AU2002319833B2 - Plant treatment composition - Google Patents

Description

Technical Field

This invention relates to a plant treatment composition in the form of a

phosphorus containing solution. In one embodiment of the invention the

plant treatment composition may comprise a fertilizer. In one particularly

important embodiment of the invention the plant treatment composition

may comprise a composition for treating plant diseases, especially fungi

Background Art

The use of phosphorous acid and phosphites as fertilizers and/or

fungicides are well known. When used as a fungicide the phosphorous

acid is often injected into the trunk of the plant, but it may also be sprayed

onto the leaves of the plant, painted onto the stem and/or applied to the

soil around the plant stem.

One well-known current commercial phosphorous acid trunk injection

solution for use on avocado trees comprises an un-neutralised aqueous

phosphorous acid solution. However, in order to obtain successful

application by injection a large number of holes have to be drilled in each

trunk (up to about 20 holes) and the solution has to be injected in small

quantities at frequent intervals. This is necessary due to the phytotoxicity of the phosphorous acid solution which causes leaf burn if not applied in

this manner. A further problem is that the holes 'bleed' profusely and

secondary infection of the holes becomes a problem. Severe necrosis of

hard wood around the injection sites was also observed.

It is also know to use neutralised aqueous phosphorous acid solutions as

trunk injection solutions. Usually KOH and K₂C0₃ are used to neutralise

such phosphorous acid solutions. The neutralised solutions have reduced

phytotoxicity (less leaf burn) and reduced hole damage.

It has now been found that if a solution comprising a mixture of

phosphorous acid (and/or phosphites) and ethanol is used as a trunk

injection solution in avocado trees, improved uptake and translocation are

obtained.

Disclosure of the Invention

According to the present invention there is provided a plant treatment

composition formed by the mixture of

- a phosphorus compound; and

an organic polar solvent. The plant treatment composition preferably comprises a solution,

preferably with the phosphorus compound being dissolved in the organic

polar solvent.

The solution may comprise a concentrated solution of the phosphorus

compound. Preferably the solution has a concentration from 1 mol.dm^"3 to

7.5 mol.dm^"3 of the phosphorus compound. More preferably the

concentration is from 3 mol.dm^"3 to 7.5 mol.dm^"3. Most preferably the

concentration is about 6.1 mol.dm^"3.

The phosphorus compound may comprise an acid, preferably a compound

selected from the group consisting of phosphorous acid,

hypophosphorous acid, polyphosphorous acid, polyhypophosphorous

acid, and salts thereof.

Preferably the phosphorus compound comprises phosphorous acid.

The organic polar solvent preferably comprises a solvent for the

phosphorus compound. The organic polar solvent may comprise an

alcohol. The alcohol may include more than one hydroxyl group, but

preferably it includes a single hydroxyl group. Preferably it comprises

ethanol. In one embodiment of the invention the plant treatment composition may

consist of only the phosphorus compound dissolved in the organic polar

solvent and without the presence of a basic compound. This is especially

the case where the pH of the composition does not play an important role

in the application method. If foliar application, for example, is considered,

the pH of the solution may need to be adjusted in order that the

composition has a suitable pH for foliar uptake. In such a case a basic

compound or compounds may have to be added to the mixture.

Alternatively or additionally, the composition may also include one or more

plant nutrients such as macro-nutrients and/or micro-nutrients.

The composition mixture may accordingly include a basic compound

which increases the pH of the composition. The basic compound may

comprise a compound including an alkali metal salt or an alkaline earth

metal salt. In one embodiment of the invention it may comprise a

potassium salt. The potassium salt may comprise K₂C0₃ or KOH. It will

be appreciated that the potassium from the potassium salt can also serve

as a macro-nutrient.

The pH of the composition may be adjusted as required depending on factors such as the plants to be treated or the method of application of the

plant treatment composition. If foliar application is contemplated, the pH

of the composition should be suitable for foliar uptake. Usually this is at a

pH from about 5 to 7. Preferably the pH is from about 6 to 7. Most

preferably it is about 6.5. In the case of trunk injection or drench

applications the pH should usually be between about 0.5 and about 9.

Preferably the pH is from about 4 to 8. Most preferably it is about 6.5.

A plant nutrient such as a source of nitrogen may also be added. The

nutrient may comprise urea, ammonium nitrate, potassium nitrate,

magnesium nitrate or calcium nitrate.

The composition may also include water. Water may be added in cases

where a compound such as a basic compound and/or nutrient is added

which is not soluble in the polar organic solvent, but which is soluble in

water, or where such compound is added in such an amount that it does

not fully dissolve in the organic solvent and where water is required to

substantially fully solubilise the compound.

The volume percentage of water can vary greatly but ideally it may be at

about 39.5%. The plant treatment composition may also include a surfactant, especially

in the case where an organic polar solvent and water are included in the

composition. The surfactant may be added to ensure that a monophasic

solution forms.

The surfactant may comprise any suitable surfactant, and in one

embodiment of the invention it may comprise propylene glycol.

