Recent Research Work

New Zealand Journal of Agriculture, Volume 84, Issue 4, 15 April 1952, Page 300

Recent Research Work

WEED CONTROL

WEEDS IN CROPS

SUFFICIENT trial work has now been conducted in New Zealand to show that the more selective sodium salt of M.C.P. should be used

tor weed control in crops. The less selective sodium salt, amine, and ester preparations of 2, 4-D have reduced yields of spring-sown cereals, potatoes, peas, and linseed crops. Winter- and autumn-sown cereals are more resistant and may be treated with the less selective materials when over 6in. high. Wherever possible the weeds should be treated at their most susceptible stage of growth and the crops at the most resistant stage. Annuals and perennials that develop from seedlings should be treated as near to the seedling stage as possible, but perennials arising from root suckers should be sprayed as near to the flower-head formation as the crop will allow.

T.C.A. (mainly the sodium salt of trichloroacetic acid) has shown great promise for the control of grassy weeds that are little affected by the

GRASSY WEEDS

hormone weedkillers. T.C.A. is particularly valuable for the control of annual grasses such as Poa annua and rhizomatous grasses such as couch and various twitches. Stoloniferous and fibrous-rooted grasses in general are more tolerant and require heavier dressings for control. The most efficient way of using T.C.A., which is mainly absorbed into the plant through the roots, is to plough and spray the upturned sod. Alternative methods are to spray, then cultivate 3 to 4 weeks later, or to mow or graze heavily and then apply the T.C.A. T.C.A. requires moist soil for activation and should if possible be applied shortly before rain falls. Application in autumn usually gives the best results. The rates should be varied from 20 to 1001 b. per acre according to the type of grass and the method of application employed. —L. J. MATTHEWS ❖❖' ■ ❖ *

WEEDS ON RAILWAYS

PRE-WAR investigations with sodium chlorate and ever-rising labour problems led to the introduction by the New Zealand

Railways Department of track-spraying operations by a weed spray train outfit. Applications of a sodium chlorate-based material, •‘Atlacide”, at a rate of approximately 2001 b. in 200 gallons of water per mile are normally applied in October-November, and again in April, more or less coincidental with growth-rate peaks. In this way satisfactory weed control has been maintained, although deep-rooted perennials and well-established grasses show resistance and necessitate some hand weeding.

SODIUM CHLORATE

EXPERIMENTAL work was begun in 1946 to determine the maximum efficiency of sodium chlorate. These early studies indicated that two applications annually gave better results

than a single application at double the standard rate, that

spring applications were more efficient than autumn applications, particularly in controlling freely seeding annual weeds, and that high-volume applications are 10 per cent, more efficient than volume applications. It was demonstrated also that deeply rooted biennial and perennial weeds and grasses such as sorrel, white clover, tall fescue, and paspalum were partially resistant to sodium chloratebased materials. It was also shown that considerable advantages may be expected from the use of small, slowspeed, low-volume spray units located at suitable stations instead of one heavy high-volume unit to cover the whole system. By this means the weeds could be sprayed at the most susceptible stage.

NEW. TYPES OF WEEDKILLERS

WITH the advent of new types of weedkillers further trials were initiated using sodium chlorate-based materials, applied

at the rate of 1201 b. per acre, as a standard for comparison. These trials showed that fuel-oil mixtures containing hormones of 2, 4-D and 2,4,5-T acid base and chlorinated phenols applied by low-volume methods are significantly inferior at the rates specified by manufacturers, but their efficiency may be increased to that of sodium chlorate-based materials by doubling the rate of application. Costs would then be twice that of the sodium chlorate treatments. The efficiency of trichloro acetate applications approximates that of sodium chlorate, but superior kills of adult grasses follow the use of increased dosages. The addition of borax to sodium chlorate did not increase the toxicity of this material. These trials have shown that should supplies of sodium chlorate-based materials fail, alternative materials are now available with efficiencies equal to that of the standard material, but at some increase in costs on present figures. - —R. K. WARD

* . * . . * ■ * IN the Warkworth district field experiments have been carried out to determine the efficiency of hormone weedkillers for the control of gorse. Both 2, 4-D and 2,4,5-T ester prepara-

GORSE , CONTROL

tions were used. The esters of 2, 4-D had no effect on the gorse and are considered valueless for gorse control. Seedlings past the seed-leaf stage and bushy gorse up to 3ft. high have been effectively controlled with 2,4,5-T oilbased esters. If good results are to be obtained, it is important that the plants be completely covered with the spray. Volatile esters of 2,4,5-T are a distinct aid in securing complete over-all foliage cover. Small gorse is more easily covered and will require less spray than larger plants. It is therefore recommended that tall gorse, over 4ft., be dealt with as follows: — (a) Cut, crushed, or burnt and the regrowth sprayed. (b) Cut and a mixture of 2,4,5-T ester and dieselene applied to the cut-stump surface. One pound acid equivalent should be diluted with 20 gallons of dieselene and applied soon after cutting. Because of the necessity for a complete spray cover, it is almost impossible to obtain a 100 per cent, kill with one application. The experiments have shown the need for two sprayings if complete eradication is to be effected. The first spraying will account for 90 to 95 per cent, of the gorse and this should be followed by spot treatment to those plants showing some green foliage. The amount of spray required will depend on the density and size of the gorse. For areas thickly populated with young gorse as is often found in new pastures 11b. acid equivalent of 2,4,5-T oil-based ester will be required for each acre. To control bushy gorse the amount should be increased to 21b. acid equivalent of 2,4,5-T oil-based ester per acre. Throughout the experiments water has been used as a diluent with complete success. There is nothing to be gained by using oils and in fact their use may impair the action of the weedicide. Hormone weedkillers are most effective during warm weather and when plants are growing vigorously. Spraying at any time from October to February inclusive will give good results for seedling gorse past the true seed-leaf stage. Regrowth gorse, where translocation of the chemical through the plant is essential for root control, should be treated from December to February.

Older gorse falls into the same category. The older plants must have full and mature leaf development before the hormone is translocated into the roots. Young, immature leaves are not able to translocate hormones.

—C. M. BUCK