Tactic 3.3 Silage and hay – crops and
pastures
Silage production, and to a lesser extent hay making,
can be used to manage weeds by:
 reducing the viable seed-set of target weeds
 removing viable weed seeds so that they are not
added to the soil seedbank.
Benefits
Key benefit #1
Hay and silage are options that can be used in
crops and pastures where excessive numbers of
weeds have survived a previous tactic.
Hay and silage each offer the chance to significantly
reduce the return of weed seeds to the seedbank. In
research conducted by Gill and Holmes (1997) pasture
hay production in spring decreased annual ryegrass
density by 84% in the following wheat crop.
Research by Roy (2005) showed that silage followed
by application of paraquat reduced annual ryegrass
seed head numbers from 886/m2 to 42/m2 in the
following season.
Both hay and silage tactics are most valuable to growers
when the weeds, crop and/or pasture are nutritious.
Research in southern New South Wales (Bowcher 2002)
has demonstrated that spring cutting can also be used
to manipulate the existing pasture composition and the
future weed seedbank. Following various defoliation
methods and timing of cutting, large changes in pasture
composition had occurred 2 years later (Table T3.3-1).
Wild oats and annual ryegrass are excellent fodder
species and can be included in either silage or hay,
provided annual ryegrass toxicity is not present. On the
other hand, the spikelets on barley grass and vulpia,
when close to maturity, make them unsuitable for
hay or silage.
Practicalities
Key practicability #1
Carefully consider the options for marketing
or using the product on -farm.
sampled, and the number of seed types and seeds per
bale varied considerably. The study detected 10–30
types of seed per bale, with an average of 21. The
number of seeds per bale ranged from 104 to 364,000,
with an average of 68,700. The hay had been imported
from other areas of New South Wales, Victoria and
South Australia.
Contamination also determines marketing options.
Certain weeds such as Emex spp. are prohibited in
oaten hay exports to Japan, which must be 9 5–97%
pure oats (Carpenter 1999).
Key practicality #2
Paddock showing hay cutting (left) and brown manuring (right) –
two options to stop weed seed-set.
Photo: Alexandra Douglas
A high proportion of seeds will remain viable if hay
is cut late. This has implications both for feeding out
of the hay on-farm and for marketing of the product.
T i m e t h e h a y o r s i l a g e t ac t i c in ac c o r da n c e w it h
the physio logical developm ent of the t arget weed.
Timing the cut and the management of regrowth is
critical for hay and silage production to be successful
as weed control tactics. Cutting too early will allow any
subsequent regrowth to set viable seed and contribute
It is assumed that once seeds have been ensiled they
to the weed seedbank. Cutting too late means that
are no longer viable but that is yet to be proven for
mature weed seed is likely to have already been shed,
common Australian weeds. A Canadian study
adding to the weed seedbank in the paddock.
(Blackshaw and Rode 1991) identified low levels of
Seed-set management timed according to stage
viability in ensiled broadleaf weeds. They showed that
3% of black bindweed (Fallopia convolvulus) seed
remained viable following ensiling, compared to no
viability in wild oats.
of weed physiological maturity will deliver far more
reliable outcomes than weed management timed by
calendar dates, as weed species development will
vary with region and year.
Introduced hay or silage has the potential to transport
weed seeds. Feeding out in dedicated areas is advised
to allow for monitoring and control of any germinated
weeds. Hay in particular has the potential to contain
high proportions of viable weed seed if it has been cut
when weeds have already set seed.
A pasture trial conducted by Bowcher (2002)
demonstrated that appropriate timing of cutting
was a critical component to reduce target weed seed
production (Table T3.3-1). Control of any weed
regrowth after cutting was also essential to reduce
weed seed entering the soil seedbank.
A study of weed seeds in hay bales conducted during
the 1980–81 drought by Thomas et al (1984) found
that almost all the sampled bales in the Yass, Young
and Gundagai districts of New South Wales contained
viable seeds of prohibited or restricted weeds. There
were 233 different seed types identified in the 38 bales
After an early October cut (Bowcher 2002) annual species
such as Paterson’s curse, annual ryegrass and sub clover
were able to regrow. With sufficient growing season
remaining, this regrowth set seed and thus contributed
to seedling numbers in the following year (Table T3.3-1).