It will be appreciated that the composition of the plant treatment

composition is expressed in terms of the starting materials used in the

composition. It will be appreciated that in certain cases the phosphorus

compound, the polar organic solvent and other compounds of the mixture

such as a basic compound or nutrients may react with each other to form

reaction products and/or they may dissolve to form dissolved species. For

example where the composition includes a mixture of phosphorous acid

(H₃PO₃); ethanol, potassium carbonate (K₂C0₃) and water, dissolved

species of, KH₂P0₃, K₂HP0₃, as well as salts of the potassium and the

ethanol may form.

A source of boron may also be added.

The composition may be buffered. Preferably an imidazole and hydrochloric acid buffer is added.

The plant treatment composition may comprise a fertiliser.

In a preferred embodiment of the invention the plant treatment

composition may be used for treating plants against plant diseases.

Preferably the plant treatment composition comprises a fungicide.

Preferably it comprises a fungicide suitable for use against Oomycetes,

preferably for use against Peronosporales, preferably for use against

Phvtophthora, and Pvthium and Plasmopara species.

According to another aspect of the present invention there is provided a

method of preparing a plant treatment composition comprising the step of

mixing together:

a phosphorus compound; and

an organic polar solvent.

Other compounds, in the amounts and ratios as indicated above may also

be added to the mixture.

According to another aspect of the present invention there is provided a

plant treatment composition prepared by the method substantially as described hereinabove.

The invention also relates to the use of the plant treatment composition

substantially as described hereinabove for treating plants or a locus,

especially a locus where plants are cultivated or are to be cultivated.

Preferably the plant treatment composition is used as a fungicide.

Alternatively or additionally the composition may be used as a fertiliser.

The composition may be applied to the plants, for example by spraying the

plants (preferably spraying the foliage of the plants), painting the stems or

drenching their roots. Preferably the solution is injected into plants, and

preferably into the stems of plants.

The invention also relates to a method of treating a plant or a locus

comprising applying to the plant or locus the plant treatment composition

substantially as described hereinabove.

The invention will now be further described by means of the following non-

limiting examples: Example 1

Composition with surfactant in the form of propylene qlvcol

Ethanol (95% ethanol, 5% methanol) in an amount of 200ml was

introduced into a beaker. The ethanol was stirred and 505g of dry

phosphorous acid (99% purity) was added to the ethanol. The solution

was stirred until almost all the phosphorous acid dissolved.

Anhydrous potassium carbonate (99,5% purity) in an amount of 440g was

slowly added to the solution in order to maintain the temperature below

65°C. The potassium carbonate did not fully dissolve. The mixture was

thoroughly stirred and 395ml water was then slowly added thereto. This

mixture was thoroughly stirred until there was no further effervescence.

Two layers formed.

Propylene glycol (surfactant) in an amount of 130ml was then added to the

mixture under constant stirring. A green dye in the form of 0,005g

Hexacol Acid Green dissolved in 5ml of water was then added to provide a

monophasic solution with a green colour.

The resultant solution had a pH of about 6.5 and a specific gravity of about 1 ,322 g/ml.

Example 2

Composition without surfactant (propylene glvcol)

Ethanol (95% ethanol, 5% methanol) in an amount of 200ml was

introduced into a beaker. The ethanol was stirred and 505g of dry

phosphorous acid (99% purity) was added to the ethanol. The solution

was stirred until almost all the phosphorous acid dissolved.

Water in the amount of 462ml was then added to the solution, which was

stirred until all phosphorous acid had dissolved.

Anhydrous potassium carbonate (99.5% purity) in an amount of 320g was

slowly added to the solution in order to maintain the temperature below

approx. 65°C. Once all the potassium carbonate had been added, the

solution was stirred until no more effervescing occurred. A monophasic

solution was obtained.

Lastly a dye, in the form of Hexacol Acid Green, in the amount of 0,005g

dissolved in 5ml water was added to the solution. The resultant solution had a pH of about 3.0 and a specific gravity of about

1.31g/ml.

Example 3

Comparison with aqueous phosphorous acid solution

1. Preparation of aqueous phosphorous acid solution.

Phosphorous acid flakes (99% purity) in the amount of 205g, was

dissolved in 300ml water.

Anhydrous potassium carbonate (99.5% purity) in an amount of

169g was slowly added to the solution to limit the amount of

effervescing. The solution was stirred until no further effervescing

was observed.

Potassium hydroxide flakes (90% purity) in an amount of 122g was

slowly added to the solution. The solution boiled due to the

exothermic reaction. This was also stirred until all had dissolved. Urea low biuret (46% nitrogen mass/mass) in the amount of 10g

was then added and dissolved.

A buffering system in the form of imidazole/hydrochloric acid buffer

(3.5g imidazole/2.43g hydrochloric acid 32%) was then introduced

into the solution.

A dye in the form of 0,005g Hexacol Acid Blue, dissolved in 5ml

water was then added to the solution.

