Home' Otago Southland Farmer : January 25th 2013 Contents 25.1.13 Farmer
Prompt service Specialists in all types of aerial work
Group and bulk discount schemes available
Aircare Accredited Agriculture Aviation Operator
(03) 208 4735
Balclutha (03) 418 1418 Central Otago (03) 449 2502
Lumsden (03) 248 7087
OFFICE 0800 746 364
For more information contact
Harliwich Holdings Ltd
Coal Creek Road, RD 1
Call Free :
0800 111 221
Ph: 03 446 8622
Fax: 03 446 8575
Energy in the Soil
source of humic acid
Boost soil carbon and rebuilds soil
Stimulates microbial and fungal
bioactivity necessary for healthy soil
Low levels of calcium can affect milksolids
production, mating outcomes and growth
rates of young stock. Supplementing your
herd with Calcimate will keep them
performing at their peak and improve
your bottom line.
Find out your herd's
Cows absorb an average
of 70% of calcium in
with only 30% of calcium
in your pasture.
0800 107 475
Fertiliser Advertising Feature
Thistles can be controlled -- but
there's no silver bullet
By CARMEN HALL
From a control point of view, there are
two groups of thistle---Californians
(calies) and the others.
Calies are the most economically important
weed of New Zealand pastures. According
to information from Tectra, they can
rapidly colonise pastures from their
network of thick fleshy rhizomes. Their
seeds are also spread by the wind.
Other thistles are mainly annuals or
biennials. Of these, nodding thistles are
among the hardest to control. They can
also be serious weeds of improved
pastures, especially in summer dry areas,
and in open ground in new pastures.
Methods that control nodders will work
well with other non-Californian thistles.
Annual and biennial thistles
As annual and biennial thistles only
reproduce through seed, control measures
should focus on reducing seed production
Where flower heads are immature and at a
similar stage of maturity, topping or
mowing may prevent regrowth and reduce
seed production by as much as 80 per cent.
If thistles are cut too early---before terminal
buds have formed---they are likely to re-
grow. But if cut too late, when flowers are
close to maturity, viable seeds can still be
produced in the severed heads.
Hand grubbing is effective for small
infestations, or for follow-up treatment
after broadacre treatment. To prevent re-
sprouting, plants must be grubbed 5--10
cm below the surface and detached from
Deep ploughing will bury thistle seeds too
deeply for them to emerge if they
germinate. The downside is that deeply
buried seeds survive longer in the soil---
about 10 years.
Shallow cultivation risks creating an ideal
seedbed for new thistle seedlings. But
these are easily killed by herbicides or by
repeated cultivation. Seeds remaining near
the surface have far shorter life---about
The best way to achieve long-term control
is to establish and maintain dense pastures,
especially during late summer and autumn
when the thistles are shedding their seed.
Seedling thistles are intolerant of intense
competition, especially for light. A pasture
cover of 6cm or more can reduce nodding
thistle by more than 90 per cent.
Rotational grazing with high grazing
pressure for short periods, followed by long
spells, will encourage rapid dense pasture
re-growth. Set-stocking and overgrazing
open up pastures in late summer/autumn,
favouring thistle infestation.
If pasture is short, feed silage or hay at this
time, rather than risk over-grazing. Over-
sowing of open pastures with vigorous grass
species will help reduce thistle infestation.
The seedhead weevil reduces seed production
by about 60 per cent a year, but will not
reduce thistle populations when open pasture
allows seedling establishment. It only takes
one seedling in 2,000 to survive and
reproduce to maintain thistle populations and
it takes at least seven years before soil seed
stocks are exhausted.
Goats eat thistle flowers as well as re-growth,
reducing the ground cover of some thistle
species by more than 90 per cent. They reduce
the height and vigour of tall thistles and
Several herbicides are useful for thistle control
in pasture, but the phenoxy (hormone)
herbicides MCPA and MCPB are generally
Phenoxy sprays work best when thistles are
small. In trials at Ruakura, nearly 90 per cent of
small (under 10 cm diameter) nodding thistles
were killed using MCPA, compared with 75 per
cent of large thistles. If thistles are taller than
the sward, a wick or boom wiper can be used,
to reduce damage to clovers.
MCPA is superior to MCPB, but is hard on
clovers. It is best used in winter, when clovers
are not actively growing.
In most parts of the country, blanket spraying
in autumn with MCPB is recommended to kill
seedlings. In warmer districts where germi-
nation occurs in winter, many farmers prefer
early spring treatments (August--early Sept-
In newly-sown pastures, MCPB should be
applied only when clovers have two true
leaves and pasture cover exceeds 50 per cent.
Sprays containing glyphosate (e.g. Roundup®),
Picloram (e.g. Tordon®) and dicamba are very
effective for spot treatment of large rosettes.
However, they are non-selective to clovers and
should not be used for broadacre thistle
Rain within 1--2 days of herbicide application is
one of the main reasons for poor control. If
20--25 cm of rain falls a day after spraying,
control is likely to be reduced by 50 per cent.
Herbicide treatments are not 100 per cent
effective against seedlings in autumn or
rosettes in spring, and are no substitute for
maintaining a dense sward. They are probably
most appropriate to use in seasons when
drought has allowed pastures to open up.
Repeated use of phenoxy herbicides can lead
to the development of herbicide resistant
weeds, as has occurred with nodding thistle.
To reduce the risk of this occurring, observe
label directions and ensure your equipment is
Links Archive December 14th 2012 February 8th 2013 Navigation Previous Page Next Page