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Weed Seed Survival in Livestock Systems

Authors:
Weed Seed Survival in Livestock Systems
Jeanie Katovich and Roger Becker
Department of Agronomy and Plant Genetics, University of Minnesota
Jerry Doll
Department of Agronomy, University of Wisconsin
For more information,
please contact:
Jeanie Katovich
University of Minnesota
612.625.5230
katov002@umn.edu
Roger Becker
University of Minnesota
612.625.5753
becke003@umn.edu
Jerry Doll
University of Wisconsin
608.263.7437
jddoll@wisc.edu
Introduction. Manure is an important
soil amendment. In addition to providing
valuable nutrients, manure enriches the
microbial population and diversity and
adds organic matter to the soil. However,
many assume manure is always rich in
weed seeds. The opposite is probably the
case as most of our harvested forage is
relatively free of weed seeds. Exceptions
obviously exist. There is no simple
method to extract weed seeds from feed
or manure and to then test them for vi-
ability. So the best advice is to understand
current knowledge about weed seeds in
manure and how they may impact your
operation. Key factors that determine the
potential for weed seed problems from
livestock systems are feed sources, type
of animals, and type of feed and manure
handling systems.
Feed Sources. Weed seeds enter live-
stock systems from forages, grain, and
palletized feed products. Cash et al.
(1998) estimated that for palletized prod-
ucts, less that 1% of weed seed survive
feed grinding and palletizing. Though
small in number, feed pellets can be a
source of introduction of new weed spe-
cies to a farm, and if one considers the
volume of palletized feed fed, can be a
significant source of weed seed. The big-
gest contribution of weed seed can come
from contaminated hay and grain, how-
ever. A portion of weed seed present in
feed can remain viable after passing
through an animal’s digestive tract.
Weed seed present in bedding or in spilt-
feed bypasses the animal directly entering
the manure stream.
Type of animals, ensiling, digestion,
and manure handling. The animal
source of manure can be important. Two
studies in Nebraska characterized the
effects of the digestive tract and manure
on weed seeds (Harmon and Keim
1934). Weed seeds were fed to calves,
horses, sheep, hogs, or chickens. Nearly
25% of the seeds fed to hogs and cattle
were recovered in the manure, while
only 10 to 12% were recovered from
horses and sheep. Chickens were the
most effective in destroying weed seeds
with only 2% of the velvetleaf seeds fed
recovered, while none of the bindweed,
sweet clover, smooth dock, smartweed,
wild rose and pepperweed seeds fed were
recovered.
Beauty is in the
eye of the be-
holder. Manure
is a valuable
nutrient amend-
ment, but may
harbor weed
seeds.
Both of these weed seed sources may
result in manure containing viable weed
seeds. A study conducted in New York
State (Mt. Pleasant and Schlather 1994)
showed that farms with low amounts of
weed seed in dairy manure used feed
with low numbers of weed seeds. Farms
with high manure weed seed counts ei-
ther harvested feed from weedy fields or
imported feed containing weed seeds. A
California study showed that dairy ma-
nure from producing cows had fewer
weed seeds than manure from dry cows,
presumably because the dry cows re-
ceived lower quality (weedier) feed
(Cudney et al. 1992).
A PUBLICATION OF:
December 2005
Page 2
Of the seeds recovered from
calves, horses, sheep or hogs, an av-
erage of 25% germinated. Although
few in number, 62% of the velvetleaf
seeds that survived the trip through a
chicken germinated, suggesting that
the gizzard may have actually scari-
fied the seed and stimulated germina-
tion. Combining seed recovered and
germination of weed seeds fed, sheep,
horses, pigs, and calves passed 6, 9,
9, and 10% viable seeds, respectively,
while poultry passed only 1% viable
seed owing to the grinding action
within the gizzard. Olson and Wal-
lander (2002) found that only 4% of
mature leafy spurge seed was recov-
ered when fed to sheep, and for graz-
ing, recommended feeding livestock
uninfested feed for 4 to 5 days before
transfer to grazing land not infested
with leafy spurge.
