Weed Control News

Biological Control of St. John's Wort

In many areas of North America the introduced weed Hypericum is controlled by several leaf feeding Chyrsolina beetles. A highly virulent and host specific pathogen, the fungus Colletotrichum gloeosporioides, was recently discovered in Nova Scotia. Kimberly Morrison examined the relationship between this pathogen and the beetle C. hyperici as part of her Masters degree program at Acadia University in Nova Scotia.

Defoliation alone by larval and adults stages of the beetle never exceeded 25-50%. Plant mortality (36-96%) was always related to infection by the fungus and few infected plants survived the winter. The beetles may be important in the spread of the disease, however, as they carry fungal spores on their bodies. Under controlled conditions, contaminated beetles infected up to 36% of healthy plants. In outdoor cages, releases of adult beetles contaminated with spores onto potted plants gave up to 75% control. Weed mortality has a major effect on the beetle, as plants often die before larvae complete their development.

This study demonstrated the potential of enchancing weed control by integrating a plant pathogen with a host-specific insect.

For more information contact Klaus Jensen at

Atlantic Food & Horticulture Research Centre
Kentville, N.S.
phone (902) 679-5761
fax (902) 679-2311

- Source: Pest Management News 8(4): 6, Winter 1996

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