhamnaceae. Journal of Ecology 31, 66-92.
Hanson, E.W.; Gmu, G.R. (1979) The buckthorn menace to oal production. University of Wisconsin Extension Bulletin A 2860,2 pp.
Harder, D.E. (1975) Crown rust of oats in Canada in 1974. Canaditln Plant Disease Survey 55, 63-65.
Harder, D.E. (1978) Crown rust of oats in Canada in 19n. CafUldian Plant Disease Survey 58, 39-43.
Harder, D.E.; McKenzie, R.l.H. (1974) Crown rust of oats in Canada in 1973. CafUldian Plant Disease Survey 54, 16-20.
Malicky, H.; Sobhian, R.; Zwolfer, H. (1970) Investigations on the possibilities of a biological control of Rhamnus cathartica L. in
Canada. Host mnges, feeding sites, and phenology of insects associated with European Rhamnaceae.
Zriuchri/t fUr angewantlte Entomologie 6S, n -97.