Table T3.3-1 Effect of grazing by wethers (10 DSE/ha) and cutting times on weed seed production (seeds/m 2)
of a mixed annual grass/sub clover/perennial grass pasture after spring cutting with no regrowth control, or
continuously grazing for 1 or 2 years (Bowcher 2002)
Annual weed seed production (seeds/m 2 )
D e fo l i a t i o n m e t ho d
Grazing
Annual ryegrass
Vulpia
Paterson’s curse
1 year
2 years
1 year
2 years
1 year
2 years
1,481
1,669
6,824
18,469
20
22
Cut early October
981
834
1,004
56
973
877
Cut late October
95
7
208
29
303
86
Cut early November
237
2,896
2,248
13,650
7
223
Cut late November
990
6,879
11,985
29,895
208
2,153
By comparison, the late October cut was far more
increased by cutting in October, which is equivalent to a
effective as a seed-set control tactic because the weeds
silage cut in the study region (Kaiser et al 2004). An early
had matured further. Cutting removed the weeds prior
November cut, which is equivalent to a traditional hay
to seed maturation or contribution to the seedbank,
cut in the study region, would have been a better option
and subsequent regrowth did not set significant
for weed control (Table T3.3-2) as the later timing was
volumes of seed.
better suited to the physiological development of these
The late October cut in this case represents only a
species. If an October cut (silage) must be employed,
window of opportunity. Delaying cutting until later
(early November) meant that significant numbers of
care must be taken to manage the regrowth and viable
seed production of annual ryegrass or Paterson’s curse
viable weed seed had entered the seedbank prior to
to prevent further additions to the soil seedbank.
the cut taking place, and thus substantial numbers of
Although the early November defoliation was the most
seedlings resulted in the following year (Table T3.3-1).
effective timing for annual ryegrass and Paterson’s curse,
There is also opportunity to improve the effectiveness
this timing was too late for effective management of
of the late October cut demonstrated in the Table T3.3-1
vulpia. The vulpia had matured earlier than the annual
trial, because the pasture regrowth was not grazed until
ryegrass and Paterson’s curse, and had produced and
mid-summer. Strategic grazing and/or use of herbicide
shed vast quantities of viable seed before the defoliation
on the spring regrowth that resulted from the cut may
occurred (Table T3.3-2). In contrast with the annual
have further minimised seed production for some species
ryegrass and Paterson’s curse, it was an early October
(eg Paterson’s curse).
cut that greatly reduced vulpia seed production and
vulpia content in the following year.
Key practicality #3
Understand the biological traits of the target
weed to improve efficacy of the tactic.
Individual species’ responses to cutting, in terms of
subsequent growth and seed production, will be determined by the stage of maturation of the weed at the
time of defoliation. Understanding species differences
allows for more suitable timing and can thereby improve
the effectiveness of the hay or silage tactic (see Section
6: Profiles of common weeds of cropping ).
The key is to identify the target weed species and to
strike a balance between the problem weeds and other
species which contribute to the pasture mix. In the trial
presented in Table T3.3-2 the optimum stage for seed-set
control of annual grass weeds was found to be when the
majority (eg 75%) of the most advanced seed heads
were between post-flowering and very early seed fill.
For Paterson’s curse the optimum cutting time was
found to be when the majority of the earliest flowers
(lowest on the stem) had started to form green seeds
The percentages of pasture content and seed production
of both annual ryegrass and Paterson’s curse were
on the most advanced flowering heads.
Table T3.3-2 Effect of grazing by wethers (10 DSE/ha) and cutting times on species composition of a mixed annual
grass/sub clover/perennial grass pasture the third spring (year 3) after cutting or grazing in each of the two previous
springs (Kaiser et al 2004)
Species
Initial pasture
Grazing
composition (%)
only
Grazed then cut in spring (no control of regrowth)
Early Oct
Late Oct
(silage)
Early Nov
Late Nov
(a
ltesla
ige(tradtionah
lay–(a
ltehay)
o r ear l y hay ) Wag ga d is tr ic t
practice)
(% of species in pasture in year 3)
Phalaris + cocksfoot
15.9
15.4
18.4
14.2
14.1
16.6
Sub clover
31.4
18.1
36.6
11.6
15.6
19.9
3.9
0.5
4.5
0.3
4.0
6.6
Annual ryegrass
25.1
17.7
28.3
52.8
9.8
9.2
Vulpia (silver grass)
Naturalised clovers
16.4
26.3
2.0
10.3
53.2
41.3
Great brome
1.0
14.1
2.1
0.2
1.3
3.9
Barley grass
0.3
4.8
0.2
0
0.4
0.1
Paterson’s curse
3.5
0.3
6.9
4.4
1.4
1.5
Other broadleaf weeds
2.3
2.7
1.2
6.0
0.8
0.2
Key practicality #4
Regrowth can produce enough seed to keep the
seed bank topped up.
