Note: Descriptions are shown in the official language in which they were submitted.
- 1 - Case 133-0671
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~ICRO~NCAPSULATXD AGRICULTURAL C~BKICALS
The present invention concerns a microencapsulated agrochemical,
compositions containing it ant processes for its production.
Uhen putting agrochemicals in a suitable form for application,
formulations are desirable which optimise the effect of the active
ingredient on the target organism whilst at the same time minimising
its effect on the environment, particularly with respect to animals
and plants which are not targeted. One such formulation technique
which in recent years has been extensively investigated with respect
to agrochemicals is microencapsulation. Various techniques for
microencapsulation have been known for some time particularly in
connection with pharmaceuticals and dyestuffs.
Examples of known microencapsulation techniques are disclosed
for example in the following patents.
USP 3,516,941 describes the use of urea-formaldehyde (UF) resins
for encapsulating water insoluble fill material including
agrochemicals.
USP 4,105,823 describes the use of UF and melamine-formaldehyde
(MF) precondensates for crosslinking with other soluble polymers to
microencapsulate finely divided particulate material.
U5P 4,534,783 describes a discontinuous two-phase
microencapsulation procedure for water soluble materials including
agrochemicals.
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USP 4,557,755 describes microencapsulation of agrochemicals
employing a cationic urea resin forming polycondensates with UF, MF
or thioureaformaldehyde (TUP) prepolymers.
Each of these references in turn describes further
microencapsulation techniques.
A particular problem encountered with certain agrochemicals
especially herbicides when applied to the soil is their tendency to
leach rapidly from the target zone when sub~ected to rainfall or
irrigation particularly in lighter soils which include coarse to
moderately coarse texture soils and soils of low organic matter
content, e.g. < 2.0 weight Z organic matter. This problem usually
precludes or restric~s the use of such agrochemicals for preemergent
application. Thus in the case of a herbicide suffering from this
drawback persistence in the soil zone where germination of early
weeds occurs can only be achieved, if at all, by repeated application
or application at higher rates which increase the risk of damage to
young crop plants or i9 uneconomical and environmentally undesirable.
In spite of the existence of many varied microencapsulation
techniques in some cases for decades it has until now not been
possible to provide a com ercially viable microencapsulated form of
such rapidly leaching agrochemicals which will achieve the four main
objectives of maintaining weed control, reducing leaching below the
targeted soil zone, increasing persistence in the soil, particularly
the weed seed germination zone, and preventing crop in~ury.
It has now surprlsingly been found that excQllent results can be
obtained by microencapsulating a rapitly leaching agrochemical in a
crosslinked polymer formed from urea-, thiourea- and/or
melamine-formaldehyde prepolymers.
The present invention therefore provides a process for
microencapsulating a rapidly leaching agrochemical comprising the
steps of
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a) adding to a suspension of the agrochemical in a liquid a
urea-, thiourea- or melamine-formaldehyde prepolymer or mixtures
thereof and
b) curing said prepolymer to provide a crosslinked polymer
enclosing the agrochemical.
This microencapsulation process may be carried out in a single
stage or in successive stages by repeating steps a) and b).
In another aspect the invention concerns an agricultural
composition comprising a rapidly leaching agrochemical
microencapsulated in a crosslinked urea-, thiourea, or
melamineformaldehyde prepolymer or mixed prepolymer together with an
agriculturally acceptable carrier.
A further aspect of the invention concerns a method of
controlling undesirable pests or plant growth which comprises
applying to the locus or anticipated locus of said undesirable pests
or plant growth an effective amount of a rapidly leaching
agrochemical microencapsulated in a crosslinked urea-, thiourea- or
melamine-for~aldehyde prepolymer or mixed prepolymer.
A further aspect of the invention concern~ new, very sparingly
soluble salt forms of rapidly leaching agrcchemicals.
Microencapsulation according to the invention is particularly
suited for agrochemicals where the usual locus of the pests or
undesired plant growth to be combatted is in the upper layers of the
soil. Microcapsules according to the inventlon can also be used in
watery loci such as mosquito breeding areas or paddy fields.
Microencapsulation according to the invention is especially
suited to agrochemicals where rapid leaching ability would normally
preclude or restrict pre-emergent long lasting application. Examples
of such agrochemicals are those containing a carboxylic acid group.
