Managing Michaelmas daisy


At Ashstead Common National Nature Reserve in Surrey (southern England), grassland had been invaded by a number of non-native plant species. One, Michaelmas daisy Aster spp., was considered worryingly invasive with native plants suffering over large areas where a tall, dense Aster sward had developed. Hand-pulling was attempted but abandoned as it proved impractical and ineffective. Alternative methods of control were required.

In 1997, Aster control trials were initiated to evaluate the effectiveness of mowing, rolling, herbicide-spraying and grazing. Trial areas were chosen both for their dense stands of Aster (about 95% cover, with 17 native grassland species occurring at low density) and isolated locations (less susceptible to colonisation via seed). A control area (no management) was also established.

Mowing: A flail-collector type mower was used (cutting height of 5 cm) mounted on a compact tractor, which picks up cuttings and dry vegetation. Each year a cut was undertaken after August surveys, i.e. before the Aster flowered (mid-September), the aim being to weaken the under-ground rhizomes and prevent seeding.

Rolling: A roller technique (heavy roller drawn by tractor) was introduced in 1999. It works by crushing the stems which causes the sap to weep, thereby reducing the quantity of sugars transferred to and stored in the rhizomes over-winter.

Herbicide spraying: No specific herbicide for Aster is available, therefore the broad spectrum herbicide Roundup (active ingredient glyphosate) was used. Application was late in the season (September) to reduce non-target damage to other plants. Prior to spraying, aiming to create  the most advantageous conditions for herbicide application, a shorter Aster sward was required. Mowing was undertaken in early August designed to create 100% Aster cover at a height of less than 15 cm.

Grazing: Preliminary observations indicated that goats Capra hircus only nibbled Aster leaves, whilst Sussex cows ate them, especially early in the season before plants became too woody. They also tended to pull and often uproot Aster plants. Cattle were therefore used to graze the Aster.

Monitoring: Each year (1997-99) in all study areas, during the first week of August, 20, 1 m² quadrats were surveyed and plants recorded using the DOMIN scale to assess vegetation response.

Mowing: Mowing increased Aster cover in the first year, probably as a result of growth from the rhizomes. However, after mowing in the two subsequent years, stem abundance and vigour of growth declined. Although species diversity increased in response to the first cut, a varied sward only really developed as the Aster decreased in the second and third years. The results indicate that it is possible to control Aster by annual mowing . It should be noted that mowing may kill small animals and damage grass tussocks and anthills.

Rolling: Although only surveyed once, rolling reduced Aster cover from an estimated 80% containing 20 plant species prior to rolling, to 30% cover containing 24 species after.

Herbicide spraying: Mowing prior to spraying took place late in the growing season but by the time of spraying in September, regrowth had only formed 50% cover (leaf rosettes close to the ground). Despite this, results were encouraging. After the first spraying, Aster cover declined by 95% to less than 5% cover in the following year. Initially only 13 other plant species were recorded in the spring/summer following initial spraying, rising to 30 in the third year. It was considered that a desirable sward was created by a single Roundup application.

Cattle grazing: Grazing greatly reduced Aster vigour and abundance; 95% cover was reduced to 20% in one year, with the number of other plant species rising from 13 to 17. Overall, grazing was deemed the best management option.

Note: If using or referring to this published study, please read and quote the original paper.

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