Control of toxic pasture plants (horses) #horsecare

Control Of Toxic Pasture Plants
Horses

Land Management Advisory Service
Andy Cole
Land Management Consultant
(17 Years Consulting for Small Landholders)
Contact: 0437 299 268

CONTENTS
Useful References
Problem Plants and Weeds
Approaches to Weed Control

Melissa Offord, Plants Poisonous to Horse - An
Australian Field Guide
https://www.horsecouncil.org.au/wp-
content/uploads/2015/11/Plants-Poisonous-to-
Horses-Aust-field-guide.pdf
USEFUL REFERENCES

http://www.pir.sa.gov.au/biosecurity/weeds_and_p
est_animals/weeds_in_sa
USEFUL REFERENCES

PERENNIAL RYEGRASS (Lolium perenne)
Some cultivars of perennial ryegrass contain an
endophyte fungus which can affect the nervous
systems of animals causing ‘grass staggers’. The
levels of endophyte differ between varieties and
between seed batches.
Horses and alpacas are particularly
susceptible and can display symptoms
of trembling, staggering and loss of
balance. It is not usually fatal, although
animals can be severely injured as a
result of falling.

PERENNIAL RYEGRASS (Lolium perenne)
They will generally recover quickly if removed from those
paddocks and fed non-toxic feed.
In severe cases pastures may have to be re-sown with
cultivars which are ‘Low’ endophyte or ‘No’ endophyte.
Avoid older varieties with ‘wild’ type fungus.
Low endophyte cultivars include
- Ausvic (550 to 650mm).
AR1 cultivars have a strain of novel fungus producing low
levels or no toxins. For example:
- Arrow (>650mm) and Bronsyn (> 650mm).

ANNUAL RYEGRASS (Lolium rigidum)
Annual ryegrass toxicity (ARGT)
is caused by a bacterium
Rathayibacter toxicus which can
be carried by an Aguina spp.
nematode into the developing seed
heads of some annual grasses,
such as Wimmera Ryegrass, where
it eventually produces a powerful
poison called corynetoxin.
Poison production occurs when the
grass is haying off, or ’senescing’.
Healthy annual ryegrass seed
head.

The toxin is cumulative, so animals
can consume small amounts over
time until fatal symptoms appear.
Any livestock that eat infected seed
heads may die.
Symptoms include: not eating,
muscle tremors, poor coordination,
falling and severe convulsions.
‘Safeguard’ annual ryegrass is
resistant to this toxicity
Infected seed heads with yellow
slime.

Contact your local vet if ARGT is suspected
For hay or pasture testing for ARGT contact Russell Burns
SARDI. Phone 0401 122 115, email Russell.burns@sa.gov.au
Cost is $81 per sample
PIRSA hotline to notify of suspected ARGT is: Emergency
Animal Disease Watch Hotline - Phone 1800 675 888
For further information and to discuss support services from
PIRSA with respect to ARGT related illness or deaths go to the
following website for your regional contact:
http://www.pir.sa.gov.au/biosecurity/animal_health/contact_us

Cape Tulip (one or two leaved)
CAPE TULIP (Moraea species)

Cape tulip (one and two leaved) develops a deep corm and is
hard to grub out. Toxins called cardiac glycosides are
produced – cattle are most susceptible. Horses can be
affected, sheep less so.
Is a common contaminant of hay.
Herbicide control
Metsulfuron methyl (sold as brushoff® or ally) June to
September.
24D amine June to September
CAPE TULIP (Moraea species)

MARSHMALLOW (Malva parviflora)
Small flowered mallow has been
implicated in poisoning of
horses, sheep and cattle.
It is not that common since the
plants are generally unpalatable.
Ensure plenty of paddock feed.
Symptoms include: profuse
sweating; rapid breathing;
staggers and muscle tremors.

Avoid putting horse onto paddock where this weed
dominates.
It can be controlled with herbicides. Spot spray with
glyphosate if only a few plants. A broad leaf spray using a
mix of Hammer® and 24D Amine when plants are small (ie
4 to 10 leaf stage) is effective. Include a wetter such as
Hasten® (0.5%).
If plants become woody consider spot spraying with a woody
weed killer such as GrazonDS®.
MARSHMALLOW (Malva parviflora)

CAPEWEED (Arctotheca calendula)
Capeweed can cause
nitrate/nitrite poisoning.
Injesting plants with high
nitrate can cause death.
Haemoglobin is affected
causing lack of oxygen in
blood. Avoid heavy grazing of
weeds sprayed with 24-D
herbicides. Sheep & cattle are
likely to suffer nitrite
poisoning, horses nitrate
poisoning.

