Chemical Control

The following information on chemical control measures is supplied by the Department of Primary Industries, Water and Environment.

Although the top growth of Californian thistle is susceptible to many herbicides long term control is difficult to obtain, as it is with most deep rooted perennials.

Correct spray timing is essential for optimum results.

MCPA has been found to be a suitable chemical for general use. Because it acts fairly slowly, good translocation is achieved down into the thistle's root system. However, at the rates required to control established infestations in pastures, it may cause significant short-term damage to clovers.

In lucerne, or in areas where clover damage must be minimal, 2,4-DB gives reasonable short-term control. In cereal crops 2,4-D amine can be used although MCPA or MCPA-dicamba mixtures are more effective.

The use of 2,4-D is restricted to between 15 April and 15 September. A permit is required to use 2,4-D outside this time period.

Trials have shown that clopyralid is very effective for Californian thistle control. Some well-established infestations have been eradicated after applications in two successive years. Clopyralid is most effective when applied as a spot spray or by wiper application.

Clopyralid applied as a boom spray will kill clover present in the treated area and may prevent establishment of clover from seed for up to two years after application. Apart from the expense, boom spray application is not recommended for pastures or for areas where other legume or broad-leaved species are to be sown within two years of treatment.

Clover damage is restricted by spot spraying and generally avoided by wiper application. Grasses are not affected by clopyralid at recommended rates.

For situations where a non-selective herbicide can be used glyphosate is suitable. Glyphosate is translocated readily into the root system and is non-residual in the soil and can therefore be used shortly before a crop is sown. As glyphosate is non-selective and will kill most plants, it should not be boom sprayed unless a broad spectrum kill is required. However in pasture situations glyphosate may be applied broad acre by weed wiping equipment.

As with other thistle species, seedlings are the most susceptible growth stage and provided the plants are growing vigorously, treatment should be applied as soon as germination is complete. Care should be taken to differentiate between seedlings and rosettes that have regrown from root stock as the response to control methods are different.

In established infestations chemical treatment should be delayed until the plants have grown their flowering stems and are at the bud stage. At this point root reserves are at a minimum and the plant begins to move nutrients back down into the roots. This transfer assists in the movement of herbicide throughout the plant. A practical indication of timing is to spray as soon as the first flowers are seen in an infestation. This is likely to occur between December and January.

In contrast to this research in Canada has found application of glyphosate to flowering plants is less effective (but still works) than when applied to rosettes in autumn. When applied to flowering plants the majority of herbicide was retained in the shoot. Application to rosettes in autumn results in a much larger movement of herbicide into the root system. This research has not been duplicated in Tasmania.

Note: These herbicide recommendations are made subject to the product being registered for that purpose under relevant legislation. It is the user's responsibility to check that registration or an off-label permit covers the proposed use. If in doubt, check with the Registrar of Pesticides, Department of Primary Industry and Fisheries, Hobart.

BOOM SPRAY APPLICATION ^#

Herbicide(active ingredient)	Commercial product (content of active ingredient)	With-holding period prior to grazing	Application rate of commercial product *	Comments
MCPA sodium	(250 g/L)	7 days	4 to 4.5 L/ha	Registered for use in various crops only. Rates vary accordingly. Consult product label for further information. 0
MCPA amine	(500 g/L)	7 days	2.2 to 3.5 L/ha	Lower rate for non-crop situations, higher rate for turf. Transitory damage to turf and strawberry clover likely.
2,4-DB	(400 g/L)	7 days	3.5 L/ha	Apply when weeds are as small as possible. Clover - apply from 1st to 8th trifoliate leaf stage.
2,4-D amine	(225 g/L)	7 days	1.7 - 3.0 L/ha	Cereal crops and pasture. Rates vary according to use. Check label for correct rates.
2,4-D amine	(500 g/L)	7 days	0.7 - 4.7 L/ha	Use for thistle seedlings in pasture and cereal crops. Lower rate for crops and pasture with legumes. Higher rate for non-legume pasture. Rates exceeding 2.1 L/ha will cause permanent clover damage.
Clopyralid	Lontrel L ® (300 g/L)	28 days	2.0 L/ha	Use for established infestations in pastures and non-crop situations. Use with MCPA if rosette larger than 20cm. Clopyralid is a residual herbicide and may limit crop rotations. Check the label.
Glyphosate	e.g. Roundup, Glyphosate 360 (360 g/L)	1 day (Allow seven days for improved control)	6.0 L/ha	Use on established infestations in fallow, pre-sowing, orchards or non-crop situations. Lower rates required for pre-emergent use in onion, check the label.

# Use a spray volume of 200 to 250 litres per hectare for dense infestations.

* Rates given are summaries. Always refer to the label for exact rates applicable to the situation.

SPOT SPRAY APPLICATION

Herbicide (active ingredient)	Commercial product (content of active ingredient)	With-holding period prior to grazing	Application rate of commercial product*	Comments
MCPA	(250 g/L)   (500 g/L)	7 days	4 to 8 ml   2 to 4 ml	The higher rate will improve control but will increase clover damage in pasture situations.
2,4-DB	(400 g/L)	7 days	5 ml
Clopyralid	Lontrel L ® (300 g/L)	28 days	2.5 to 5.0 ml	As for MCPA. The addition of a wetting agent improves control.
Glyphosate	e.g. Roundup, Glyphosate 360 (360 g/L)	1 day (Allow 7 days to improve control)	10 ml	Non-selective. Clean water must be used when spraying glyphosate. The addition of a wetting agent improves control.

* Rates given are summaries. Always refer to the label for exact rates applicable to the situation.

WIPER APPLICATION

Herbicide (active ingredient)	Commercial product (content of active ingredient)	With-holding period prior to grazing	Application rate of commercial product	Comments
Glyphosate	e.g. Roundup, Glyphosate 360 (360 g/L)	1 day (Allow 7 days to improve control)	1 part : 2 parts water	Glyphosate is non-selective. When wiping with glyphosate, clean water must be used. The addition of a wetting agent improves control.
Clopyralid	Lontrel L (300 g/L)	28 days	1 part : 2 parts water	The addition of a wetting agent improves control.