EP0732877A1

EP0732877A1 - Nonphytotoxic aqueous polysulfide contact fungicides and their use

Info

Publication number: EP0732877A1
Application number: EP95903660A
Authority: EP
Inventors: Jorge Miller; Alberto Kling
Original assignee: PUNTO QUIMICA Ltda
Current assignee: PUNTO QUIMICA Ltda
Priority date: 1993-12-10
Filing date: 1994-11-30
Publication date: 1996-09-25
Also published as: WO1995015692A1; AU1264195A; EP0732877A4

Abstract

Lime-sulfur solutions are used to make effective aqueous polysulfide contact fungicides useful for application to plants.

Description

NONPHYTOTOXIC AQUEOUS POLYSULFIDE CONTACT FUNGICIDES AND THEIR USE

Field of the Invention

Stable aqueous polysulfide compositions are useful fungicidal compositions for plants.

Background Sulfur has many allotropic forms. When sulfur is vapor vaporized at a high temperature and quenched in carbon disulfide, a linear chain of sulfur forms; such sulfur chain is insoluble in carbon disulfide. The same happens when acid is added to calcium polysulfide; part of the sulfur formed in also linear and insoluble in carbon disulfide.

Normal sulfur, S8, is soluble in carbon disulfide and is a closed ring octahedron. When hydrogen end bonds are present, they prevent ring closure, except when the linear polysulfidric molecule is too long, where it can break in to S8 and hydrogen sulfide or short polysulfides. Eventually all linear sulfur reverts to S8.

Sulfur and polysulfides are effective contact fungicides. Polysulfides are more effective than sulfur alone; calcium polysulfide (lime-sulfur) is most effective, but has a disadvantage in being phytotoxic in view of its high alkalinity. The active fungicidal ingredient in lime-sulfur is actually the polysulfide ion.

Unfortunately, the polysulfide ion, even a double sulfur sulfide ion, decomposes to hydrogen and free sulfur, thus decreasing its fungitoxic properties. According to Kirk and Othmer's "Encyclopedia of Chemical Technology", Third edition, Vol. 22, p. 122, except for hydrogen sulfide, the sulfanes (H₂S_X) "have had no practical utility." "Individual hydrogen polysulfides have been characterized from H₂S₂ up to at least H₂S₈. They are of no commercial utility by themselves...". Lime-sulfur is prepared, e.g., by boiling together one part by weight of stone lime, two parts by weight of ground sulfur, and eight parts by weight of water to obtain a water soluble mixture of calcium pentasulfide (CaS₅) , calcium tetrasulfide (CaS₄) , calcium thiosulfate (CaS₂0₂) and insoluble calcium sulfite (which can be removed by filtering to obtain a lime-sulfur solution) .

By adding acid to the lime-sulfur solution, pentasulfhydric acid (HSSSSSH) and tetrasulfidric acid (HSSSSH) are formed. These polysulfidric acids rapidly decompose into hydrogen sulfide and colloidal sulfur which, in time, crystallizes to octasulfide (S8). Summary of the Invention

An object of this invention is to find and to prepare a polysulfide fungicide comprising polysulfide ions protected from losing their ionic characteristic and their fungitoxic properties. A further object of this invention is to produce aqueous fungicidal compositions which are not phytotoxic or deleterious to plant leaves. A still further object of the invention is to provide a contact fungicide for plants which can be applied by spraying. Other objects of this invention are apparent from the following details.

Details There are a number of distinct aspects of this invention. One aspect of the invention is an admixture of equal parts by volume of an aqueous li e- sulfur solution containing about 2 gram mols per liter of calcium and an aqueous solution containing about 4.4 gram mols of ammonium salt and about 0.4 gram mol of ammonia per liter. Another aspect of the invention is such a composition which is freshly prepared. A further aspect involves such admixture, particularly one which is freshly prepared, in combination with from about 175 to about 500 parts by volume of water per part by volume of the admixture.

