The effects of cutting on pollen and seed production in ragweed
An Agriculture and Agri-Food Canada study obtained significant results in a greenhouse experiment involving the cutting of ragweed. Plants measuring 25 cm tall were cut to a height of 10 cm just before flowering. A second cut was made when plant regrowth had reached 25 cm in height.
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Unmowed ragweed plant produce flowers from 46 days after germination and up to 58 days after germination. The number of flowers produced varies anywhere between 5 and 30 inflorescences per plant with the highest number (95 inflorescences) being produced at 58 days after germination. If ragweed plants are mowed twice (41 and 51 days after germination), the production of flowers starts at 54 days and continues until 82 days after germination. However the number of flowers produced is much smaller ranging between 1 and 13 inflorescences per plant with a peak production of 32 inflorescences per plant at 68 days after germination.
These two successive cuts delayed flowering by 17 days and reduced the number of flowers.
Pollen production was reduced by a factor of 9 in the cut plants.
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Graph comparing the number of pollen grain produced by mowed and unmowed ragweed to demonstrate a 9-fold reduction from approximately 400 to approximately 50 in pollen count in mowed plant.
Cutting was associated with a decrease in the number and mass of seeds in a plant. Viable seed production was reduced by a factor of 5 in the cut plants. However, cut plants produced enough seeds to replentish the soil. This method will not reduce the number of plants present the following years.
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Graph comparing the number of viable seeds per plant reduced by mowed and unmowed ragweed to demonstrate a 5-fold reduction from approximately 200 to approximately 40 in viable seeds in mowed plant.
In summary, mowing twice - once before flowering in mid-July and 15-20 days later around mid-August - considerably reduce the amount of pollen released in the air.
© Her Majesty the Queen in Right of Canada, 2011
Cat. No. A52-188/2011E-PDF
ISBN 978-1-100-18867-6
AAFC No. 11485B