The fermentation process that is
part of ensiling corn or forages can
reduce the viability of weed seed, as
can digestion in the rumen of cattle.
In general, grass weed seeds are more
likely to be killed by ensiling or ru-
men digestion than broadleaf weeds.
In a study by Blackshaw and Rode
(1991), seeds of downy brome, fox-
tail barley and barnyardgrass died if
ensiled for 8 weeks or by rumen di-
gestion for 24 hours (Table 1). Some
green foxtail seed survived rumen
digestion but were killed by ensiling.
Broadleaf weeds are more likely to be
killed by ensiling than by rumen di-
gestion, but both processes are
needed to kill the greatest number of
seed.
In this study, Blackshaw and
Rhode reported that ensiling redroot
pigweed, common lambsquarters or
wild buckwheat seed for 8 weeks re-
duced weed seed survival more than
rumen digestion. Both ensiling and
rumen digestion reduced but did not
eliminate the viability of flixweed,
pennycress, kochia, pigweed, lamb-
squarters, wild buckwheat and round-
leaved mallow. A few seeds remained
viable in all treatments and could ger-
minate in the field. Harmon and Keim
(1934) found hard-seeded broadleaf
weed seeds such as velvetleaf, field
bindweed and common lambsquar-
ters, were less likely to be killed by
rumen digestion than other broadleaf
seeds.
Recent research on the effects of
manure handling on weed seed is lim-
ited, but earlier works add valuable
insight. An early 1900 Maryland Ex-
tension Bulletin was one of the first
to report the effects of animal diges-
tion and manure handling on the vi-
tality of weed seeds (Oswald 1908).
Two sources of weed seeds in manure
were studied: either contaminated
feed that passed through the animal
or seeds in the bedding which by-
passed the animal. These seeds from
52 weed species were placed in piles
of horse, cow, or a mixture of horse
and cow manure. The temperature in
the piles reached 201o F for horse ma-
nure, 168o F for cow manure, and
188o F for the mixture. After 60 days,
the temperature of the manure pile
cooled to ambient temperature so the
seeds were recovered and germina-
tion tests conducted. All seeds of all
52 weed species died at these tem-
peratures in manure piles.
Oswald (1908) also reported on
seeds of 21 species that were fed to 1-
year-old dairy animals, with the ma-
nure managed in ways common at the
time. When manure was hauled daily
to fields and shallowly mixed with
soil, 13% of the fed seeds germi-
nated. The species that survived feed-
ing were roundleaf mallow, jimson-
weed, common ragweed, wild mus-
tard, pepperweed, smartweed, horse
nettle, cockle and dock. If fresh ma-
nure was plowed into the soil, only
3% of fed seeds germinated. In mod-
Digestion of weed seeds by animals kills many, but not all seeds. Spilt-feed
that is not digested puts viable weed seed directly into the manure stream.
Table 1. Average weed seed viability after ensiling in a silo, fermentation in a
rumen, or both. Lethbridge, Alberta. 1986-1989.
Species
Control
Ensiling
in a silo
Rumen
Silo and
rumen
- - - - - - - - - - - - Viable seed (%) - - - - - - - - - - -
Green foxtail 96 0 17 0
Downy brome 98 0 0 0
Foxtail barley 87 0 0 0
Barnyardgrass 97 0 0 0
Flixweed 92 5 7 5
Kochia 94 10 15 10
Redroot pigweed 93 6 45 4
Lambsquarters 87 3 52 2
Wild buckwheat 96 30 56 16
Rounded-leaf mallow 93 23 57 17
Pennycress 98 10 68 10
Adapted from Blackshaw and Rode. Weed Sci. 39:104-108. 1991.
