GB2074448A - Selective weed control and compositions therefor - Google Patents

Abstract

The selective weed control given by terbutryne is improved, particularly against blackgrass, by combination with linuron, preferably in a weight ratio of at least 3:1.

Description

SPECIFICATION Selective weed control and compositions therefor This invention relates to herbicidal compositions and their use in selective weed control.

In recent years a large number of synthetic herbicidal compounds has been developed and many of these have been put to commercial use. In many cases, however, the activity of the individual com- pounds has left something to be desired and their use has not been without drawbacks.

Among known herbicides is terbutryne (2 - methylthio - 4 - ethylamino - 6 -tert. butylamino - S - triazine). This triazine herbicide has been used widely for selective weed control in various crops. It is a substituted triazine herbicide of the general type disclosed in British Patent Specification 814,948, and it is specifically disclosed in British Patent Specification 978,249. British Patent Specification 1,168,274 describes its use in combating grass-type and broad-leaved weeds in cereals, and weed control literature contains other evidence of its use on a wide variety of crop types.

Although terbutryne is unquestionably a useful herbicide, it tends in practice, particularly with some crop types and geographical and/or climatic situations, to be unsatisfactorily effective. In particular when used on cereal crops it tends to have an insufficiently wide spectrum of activity against grassweeds and broad-leaved weeds.

We have now found that substantially improved selective weed control may be obtained in both cereal and other crops by use of a combination of terbutryne and linuron.

Linuron is a known herbicide of the substituted urea type and is 3 - (3,4 - dichlorophenyl) - 1 methoxy - 1 - methyl - urea.

We are aware that terbutryne and linuron interalr'a have been recommended as ingredients of various herbicide "cocktails", but it has not previously been suggested that these compounds should be used in a weight ratio of at least 3:1, nor that they should be used without admixture or other herbicides, in accordance with the preferred practice of our invention.

The combined use of terbutryne and linuron leads to a very satisfactory weed control both in cereal and other vegetable crops. The combination is of particular value on winter and spring cereals but it may also be used on root vegetable crops such as parsnips, carrots, potatoes and beet and on legumes such as peas and beans. It is likely also to be of value in tropical crops such as tobacco and cotton.

It is particularly notable that the terbutryne/linuron combination gives enhanced control of blackgrass (A.myosuroides), which is a troublesome weed in cereal crops. The literature states that blackgrass is not effectively controlled by linuron (Meded. Cent.

Onkruidonderz, Gent, 1965, 1,2-8). It is therefore surprising that the inferior control of blackgrass given by terbutryne is considerably enhanced by combination with a minor proportion of linuron.

The terbutryne and linuron may be applied to the site of the crops to be treated either pre-emergence or post-emergence, pre-emergence application being preferred. They may be applied in any of the customary fashions. Thus the materials may be formulated in conventional manner with customery carriers and/or adjuvants. They may suitably be formulated e.g. as a liquid or flowable composition, a wettable powder, granules, microgranules or as a tank mix. It is not necessary to mix the terbutryne and linuron prior to application but it is of course usually convenient to produce them as a single formulation ratherthan having to use atwin packorto carry out two applications to the crop.Thus, such carriers may be liquid or solid and designed to aid the application of the compounds either by way of dis persing them where they are to be applied orto provide a formulation which can be made by the user into a dispersible preparation.

Liquid preparations thus include preparations of the compounds in the form of solutions or emulsions which can be used on their own or be adapted to be made up with water or other diluents to form sprays etc; in such cases the carrier is a solvent or emulsion base nonphytotoxic underthe conditions of use. Generally such preparations will include a wetting, dispersing or emulsifying agent.

Solid preparations include dusts and wettable powders, granulates and pellets, and semi-solid preparations such as pastes and flowable formulations. Such preparations may include inert solid or liquid diluents such as clays, which may themselves have wetting properties, and/or wetting, dispersing or emulsifying agents; binding and/or adhesive agents may also be included.

The relative proportion of terbutryne to to linuron may vary within relatively wide limits, for example from 15:1 to 3:1 by weight, the particular ration being dependent upon the type of crop expected and the type of weed expected. The preferred ratio of terbutryne to linuron by weight, especially in the case of pre-emergence application for winter and spring cereals, is from 8:1 to 4:1, with about 6:1 being highly preferred.

The rate of application may likewsie vary fairly widely dependent upon the crop type and expected type of weed infestation. Generally rates of from 1.5 to 4 kg/ha terbutryne and from 0.125 to 0.5 kg/ha linuron in a weight ratio of at least 3:1 can be used.