Do not overgraze pastures, always maintain 70% minimum
ground cover. The following herbicides, applied in autumn,
will control capeweed, geranium and salvation jane:
Agtryne® MA, 1 litre per hectare. Rosettes need to be less
than 10cms. Do not use near vines.
Tigrex®, 1 litre per hectare. Rosettes need to be less than
10cms. Do not use near vines.
Jaguar®, 750 mls per hectare. Rosettes need to be less than
15cms.
CAPEWEED (Arctotheca calendula)

SALVATION JANE (Echium plantagineum)
Salvation jane contains up to
ten types of toxic
pyrrolizidine alkaloids
which are toxic to the liver.
The weed has been
associated with many horse
deaths in recent years. All
parts of the plant are toxic
and the toxicity is not lost in
dried plants.

If a herbicide application is necessary use that
recommended for capeweed control. Control any spring
germinations.

Crown weevil
(Mogulones
larvatus)
Flea beetle
(Longitarsus
echii)
Pollen beetle
(Meligethes
planiusculus)
Root weevil
(Mogulones
geographicus)
In recent years Salvation jane (declared weed) has declined, in
part, as a result of biological control measures.

Guildford grass (Onion grass)
GUILDFORD GRASS (Romulea rosea)

Guildford grass (Onion grass) can cause death by blocking the small intestine

Guildford Grass is a bulb from the Iridaceae family. It’s
tough leaves can form an indigestible fibre ball which
blocks the small intestine causing death.
It thrives in acidic soils with low phosphorus levels.
Prevention
- Lime highly acidic soils and improve phosphorus levels.

Herbicide Control
Dense stands need to be
sprayed out with
metsulfuron methyl
(Brushoff®) in July.
A dense stand sprayed with metsulfuron
methyl in July. Rate 15g/ha.

BARLEY GRASS (Hordeum leporinum)
An annual grass which, after
it dries off in spring, can
cause problems with eyes,
ears and gums of livestock.
Control measures include
slashing or grazing heavily
with sheep in spring to
reduce seed set.

BARLEY GRASS (Hordeum leporinum)
Herbicide control
Spray - topping in spring. This
involves applying a low rate
of herbicide after seed head
emergence. It does not kill the
plant, but will sterilise the
seed and therefore reduce
seed-set.
Glyphosate (450g/L) is
applied at a rate of 360mL/ha.

SOURSOB (Oxalis pes-caprae)
Over the period 2004–2015, 14
miniature horses in six separate
outbreaks presented with clinical
signs consistent with acute or
chronic oxalate toxicity. All animals
had access to Oxalis pes-caprae or
soursob. Miniature horses with
acute oxalate toxicity and
hypocalcaemia had muscle
fasciculations, tremors and
synchronous diaphragmatic flutter.

These horses responded to treatment
with intravenous and oral calcium.
Herbicide control
Apply metsulfuron methyl @
10g/ha just as flowers are emerging.
SOURSOB (Oxalis pes-caprae)

FLATWEED (Hypochaeris radicata)
This weed may be associated
with Australian stringhalt but
this has not been confirmed.
Stringhalt usually occurs in late
summer or early autumn and it
most commonly occurs after a
break in dry weather or drought
conditions. Damage to the long
nerves results in involuntary
flexion and delayed extension
of the hocks.
.

Herbicide control
Apply Dicamba and MCPA, or
24D amine in April to July.
FLATWEED (Hypochaeris radicata)

NIGHTSHADE (Solanum Species)
Silver leaf nightshade and Black
leaf nightshade are common.
They belong to the genus
Solanum. In general the leaves
and green fruits of solanums are
the most toxic parts of the plants,
producing a glycoalkaloid toxin
which can have effects on the
gastrointestinal tract and/or the
nervous system.

BLACK NIGHTSHADE (Solanum nigrum)
The ingestion of large amounts
of toxic solanum plant
material can result in sudden
death, or death within 3 - 4
days in the most severe cases.
Herbicide control
Spot spray with 24-D and
picloram September to
January.

COMMON HELIOTROPE (Heliotropium europaeum)
A summer growing annual herb,
the seeds can pass through stock
unharmed and so its’ spread is by
stock and contaminated fodder.
Contains pyrrolizidine alkaloids
which are poisonous to all stock
but particularly toxic to horses.
Usually not palatable to stock.