December 2005
Page 3
ern containment systems, sediments
from either solid separators or sedi-
mentation ponds, may concentrate the
weed seed in liquid manure, creating
manure with very high numbers of
viable weed seeds (Cudney et al.
1992) compared to that observed by
Oswald.
In Idaho, Atkeson and colleagues
(1934) assessed the impact of cattle
digestion and subsequent manure
storage on the viability of weed
seeds. Milk cows were fed 2 quarts of
weed seeds in a single day and the
manure collected, mixed with straw
to simulate barn manure, and stored
for 3 months. Seeds passed through
the animals for 4 days.
Weeds with soft seed coats were
more affected than those with hard
seed coats. Digestion alone reduced
the viability of wild oats, yellow
sweet clover, broadleaf plantain and
alfalfa by more than 80%, but had
considerably less impact on green
foxtail, common lambsquarters,
curled dock, redroot pigweed and
cow cockle. Add 3 months storage in
manure, and very few viable weed
seeds were found. Only pigweed,
curled dock, lambsquarters, and cow
cockle seed survived both digestion
and manure storage. All seeds of the
following species died: yellow sweet
clover, buckthorn plantain, green fox-
tail, pennycress, dodder, wild oats,
tumble mustard, and Russian thistle.
More recently, Mt.Pleasant and
Schlather, (1994) collected manure
from fresh droppings in the barn or
from piles of manure just prior to ap-
plication in the field on 20 dairy
farms in upstate New York. They
found apparently viable seed from 13
grass and 35 broadleaf weed species.
Lambsquarters seed was in the ma-
nure of more than half the farms, yel-
low foxtail in 35%, common chick-
weed and dandelion in 30%, and wild
mustard, redroot pigweed, and
barnyardgrass in 25%. One farm had
400,000 seeds per ton of manure, pri-
marily common lambsquarters seeds.
Four farms had no weed seed in the
manure and the rest averaged more
than 75,000 seeds per ton of manure.
Applying 30 tons per acre of ma-
nure with 75,000 seeds per ton would
increase the seedbank by 2.25 million
seeds per acre. Is this a serious situa-
tion? This depends on the current
number of weed seeds in the seed
bank. Estimates of weed seed in tri-
als in Wisconsin showed 15 million
weed seed per acre, in which case,
adding the typical manure in the New
York study would increase the weed
seed bank by 15%, a noticeable
amount. In fields with high seed
populations in the seedbank, this ad-
dition would be less noticeable. Con-
versely, this addition would result in
dramatic increases in weed popula-
tions in relatively clean fields.
This New York study seems to
contradict earlier reports leaving us
with less assurance that ensiling, di-
gestion and manure storage will
greatly reduce or eliminate weed seed
viability. Given that the New York
work was conducted with current
farming practices, one cannot dis-
count the seriousness of weed seed
contamination in manure in today’s
livestock systems. Earlier studies do,
however, indicate that ensiling or
passage through poultry does destroy
many weed seeds.
An equally serious consideration
is the introduction of new weed spe-
cies. Velvetleaf became widely dis-
tributed in New York from feed
grains purchased from the Midwest in
the 1970s. We believe the migration
of velvetleaf northward into Wiscon-
sin and Minnesota has primarily been
the result of contaminated feeds.
Composting manure. Composting
is a biological process where the me-
chanical mixing of manure incorpo-
rates air into the manure pile, which
in turn, stimulates the decomposition
of manure to organic materials, such
as humus. The effectiveness of com-
posting manure as a means to kill
weed seed depends on the tempera-
ture generated by the heating process,
available moisture, and the species of
weed seed present.
Texas A&M scientists found that
if composted manure with 35% mois-
ture reached 120o F for three days,
barnyardgrass, pigweeds and kochia
seeds were killed (Wiese et al. 1998).
Additionally, Johnsongrass seed was
killed with three or more days of ex-
posure at 160o F, but 7 days at 180o F
was needed to kill field bindweed
seeds.