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Preferred examples of such compounds are herbicides particularly
pre-emergent herbicides such as benzoic acid and phenoxycarboxylic
acid derivatives e.g. dicamba, MCPA, 2,4-D or as well as other
herbicides e.g. glyphosate, alachlor, acetochlor, metolachlor and
2-chloro-N-[l-methyl-2-methoxyl-N-(2,4-dimethyl-thien-3-yl)acetamide,
which is described in US Patent No. 4,666,502.
The agrochemical may be in a solid crystalline or amorphous form
or in liquid form, e.g. an oil. The agrochemical can be soluble in
the liquid in which it is suspended, but in these cases, the
agrochemical must be present in excess amount, i.e. the liquid should
be super-saturated with agrochemical.
This application is especially directed, therefore, to salt
forms of the aforementioned herbicides which are only sparingly
soluble in the liquid, e.g. water, in which they are suspended, e.g.
inorganic salts such as sodium, potassium, calcium, copper, iron,
aluminium or organic salts such as dimethylamine,
aminopropylmorpholine, and the fatty amine organic salts having
carbon chains of fourteen or more atoms such as the triamylamine,
tridecylamine, dimethyldodecylamine, AdogenR (primary, n-alyl, C16
ave.) and Primene~ (primary tert-alkyl, Cl~ ave.) salt forms.
Preferred salt for-s are those which are only sparingly water soluble
and are stable under hydrolytic conditions, e.g. the aluminium, iron,
copper and calciu- salts.
The aluminium and iron, i.e. the Al(III) and Fe(III) salt forms
of dicamba, HCPA and 2,4-D are the preferred salt forms. It is
believed that the aluminium salt of HCPA and the Fe~III) salt of HCPA
and dicamba are novel.
Such salt forms can be prepared according to conventional and
known procedures for preparing alu-inium or iron salts of compounds
that bear a carboxylic acid group, e.g. by co-bining the compound
with a desired metal e.g. FeCl3 or AlCl3 in solution. In some
situations, metal complexes of the co-pounds will be formed.
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This application is also especially directed to herbicides which
are only sparingly soluble in water, e.g. alachlor, acetochlor,
metolachlor and 2-chloro-N-[1-methyl-2-methoxyl-N-(2,4-dimethyl-
thien-3-yl)acetamide.
Suitable liquids for suspending the agrochemical are inert and
are typically selected such that the agrochemical is only sparingly
soluble therein while the prepolymer or prepolymer mix i9 miscible
therein Typically, the liquid will be water, although organic
liquids that are inert and in which the prepolymer or prepolymer mix
is miscible are also envisaged.
Urea-, thiourea, and melamine-formaldehyde resins, prepolymers
and polymers and their preparation are known in the art and are
described for example in "The Organic Chemistry Synthetic High
Polymers", Robert W. Lenz, Interscience Publishers (1967) pp.
142-151; KIRK-OTHMER Encyclopedia of Chemical Technology, 3rd ed. v.
2 pp. 440-469. Many such resins are prepolymers and are also
commercially available.
Particularly preferred in the practice of the invention are
urea- or melamine-formaldehyde resins and prepolmyers or mixtures
thereof that are miscible in the liquid in which the agrochemical is
suspended, with melamine-formaldehyde resins and prepolymers being
especially preferred optionally mixed with urea-formaldehyde
prepolmyers. ~here mixtures of melamine-formaldehyde (MP) prepolymers
and urea-formaldehyde prepolymers ~UF) are employed, the weight ratio
of HF:UF preferably ranges from 1:4 to 4:1.
In order to optimise the amount of material incorporated in the
microcapsules it may be desirable to have the agrochemical in
sparingly soluble form e.g. preferably in a form that is less than 2
X by weight soluble in the liquid in which it ls suspended, more
preferably less than 1 % by weight soluble. In the case of
agrochemicals capable of forming salts with bases for example
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crystalline salts with heavier metals such as aluminium or iron are
preferred.
To further increase the amount of crystalline material available
for encapsulation and especially in situations where wet milling of
the material to a desired particle size is required prior to
microencapsulation it is advantageous to reduce the amount of liquid
(preferably water) used to suspend the material in most cases to form
a slurry.