Other aspects of the invention include the use of thus-diluted admixtures as contact fungicides for plants. A significant aspect of the invention is an aqueous fungicidal polysulfidric acid composition which has a basic pH and is not phytotoxic or deleterious to plant leaves, particularly such compositions having a protected polysulfide ion. A still further aspect of the invention involves spraying such an aqueous fungicidal composition on plants as a contact fungicide.

In the context of the disclosure and claims, a number of terms are used which warrant further definition. The term "about" means plus or minus ten percent; the term "polysulfidric acid" means a compound having a chain of sulfur atoms with a hydrogen atom at each end; the term "protected" means that the polysulfide ion is storage stable under normal ambient conditions for up to 5 days; the term "promptly" means within 5 days, advantageously within less than 4 and preferably within one day; the expression "freshly prepared" means prepared within one day and preferably within four hours.

By adding a water-soluble ammonium salt (rather than acid) to the lime-sulfur solution (filtrate) , the corresponding calcium salt and ammonium polysulfides are formed. When the ammonium salt is, e.g., ammonium nitrate, calcium nitrate and ammonium polysulfides are formed. The pH of the resulting solution is practically neutral, and part of the ammonium polysulfides decomposes, forming ammonium sulfide and free sulfur.

2NH₄-S-S-S-S-S-NH₄ → 2(NH₄)₂S + 8S (I) The equilibrium reaction: 2NH₄OH + H-S-S-S-S-H → NH₄-S-S-S-S-NH₄ + 2H₂0 (II) indicates that, according to the law of mass action, a higher concentration of ammonium hydroxide than for the simple neutralization of the lime-sulfur solution with an ammonium salt is required to preserve the polysulfidric ion. By providing an excess of ammonium hydroxide, in addition to a water-soluble ammonium salt, protection of the polysulfide ion is ensured. The resulting pH of the solution is that of ammonium hydroxide, which is not phytotoxic or deleterious to plant leaves. When ammonium nitrate is the water- soluble ammonium salt employed, the formed calcium nitrate simultaneously serves as a foliar fertilizer. The excess ammonium hydroxide also prevents formation of ammonium hydrosulfide, which has a high vapor pressure and is very toxic. In view of the low dissociation constant of polysulfidric acid and ammonia, ammonium polysulfide hydrolyzes to free ammonia and free polysulfidric acid, which, in turn, partially decomposes as follows: 2H-S-S-S-S-S-H → H-S-S-S-S-S-S-S-S-S-H + H₂S (III) This reaction proceeds until the sulfur chain (without losing its end hydrogen bonds) precipitates out, forming colloidal sulfur with hydrogen bonds at its ends. Such colloidal sulfur maintains its high fungitoxic properties.

The preferred method for fumigation comprises preparing and applying compositions as follows:

Boil together one part by weight of limestone, two parts by weight of ground sulfur and eight parts by weight of water to obtain a water-soluble mixture of calcium pentasulfide, calcium tetrasulfide, calcium thiosulfate and insoluble calcium sulfite. Filter out the calcium sulfite to obtain a filtrate (lime-sulfur solution) .

Mix one liter of lime-sulfur solution containing two gram mols of calcium ions (Ca⁺⁺) with one liter of a solution containing 4.4 gram mols of ammonium nitrate (NH₄N0₃) and 0.4 gram mol of ammonia (NH₃) . This mixture (primary mixture) is made immediately (preferably without any delay whatsoever) prior to dilution. Such mixture is diluted, e.g., with 400 liters of water and sprayed on plants as a contact fungicide. The resulting admixture is particularly useful for peach and other fruit trees where fungi adhere to the trunk.

When the primary mixture (two liters) is diluted with 800 liters of water and applied to rose bushes afflicted with mildew, it is found suitable for controlling the mildew completely without affecting even new-born tender leaves or rose petals. Field trials reflect that such dilution compares favorably with dilutions of one liter of lime-sulfur solution in 100 liters of water, without the phytotoxic effect of the latter.

Immediate application of the diluted primary mixture is more effective than keeping such diluted admixture for more than five days. The diluted primary mixture should be used within 4 (preferably 2 and, most advantageously, 1) days of such dilution.