In contrast, they showed the im-
portance of moist manure in seed
death in that seeds of all species sur-
vived a 140o F temperature for 30
days if not mixed with manure but
heated in dry air. Raising the dry air
temperature to 160o F for three days
killed all seeds except field bindweed.
They concluded that composting will
kill all weed seeds if the temperature
is at least 180o F for longer than three
days and that such compost would be
safe to use on lawns, nurseries and
agricultural land without fear of
spreading weed seeds.
Work in Nebraska showed that
moist compost killed cocklebur,
morningglory, pigweed, sunflower,
velvetleaf, foxtail, smooth brome and
shattercane faster and more com-
pletely than dry compost, in part due
to increased compost temperatures
when moist (Eghball and Lesoing
2000). In contrast to the Texas A&M
study, the methods used in the Ne-
braska study were essentially those of
Composting can kill all weed seeds if
properly managed.
December 2005
Page 4
on-farm composting comparing water
added to dry composting. One week
after weed seed placement, compost
piles were turned. All seed in moist
cattle manure were dead, while most
seed in the dry dairy and dry beef
manure were still alive. Adding wa-
ter to beef manure greatly enhanced
the destruction of weed seeds. All
weed seeds in the dry dairy manure
eventually did die after 4 to 5 months
of composting, with the exception
that 14% of velvetleaf seeds were still
viable.
Some seed death occurred even
though the temperature of dry com-
post windrows never exceeded 140o
F, the temperature assumed necessary
to kill weed seed. The authors con-
cluded that composting that generates
high temperatures (above 140o F) can
destroy seed viability after only one
turning and that keeping compost
moist for most of the composting pe-
riod reduces weed seed viability even
though the critical temperature may
not be reached. To put the benefits of
composting into perspective, Chud-
ney et al. (1992) noted the number of
viable weed seed in California dairies
was reduced from approximately
11,000 per ton to 300 to 4000 viable
seed per ton through composting.
They recommended that dairies com-
post longer than the typical 6 to 8
weeks, in deeper piles, and to add
supplemental water to increase tem-
peratures.
Based on these studies, we con-
clude that moist compost with tem-
peratures above 140o F for two weeks
should kill most weed seed. Some
hard-seeded weeds such as velvetleaf
and field bindweed would require
temperatures in the range of 160 to
180o F and longer composting times
to kill all seed. Larney and Black-
shaw (2003) provide an excellent re-
view of recent findings on the re-
sponse of weed seeds to variable tem-
peratures and moisture during com-
posting.
Anaerobic digesters. Confined
animal operations are coming under
increased regulatory pressure to man-
age animal manure in ways that mini-
mize environmental problems and
reduce odors. This has increased in-
terest in anaerobic manure digestion.
This process biologically converts
manure under anaerobic conditions
into an effluent with properties that
differ from raw manure, produces
methane, which can be converted into
electricity, and greatly reduces ma-
nure odor, Nelson and Lamb (2000).
A University of Minnesota study
assessed the effect of anaerobic ma-
nure digestion on weed seed survival
(Katovich and Becker 2004). In the
fall of 2001 and 2002, seed of 6 weed
species were subjected to rumen fer-
mentation and a subset of seed placed
in a plug-flow anaerobic digester for
20 days (the length of time for one
batch of manure to pass through the
digester), and another subset stored
for the same time period in the ma-
nure collection pit before entering the
digester. A field germination assay
was conducted by removing sod from
a long-term bluegrass area to expose
bare ground. The retrieved seed and
digested or non-digested manure were
fall-applied to the bare ground at
6000 gal./A. A subset of weed seed
not stored in manure was applied with
inorganic N fertilizer as a control.
Weed emergence was monitored for
next two growing seasons (Table 2).
A method of composting manure to kill
weed seed can be adapted for any type of
livestock system.