The desired particle size of the material to be encapsulated
will vary according to the nature of the material, its intented use
and prepolymer employed. As a rule satisfactory results are obtained
with crystal particle sizes from 1 to 20 ~, preferably 1 to 5, more
preferably 2 or 3, especially ca. 2 ~.
The desired particle size and active ingredient content of the
finished microcapsules will also depend on intended applications.
Satisfactory results are obtained with microcapsules of between 1 and
120 ~, especially 10 to 50 ~, particularly 10 to 25 ~ having active
ingredient content of 10 to 60 X a.i. especially 25 to 35 X for use
in crops. Considerably lower a.i. content of e.g. 1 to 2.5 X may also
be employed for example where use in home gardens or lawns is
envisaged or where tbe active ingredient is highly active at low
concentrations.
The desired particle size can be achieved by milling of finished
agglomerated microencapsulate product or preferably by controlled
crosslinking by employing multi-step addition/curing of prepolymers.
In carrying out the process according to the invention the
material to be encapsulated is suspended or slurried in a liquid,
preferably water. It is a property of rapidly leaching agrochemicals
that they exhibit relatively high solubility in water. Thus when
practising the process of the invention it is desirable to have the
agrochemical in a form which i~ of reduced solubility in order to
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provide an optimal amount of material available for
microencapsulation. More soluble salt forms may be also used but are
subject to stricter control of solvent amount or repeated recycling
to obtain a higher percent content of a.i. if desired.
In order to avoid premature crosslinking of prepolymer it may be
necessary for the suspension of a.i. to be encapsulated to be not too
strongly acid at the initiation of polymerization, e.g. to have a pH
of >4, especially >5Ø This can be achieved by basifying the
suspension with a base however this is less desirable as it may
increase solubility of the crystals. Advantageously the desired pH is
achieved by having the a.i. in a crystalline form which upon
suspension in the desired solvent results in the pH desired, e.g. in
the form of the aluminium or iron salt.
The suspension may optionally contain further additives such as
dispersants, surfactants, antifoaming agents, etc., e.g. those based
on naphthalene sulphonates or acetylenic diols.
Uhen pre-milling of the crystalline a.i. to a desired particle
size is desired the suspension is preferably in the form of a slurry
which may be wet-milled, e.g. by pebble milling.
Advantageo w ly the UF/TUF/MP resins or mixtures thereof are
employed in the form of prepolymers. This has the advantage of
allowing elimination of undesirable traces of unpolymerized urea,
thiourea, melamine and formaldehyde prior to use in the mlcroen-
capsulation process.
The prepolymer or prepolymer mix is preferably added in the same
liquid used to form the slurry and is miscible in such liquid,
usually water. By miscible is meant that the prepolymer or prepolymer
mix is capable of mixing or dissolving in the liquid such that it
surrounds the suspended agrochemical when poly-erization is
initiated. Addition of the desired amount of prepolymer can be
carried out in one aliquot or in a series of lesser aliquots with
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curing after each addition. This latter procedure facilitates careful
control of the particle size of the finished microcapsules and is
preferred.
Alternatively, prepolymer can be formed in situ according to
known methods e.g. as referenced above, and the act$ve ingredient
then added.
The ratio of prepolymer to active ingredient will vary according
to the nature of the a.i. and the prepolymer themselves as well as
the desired properties of the finished product. For some applications
of finished product, satisfactory results are obtained with an excess
of prepolymer e.g. a 1.5 to 6 fold, preferably 2 to 5 fold,
especially 2 to 4 fold. For other applications of finished product,
satisfactory results are obtained with an equivalent to excess amount
of active ingredient, e.g. a weight ratio of prepolymer to active
ingredient of 1:1 to 1:2. Thus, the weight ratio of prepolymer to
active ingredient employed to prepare a finished product suitably
varies from 6:1 to 1:2. Moreover, for some applications, the finished
product may consist of a mixture of microcapsules having various
prepolymer to active ingredient weight ratios.
In cases where dicamba is employed as a.i., it is preferably
employed in iron or aluminium salt foem. ~elamine-formaldehyde and
urea-formaldehyde are preferred prepolymers and are preferably
employed in a weight ratio of prepolymer to dica~ba salt of 4:1 to
1:2, more preferably 2:1 to 1~1.
