Minimizing environmental impacts of grassland weed management: can Cirsium arvense be controlled without herbicides?

Abstract

Pywell, R. F., Hayes, M. J., Tallowin, J. B., Walker, K. J., Meek, W. R., Carvell, C., Warman, L. A., Bullock, J. M. (2010). Minimizing environmental impacts of grassland weed management: can Cirsium arvense be controlled without herbicides? Grass and Forage Science, 65 (2), 159-174. IMPF: 01.10Invasion by undesirable plants, such as Cirsium arvense, can constrain attempts to conserve and restore biodiversity in extensively managed temperate grasslands, but control with herbicides can cause environmental harm. We contrasted herbicides with more environmentally sustainable weed control strategies. Six-year, large-scale randomized block experiments were established to determine optimum combinations of grazing management and mechanical or herbicide treatments to control thistles within lowland and upland grazing systems. Factorial combinations of tight vs. lenient grazing in spring and autumn with additional treatments of winter grazing were compared. Thistle control methods were applied in sub-treatments for the first 2 years: cutting twice yearly, herbicide wiping, and cutting followed by herbicide application. Thistle abundance decreased under lenient grazing in spring, autumn and winter at the lowland site, under lenient spring and winter grazing in the uplands and under cattle compared with sheep grazing. Herbicide wiping was the most effective control measure and cutting the least, but effects of all weed control sub-treatments were lost rapidly, so lenient grazing was sufficient to give long-term thistle control. Lenient grazing and herbicide wiping also caused small declines in non-target forb diversity. Control of creeping thistle can therefore be achieved without herbicides because lenient grazing in spring and autumn can decrease thistle populations to sufficiently low levels. Severe infestations can be more rapidly controlled using herbicides, but are better avoided at botanically diverse sites. Ecologically-based weed control strategies have great potential, but require well designed field experiments, which run for sufficiently long periods to allow community-level impacts to develop.Peer reviewe

Exotic-Dominated Grasslands Show Signs of Recovery with Cattle Grazing and Fire

“…Although domestic grazing is often the causative agent of exotic plant species dominance [31], careful manipulation of timing and intensity of grazing can reduce exotic plant species dominance [32]. Reducing cover of exotic plant species via grazing [33–36] can allow rarer plant species a chance to recover [37]. Using grazing to reduce exotic plant species cover does not work in every instance [38], and results will vary depending on the specific grazing regime employed [33].…”

Using strategically applied grazing to manage invasive alien plants in novel grasslands

“…Cirsium arvense; De Bruijn and Bork 2006) and Chrysanthemum leucanthemum (Olson et al 1997)). Pywell et al (2010) found the most effective control strategy for Cirsium arvense was low intensity grazing because it maintained a competitive cover of other plant species. Many unpalatable species have life-history stages that are palatable and sensitive to grazing, and the timing of grazing (and the intensity) can be altered to periods when the invasive species is most susceptible (Hartley et al 1984;Thomsen et al 1993;Rinella and Hileman 2009).…”

Does crotalaria (Crotalaria breviflora) or pumpkin (Cucurbita moschata) inter-row cultivation in restoration plantings control invasive grasses?

“…As a result, we may have a trade-off between the use of alternative methods of grass control and the development of the forest community under restoration. Nevertheless, green manures reduced spontaneous grass coverage compared to control plots (Favero et al, 2001) and that species richness is reduced in natural regeneration by the use of herbicides (Pywell et al, 2010). Therefore, this dichotomy must be further investigated in order to provide non-chemical methods of grass control in restoration plantings, but with minimum efficiency levels; otherwise, although we may avoid the risks of soil and water contamination associated with herbicide use, we may fail to achieve a well-established native tree community in degraded sites if ineffective alternative methods of grass control are adopted.…”

“…On the other hand, herbicide use, especially of glyphosate, enhances weed control in ecological restoration efforts (Ansley and Castellano, 2006;Carlson and Gorchov, 2004;Cornish and Burgin, 2005). While there is no consensus on the use of herbicides in riparian areas as a safe strategy of weed control in forest restoration, alternative, non-chemical methods of weed control are especially demanded and necessary (Pywell et al, 2010). Following this trend, in Brazil, legal instruments have allowed inter-row cultivation of green manures and short-lived crops with native tree species, such as the São Paulo state environmental office (SMA) resolution nº 8 of 2008.…”