New Zealand Weed Control Conference

New Zealand Journal of Agriculture, Volume 99, Issue 4, 15 October 1959, Page 373

New Zealand Weed Control Conference

INTEREST in chemical methods of weed control is increasing throughout New Zealand as the successful practical use of chemicals becomes widespread. The subject is also becoming more complex as the range of chemicals available for weed control becomes greater, and a representative gathering, the Weed Control Conference, meets annually to keep up to date with developments. At the twelfth annual conference held at Tauranga in July this year about 150 members were present, representing manufacturers and distributors of weedkillers, Instructors in Agriculture and research staff of Government departments, farm advisers, weed-spraying contractors, farmers, noxious weeds inspectors, and other local body officers.

THE first paper was by A. V. Allo and dealt with weed problems of the Bay of Plenty. The type of farming practised in the early days of the settlement of the area had been responsible for many of the present weed problems. For instance, Indian doub, which is a problem in cultivated land, was sown in the early days, as it was. one of the few pasture species capable of growing under the prevailing lowfertility conditions. The same could be said of browntop. Ragwort would never have been so serious a problem had not bush sickness prevented sheep being carried on much of the country. On land developed after burning bush or scrub subsequent weed problems can be largely avoided if the new pasture is properly established and managed. Where adequate phosphatic fertilisers are applied and the area fenced so that stock can be crowded on to it weeds can be kept under control and a satisfactory sward developed provided “cheap” seed containing weeds is not used and, if the area has been cultivated, the seedbed is well consolidated. If due attention is not given to all of these factors, a poor sward may result which could become invaded with any of the following weeds according to the circumstances: Ragwort, Australian fireweed, fleabane, inkweed, sorrel, foxglove, and flat weeds. Mr Allo also dealt with weed problems of both low- and high-fertility pastures, swamps, and cropping and horticultural areas. In conclusion he said that weed control in the Bay of Plenty has made great advances since 1946 largely because of the introduction of hormone weedkillers, but there are still some weed problems for which satisfactory control measures are not available.

Dalapon Several papers dealt with the use of dalapon, a grass weedkiller becoming more important because it is being used for various purposes such as control of barley grass, grasses on drain banks, and grasses in lucerne. When it is used for the control of barley grass in pasture it is important to know how much can be applied without causing too much damage to the desirable pasture grass. On the other hand when dalapon is applied to destroy . existing swards before cropping, as in chemical ploughing, it is necessary to use sufficient to kill the pasture grasses. Dalapon is also used to control grassy weeds on drain banks. It is therefore important to know how much dalapon is required to kill various grasses under different conditions. In a paper by A. Thompson results were given of trials to study factors which influence the effect of dalapon on grasses. It was shown that ryegrass tends to be more susceptible to dalapon damage when treatments were applied to very short or immature growth. Higher and more mature growth was more resistant. Ryegrass growing on high-fertility spots was more resistant than that growing on areas of lower fertility. Cocksfoot when small and leafy showed variations in resistance similar to ryegrass. On the other hand clumpy cocksfoot of the type which develops on ungrazed areas was more susceptible to dalapon when the regrowth after mowing was 10 in. high than when it was shorter. F. A. H. Meeklah dealt with the results of trials with dalapon for controlling grassy weeds in lucerne. When dalapon was applied to established lucerne in early spring, though there was an appreciable reduction in yield at the first cut, the treatment had little or no effect on subsequent yields.

Treatments after the first cut, after the last cut, and in the late dormant stage, however, resulted in more prolonged depression of yield. The use of dalapon, amitrol, and 2,4-D for controlling weeds in drains has reduced the cost of maintaining drains in the Hauraki Plains, according to G. L. Banfield. “There is no doubt,” he said, “that we now have a remarkably effective range of weedicides suitable for complementing the work of the mechanical drain cleaner. By their use we cannot fail to increase drainage efficiently and reduce drain maintenance costs to a fraction of their former level.” In a paper by L. J. Matthews on chemical ploughing results of a trial were quoted which showed that chemical ploughing gave higher yields of white-fleshed turnips than those obtained on cultivated plots, provided the rate of chemical used was sufficient to kill the grasses in the previous sward. The chemical, method may have application where it is not possible or convenient to cultivate or where cultivation results in weed problems for which there is no satisfactory method of control; for example, fathen in brassica crops. However, more information is required regarding the factors governing pasture and crop establishment with the chemical method before it can be recommended generally. Some of these factors are the seeding rates, fertiliser requirements, and the residual toxicity of the chemicals. Gorse Control The results of a trial in which costs were obtained of various methods of controlling gorse and developing un-

ploughable hill country were given by J. D. Currie. The gorse on different blocks was burnt, sprayed from the air with 2,4,5-T, or sprayed from the ground. After oversowing there was some gorse regrowth on each block which could not be controlled by stock and this was spot sprayed. Burning of the gorse was the cheapest method because the other methods had the additional expense of prior spraying with 2,4,5-T.