Curing of the pr-polymer or prepolymer mix can be accomplished
ln conventional manner, e.g. by warming or acit catalysis or both.
Preferably curing is carried out by lowering pH with an acid,
preferably a mild acid such as citric acid or fumaric acid to a pH
below about 6, e.g. pH about 3-6, depending on the particular
prepolymer and reaction conditions and warming to ca. 35 to 50C for
2 to 10 hours with optional additional stirring at room temperature
for ca. 24 hours. Preferably, the pH is about 5 at the initiation of
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polymerisation and can subsequently be lowered to, e.g. 3.
Microencapsulation may be accooplished in a single stage or in
repeated stages, e.g. two, three, four or more stages depending on
the desired release rate of agrochemical and/or particle size. Each
successive stage is carried out by repeating the steps meneioned
above, i.e. by adding a quantity of prepolymer to the reaction
mixture and curing by warming or acid catalyst or both.
The microcapsules may be isolated from the reaction mixture in
conventional manner e.g. by filtration and/or drying.
To facilitate application the microcapsules of the invention may
be formulated in conventional manner, e.g. as dusts, granules,
solutions, emulsions, wettable powders or flowables, suspensions and
the like with conventional carriers and optionally other adjuvants.
To prevent premature release of a.i. solid formulations are
preferred. Such formulated microcapsules may be prepared in
conventional manner e.g. by mixing, spray-drying and the like.
Application of the microcapsules of the present invention is
made according to conventional procedure to the weeds or pests or
their locus using an effective equivalent amount of active
ingredient.
In the case of commercial available products, the effective
amount will be based on the a.i. content and release profile of the
microcapsules to correspond to the known effectlve application rate
e.g. in the case of dicamba 0.05 to 2 lb/ac (approximately O.OS5 to
2.2 kg/ha), especlally 0.1 to 1 lb/ac (spproximately 0.11 to 1.1
kg/ha). The optimum usage of the lcrocapsules of the present
invention is readily by one of ordinary skill in the art using
routine testing such as greenhouse testing and small plot testing.
For example, in the pre-emergent control of weeds a half-life of
from 30-45 days would be desirable (ti-e required for 50 X of a.i. to
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be released from the microcapsule).
Suitable formulations contain from 0.01 to 99 Z by weight of
active ingredient, from 0 to 20 X of surfactant and from 1 to 99.99
of solid or liquid diluent(s). Higher ratios of surfactant to active
ingredient are sometimes desirable and are achieved by inccrporation
into the formulation or by tank mixing. Application forms of a
composition generally contain between 0.01 and 25 X by weight
equivalent of active ingredient. Lower or higher levels of active
ingredient can, of course, be present depending on the intended use,
the physical properties of the microcapsules and the mode of
application. Concentrate forms of a composition intended to be
diluted before use generally contain between 2 and 90 X, preferably
between 5 and 81 X by weight equivalent of active ingredient.
The microcapsules can be combined with a cyclodextrin to make a
cyclodextrin inclusion complex for application to the pest or its
locus.
Agriculturally acceptable additives may be employed in the
composition to improve performance and to reduce foaming, caking and
corrosion, for exa ple.
"Surfactant~ as used herein means an agriculturally acceptable
material which imparts emulsifiability, spreadlng, wetting,
dispersibility or other surface-modifying properties. Examples of
surfactants are sodium lignin sulfonate and lauryl sulfate.
"Diluent~ as used herein m ans a liquid or solid agrlculturally
acceptable material used to dilute a concentrated material to a
usable or deslrable strength. For dusts or granules it can be e.g.
talc, kaolin or diatomaceous earth, for liquid concentrate forms for
example a hydrocarbon such as xylene or an alcohol such as
isopropanol, and for liquid application forms e.g. water or diesel
oil.
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Microcapsule formulations may optionally contain further active
ingredient such as herbicide, insecticides, acaricides, fungicides
and the like. For example, it may be advantageous to formulate
microcapsules according to the invention together with the same or
other active ingredient in unencapsulated form to achieve initial
control prior to the onset of controlled release from the
microcapsules. Such unencapsulated material can for example be
applied in the form of a spray dried coating on the microcapsules.
Alternatively, premix or tank-mix of unencapsulated with encapsulated
material can be appropriate.
