Livestock grazing for weed management - Ecological Management of Agricultural Weeds - page 421

Figure 9.4 Effects ofgeese and herbicides for control ofgrasses and unpalatable
weeds in the second year ofan ornamental tree nursery.(Adapted from Wurtz,
1995.)
evergreen Picea glauca .In the first year geese were placed on the plots when pal-
atable weed cover exceeded 5%. The lack of sufficient forage contributed to
trampling losses in the crop of greater than 30%. In the second year, the weed
cover threshold was increased to 15% and tree mortality declined by half to
levels similar to herbicide treatments.By the end of the second year,weed flor-
istic composition varied significantly among treatments. With geese only,
unpalatable broadleaf species such as Matricaria matricarioides , Polygonum avicu-
lare , and Tripleurospermum phaeocephalum had reached 50% cover and grasses
were unimportant. With a recommended herbicide for Christmas trees,
grasses such as Agropyron repens and Hordeum jubatum reached 50% cover and
the unpalatable broadleaf species were not present (Figure 9.4). By the end of
the second year in both the geese and herbicide treatments the build-up of
uncontrolled weeds resulted in decreased evergreen stem diameters.
An integrated strategy to control both grass and broadleaf weeds might
consist of larger flocks of geese herded slowly by workers hoeing ungrazed
weeds. This would reduce treading damage and management costs such as
fencing and vigilance against predators, and provide more complete weed
control (Wurtz, 1995).
Aftermath and fallow grazing for weed control
Grazing fields in fallow or after the cropping period takes advantage
of the forage value of weeds and crop residues and accelerates nutrient cycling
by converting vegetation to manures with more concentrated and more
readily available nutrients. Although there are few formal studies of weed