Table 2. Average cumulative weed seed germination for two seasons in a field
assay when planted following 20 days storage in manure with or without an-
aerobic digestion on the Haubenschild farm. 2002 – 2004. St. Paul, MN.
(Katovich and Becker 2004).
Germination by Weed Species (%)
Manure/Fertilizer treat-
ment
Velea Colq Rrpw Lath Gift Wipm
Manure with anaerobic
digestion
16 12 1 0 0 0
Manure without digestion 12 18 5 0 0 0
Untreated inorganic fertil-
izer control
14 11 4 0 0 0
LSD (P=0.05%) NSb NS NS NS NS NS
a Vele = velvetleaf, Colq = common lambsquarters, Rrpw = redroot pigweed, Lath =
ladysthumb smartweed, Gift = giant foxtail, Wipm = wild proso millet. Mean of 4
reps of 100 seeds for each species. All seed were pretreated with rumen fermentation.
b NS = no significant difference. The mean values for germination of individual weed
species did not differ among manure / fertilizer treatments when tested at the 5 %
probability level.
Anaerobic digester downslope from the
dairy barn, Haubenschild farm, Princeton,
MN. Manure flows from this digester in
about 20 days to a holding lagoon where
digested manure is held until field-applied
in the spring or fall.
December 2005
Page 5
Viability of weed seed used in this
study ranged from 82% for wild
proso millet to 99% for velvetleaf and
germination ranged from 1 to 14% in
preliminary tests. The rumen treat-
ment appeared to have killed all the
giant foxtail, wild proso millet, and
ladysthumb smartweed seed, since
none germinated in the inorganic fer-
tilizer control.
Study Results. Some velvetleaf,
common lambsquarters, and redroot
pigweed survived the rumen treat-
ment, but manure management did
not alter germination of surviving
seed compared to that of the inor-
ganic fertilizer control. Temperatures
in the anaerobic digester where the
seed were placed ranged from 95 to
100o F, well below the 140o F re-
quired to kill weed seeds.
Although velvetleaf seed germina-
tion was not altered by digestion
when averaged over the entire sam-
pling period (Table 2), the rate of ger-
mination was accelerated with a
higher percentage of digested velvet-
leaf germinating the first season com-
pared to conventional manure or inor-
ganic fertilizer treatments (Table 3).
This may reduce velvetleaf prob-
lems in the future if emerged seed-
lings are effectively managed the first
season since seed dormancy perpetu-
ates annual weed problems. Velvet-
leaf seed appeared to be 'primed' for
germination as a result of anaerobic
digestion.
Anaerobic manure digestion did
not kill or reduce germination of
weed seeds in this study, however,
this process clearly reduced odor and
generated sufficient electricity
through methane conversion to not
only run the operation, but also with
excess electricity to sell. The possibil-
ity that anaerobic digestion might kill
seed in spilt-feed was not tested,
since all seed were exposed to rumen
digestion.
Contrast this with results of re-
search in the Czech Republic
(Sarapatka et al. 1993) where weed
seeds of eight species were placed at
two depths in simulated anaerobic
digester tanks for approximately 30
days (Table 4). Passage through dairy
cows did not kill all weed seeds of
any species but effectively reduced
viability of lambsquarters and
barnyardgrass. Some weed seeds at
the16-inch depth survived digestion
but no viable seeds were found at the
70-inch depth near the bottom of the
tank. These differences were attrib-
uted in part to higher initial tempera-
tures at the 70-inch depth.
Jeyanayagam and Collins (1984)
compared weed seed survival in batch
and daily-fed 3-liter jar simulated
digesters maintained at 95o F. After
simulated rumen treatment followed
by 15 to 20 days in a digester, weed
seed viability of Johnsongrass
dropped 18 and 82% and fall pani-
cum dropped 24 and 76% for dor-
mant and non-dormant seed, respec-
tively. Anaerobic digestion killed
roughly 3- to 5-times more non-
dormant seed than dormant seed.