Combinations of unencapsulated and encapsulated material should
be formulated in amounts and applied at raees sufficient to achieve
initial weed control without causing undue crop damage. In the case
of Dicamba, satisfactory results are achieved when the unencapsulated
form is applied at a rate ranging from abut 0.125 to 0.25 lb/ac
(about 0.138 to 0.28 kg/ha) whilst the encapsulated form is applied
at a rate of about 1.0 lb a.i./ac (about 1.1 kg a.i./ha). Thus,
suitable weight ratios or formulations containing unencapsulated and
encapsulated Dicamba range from 1:8 to 1:4 unencapsulated:
encapsulated a.i.
As a further alternative a formulation may consist of a mixture
of microcapsules having various prepolymer to a.i. weight ratios.
Combinations mentioned above can allow for effective, continuous
control over periods as long as 1 to 75 days.
The following examples illustrate the invention. Temperatures
are given in degrees centigrsde.
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E~PLE 1
a) Preparation of the aluminium salt of dicamba
100 g of Dicamba aminopropyl morpholine salt (prepared by mixing
technical Dicamba, aminopropyl morpholine and distilled wa.er) in 150
ml of deionized water are mixed with 21.8 g of AlCl3 6H20 in 44 ml of
water at 80 for 2 hours, cooled to 40 and filtered.
b) Preparation of Microcapsules
The wet filter-cake of example la (dicamba-Al content ca. 40 g)
is slurried ~ith 50 ml of deionized water and 2.0 g of Morwet D425
(Sodium Naphthalene Formaldehyde Condensate - Petrochemicals Company,
Inc.) was pebble milled for 9 hrs, a further 20 ml of deionized water
and 0.5 g of Morwet D425 are added and milling continued for a
further 2 hrs. to give a final median particle size of 3.7 ~. This
slurry is diluted with deionized water to 188 g. To this slurry are
added with stirring 172 g of diluted urea-formaldehyde prepolymer
(prepared by refluxing 24 g of urea and 48 g of formaldehyde for 1 hr
at 70 with stirring and diluting the result with 100 ml of deionized
water), 40 g of CYMELR 385 Resin (methylated melamine-formaldehyde
resin formulation containiDg approximately 80 % by weight active
resin, M.W. approximately 250, - American Cyanamid Company) and 2 g
of citric acid dropping the p~ of the slurry from 6.0 to 5.1. The
temperature is slowly raised to 50 with a water bath. After stirring
for 2~ hrs the pH is 4.1. After stirring for a further 4 hrs. a
further 1 g of citric acld is added reducing p~ further to 3.2. After
an additional 1~ hrs. stirring, the mixture is cooled to 40,
filtered and dried at 54 to yield 77 g of median particle size 15.7
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EXAMPLB 1.1
a) Preparation of the iron salt of dicamba
93.0 g of technical dicamba is dissolved in 250 ml water
containing 52.0 g of 45 X K08. The pH is adusted to 7.0 with extra
KOH or dicamba. Uhile the above solution is stirred a second solution
consisting of 36.7 g FeCl3 6H20 dissolved in 71.0 g water is added
dropwise over a period of 1~ hrs. Uhen complete the resulting slurry
is warmed to 60C for 2 hrs. After cooling the salt is filtered,
washed and dried at 54C.
b) Preparation of microcapsules
25.0 g of the salt from part a) is transferred to a (000) Norton
pebble mill along with 4.0 g of Morwet D425? 2 drops of SurfynolR
TG-E (acetylenic diol surfactant - Air Products and Chemicals Inc.)
and water to make a total of 100 g. This slurry is milled for 10 hrs
reducing the mean particle size to 2.2 ~.
The above milled salt is transferred to an 800 ml beaker and
while mixing with an overhead mounted stirrer, 16.6 g of Cymela 385
is added along with 2 drops of Foamastera FLM (30 X silicone emulsion
defoamer - Henkel Corp.) and citric acid to pH 5.6. Tbe system is
warmed by water bath to 50C for 30 min and cooled to 25C. During
the warming cycle a 4.4 X solution of Morwet D425 in water is added
to thin the solution and maintain proper mixing. This procedure is
repeated twice, each time using 16.6 g of Cymela 385. The total
volume is doubled after the last addltlon of Morwet solution. The
capsule slurry ls stirred for 24 hours total, filtered, washed and
dried at 54C to yield capsules containing 18.8 % a.i. with a mean
particle size of 21 ~.
