Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
This invention relates to a herbicidal method and in
particular to a method for controlling weeds in a brassica
crop.
The control of weeds in a crop by means of a selective
herbicide is common practice and in our British Patent No.
862,226 we describe the use of 4-chloro-2-oxobenzothiazolin-
3-ylacetic acid and a wide range of al~ali metal salt, amine
salt, amide and ester derivatives for this purpose.
We have now discovered that the alkyl esters of 4-chloro-
2-oxobenzothiazolin-3-ylacetic acid have the surprising advan-
tage of being safer than other derivatives for controlling
weeds in a brassica crop.
Accordingly, the method of the invention is one for
selectively controlling the growth of weeds after their
emergence in a brassica crop which comprises applying to the
crop area an alkyl ester of 4-chloro-2-oxobenzothiazolin-3-
ylacetic acid, the alkyl group of the ester containing from
1 to 4 carbon atoms, at a rate sufficient to control the weeds
but avoiding permanent damage to the crop.
The use of other derivatives of 4-chloro-2-oxobenzothia-
zolin-3-ylacetic acid can give rise to significant phytotoxic -
damage to the brassica crop when the active compound is
applied at a rate sufficient to control the weeds infesting
the crop area. This phytotoxic effect shows itself in various
ways, for instance as growth depression and fasciation, and
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leads to los~ in yield. In this respect the Cl~C4 ester~ of
4-chloro-2-oxo~enzothia~olin-3-ylacetic acid show a distinct
improvement over other derivatives. The ester is one contain-
ing an alkyl group of 1 to 4 carbon atoms for examp~e, a
methyl, ethyl, propyl or butyl derivative, the most preferred
group being ethyl.
Brassica crops include, for example, cauliflower, swede,
turnip, cabbage, kale and, in particular, oilseed rape.
Important weeds often occurring in these crops that can be
controlled bv the method of the invention include Galium
aparine (cleavers), Stellaria media (chickweed), Sinapis
arvensis (charlock), Polygonum convolvulus (black ~indweed~
and Polygonum avic~lare (knotgrass).
In order to obtain a mixture having a broader range of
weed control it can sometimes be desirable to include one or
more additional heribicide. These include for example a sub-
stituted urea such as diuroni dalaponi a triazine for example
simazine or desmetryne; a substituted acetanilide for example
propachlor a carbamate for example chlor propham; a thiol-
carbamate for example EPTC or triallate: a halobenzoic acidfor example dicamba propyzamide: or a halogenated aliphatic
acid for example sodium monochloracetate. When this additional
herbicide is in salt form it is preferably a salt of an alkali
metal or a water-soluble amine salt,
In the method of the invention the active ingredient
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is applied after the emergence of the weeds. Treatment is usually
carried out when the crop is at an early stage of growth and the
weeds are in the young plant stage, for example in the case of spring
or autumn sown oilseed rape, before the appearance of flower buds.
Both the nature and stage of growth of the crop and weeds are
considered in chcosing the optimum time for treatment. The rate of
application of the active ingredient, expressed in terms of the free
acid, is preferably within the range of from 0.1 to 2 kilograms
per hectare, more especially from 0.2 to 1 kilograms per hectare.
It can be applied in any form known in the art for the formu]~tion
of herbicidal compounds and preferably, for example, as a dispersion,
an aqueous emulsion or as microgranules.
The invention is illustrated by the following examples.
EXAMPLE 1
A field of spring-sown oilseed rape before the appear-
ance of flcwer buds and infested with chickweed (Stellaria media),
knotgrass (Polygonum aviculare), black bindweed (Polygonum convol-
vulus) and charlock (Sinapis arvensis~ at a young plant stage was
divided into rectangular areas. The areas were sprayed at various
application rates with aqueous preparations of the potassium salt
and ethyl ester of 4-chloro-~-oxobenzothiazolin-3-ylacetic acid and
later the areas were examined and the degree of control of the
weeds was assessed on an arithmetic scale of 0 to 10 (0 represents
no eff~ct; 10 represents 100 per cent kill) in comparison with
control areas which had received no chemical treatment. The results
obtained are the average of replicate values. On the arithmetic
scale of 0 to 10, a value of 7 or above represents a commercially
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acceptable degree of control of the weeds. The same scale was used
in oLder to judge the effect on the crop, a value of 0 representing
no trace of damage.