The three anaerobic digester stud-
ies differed significantly in design
which may have enabled some weed
seed survival: the first used an opera-
tional flow through digester but
placed seed artificially at a mid-depth
at the end of flow; the second used a
batch digester but temperatures ini-
A typical manure lagoon. Manure enters
the lagoon directly and is not digested.
Depending on conditions, these lagoons
may or may not emit unacceptable odors,
and methane is not utilized. Table 3. First- compared to second-season cumulative velvetleaf seed
germination for two growing seasons after planting following 20 days of
fall storage in manure with or without anaerobic digestion on the Hauben-
schild farm. 2002–2004. St. Paul, MN (Katovich and Becker 2004).
Cumulative velvetleaf
germination (%)
Manure / Fertilizer treatment First season Second season
Manure with anaerobic digestion 14 2
Manure without digestion 6 6
Untreated inorganic fertilizer control 9 6
LSD (0.05) 3 3
Table 4. Weed seed viability when seeds were fresh, after passage through
milking cows, and after one-month fermentation at two depths in a methane
generator (Sarapatka et al. 1993).
After digester a
Plant species Fresh After passage 16" depth 70" depth
- - - - - - - - - - - - - - - - - Germination b (% ) - - - - - - - - -
barnyardgrass 94 5 36 0
quackgrass 96 13 0 0
wild oat 88 N/A 0 0
lambsquarter 90 3 9 0
pigweed 74 13 4 0
pennycress 98 35 0 0
smartweed 91 50 0 0
curly dock 96 91 19 0
a Temperatures of 86o F at 16" and 113 to 122o F gradually declining to 86o F at 70".
b Though authors labeled as germination, appears to be viability, the sum of germina-
tion following repeated stratification and seeds that did not germinate but remained
firm to the touch.
December 2005
Page 6
tially were higher in the bottom layer
to which all seed may not have been
exposed; and the third study, simu-
lated digestion and used only seeds of
grass species, which often are easier
to kill compared to seeds of broadleaf
species. Regardless, in all three an-
aerobic digestion studies significant
numbers of weed seed survived
which, when scaled up to field-scale
operations, would pose a risk of in-
creased weed problems in the field.
Summary. Avoid feed high in weed
content. Livestock vary on the effect
their digestion has on weed seeds, but
all decrease weed seed viability. Well
executed composting destroys most
weed seeds. Weed species with hard
seed coats like field bindweed and
velvetleaf present the greatest risk of
surviving composting. However, if
the compost is moist, reaches the de-
sired temperature, and completes its
full cycle of decomposition, even
seeds of these species are killed. An-
aerobic digesters offer significant
benefits in odor reduction and power
generation, but will not offer the
complete kill of weed seed afforded
by well executed composting. Still, if
the weed content of feedstock is
known, particularly if produced on
the same land where manure will be
utilized, the benefits of anaerobic di-
gesters in odor reduction and power
generation likely outweigh the risks
of potential survival of weed seed and
resultant potential for increased weed
pressure in the field.
References
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Blackshaw, R.E., and L.M. Rode.
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seed viability. Weed Sci. 39:104-
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Cash, S.D., D.L. Zamora, and A.W.
Lenssen. 1998. Viability of weed
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aerobic digesters. USDA NRCS
EQIP Edu. Assis. Grant Prog. Fi-
nal Report. 7 p.
Larney, F.J., and R.E. Blackshaw.
2003. Weed seed viability in com-
posted beef cattle feedlot manure.
J. Environ. Qual. 32:1105-1113.
Mt. Pleasant, J., and K.J. Schlather.
1994. Incidence of weed seed in
cow manure and its importance as
a weed source for cropland. Weed
Tech. 8:304-310.
Nelson, C., and J. Lamb. 2000. Final
Report: Haubenschild Farms An-
aerobic Digester. The Minnesota
Project. St. Paul, MN. 35 pages.