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~XAnPLE 2
a) Preparation of aluminium salt of dicamba
110.5 g of technical dicamba acid are added with stirring to a
mixture of 62.35 g of 45 % aq ROH and 95.65 g of deionized water. A
mixture of 60.35 g of AlCl3-6H20 in 125 g of deionized water is then
added with stirring over a 5 minute period followed by further 10 g
of deionized water. A further 31.16 g of 45 X aq. KOH and 10.33 g of
deionized water are then added and the resulting mixture refluxed for
2 hours with stirring at 80. The resulting mixture is then filtered.
b~ Preparation of microcapsules
A slurry of the wet filter cake from Example 2a) (Dicamba-Al
content ca. 30 g) is pebble milled with 115 g of deionized water 4 g
of MORWET D425 and 3 drops of SURFYNOLR TG-E to a median particle
size of 1.8 ~. To this slurry is added 20 g of CYMEL 385 in 40 g of
deionized water and 1 g of citric acid to pH 5.4 and the temperature
raised (water bath) over a 2 hr period to ca. 40. After cooling to
ca 25 a further 20 g of CYMEL 385 in 50 g of deionized water are
added and the temperature again raiQed to ca 40 over 1 hr. This
procedure is repeated with a further 20 g of CYHEL 385 in 44 g of
deionized water. After final cooling the mixture is filtered and the
microcapsules dried at 54 to yield a edian particle size 18.9 ~.
BXAMPLB 3
The procedure is analogous to Exa ple 2 except that the higher
temperature in the microencapsulated phase is 50 rather than 40.
microcapsules of median particle size 20.3 ~ are obtained.
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EXAMPLB 4
The active ingredient content of the microcapsules is determined
by heating the capsules with concentrated HCl, diluting the resultant
solution, and analysing by HPLC with external standard quantitation.
The a.i. content of the capsules of Examples 1, 1.1, 2 and 3 is
33, 18.8, 33 and 31 % respectively.
~XA~PLB 5
Formulation as wettable powder
The following components are combined to yield a wettable
powder.
a) Microcapsules according to Example 2b): 94 X.
b) Aerosol OTB (American Cyanamid - Dioctylester of
Na-Sulfosuccinic acid): 3 Z and
c) Morwet D425: 3 %
The inerts are preground before mixing with microcapsules to
avoid capsule breakage.
~PLB 5.1
Sprayable formulation
75 Parts by weight of mlcrocapsules prepared according to
Examples l, 1.1, 2 or 3 are slurried in water. 25 parts of Morwet
D425 are added and the resulting mixture is spray dried to yield a
sprayable formulation.
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EXAHPLe 6
Field Test
Velvetleaf, red root pigweed and morningglory seeds are planted
and tilled ca. 2 inches (5.1 cm) deep and corn seed then sown. The
microcapsules of Examples 1, 2 and 3 (as wettable powders) and
BanvelR (dimethylamine salt of Dicamba - ~andoz Crop Protection
Corporation) are then applied to the soil surface by spraying aqueous
tank mix at a rate of 1 lb per acre (about 1.1 kg/ha dicamba acid
equivalent) with 3 replications. One inch (2.54 cm) of water is
applied immediately after application followed by 1.25 inches (3.2
cm) 2 days later. Weed control and corn in~ury are evaluated 2 weeks
after treatment. After evaluation a further 3 inches (7.6 c~) of
water are applied over a 2 day period. Plots are treated with
Gramoxone Super (paraquat, ICI Americas Inc.) at 0.5 lb a.i. per acre
(about 0.55 kg/ha) and 5 dayc later velvetleaf and pigweed are resown
and further 2.5 inches (6.4 cm) of water applied. Evaluation of weed
control takes place 42 days after replanting.
The formulations of Examples 1, 2 and 3 showed no control at two
weeks compared with BANVEL whereas after 65 days control was as
follows:
~ of Co~trol
Bxa plesVelvetleaf Pigveed
1 81 84
2 85 84
3 96 98
Banvel O O
This demonstrates the excellent persistence in the veed target
zone of the microcapsules according to the invention compared with
the same active ingredient in conventional form.
