Biological control of weeds is defined as the deliberate use of biotic agents to achieve suppression of the target weed population below economic damage thresholds (Rees et al. 1996). Biotic agents primarily involve insects and fungi (Harris 1979).

This project will attempt to build upon previous successes achieved in biological control programs in Nova Scotia as well as apply new information from on-going research across Canada to pasture cropping systems.

The five primary goals of this project are:

• To assess the current status of previously released biological control agents in Nova Scotia.

• To acquire, collect and rear insects for distribution within Nova Scotia and throughout Canada

• To monitor the establishment, development, and extent of damage of biological control agents.

• To identify indigenous insects having potential for incorporation into a biological control program.

• To determine compatibility of biocontrols with current pasture management.

This project involves native and introduced insects that have been previously introduced and released elsewhere in Canada for biological control of weeds. Greenhouse and field rearing provides a constant supply of insects without the burden of cross country shipping, during which some of the insects die due to handling and storage. It is more economical to be able to rear these insects in the Maritimes where they can be supplied in large numbers. In addition, these insects can be shipped to other areas of the country if desired.

The plan to be adopted is to set up permanent greenhouse and field populations of insects used for biological control of weeds. This may include insects not native to Canada, but which have been studied and proven safe to release under the athority of Agriculture and Agri-food Canada and the U.S. Department of Agriculture. Other insects available in eastern Canada would be collected, reared, and disseminated to areas where their current populations are low to non-existant.

Rearing of introduced insects

Insects will be obtained for release on their appropriate weeds. Plants will be maintained in the greenhouse and growth cabinets so that stock populations can be utilized for further study. All insects are not adapted to greenhouse rearing. For these, field collections will be made with release into field and sleeve cage nurseries.

The number of insects released, the number of release sites and the time of releases will depend upon availability of the insects. Release sites selected will have a uniform and dense target weed population and be guaranteed undisturbed for at least five years. Insects established in Nova Scotia will also be collected, reared, and distributed to other parts of Canada. All insects have been fully researched and approved for release in Canada to ensure they attack only the target weed and not any economically important plants. Methods for collection, rearing and release will be based on recommendations from AAFC Lethbridge Research Centre and provincial resource personnel involved with specific insect agents.

The release sites will be monitored for establishment of the insects and damage to the weed. Post release assessments will follow the rating system of Harris (1991), which includes agent abundance, damage and percentage control values. Subsequent assessments will monitor the initial release sites and allow for the determination of spread of the various insects beyond these areas. This will also allow for identification and investigation of other naturally occurring insects found on various weeds. It will be determined if these insects can be incorporated into this program.

      Herbicide use is often considered uneconomical for use in pasture and as a result weeds often go uncontrolled. The applied use biological control agents would provide economical control resulting in improvement of the pastures.

References:

Harris, P. 1979. Cost of Biological Control of Weeds by insects in Canada. Weed Sci. 27:2 p. 242-250.

Harris, P. 1991. Classical biological control of weeds: it's definition, selection of effective -agents, and administrative-political problems. Can. Entomol. 123: p. 827-849.

Harris, P. Longitarsus jacobaeae (Waterhouse) and L. flavicornis Stephens. Root Beetles . http://res2.agr.ca/lethbridge/weedbio/agents/alongflv_e.htm (28 March 2003)

Jensen, K.I.N., Harris P. and Sampson, M.G. (2002) Hypericum perforatum L., St. John’s wort (Clusiaceae). In Mason, P.Q. and Huber, J.T. Biological Control Programs in Canada 1981-2000. CABI Publishing, pp. 361-368.

Sampson, M.G. and A. Ingraham. 1989. Biological control of weeds in Nova Scotia, Final Report Project TD38. p.53.

Sampson, M.G. 1987. Biological Control of weeds in Nova Scotia. Final Project Report Canada/Nova Scotia Agri-Food Development Agreement TDP 1987-19.

Sampson, M.G. and T. McSween. 1992. Biological control of weeds in Nova Scotia, Final Report, Canada/Nova Scotia Livestock Feed Initiative Agreement, TD63 p.47.

McClay, A.S., Bourchier, R.S., Butts, R.A. and Peschken, D.P. (2002) Cirsium arvense (L.) Scopoli, Canada Thistle (Asteraceae). In Mason, P.Q. and Huber, J.T. Biological Control Programs in Canada 1981-2000. CABI Publishing, pp.318-330.

McClay, A.S. and De Clerck-Floate, R.A. (2002) Linaria vulgaris Miller, Yellow Toadflax (Scrophulariaceae). In Mason, P.Q. and Huber, J.T. Biological Control Programs in Canada 1981-2000. CABI Publishing, pp. 375-382.

McClay, A.S. and Peschken, D.P. (2002) Sonchus arvensis L., Perennial Sow-thistle (Asteraceae). In Mason, P.Q. and Huber, J.T. Biological Control Programs in Canada 1981-2000. CABI Publishing, pp. 416-424.

Mason P.G. and J.T. Huber. 2002. Biological Control Programmes in Canada, 1981-2000. CABI Publishing, New York. p.583.

Rees, N.E., P.C. Quimby, G.L. Piper, E.M. Coombs, C.E. Turner, N.R. Spencer and L.V. Knutson. 1996. Biological Control of weeds in the West. Western Society of Weed Science, Bozeman Montana.