The volume of the solution was then topped-up with water to 1

000ml.

The resultant solution had a pH of about 7.2 and a specific gravity

of about 1 ,24g/ml.

2. Application

The aqueous solution and a solution according to example 1 was

each applied to four different avocado trees of the Pinkerton

cultivar. The trees were about 8 years old with a height of about

4.0m and a diameter of about 4.0m. The trunk diameters were

about 200mm and the trees had a slight woodiness which indicated that they were mildly affected by root rot.

Four injection holes were provided in each tree at a height of about

100 to 150mm above ground level. Each hole was about 30mm

deep and had a diameter of 4.8mm. The holes were angled

downwards at 20 to 30° to the horizontal.

The aqueous solution was applied in an amount of 80ml per tree

thus providing a dose of 1 ,0g phosphorous acid per square meter of

tree area (calculated as height x width).

The ethanol solution of example 1 was applied in an amount of

20ml per tree providing a dose of 0,625g phosphorous acid per

square meter of tree area (calculated as height x width).

The trees were injected on 8 March 2000 and fruit were sampled at

14, 28 and 42 days after injection to determine phosphorous acid

residue therein.

Results

The phosphorous acid residues (mg/kg) in duplicated analyses of

the flesh of the avocado fruit were as follows:

Discussion

With the ethanol solution according to the invention the

phosphorous acid moved into the fruit much quicker than in the

case with the aqueous solution, that is despite the fact that the

aqueous solution was applied at a higher dosage rate of

phosphorous acid. Accordingly the ethanol solution according to

the invention is absorbed at a quicker rate and is more mobile in the

plant compared to the aqueous solution.

Another important aspect is that with the ethanol solution according

to the invention maximum residue of phosphorous acid in the fruit

was obtained at about 28 days, and two weeks later it reduced to

about half of the maximum residue. A maximum allowable

phosphorous acid residue value of 50 ppm in the fruit is generally

considered to be acceptable. It is known that when an aqueous

solution of phosphorous acid (without ethanol) is injected into avocado trees the residue value of the phosphorous acid only dips

below 50ppm after 100 days (the withholding period). Due to the

high mobility of the solutions according to the present invention it is

expected that the withholding period will drop to about 30 days.

The significance of the above is that if it is required to treat a tree

against root rot such treatment could previously not take place

within 100 days of picking when the known aqueous compositions

were used. With a composition according to the present invention

the withholding period can be drastically reduced. It has also been

found that in South Africa late summer rains frequently create

conditions favourable for the development of Phytophthora root rot

and there is a practical need for trunk injections in the

February/March period which falls within the 100 days withholding

period of early maturing fruit. The present invention makes this

treatment possible.

It has also been observed that with the solution according to

example 1 injection holes in the tree trunk healed substantially

completely when they were inspected about 8 months after

injection. This is opposed to the situation where conventional un-

neutralised aqueous solutions of phosphorous acid were used, in which case healing of injection holes is a major problem.

Lower volumes of the composition according to the invention can

also be used and smaller syringes can accordingly be used. Due to

the lower volumes, the injections are a lot quicker. The composition

also causes less damage to trees.

It will be appreciated that many variations in detail are possible without

thereby departing from the scope and spirit of the invention.

Claims (18)

1. A plant treatment composition formed by the mixture of

- a phosphorus compound ; and

- an organic polar solvent.

2. The composition of claim 1 which is a solution wherein the

phosphorus compound is dissolved in the organic polar solvent.

3. The solution of claim 2 wherein the phosphorus compound

comprises a compound selected from the group consisting of

phosphorous acid, hypophosphorous acid, polyphosphorous acid,

polyhyposphorous acid, and salts thereof.

4. The solution of claim 2 wherein the organic polar solvent comprises

an alcohol.

5. The solution of claim 2 wherein the phosphorus compound

comprises phosphorous acid and the solvent comprises ethanol

wherein the phosphorous acid is dissolved.

6. The solution of claim 2 which includes a basic compound which

increases the pH of the solution.

7. The solution of claim 2 which includes a plant nutrient.

8. The solution of claim 2 which includes water.

9. The solution of claim 8 which includes a surfactant.

10. The solution of claim 9 wherein the surfactant comprises propylene

glycol.

11. The plant treatment composition of any one of the preceding claims

which is a fertiliser.

12. The plant treatment composition of any one of claims 1 to 10, which

is a composition for treating plants against plant diseases.

13. A method of preparing a plant treatment composition comprising the

step of mixing together:

- a phosphorus compound; and

- an organic polar solvent.

14. The use of a composition of any one of claims 1 to 10 for treating

plants or a locus.

15. The use of claim 14 wherein the composition is used as a fertiliser.

16. The use of claim 14 wherein the composition is used as a fungicide.

17. The use of any one of claims 14 to 16 wherein the composition is

injected into plants.

18. A method of treating a plant or a locus comprising applying to the

plant or locus the plant treatment composition substantially as

described hereinabove.