A good burn and adequate stock control of gorse seedlings were important factors. In dealing with these, Mr Currie said “On a farm with an average gorse density spot spraying will soon have the gorse confined to the dense blocks, after which the number of acres able to be tackled will be entirely governed by the number of sheep available. In our experience cattle were never necessary, but up to 30 sheep per acre were required for up to three weeks at the height of the spring seedling regrowth. If we have a 20-acre block being developed, we will require 600 wethers and straight after this nearly all these 600 wethers will have to be elsewhere. On a hill farm carrying two sheep per acre a balance of 300 acres of grass would be required if we were not to lose money on our stock. It is far better to take a small block and do the job properly.

“A dense three-year-old block of gorse should be selected early and closed to let a tinder dry, thick fern and grass undergrowth build up by February. - At the same time the block must be ring-fenced to keep the stock

out while the undergrowth thickens and to crush sheep on after the burn. I believe the £2 a chain four-wire sheep electric fence has a great potential for this work. “The best burn will be obtained in February or March on a day of low humidity combined with a light

drawing wind. Oversowing in the ashes is not critical, but seed oversown must be Government certified and have a high proportion of clovers to compete vigorously with the gorse seedlings and fern fronds, and all the required fertilisers must be spread. Immediately after the burn and even before oversowing, heavy stocking with sheep is essential. Pasture establishment after gorse is usually very good and it is largely a matter of good husbandry, both field and animal, to keep those seedlings out. It is better to sacrifice your paddock by stocking too heavily and too long rather than to nurse the pasture. Sheep must be done harder on many occasions than one would like to as a good stockman, but this is absolutely necessary when you realise that every seedling that hardens is lost to stock control and must be sprayed.”

Some of the conclusions in a paper by G. R. Moss dealing with the dispersal of gorse seed and the longevity of the seed in the soil were similar to those of Mr Currie. Mr Moss said: “On unploughable areas burning is essential to reduce the

potential danger from hard seeds in the soil. The aim should be for a hot fire to kill or to render permeable to soil moisture as many gorse seeds as possible so that they can germinate quickly. This reduction in the number of hard seeds in the soil is an important factor in gorse control. It may be possible to burn some areas satisfactorily without prior treatment or it may be necessary to cut and burn or spray and burn. It is impossible to generalise on gorse eradication because of differences in topography and climate.

“If a cleared area is not reseeded, some of the gorse seeds could survive in the soil and germinate for up to 30 years. The first 10 years are the critical years where pasture management is very important. If at any time the sward is opened up by overgrazing or slips and stock are unable to control seedling growth, spraying will be necessary.

“The cheapest method of controlling seedling growth is with stock. If stock are to be used efficiently, they must be concentrated.

“There would be no gorse problem in New Zealand today if we had not planted gorse hedges. We can never hope to get rid of gorse as a weed until every gorse hedge has been destroyed.”

Other Papers

G. S. Harris in a paper on buried weed seeds said: “In one sample from a five-year-old pasture there were present 24 million fathen, 16 million dock, and 160 million other seeds per acre. Under such conditions the probability of weed competition with any succeeding crop, arable or pastoral, is self-evident as is the cost of adequate weed control measures.”

On barley grass seeds, he said: “They may last over one winter, but certainly no longer. Unless seeding is prevented, there can be a rapid and appreciable build-up in buried seed numbers by the end of summer, but this will not last for long owing to prompt germination of the majority of the seeds.”