Preferred rates are often in the ranges 2 to 3 kg/ha and 0.25 to 0.4 kg/ha respectively.

The herbicide mixture according to the invention gives good control of a wide variety of broad leaved weeds and grass weeds, including blackgrass, while showing a good margin of safety on most crops.

Control of blackgrass can be in the range 85-95%, while control of many other weeds such as speedwell, chickweed, cleavers, fumitory and cranesbill is often virtually 100%. Generally the addition of further herbicides is unnecessary; if such further herbicides are used, our invention extends to combinations wherein the weight ratio of terbutryne to linuron is in the range from 15:1 to 3:1.

However it is an advantage of our invention that effective and broad-spectrum weed control is obtained with only two compounds, thus obviating the practical difficulties of "cocktail" multi component mixtures. If these mixtures are made up by the farmer, he has to stock a number of different compositions and is liable to make errors of calculation in formulating his tank mix, perhaps with disastrous consequences to the crop. Combined compositions often cause formulation difficulties such as chemical instability or separation of components.

Our invention is illustrated in the following nonlimiting Examples.

Example 1 Terbutryne alone and a terbutryne/linuron mixture were applied pre-emergence to a crop of winter wheat, var. Mardler, drilled into sandy clay loam.

The treatments were applied in four replicates on 2nd October 1980 and the results were assessed on 12th January 1981. The crop stand was also assessed. The treatments were applied as sprays in 250 I/ha water.

The results for blackgrass were as follows; the other weeds assessed were controlled effectively by both treatments.

Terbutryne Linuron %Blackgrass kgJha kglha control 2.25 - 75.3 2.0 0.33 86.7 The terbutryne treatment increased the crop standby 20.6%, and the combined treatment increased it by 21.8%. Thus blackgrass control was greatly improved without any damage to the crop.

Example? Terbutryne alone and terbutryne/linuron mixtures were applied pre-emergence to a crop of winter wheat, var. Flanders. The treatments were applied in four replicates on 9th October 1980 and assessed on 13th January 1981. The treatments were applied as sprays in 250 I/ha water.

The results for blackgrass, the most resistant weed tested were, as follows: Terbutryne Linuron % Blackgrass kglha kglha control 2.25 - 85.6 2.8 - 92.4 2.0 0.33 92.7 2.25 0.375 95.2 The control of blackgrass was significantly enhance by the low rates of linuron tested.

Claims (19)

1. A method of selective weed control in crops which comprises applying pre-emergence or postemergence to the site of the crop effective amounts of terbutryne and linuron n a weight ratio of from 15:1 to 3:1.

2. A method according to claim 1 wherein said weight ratio is in the range 8:1 to 4:1.

3. A method according to claim 2 wherein said weight ratio is approximately 6:1.

4. A method of selective weed control in crops wherein there is applied pre-emergence or post emergence to the site of the crop a herbicide mixture consisting of terbutryne and linuron.

5. A method according to claim 4 wherein the weight ratio of terbutryne to linuron is in the range 15:1 to 3:1.

6. A method according to claim 5 wherein said ratio is in the range 8:1 to 4:1.

7. A method according to claim 6 wherein said weight ratio is about 6:1.

8. A method of selective weed control in crops which comprises applying pre-emergence or postemergence to the site ofthe crop from 1.5 to 4 kg/ha terbutryne and from 0.1.25 to 0.5 kg/ha linuron, in a weight ratio of at least 3:1 respectively.

9 A method according to claim 8 wherein from 2 to 3 kg/ha terbutryne and from 0.25 to 0.4 kg/ha linu ron. are applied.

10. A method according to claim 8 or 9 wherein the weight ratio of terbutryne to linuron is approximately 6:1.

11. A method according to. any of the preceding claims wherein blackgrass (A.myosuroides) is con trilled

12. Amethod according to anyofthe preceding claims wherein weeds are selectively controlled in a cereal crop by pre-emergence application.

13. Amethod according to anyofthe preceding claims, substantially as described herein.

14. A method according to any of the preceding claims, substantially as illustrated in the Examples herein.

15. Acomposition suitable for use in the method of claim 1 comprisingterbutryne and linuron in a weight ratio of from 15:1 to 3:1, together with a carrier and/or adjuvant.

16. Acomposition according to claim 15 wherein said weight ratio is in the range 8:1 to 4:1.

17. Acomposition according to claim 15 wherein said weight ratio is about 6:1.

18. A composition according to any of claims 15 to 17 consisting of terbutryne, linuron and one or more carriers and/or adjuvants.

19. A composition according to any of claims 15 to 18, substantially as described herein with reference to the Examples.