Continual ingestion of this weed (fresh
or dry) can cause liver damage and
secondary brain damage.
Clinical symptoms include: weight
loss, poor co-ordination, respiratory
difficulties and ultimately death.
Herbicide control
Apply KambaM® (Dicamba and
MCPA) in October to December when
plants are small but actively growing.
COMMON HELIOTROPE (Heliotropium europaeum)

In most cases successful weed control will involve the use
of a range of methods and not just rely on herbicide
applications.
1. Prevent weed problems before they start (by limiting
their introduction and spread).
2. Restrict weed growth (by helping your crops or pastures
to compete), and do not overgraze.
3. Soil test & add fertilizer. Lime acid soils.
4. Ensure control measures are effective (e.g. when using
herbicides follow label instructions).
INTEGRATED WEED MANAGEMENT

Manual Removal - is quite effective in controlling small
infestations and isolated plants.
Mowing or Slashing - can be used in conjunction with
grazing for pasture weed control. Slashing or grooming
woody weeds is also be effective
Grazing - can be used in a variety of ways to control weed
growth, but it can also encourage weed invasion if not
managed well.
Spray topping - light applications of certain herbicides are
used to kill seeds within seed heads.
CONTROL METHODS

Foliar spraying – applications of herbicides are a common
way of reducing weeds. This a very effective way of
controlling large infestations weeds e.g. woody weeds,
pasture weeds and bulbs.
CONTROL METHODS

Non selective herbicides - are those which destroy all types
of plants whether grasses or broadleaf weeds. e.g.
glyphosate which translocates to roots which die, thus
killing the plant.
Selective herbicides – are those which will not destroy
certain groups of plants.
e.g. Fluazifop-p-butyl (Fusilade®) will kill grasses but not
damage broadleaf plants.
e.g. Dicamba and MCPA will kill broadleaf weeds but not
harm grasses.
HERBICIDE TYPES

Glyphosate (sold as Roundup®)– non selective, often used
prior to re-seeding pastures. Can be used on most types of
weeds and is sometimes mixed with other herbicides.
Metsulfuron methyl (sold as Brushoff® or Ally®) –
specifically designed for the control of perennial broadleaf
weeds, woody weeds and bulbs. Caution is necessary when
using this near native vegetation.
Triclopyr (sold as Garlon 600®) - is a herbicide that is used
for cutting and swabbing of large woody weeds in bushland
situations. It can also be used as a spray at 1:400 with water
to successfully kill blackberry, brooms and bridal creeper.
COMMON HERBICIDES

Diflufenican and MCPA (sold as Tigrex®) – a selective
herbicide, often used to control capeweed in pastures
during Autumn. Should not kill grasses or clover.
Dicamba and MCPA (sold as KambaM®) – a selective
broadleaf herbicide often used to control perennial
broadleaf weeds in pasture.
Triclopyr and Picloram (sold as GrazonDS®) used as a
woody weed herbicide. It has a long residual life in the soil
which can prevent seed germination.
COMMON HERBICIDES

Most herbicides are effective when applied to actively
growing plants.
Avoid applying herbicides when plants are under water
stress in dry seasons.
Always follow label instructions, and ensure appropriate
safety equipment is used when mixing or applying
chemicals.
Surfactants (e.g. BS1000®) and penetrants (e.g. Pulse®)
are often mixed with herbicides to maximise their
effectiveness.
COMMON HERBICIDES

Broadacre application rates for herbicides are usually
given in litres per hectare. The chemical is added to a
tank of water, often 100litres. So it is important that
landholders know how much of the mix is being put out
per hectare.
Nozzle types and settings, along with the tractor speed
will influence the amount being applied to each hectare.
If unsure how to calibrate your spray unit seek
professional advice before applying any chemicals.
CALIBRATING SPRAY UNITS

Development of a weed management plan will ensure that
the control program is integrated, delivered in a timely
manner and achieves successful control.
Develop distinct objectives for the control program.
- identify the weed(s),
- map the weeds – a mud map is fine,
- prioritise the weed(s) for control,
- determine management options for the weed(s),
- develop a realistic weed control timetable with
management options, include follow-up work
- develop monitoring measures.
WEED MANAGEMENT PLAN

Andy Cole - Consultant
Land Management Advisory Service
M: 0437 299 268

Control of toxic pasture plants (horses) #horsecare

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