Results of trials with monochloracetate (MCA) for control of weeds in brassica crops were given by F. B. Thompson. Applications of 15 lb per acre of MCA can be recommended for control of most broad-leaved weeds in chou moellier and swedes, if the material is applied after the crops have four true leaves. Fathen and grassy weeds resist MCA, and it is of little value if these are the dominant weeds. White-fleshed turnips are more susceptible than the other brassica crops and should preferably not be sprayed before the six true, leaf stage. At this stage the crop is liable to cover most of the ground and ’ shelter the weeds

from the spray, and in practice it is probably better to wait until the weeds rise above the crop and then to spray. Keen interest was taken in all papers, and discussion time was fully occupied. Field Day Four bus-loads of conference members were shown the type of farming in the district during a trip to Mt Maunganui and Papamoa. A stop was made at a farm for a demonstration of a logarithmic sprayer made by I. C. Sweetman, Technician, Rukuhia Soil Research Station, Hamilton. This sprayer continually dilutes at a constant rate the chemical being sprayed. Consequently on a strip thus sprayed there is a high rate of chemical at one end and a low rate at the other. The rate of application at any point along the strip can be determined by measuring the distance from the starting point. This was clearly demonstrated in the field by spraying a dye on a strip of paper. By using this type of sprayer the minimum rate of weedkiller required to kill a particular plant can be determined more easily than by spraying individual plots with various rates of the material. The visitors were shown a drain bank which had been sprayed in March with the logarithmic sprayer. This showed good control of the weeds

with lower rates of chemical than had been recommended previously. Various types of logarithmic sprayers have been developed overseas since the first one was made in England several years ago. These are cumbersome because it is necessary to include mechanism to mix rapidly the diluent and concentrate. Mr Sweetman had modified parts of an imported sprayer, and he used compressed air for both mixing and delivering the spray solution. The modification was fitted to a portable spray unit designed by officers of the Department of Agriculture, and the complete sprayer was inexpensive, easily carried, and would fit in the boot of a car. This sprayer was considered an advance on those available overseas for experimental work. Next Conference The general meeting decided that the next conference should be held in Invercargill in July 1960. The officers elected for the ensuing year were: President, J. N. Fitzgerald (Wellington); vice-president, F. C. Allen (Christchurch); secretary, L. J. Matthews (Wellington); ", committee, J. E. Bell (Auckland), P. S.. Ferens (New Plymouth), M. S. Foreman (Christchurch), P. B. Lynch (Wellington), A. R. Rankin (Invercargill), and F. B. Thompson (Hamilton).

Papers and Speakers "Weeds of the Bay of Plenty" A. V. Allo, Farm Advisory Officer, Tauranga "Effect of Dalapon and Amitrol on Various Grasses" A. Thompson, Technician, Rukuhia Soil Research Station, Hamilton "Lucerne Tolerance to Dalapon" F. A. H. Meeklah, Technician, Invermay Research Station, Mosgiel "Simazine" D. V. Gordon, Ivon Watkins Ltd.,-New Plymouth "Use and Limitations of Chemical Ploughing" L. J. Matthews, Senior Scientific Officer, Wellington "Review of the Use of the Phenoxybutyrics in New Zealand" J. N. Fitzgerald, Technical Officer, J. H. Barbour and Son Ltd., Wellington "Use of Seeding Rates and Weedkillers for Control of Weeds in Newly Sown Pastures" N. A. Cullen, Scientific Officer, Invermay Research Station, Mosgiel "Gorse Control on Unploughable Hill Country" J. D. Currie, Farm Advisory Officer, Hamilton "The Gorse Seed Problem" G. R. Moss, Farm Advisory Officer, New Plymouth "New Aspects of Chemical Control of Weeds in Drains" G. L. Banfield, Farm Advisory Officer, Thames "Manchurian Rice Grass" E. H. Arnold, Assistant Fields Superintendent, Department of. Agriculture, Auckland ■ "Barley Grass Control" D. E. Merry, Farm Advisory Officer, Pukekohe "The Significance of Buried Weed Seeds in Agriculture" G. S. Harris, Scientific Officer, Grasslands Division, D.5.1.R., Palmerston North "Absorption and Translocation Studies Using Labelled Herbicides" O. Leonard, Botany Department, University of California, and J. S. Yeates, Head of Agricultural Botany Department, Massey Agricultural ’ College, Palmerston-North "Weed Control in Fodder Crops with Monochloracetate" F. B. Thompson, Principal Scientific Officer, Rukuhia Soil Research Station, Hamilton "Weed Control in Berry Fruits" J. Porter, Scientific Officer, Horticultural Research Station, Levin Printed Proceedings of the Conference, containing all the papers and discussions, may be obtained for 15s. a copy from the Secretary, Weed Control Conference, Department of Agriculture, P.O. Box 2298, Wellington.

—F.B.T.