Regrowth monitoring is important because late cutting
of hay does not reduce seedbank numbers. Roy (2005)
showed that where paraquat was not used, and hay
was cut 2–3 weeks after the silage production, almost
no reduction in annual ryegrass numbers resulted
(886 seedlings/m 2 to 860 seedlings/m 2).
A knockdown herbicide or intensive grazing used after an
early cut is a reliable way of controlling weed regrowth.
Cutting silage to target forage quality is often too early
for weed management. Regrowth is likely and will require
subsequent additional management. Bowcher and
Holding (2004) showed that when cut early, Paterson’s
curse regrowth produced around 1,000 seeds/m2. When
the forage was cut about 4 weeks later (targeting early
seed-fill of the weed) the regrowth of Paterson’s curse
was limited, producing only 10 seeds/m 2.
The effect of cutting a portion of a crop and making silage (left)
compared with harvesting grain (right) on annual ryegrass seedling
numbers the following autumn.
Photo: Warwick Holding
A summary of issues to be considered when
deciding whether to cut for silage or hay is outlined
in Table T3.3-3.
Key practicality #5
Consider the balance of using hay or silage as a weed
Spraying with glyphosate prior to cutting ensures that
weeds like annual ryegrass will not regrow and reduces
the risk of mature seeds forming.
managem ent tact ic with oth er f arm ent erpr ises .
A balance between fodder quality and weed
management benefit should be considered, as the
cut that best controls weed seed-set may not produce
the best quality fodder. Cutting too late results in a
significant reduction in feed quality and digestibility
of the hay or silage.
Whole-farm considerations
 Hay and silage production are better suited to farms
with a livestock enterprise. However, there is a limit
to the area of pasture or crop that can be cut for hay
or silage simply because too much of either can
create an over-supply problem.
 Because hay portability is much better than silage,
hay is preferred when the product must be
transported to a market.
The impact of cutting and baling pasture infested with Paterson’s
curse can be seen 2 years later. Here only the left hand side of the
paddock was cut for hay in 2003. Photo was taken in spring 2005.
Photo: Warwick Holding
Contributors
Annabel Bowcher, Helen Burns and Steve Sutherland
Table T3.3-3 Considerations to be made when choosing between hay and silage as a weed management tactic
Issue
Hay
Prevention of viable seed addition to
before the weed seedbank in the paddock
Similarly
effective, assuming no target weed seed production has occurred
the cut and regrowth is controlled to prevent further weed seed production
Potential for weed seeds to be spread
to ot her area s dur ing fe ed ou t
Moderate to high
Potential for weed regrowth
Depends on growth stage of weed at time of cut
Feasibility
Silage
Low if properly ensiled
Depends on the scale of the operation, livestock enterprises within the business,
distance to end-use point and demand for the product
References
Blackshaw, R.E. and Rode, L.M. (1991). Effect of
ensiling and rumen digestion by cattle in weed seed
viability. Weed Science 39: 104–108.
Bowcher, A.J. (2002). Competition between temperate
perennial pasture species and annual weeds: effect
of pasture management on population dynamics and
resource use. PhD Thesis, Charles Sturt University,
New South Wales.
Bowcher, A. and Holding, D. (2004). Cultural weed
management: Paterson’s curse. CRC for Australian
Weed Management fact sheet. www.weeds.crc.
org.au/documents/fs25_cultural_pato.pdf
Carpenter, J. (1999). Quality oaten hay for export
to Japan – a guide for growers. Farmnote 39/9 5
Department of Agriculture, Western Australia.
http//agspsrv34.agric.wa.gov.au/agency/pubns/
farmnote/1 995/F03995.htm
Gill, G.S. and Holmes, J.E. (1997). Efficacy of cultural
control methods for combating herbicide resistant
Lolium rigidum. Pesticide Science 51: 352–358.
Kaiser, A.G., Doonan, B.M. and Bowcher, A.J. (2004).
Silage as a pasture management tool. In A.G. Kaiser,
J.W. Piltz, H.M. Burns and N.W. Griffiths (eds)
Successful Silage. New South Wales Department
of Primary Industries and Dairy Australia, pp. 57–72.
Roy, W. (2005). Eight years managing herbicide
resistant ryegrass. Western Australian Agribusiness
Crop Updates 2005.
Thomas, A.G., Gill, A.M., Moore, P.H. and Forcella, F.
(1984). Drought feeding and the dispersal of weeds.
Journal of the Australian Institute of Agricultural
Science 50: 103–1 07.