Spraying was carried out when the crop was at the 5-6
leaf stage and assessments were made at intervals of two and seven
weeks after spraying. Quantities are expressed in terms of the
free acid (oz per acre).
(a) After two weeks
Active ingredient Active ingredient
_ (potassium salt) _ (ethyl ester)
80z lOozl20zl60z 80z lOoz l20zl60z
Crop 2.0 1.02.3 4.3 0 0 1.7 3.0
Charlock 8.3 8.79.0 9.3 8.3 8.7 9.0 9.0
Chickweek 8.7 8.78.7 9.0 7.7 8.0 8.0 8.3
Black bindweek 4.7 5.07.3 7.3 4.0 S.0 7.3 7.0
Knotgrass 4.7 5 07.3 7.3 4.0 S.0 7.3 7 0
(b) After seven weeks
_ _ _
Active ingredient Active ingredient
(potassium salt) (ethyl ester)
80z lOoz 120z ¦ lEoz 80z lOoz 120z160z
Crop 0.7 0.3 0.7 1.3 0 0 0 0
. .
Charlock 10 9.3 9.7 9.7 9.3 9.3 9.3 9.3
Chickweed 10 10 10 10 10 10 10 10
Black bin~weed 10 10 10 lQ 10 10 10 10
Knotgrass 7.0 8 3 7.7 7.7 7.7 8.7 8.0 10
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It can be seen rom the above results that good weed
control is obtained using both the potassium and ethyl ester forms
of 4-chloro-2-oxobenzothiazolin-3-ylacetic acid but that a con-
sistent phytotoxic effect on the crop was observed when the
potassium form was used. A small degree of phytotoxicity was
observed at the higher rates of app~ication of the ester after the
short interval of two weeks but this had entirely disappeared
after seven weeks. In the case of the crop treated with potassium
salt damage persisted until harvest.
EXAMPLE 2
A field of autumn-sown oilseed rape before the appearance
of flower buds and infested with weeds was divided into test plots
which were sprayed at a rate of 500 gms. per hectare with aqueous
preparations of 4-chloro-2-oxobenzothiazolin-3-ylacetic acid in the
form of various derivatives. An evaluation of the effect of the
herbicide on the crop was made after an interval of six weeks from
spraying, with the following results.
Active Ingredient Effect on Crop
Potassium salt 4
Dimethylamine salt 3
Ethyl ester 0
Good control of weeds was observed in all three instances.
The effect on the crop was judged according to the scale described
in Example 1, 0 representing no trace of damage. These results
indicate that the ester of the active ingredient was much the
safest of the derivatives. No phytotoxic effect was observed with
its use, in contrast to the potassium and dimethylamine salts which
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badly damaged the crop.
A similar trial was carried out at the same time as that
described above on plots of swede, at an application rate of 450
gms. per hectare, ~ith the following results.
Active Ingredient Effect on crop
Potassium salt 4
Dimethylamine salt 5
Ethyl ester O
Good control of weeds was again observed with no damage
to the crop in the case of the ethyl ester. The potassium and
dimethylamine salts, however, resulted in significant damage to
the crop.
EXAMPLE 3
This example describes a dispersibl~ powder formulation
suitable for use, when diluted with water, in the method of the
in~ention.
~ The dispersible powder was prepared by grinding together
a mixture of the following ingredients in a hammer mill.
% W/w
Ethyl 4-chloro-2-oxobenzothiazolin-3-ylacetate 27.87
Dyapol PT* ~Trade Mark) 5.0
Sodium dioctylsulphosuccinate 0.5
Colloidal silicic acid 5.0
2~ Koalin to 100.0
* A sulphonated condensate of urea, cresol and formaldehyde.
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EXAMPLE 4
This example describes an emulsifiable concentrate
suitable for use, when diluted with water, in the method of the
invention.
The emulsifiable concentrate was prepared by mixing the
following ingredients.
% w
Ethyl 4-chloro-2-oxobenzothiazolin-3-ylacetate 16.75
Wettol EMl* (Trade Mark) 3.2
Wettol EM3+ (Trade Mark) 4.8
Cyclohexanone 30.0
Xylene to lOO.OO
*A calcium alkylarylsulphonate emulsifier.
+An ethoxylated alkylated vegetable oil emulsifier.
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