Agriculture Reference
In-Depth Information
CONTROLLING WEEDS WITH
INTEGRATED WEED
MANAGEMENT SYSTEMS
tors or tillage implements, then weed migration
easily occurs from fi eld to fi eld. This may result
in the introduction of a new weed species in a
particular fi eld with serious consequences. Careful
cleaning of tractor tires, seeders, and tillage equip-
ment should be a high priority for all farmers but
is routinely ignored in the rush of getting farm
work completed in a timely manner.
Harvesting equipment has been shown to be a
signifi cant contributor to weed dispersal (Thill
and Mallory-Smith 1997; Blanco-Moreno et al.,
2004). Seed dispersal with grain harvesters is
dependent on the number of weed seeds remain-
ing on the plant at harvest and varies considerably
with seed size and shape. Seed dispersal by
combine harvesters has been found to range from
18 to 50 m (Ghersa et al., 1993; Blanco-Moreno
et al., 2004). Shirtliffe and Entz (2005) docu-
mented that 74% of wild oat seed dispersed from
a combine was distributed in the chaff spread on
the fi eld. Modifi cations to harvesters, such as
chaff collectors, can markedly reduce in-fi eld
weed seed distribution (Matthews et al., 1996;
Shirtliffe and Entz 2005). Combine harvesters
should be thoroughly cleaned before moving to
the next fi eld or farm to prevent long-distance
weed transport. Custom combining has been
implicated in the spread of jointed goatgrass
throughout the wheat-producing regions of the
US (Donald and Ogg 1991).
Harvest operations that remove the entire crop
plant greatly increase the likelihood that weed
seed will also be harvested and potentially dis-
persed. Transport of hay and straw has been
found to be a major source of long-distance move-
ment of weed species (Zimdahl 2007). Thus, care
is required when purchasing livestock feed from
outside the local area.
Weed seed present in forage and grain fed to
livestock can sometimes remain viable after animal
ingestion. Weed seed viability in manure will
depend on the weed species and on the animal
consuming it. Weeds with hard seed coats have
the greatest chance of surviving animal digestion.
Blackshaw and Rode (1991) found that weed seed
viability in beef cattle manure was near zero for
grass species such as downy brome (
Bromus
tectorum
L.) and foxtail barley but could be as
Preventative control
Prevention has been a cornerstone of weed
control throughout history and remains a pillar of
integrated weed management (IWM) systems.
Preventative approaches are recognized as being
highly cost-effective methods of weed manage-
ment, but they are routinely overlooked (Jordan
1996). This occurs because preventative weed
management involves complex integration of
many practices with the goal of preventing the
introduction, establishment, and dispersal of
weed species. Weed prevention is often thought
of as something that occurs at a regional or national
level, where preventing introduction of new weed
species is the main focus. However, weed preven-
tion can be very effective at the individual farm
level.
Preventative weed management should be
implemented year-round and at all stages of crop
production. Planting weed-free crop seed is a
good starting point to prevent introduction of
new weed species and to reduce overall weed den-
sities. Additionally, crop seed should have high
germination and vigor to ensure rapid crop estab-
lishment. Early crop emergence and rapid canopy
closure will inhibit weed emergence and growth
and thus contribute to reduced weed infestations
(O'Donovan et al., 2007). Wheat farmers often
plant farm-saved seed to reduce input costs, but
this is not always a cost-effective practice. Quality
of farm-saved wheat seed can be highly variable
(Edwards and Krenzer 2006) and weed seed
content can be high (Dastgheib 1989). Thus, a
more economical long-term approach may be the
purchase of certifi ed seed each year.
Agricultural machinery disperses weeds from
farm to farm and from fi eld to fi eld within a farm
(Thill and Mallory-Smith 1997). Cultivation dis-
perses weed species that propagate vegetatively,
by seed, or by both methods. Cultivation will nor-
mally transport weed seed, rhizomes, or roots
only a few meters within a fi eld, but if propagules
are embedded in soil or debris adhering to trac-
