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102 P. Harris
The Future
Literature Cited
It is axiomatic that biological control is only justified if it is likely to produce a
satisfactory return on investment which is greater than can be obtained by other means
of control. The biological control of a suitable target weed is likely to require 20 scientist
years ($2 million at present costs) (Harris 1979). These costs are less if host specificity
testing has been done elsewhere. Determination of benefit requires quantification of
savings and increased yields minus any detrimental effects of control such as the
reduction of a nectar source. Costs and benefits that cannot be quantified in monetary
units should be expressed in ecological terms. The study should be published before
biological control is started. This gives an opportunity for objections to be voiced and
the proposal debated.
Classical biological control of weeds is likely to continue to be directed primarily against
introduced species that form extensive dense stands on uncultivated land. For this type
of problem there is a hgh rate of success and the return is excellent, particularly when
considered on.a national or a continental basis. There are, however, a limited number of
weed species that are prime targets in Canada. As work on these is completed or the
possibilities for biological control are exhausted, as is happening for C. arvense, the
programme will be directed increasingly against weeds of more minor importance. One
way of maintaining a favorable benefit-cost ratio is to tackle them as joint projects with
the United States or other countries so that the costs are shared and the benefits accrue
on an international scale. At present international cooperation is informal and this will
probably need to be replaced by more formal cooperative agreements against specific
target weeds.
There is room to increase the rate at which present projects are completed but the
long-term prospect is for a continued small Canadian participation in classicial biological
control of weeds. There has been an increase in staffing since the 1968 review (Harris
1971) that reflects the economic seriousness of some of the projects such as knapweed
and leafy spurge. Thus Agricultural Canada has increased its participation from 2 to 4
full-time scientists; McGill University (Macdonald College) has an active programme
that emphasizes pathogens; the Province of Alberta is recruiting a scientist, and the
University of British Columbia has a programme elucidating the effects of some of the
agents. The programme will probably stay at this level with more emphasis placed on the
selection of both the target weeds and the agents.
The main area for expansion is in augmentative biological control in which a pathogen
is applied periodically as a bioherbicide. Two centres, Macdonald College and the
Regina Research Station have started investigations in this area. The work has not been
reported in this review as it has yet to lead to the licensing of a bioherbicide in Canada.
The few bioherbicides currently in use in the United States are for weeds of crops that
are hard to control by other means (Templeton 1982). One ofthe attractions of bioherbicides
is that they can be produced in small amounts at a reasonable cost. Thus they can
be used for weed problems of minor crops in which the area involved does not justify the
development of a specific herbicide. The method has a profit potential so it is likely to be
developed primarily by industry and this could occur rapidly. The main obstacle to date
has been the lack of licensing regulations. These have now been drafted in the United
States and it is probable that Canada will adopt similar requirements. There is an initial
role for government research to get the industry started. Subsequently the government
role may be largely regulatory.
Ellison, L. (1960) Influence of grazing on plant succession of range plants. Botanical Review 26, 1-66.
Feeney, P. (1976) Plant apparency and chemical defense. In: Wallace, l.W.; Mansell, R.L. (Eds.). Biochemical interactions between plants
and insects. Recent Advances in Phytochemistry 10, 1-40. New York; Plenum Press.