Individual study: The influence of mechanical cutting and fungal pathogen application on creeping thistle Cirsium arvense at Göttingen, Niedersachsen, Germany
Kluth S., Kruess A. & Tscharntke T. (2003) Influence of mechanical cutting and pathogen application on the performance and nutrient storages of Cirsium arvense. Journal of Applied Ecology, 40, 334-343
Creeping thistle Cirsium arvense can be a persistent perennial weed that causes problems in arable fields, grasslands and pastures, including within nature conservation areas. In order to develop an effective biological control technique, the influence of cutting and fungal pathogen treatments on this species was evaluated at the University of Göttingen, Niedersachsen, Germany.
Treatments: Treatments were applied to potted C. arvense plants in the field on fallow land. Pieces of horizontal thistle root derived from one clone were collected in spring 1998, and potted and reared in a greenhouse. In April 1998, when thistle plants were approximately 15 cm tall, they were potted separately and transferred outdoors. One of four treatments (10 replicates of each) were applied in June 1998 and 1999:
i) cutting thistles at 30 cm height to simulate mowing;
ii) application of a spore suspension of the rust fungus Puccinia punctiformis (a C. arvense pathogen) with a manual atomiser;
iii) cutting and rust application;
All treatments were covered for 48 hours with plastic bags to maintain high humidity. Weather conditions were comparably dry during the summer months (May-August) in 1998 and 1999.
Sampling: Samples of lower leaves were taken in August 1998 to assess the extent of rust spread. Thistle size and number of flower buds and fertile flower heads were recorded monthly in July and August 1998 and from May to August in 1999. Above-ground dry matter was measured at the end of September 1998. Plants were harvested in September 1999 and both above and below-ground dry matter measured.
Application of the rust fungus reduced above ground biomass in the first year. First year cutting reduced the number of thistle shoots but stimulated compensatory growth with an increased growth rate and biomass. However, a second year cut significantly reduced above-ground biomass, despite an increased growth rate. The number of flower heads (hence seeding potential) was greatly reduced by cutting and the combined treatments. The proportion of fertile flower heads was increased by cutting whereas the combination treatment strongly reduced it. Second year effects of treatment were generally more extreme than the first year indicating that long-term treatment with a combination of cutting and rust inoculation might result in additive or possibly synergistic effects compared to a single treatment.
Therefore whilst the traditional management technique of cutting was effective in reducing plant reproductive success, additional infection with the rust further restricted sexual reproduction indicating that combined treatments are more effective at controlling this perennial weed.
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