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North West Weeds
ABN 16 052 158 879
Postal address:
20 Dinoga Street
BINGARA
NSW 2404
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PRINT VERSION Identification
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Effect on animals
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More info?
│ Control
methods │Using
pesticides │Disclaimer
  One
of our most serious noxious
weeds, St John's wort (Hypericum perforatum) threatens all properties in northern
New South Wales. One plant of St John's wort can produce 30,000 seeds. The
(sticky) seeds are spread by animals, and the seeds can remain viable in the
ground for twenty years or more. So, it only takes one plant to start a major
infestation!
Early detection and
TREATMENT, BEFORE PLANTS SET SEED, is critical.
Unfortunately, this "TIME TO
TREAT" window is very small: St John's
wort plants are very difficult to find until their bright, yellow-golden flowers start to
appear, and then it is a matter of only two or three weeks before the seeds
mature. Because the plants do not all flower at
 once, continuous surveillance and treatment is necessary to ensure all plants are treated before seed
set. Depending on how wet the season is, the flowering
period can extend from October right through to April.
Click on these photos to see the impact
St John’s wort can have on grazing
land. In these examples the owners can expect recurring seedling
growth for many, many years! The photos below show the other side of the St
John's wort problem
 THE PROBLEM
 Apart
from its invasiveness, St
John’s wort contains the toxin, hypericum. Over-exposure to St John’s wort
causes health problems for animals, particularly horses, sheep and cattle.
Livestock grazing in a paddock containing a heavy infestation of flowering St
John’s wort can, on a sunny day, develop clinical signs of hypericum poisoning
within five hours.
Later symptoms include agitation, head-rubbing, hind limb
weakness, panting - leading
eventually to raw, weeping areas of skin (ref. NSW
DPI Primefact 694). The graphic photos (left and right)) show some of
this effect on a horse that had
been grazing in a paddock of heavy St John’s wort for about five days. Note that
the white parts are mostly affected.[photo horse - Ian Davidson, Inverell]
Some humans can also be affected
by excessive contact with St John's wort.
St John's wort is recognised
world-wide for its herbal attributes. It has a medicinal history going back
thousands of years. Its proper use and benefit in that area is not denied, but,
this same plant is a serious, invasive weed threatening all grazing properties within the north-west
and beyond. It is a declared noxious weed for a good reason!
IDENTIFICATION
  Apart
from the distinctive flowers (right), a
positive way to identify St John’s wort is by close examination of the leaves.
Hold a leaf up to the light and
(if your eyes are good enough) you will see what look like tiny pin holes
through every leaf (photo, left). These are the hypericum oil glands.
CONTROL
METHODS
Non-Chemical Options:
Perennial pastures and grazing management will offer some control (for details
see NSW DPI Agfact referred to in “More Information” below).
Converting an infested area
to a well-worked cultivation paddock - where that is possible - is probably the only effective way to
eradicate St John's wort.
Chemical options for St John's wort:
According to
NSW DPI’s excellent booklet “Noxious and Environmental Weed Control Handbook
4th Edition”, treatments include:
|
Chemical options |
Rate: Spot/Boom |
Comments |
|
Triclopyr
600 g/L +
picloram
600 g/L
eg Grazon DS® |
500
ml in 100 L of water
Boom rate: 2.0 – 4.0 L per hectare: |
Late
spring to early summer, during flowering to early seed set. Boom:Apply
November to January, use higher rate on dense infestations. |
|
Triclopyr 300
g/L + picloram
100 g/L + Aminopyralid 8 g/L
Grazon Extra® |
500
ml in 100 L of water
Boom
rate: 2.0 – 4.0 L per hectare: |
Foliar application from late spring to early summer, during flowering to
early seed set.
Apply November to January, use higher rate on dense infestations. |
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Fluroxypyr
200 g/L
eg Starane® |
500 mL per
100 L water
3.0 L/ha |
Spring to mid
summer application.
Boom appln. Observe withholding period. |
|
Fluroxypyr
333 g/L
Starane Advanced® |
300 mL per
100 L water
1.8 L/ha |
Foliar
application from flowering to seed set. Observe withholding period.
Observe withholding period. |
|
Fluroxypyr
333 g/L
eg Starane Advanced® |
1.8 L/ha |
Apply from
bud to full bloom. Some regrowth will occur. Treat regrowth the
following season for best results. Use at least 200 L water/ha. |
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Glyphosate 360 g/L
Various trade names |
3.0
L per hectare |
Apply November to May, flowering to post flowering. (Suitable
isolated plants only) |
|
2,4-D ester
600 g/L
Various trade names |
3.7
to 5.3 L per hectare |
For
use in grass pastures, before flowering,when the plants are less that 40
cm high. |
|
Metsulfuron methyl
600 g/L
eg Brushoff ® + glyphosate 360 g/L various trade names |
10 g
metsulfuron methyl PLUS 200 ml glyphosate per 100 L water |
Spray to wet, but not to cause run-off. |
IMPORTANT:
USE OF PESTICIDES – ALWAYS READ THE LABEL
Pesticides
must only be used for the purpose for which they are registered and must not be
used in any other situation or in any manner contrary to the directions on the
label. Never use a herbicide in any way contrary to the label recommendations.
MORE INFORMATION:
Detailed St John’s wort information (a 12-page Agfact) is available on the
NSW DPI Weeds
Sub-Program website (PDF format - large document, takes some minutes to
download but worth the wait!). Another excellent reference is the book "Noxious Plants of Australia", by Parsons and Cuthbertson
[Inkata Press].
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DISCLAIMER: The information contained in this
web site is based on knowledge and understanding at the time of writing.
However, because of advances in knowledge, users are reminded of the need to
ensure that information upon which they rely is up to date and to check currency
of the information with the appropriate officer of North West Weeds or the user’s independent adviser.
LRT 27/11/2010
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North West Weeds
