Control of Weeds in Grass Seed Crops by Hormone Sprays

New Zealand Journal of Agriculture, Volume 84, Issue 3, 15 March 1952, Page 192

Control of Weeds in Grass Seed Crops by Hormone Sprays

METHODS of applying hormone sprays for the control of weeds in grass seed crops in Hawkes Bay are described in this article by ’R. P. Hill, Fields Instructor, Department of Agriculture, Hastings. Any of these methods is suitable for weed control in grass seed crops and will not cause injury either to the crop or to the seed harvested, but they are not recommended for clover seed crops. Because of the risk of damaging viability of the seed produced sprayings should not be delayed until after October.

J UNQUESTIONABLY the best.method of weed control is by fallow and summer cultivation, which not only helps to eradicate weeds but is of inestimable benefit to the soil. Unfortunately in Hawkes Bay this is not common and the usual practice in grass seed production is to take the land out of crop . or pasture and sow it immediately with perennial ryegrass for seed production. Naturally weeds are aggressive under these conditions, the principal ones affecting grass seed crops being hedge mustard, Scotch thistle, buttercup, burr clover, shepherd’s purse, speedwell, amaranthus, and fat-hen, all of which are easily controlled by hormone sprays in their young stage. It is customary for lowvolume sprays to be used; few farmers resort to the old high-volume method, with its water transport difficulties. The first method adopted in the district and still in common use was the application of the hormone weedkiller about a week after stock had been removed at the end of October and when the paddock had been grazed bare preparatory to closing the area for grass seed. If a week is allowed to pass before spraying, the weeds have time to “lift” and are easily sprayed. The quantities of commercial preparations of 2, 4-D used are 1 to 11 pints of the oil-based ester or the amine salt diluted with 6 to 10 gallons of water per acre. These products contain 3.6 or 41b. of acid equivalent per gallon. Each of the formulations of 2, 4-D has its specialised use in pasture spraying. Under conditions most suitable for plant growth the cheapest formulation of 2, 4-D (sodium salt) will control susceptible weed species in pastures at low rates of application; heavier rates

of application of the sodium salt or the amine salt should be used under adverse spraying conditions, that is, cold soil and atmospheric conditions unsuitable for plant growth. The amine salt and sodium salt are water soluble and therefore best results are secured when dry weather follows application. Heavy rain tends to wash the water-soluble sprays off the plant foliage. The oil-based esters should be used only when weather conditions, for example, rain after application, would adversely affect the water-soluble sprays. The use of the sodium salt also reduces the damage to clovers, especially red clover, which are susceptible to the oil-based ester and to a less degree to the water-based amine salt. A second method is to graze hard up to the first week in October, remove the stock, then spray, and a week or 10 days later place the stock back on the area, when they will graze off all the wilted weeds as well as the grass. They should remain on the area until the

normal ciosing-up time, about the end of October. The third and probably the most efficient method is to remove the stock for a short time in early spring (at the end of August or early in September) and then to spray, only half the quantity of hormone, as low as J pint to f pint to 6 to 10 gallons of water, being used. When the weeds are very young it takes very little to kill them; small docks are susceptible in the early

stage. It may be necessary, depending on the season, to give a second spraying, but this is rarely necessary, except , perhaps when fat-hen and amaranthus show up later. As spraying takes place early in the season, fat-hen or amaranthus, if present, are in the very young stage and are readily killed. Some farmers have mixed hormone dusts with fertiliser and topdressed their paddocks in spring. Though this method has been effective, it has been more expensive. Hormone spraying has now been done for several years. It has produced much cleaner crops and has had no detrimental effect on the germination of the seed harvested. If applied late, it has had a retarding effect on white clover growth, which has quickly recovered, but it has completely controlled burr clover, one of the greatest hindrances in the production of ryegrass crops in moister areas. Many farmers now have their own spraying equipment. One uses a small tractor for haulage, a 1 h.p. engine on a trailer, a pump, and a 27-gallon tank, and with a 301 b. pressure and a boom with low-volume nozzles mounted on the back of the trailer he is able to cover up to 80 acres per day, travelling at 7 miles per hour. His weeds are principally Scotch thistle. He always sprays early in the season, using from 5 to 8 fl. oz. of 2, 4-D solution (41b. of acid equivalent per gallon) with 1J gallons of water per acre. The cost of spraying, excluding wages for himself, is about 7s. per acre, depending on the type of hormone he is using. To save time he has an independent pump mounted on the back of the tractor. This pump is driven by the power take-off and is used to fill the spray tank. This farmer endeavours to spray on an overcast day, as he is convinced that the lethal effect is better when the sun’s rays do not dry the spray off the plants quickly.