GB1589362A - Herbicide materials - Google Patents

Description

(54) HERBICIDE MATERIALS (71) We, STANDARD TELEPHONES AND CABLES LIMITED, a British Company of 190 Strand, London, W.C.2, England, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to herbicide compositions and in particular to a two component herbicide of the controlled release glass type.

Our published specification No.

1,512,63 describes a biologically active slow release medium consisting of a vitreous matrix including one or more water soluble biologically active constituents together with phosphorus pentoxide, which vitreous matrix may include one or more dispersed phases, the vitreous matrix having a slow rate of dissolution in water such that, when the medium is immersed in water, biologically active constituents are slowly released into solution.

Such a material is particularly suitable for the production of fertiliser as a small run-off of the active materials from a treated area can be tolerated. In the case of a herbicide, however, such run-off can cause damage to plants in surrounding areas. Furthermore it is also an advantage if the persistence of the herbicide in a treated soil area can be controlled thus allowing, e.g. planting of crops, once the previous plant growth has been destroyed.

It has long been established that boron is an important trace element for higher plants but becomes toxic to the plant above a critical concentration. Thus, although boric acid and borates are very effective herbicides, their use has been discontinued because of the intolerably high levels of borate which develop in the run-off water and which may eventually find their way into an aquifer or into the sewerage system.

According to the present invention there is provided a controlled release herbicidal composition, including first and second water soluble glass materials, wherein said first glass comprises a calcium aluminium borate glass whose water solubility is such that, when in contact with an aqueous medium, borate ions are released at a rate sufficient to provide a boron concentration of 3 to 100 weight parts per million in the aqueous medium, and wherein said second glass contains a water soluble cation which, when in contact with borate ions, forms an insoluble product.

Embodiments of the invention will now be described with reference to the drawings accompanying the Provisional Specification in which Fig. 1 shows the aqueous dissolution rates of a series of borate glasses, and Fig. 2 shows the effect of herbicide leaching from treated soil.

Referring to Fig. 1, calcium aluminium borate glasses are employed as non selective herbicides by mixing with the top layer of the soil to be treated. The rate of dissolution of the glass may be controlled by variation of the aluminium content, i.e. increasing the aluminium content decreases the solubility of the glass. The quantity of the glass composition to be added to the soil is calculated from the dissolution rate to maintain a predetermined concentration of borate ion in the total amount of water expected to be received by the soil over an extended period.

The glasses are formed by co-melting the various constituent oxides e.g. calcium oxide, aluminium oxide and boric oxide. As boric oxide is volatile it is necessary to add an excess to the oxide mix to compensate for losses which are generally in the range 1 to 10 percent of the initial quantity of basic oxides. The glass melt, when homogeneous, is allowed to cool and solidify and is then ground to a powder.

The borate glass herbicides of the type described herein are employed in conjunction with a second glass material containing a water soluble cation which is slowly released and which, in aqueous solution, combines with the borate ion to produce an insoluble and/or inert product. The second glass material is uniformly distributed together with the first glass material in particle form over the area of soil to be treated.

Each glass dissolves independently and forms the insoluble/inert borate in part of the regions of soil between the particles.

The concentration of borate ions is thus high in the vicinity of the borate glass particles but rapidly falls off with distance from these particles.

The average borate ion concentration in the treated region of soil is sufficient to act as a herbicide whilst beyond the treated region the concentration is very low, in fact at trace nutrient level. By suitable choice of the relative rates of solution of the two glasses and their particle sizes it is possible to adjust the average concentration of borate ions in the treated soil, and by maintaining overall stoichiometry for the treated soil area the run-off of borate ions from the area is reduced substantially to zero.

The following example illustrates the invention. Trays of top soil sown with grass seed were treated with controlled release borate glass compositions, one half of each tray being left untreated as a control. The glass was added as particles mixed with the top soil, the quantity of glass being calculated to give a predetermined boron concentration in the total amount of water to be given over a period of one ear. The watering rate was equivalent to 50 inches of rain per annum applied daily as a spray. The amount of glass material was appropriate to give 3, 10, 30 and 100 ppm (by weight) of boron in the water. The glass matenal was compared with a commercial organic herbicide (containing SIMAZINE as its active ingredient) for duration of effectiveness and for lateral spread.