Olson, B.E. and R.T. Wallander.
2002. Does rumninal retention
time affect leafy spurge seed of
varying maturity? J. Range Man-
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Oswald, E.L. 1908. The effect of ani-
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128. 26 pages.
Sarapatka, B., M. Holub, and M.
Lhotska. 1993. The effect of
farmyard manure anaerobic treat-
ment on weed seed viability.
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Wiese, A.F., J.M. Sweeten, B.W.
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Acknowledgments
Thanks to the USDA NRCS EQIP
program for partial funding of the
anaerobic digester weed seed research
conducted at the University of Min-
nesota. Thanks to Haubenschild
Farms for their kind assistance and
use of their facilities. Thanks to our
colleague, Dr. Jerry Doll, University
of Wisconsin, for laying the ground-
work for this publication and gra-
ciously sharing his knowledge.
Photo credits
University of Minnesota
Agricultural Experiment Station
Dave Hansen
- Cows on a hill (cover)
- Tree and barn (cover)
- Cows eating (p. 2)
- Farmsted (p. 4)
Roger Becker
- Anaerobic digester (p. 4)
- Generator (p. 6)
University of Wisconsin
Jerry Doll
- Cow pie (p. 1)
- Compost pile (p. 3)
- Manure lagoon (p. 5)
A generator on a diesel motor converted
to run on methane from the digester pro-
vides electricity for the Haubenschild farm
operations, Princeton, MN.
The University of Minnesota and the University of Wisconsin are committed to the policy that all persons shall have equal access to its programs,
facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status,
veteran status, or sexual orientation.
December 2005
... In the same study, composted dairy manure had destroyed all seeds except velvetleaf (Abutilon theophrasti) which was <17% viable after 3 to 4 months of composting. Anaerobic digesters also are able to reduce the viability of weed seeds (Katovich et al., 2006). However, neither an animal digestive tract, composting, nor anaerobic digesters consistently eliminated all weed seeds. ...
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Dairy manure collected for 2 years from various sites in seven Central California dairies was found to contain viable weed seed. Weed seed Contamination Was most Severe when manure was taken from dry COW pens and liquid manure sedimentation handling facilities. Composting did not eliminate all viable weed seed.
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Introduction of weed seeds is a concern when using animal manure as a nutrient source on croplands. The viability of weed seeds can be reduced through composting. Experiments were conducted in 1996 and 1997 to determine the effects of manure windrow composting on seed viability of eight weed species. Weed seeds were placed in nylon bags and buried at 25 and 75-cm within the composting windrows of dairy manure and beef cattle feedlot manure with or without water addition. After one turning a week later, the seeds of most weed species survived the composting conditions in the dairy cattle manure. Following the four to five month dairy manure composting process, all weed seeds lost viability except for 14% of the velvetleaf (Abutilon theophrasti) seeds. This occurred even though the temperature within the composting dairy manure windrow never reached 60°C, which is considered necessary for weed seed destruction. In the watered beef feedlot manure, all weed seeds lost viability after one turning. However, seeds of most species survived after the first turning of the unwatered beef feedlot manure. The temperature in the feedlot manure windrows with water addition was higher and stayed high longer than other manure windrows. Composting process that generates high temperature (≥60°C) can destroy seed viability after only one turning. When the composting materials are moist for most of the composting period, the viability of weed seeds can be reduced even though the critical temperature is not achieved possibly because of compost phytotoxins.
