Livestock grazing for weed management - Ecological Management of Agricultural Weeds - page 420

incipient future state of recovery or degradation (Bellamy & Brown, 1994).
Seasonal fluctuations repeated year after year are not considered different
states. In semiarid northern Australia, McArthur, Chamberlain & Phelps
(1994) identified a single sustainable productive state dominated by Astrebla
and Dichanthium , a state with less vigorous perennial tussock grasses, two
transitory stages with initial weed invasion, and three states of degradation
dominated by herbaceous or woody weeds or annual grasses and forbs (Figure
9.3).
Once the states are defined, information can be assembled on the probabil-
ity of transitions and reasons for such transitions.Transitions occur due to rel-
ative species performance and site and propagule availability.Transitions may
be gradual or sudden, and easy or difficult to reverse. Transitions, occurring
with a particular combination of weather events,may be due to overgrazing or
fires and recovery management. Recovery management includes reseeding,
fuel accumulation, and reduced or increased grazing (Figure 9.3).
The farmer's ability to adjust planned management to stochastic events is
critical for reducing weed density and avoiding new weed problems. Timely
management in response to variability and uncertainty depends on systematic
observation and record-keeping (Chapter 3).The use of planned grazing man-
agement to reduce weed problems in annual crops, perennial crops, and in
grazing lands will be discussed in the remainder of the chapter.
Weed control through herbivory in short-cycle crops
In annual and nursery crops, weeds are most vulnerable as seedlings
in the early phases of the crop cycle. The domestic goose preferentially grazes
tender grass seedlings. This ability to control specific weeds early in the crop
cycle has made geese useful for weed control in a diversity of crops including
annuals such as cotton, onion, and potato, herbaceous short-cycle perennials
such as strawberry, and perennial nurseries (Wurtz, 1995). Doll (1981) recom-
mended 10 to 20 geese ha 1 in strawberry depending on weed pressure and
growing conditions. Fencing, vigilance for predatory dogs and foxes, installa-
tions for water, supplementary feed, and plant losses to treading are among
the management costs.To encourage the geese to graze uniformly throughout
the fenced area and to prevent treading damage where they concentrate, feed,
water, shade, and shelter must be distributed strategically and redistributed
frequently. In the case of strawberry, geese must be withdrawn when fruits
begin to ripen.
In a two-year study Wurtz (1995) compared geese alone and in combination
with hoeing and herbicides for weed control in seedlings of the unpalatable