The overall results of these trials showed that germination of the grass seed was effectively prevented on all the treated areas. On the untreated areas of the trays treated with the glass composition little or no lateral spread of the herbicide had occurred. there being a sharp division between the healthy growth of the untreated area and the bare soil of the treated area. The organic herbicide had however spread laterally to some extent and germination on the untreated area was reduced.

As shown in Fig. 2, the wash-through of boron showed an initial induction period of about four weeks while, presumably, boron was absorbed by the soil. Thereafter there was a sharp increase to a linear rate of wash-through which persisted until the glass herbicide was exhausted.

The length of effectiveness of the glass compared favourably with the organic herbicide, germination being prevented for up to 30 weeks by the glass material and for up to 12 weeks by the organic herbicide. However, the period of effectiveness of the glass material may be altered by varying the quantity, particle size and chemical composition of the glass.

WHAT WE CLAIM IS: 1. A controlled release herbicidal composition, including first and second water soluble glass materials, wherein said first glass comprises a calcium aluminium borate glass whose water solubility is such that, when in contact with an aqueous medium, borate ions are released at a rate sufficient to provide a boron concentration of 3 to 100 weight parts per million in the aqueous medium, and wherein said second glass contains a water soluble cation which, when in contact with borate ions, forms an insoluble product.

2. A controlled release herbicide composition substantially as described herein with reference to the drawings accompanying the Provisional Specification.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (2)

**WARNING** start of CLMS field may overlap end of DESC **. Each glass dissolves independently and forms the insoluble/inert borate in part of the regions of soil between the particles. The concentration of borate ions is thus high in the vicinity of the borate glass particles but rapidly falls off with distance from these particles. The average borate ion concentration in the treated region of soil is sufficient to act as a herbicide whilst beyond the treated region the concentration is very low, in fact at trace nutrient level. By suitable choice of the relative rates of solution of the two glasses and their particle sizes it is possible to adjust the average concentration of borate ions in the treated soil, and by maintaining overall stoichiometry for the treated soil area the run-off of borate ions from the area is reduced substantially to zero. The following example illustrates the invention. Trays of top soil sown with grass seed were treated with controlled release borate glass compositions, one half of each tray being left untreated as a control. The glass was added as particles mixed with the top soil, the quantity of glass being calculated to give a predetermined boron concentration in the total amount of water to be given over a period of one ear. The watering rate was equivalent to 50 inches of rain per annum applied daily as a spray. The amount of glass material was appropriate to give 3, 10, 30 and 100 ppm (by weight) of boron in the water. The glass matenal was compared with a commercial organic herbicide (containing SIMAZINE as its active ingredient) for duration of effectiveness and for lateral spread. The overall results of these trials showed that germination of the grass seed was effectively prevented on all the treated areas. On the untreated areas of the trays treated with the glass composition little or no lateral spread of the herbicide had occurred. there being a sharp division between the healthy growth of the untreated area and the bare soil of the treated area. The organic herbicide had however spread laterally to some extent and germination on the untreated area was reduced. As shown in Fig. 2, the wash-through of boron showed an initial induction period of about four weeks while, presumably, boron was absorbed by the soil. Thereafter there was a sharp increase to a linear rate of wash-through which persisted until the glass herbicide was exhausted. The length of effectiveness of the glass compared favourably with the organic herbicide, germination being prevented for up to 30 weeks by the glass material and for up to 12 weeks by the organic herbicide. However, the period of effectiveness of the glass material may be altered by varying the quantity, particle size and chemical composition of the glass. WHAT WE CLAIM IS:

1. A controlled release herbicidal composition, including first and second water soluble glass materials, wherein said first glass comprises a calcium aluminium borate glass whose water solubility is such that, when in contact with an aqueous medium, borate ions are released at a rate sufficient to provide a boron concentration of 3 to 100 weight parts per million in the aqueous medium, and wherein said second glass contains a water soluble cation which, when in contact with borate ions, forms an insoluble product.

2. A controlled release herbicide composition substantially as described herein with reference to the drawings accompanying the Provisional Specification.