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Federal and state agencies in several western states now require the use of noxious weed-free or noxious weed seed-free forage to hinder the spread of noxious weeds, Forage can be certified as noxious weed-free through state administered programs, Processed feeds such as pellets or cubes made from noncertified hay and uncleaned grain are some of the forage products that may be potential sources of weed infestations, This study was conducted to determine levels of weed seed contamination in alfalfa hay/grain feed pellets manufactured with commercial-grade equipment. Seeds of whitetop [Cardaria draba (L.) Hand.], spotted knapweed (Centaurea maculosa Lam,), Canada thistle [Cirsium arvense (L.) Scop.], leafy spurge (Euphorbia esula L.), and common yellow sweetclover [Melilotus officinalis (L.) Lam.] were added in known quantities to alfalfa/grass mixed hay and to barley, The hay was ground in a hammermill through a screen with 7.9-mm diameter perforations, and the barley was ground to pass through a 2.4-mm screen, In a second experiment, uncertified 'Ladak 65' alfalfa (Medicago sativa L.) seeds were ground with alfalfa/grass mixed hay in a hammermill and extruded through a pellet die before being ground in another hammermill with barley grain followed by extrusion through a pellet die, The Montana Department of Agriculture collected pelleted feed from various manufacturers in the state during 1993 and 1994 to estimate potential weed contamination frequency, Grinding of weed seeds with alfalfa hay or barley grain reduced emergence by 98 to 100%. Grinding and pelleting reduced emergence of alfalfa seed by over 99%, Weed seedlings emerged from 11% of random feed pellet samples collected from Montana manufacturers, Rigorous processing such as occurs when manufacturing hay/grain pellets reduces the risk of disseminating weed seeds from pelleted feed.
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The temperature and exposure period required to kill seed of johnsongrass, (Sorghum halepense); pigweed, (mixture of Amaranthus sp. primarily hybridus and Palmeri); kochia, (Kochia scoparia (L.) Schrad); barnyardgrass, (Echinochloa crus-galli (L.) Beauv); sorghum, (Sorghum bicolor L. Moench 'DeKalb 42Y'), and field bindweed, (Convolvulus arvensis L.) buried in compost during laboratory experiments or compost manufacturing process was determined. When buried in compost, seed of all species except field bindweed were killed with three days or more exposure at 49°C (120°F). It required seven days of exposure at 83°C (180°F) to kill all field bindweed seed in compost. In dry air, rather than compost, all species survived 60 C (140°F) for 30 days. All seed except field bindweed were killed in dry air by 72°C (160°F) for three days. It took seven days of exposure at 83°C (180°F) to reduce viability of field bindweed from about 30 to 7% in dry air. At 83°C (180°F) viability was reduced only to 5% with 30-day exposure. Seed of all species except field bindweed were killed in a three-day composting process where temperature was maintained at 72°C (160°F) or higher. Field bindweed seed were killed with a 12-day exposure in an outside storage pile of compost. Compost manufactured at this location is probably free of viable weed seed and would be suitable for lawns, nurseries, and agricultural land.
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Grazers ingest seeds of invasive forbs and may contribute to their spread by depositing viable seeds in uninfested areas. Some mature seed pass through the gastrointestinal (GI) tract of ruminants, but grazers consume flowerheads of invasive species from anthesis to dehiscence. We collected seed from the Eurasian leafy spurge (Euphorbia esula L.) at 3 stages of maturity (soft dough, hard dough, mature). With seed collected from these different stages, our objectives were to determine effects of 1) rate of passage through the GI tract of sheep on leafy spurge seed recovery, germinabilty and viability, 2) residence time in sheep rumen on seed germinability and viability, and 3) acid pepsin digestion, simulating the lower GI tract, on seed germinability and viability after different residence times in the rumen. More seed from the later stages of maturity were recovered in the manure. The greatest number of seed recovered only represented 3.9% of the number of ingested seed. Few seeds were recovered after day 4. Soft dough seed in manure would not germinate and was not viable, whereas hard dough and mature seed collected from manure during the first 4 day were viable. Pepsin had a slight effect on the number of mature seed recovered, but eliminated viability of recovered seed. Viability of non-pepsin treated seed from the hard dough and mature stages declined with greater residence time in the rumen. Thus, managers should be aware that livestock ingesting hard dough as well as mature seed may be dispersing viable weed seed.