Maintaining the primary solution without dilution is counterproductive and ill-advised; it increases the size of the polysulfide. Leaves to which the composition is applied thus require higher doses for the same coverage.

Although fungitoxic properties and non- phytotoxicity remain high, compared to those of different wettable sulfur fungicides available on the market, freshly-prepared fungicidal compositions of this invention are even more effective and more economic to use than compositions that have been stored for any period of time. The invention and its advantages are readily understood from the preceding description. Various changes may be made in the method of making and the method of using the compositions, as well as in the compositions themselves, without departing from the spirit and scope of the invention or sacrificing its material advantages. The methods and compositions described herein are merely illustrative of preferred embodiments of the invention.

Claims

WHAT IS CLAIMED IS:

1. A composition comprising an admixture of two aqueous solutions in equal parts by volume: a) a lime-sulfur solution containing about 2 mols per liter of calcium, and b) a solution containing about 4.4 mols of water- soluble ammonium salt and about 0.4 mol of ammonia per liter.

2. A composition of claim 1 which is freshly prepared.

3. A composition which comprises an admixture of from about 175 to about 500 parts by volume of water per part by volume of a composition of claim 2.

4. A composition of claim 3 which is less than 5 days old.

5. A composition of claim 4 which is freshly prepared.

6. A composition which comprises an admixture of about 200 parts by volume of water per part by volume of a composition of claim 2.

7. A composition which comprises an admixture of about 400 parts by volume of water per part by volume of a composition of claim 2.

8. In a method which comprises spraying an effective amount of a contact fungicide on a plant, the improvement wherein the contact fungicide is an admixture of from about 175 to 800 parts by volume of water per part by volume of a composition of claim 2.

9. A method of controlling mildew on a rose bush which comprises applying to the bush an effective amount of a composition of claim 7.

10. An aqueous fungicidal solution of a polysulfidric acid, which solution has a basic pH and is not phytotoxic or deleterious to plant leaves.

11. A solution of claim 10 wherein the polysulfidric acid comprises octasulfide.

12. A solution of claim 10 which comprises a protected polysulfide ion.

13. In a method which comprises spraying a contact fungicide on a plant, the improvement wherein the contact fungicide is a solution of claim 10.

14. A method which comprises: a) boiling together about 1 part by weight of limestone, about 2 parts by weight of ground sulfur and about 8 parts by weight of water to obtain an aqueous composition comprising calcium pentasulfide, calcium tetrasulfide, calcium thiosulfate and insoluble calcium sulfite; b) filtering out insolubles to obtain a lime-sulfur solution; c) adding a sufficient amount of water-soluble ammonium salt to the lime-sulfur solution to form ammonium polysulfides, and adding a sufficient a ount of ammonium hydroxide to the lime-sulfur solution to protect thus-produced polysulfide ion and its fungitoxic properties.

15. A method of claim 14 which further comprises d) diluting the product of step (c) from about 200 to about 400 times with water.

16. A method of claim 15 wherein step (d) is effected promptly after step (c) .

17. An aqueous sprayable polysulfide fungicidal composition which is neither phytotoxic nor deleterious to plant leaves and which is a product of a method of claim 15.

18. An aqueous fungicidal composition which is neither phytotoxic nor deleterious to plant leaves and which is a composition selected from the group consisting of

I. an admixture of two aqueous solutions in equal parts by volume; a) a lime-sulfur solution containing about 2 mols per liter of calcium, and b) a solution containing about 4.4 mols of water-soluble ammonium salt and about 0.4 mol of ammonia per liter, further diluted from about 200 to about 400 times with water;

II. an aqueous fungicidal solution of a polysulfidric acid, which solution has a basic pH; and

III. a composition of claim 17.

19. In a method which comprises spraying an effective amount of a contact fungicide on a plant, the improvement wherein the contact fungicide is a composition of claim 6.

20. In a method which comprises spraying an effective amount of a contact fungicide on a plant, the improvement wherein the contact fungicide is a composition of claim 7.