Livestock grazing for weed management - Ecological Management of Agricultural Weeds - page 410

2. To apply grazing pressure when weed vulnerability is greatest , farmers must rou-
tinely observe and analyze the floristic makeup of the forage and weed biomass.
Timely management decisions vary with weather conditions,changing
economic factors,and with the species,number,and condition ofthe
animals that the farmer has at the moment.As the botanical composition
ofa grazing area fluctuates or changes,farmers must adjust their prac-
tices.
3. To manipulate grazing pressure for weed management , farmers must have access to
the appropriate species and number of animals and the means , such as fencing , to
confine them in the indicated grazing area. Animal grazing pressure must be
increased or reduced to coincide with weed vulnerabilities and to main-
tain the productivity ofdesirable crop or forage species.At the same time
the farmer must also insure the animals'nutritional needs.Animals with
low nutritional needs may be best suited for heavy grazing ofweedy
fields,but weed problems can also be prevented with highly productive
animals by adjusting grazing season and intensity.
Matching grazing strategies with weed problems
Grazing animals are useful for three types of weed control. First,
grazing can reduce the total biomass of possible competing vegetation, for
example, in timber tree plantations or orchards. Second, grazing can be
directed at the biomass of a single species or groups of species. Geese grazing
for grass seedling control in horticultural crops and goat grazing for shrub
control on sheep or cattle pastures illustrate this case. Third, grazing can be
used to reduce weed seed production and survival as, for example, when
animals graze weeds and crop residues during fallow periods.
A grazing plan to reduce specific weed problems should consider differ-
ences in animal grazing habits, vulnerability of weed species to grazing, and
the plant community response to grazing.
Grazing species differences
Three sets of characteristics are particularly important for under-
standing the effect of different types of grazing animals on weeds and using
animal species differences in grazing management for weed reduction.
First, grazing animal species have different grazing actions and dietary
preferences.A goose's beak is suitable for small, precise bites and very shallow
furrowing action in the soil. Pigs dig to much greater depths in search of per-
ennial plant storage organs. Based on their dietary preferences, grazers,
browsers, and intermediates can be distinguished (Vallentine, 1990, pp.