Thirteenth Weed Control Conference

New Zealand Journal of Agriculture, Volume 101, Issue 3, 15 September 1960, Page 225

Thirteenth Weed Control Conference

THE range of subjects covered by the papers presented at the thirteenth Weed Control Conference in Invercargill in July showed that intensive research work is being conducted to determine how the many chemical weedkillers now available can be best used in dealing with weed problems in New Zealand. Some of the papers dealt with the control of specific weeds such as sweet brier, spurrey, nodding thistle, ratstail and cutty grass, Others described recent experimental work on general weed control in crops oF peas, maize, fodder beet, lucerne, and brassicas.

IN his paper on weed problems of South Otago and Southland A. R. Rankin said of pasture weeds: “Once the pasture has passed beyond the initial establishment stage Californian thistle is the major enemy of not only the higher producing pastures, but of much of the second-class country. Before the advent of hormone weedkillers, cultivation when the paddock was under the plough, followed by frequent mowings when it was sown to pasture, was the main technique for controlling Californian thistle.” Dealing with crop weeds Mr Rankin said that the main winter feed crops

were swedes, turnips, and chou moellier, which were usually sown in ridges 24 or 26 in. apart. Scuffling between the ridges controlled the weeds until the crop was big enough to smother the weeds. After feeding off the crop the area was frequently sown to a cereal in spring. Californian thistle was often a bad weed in cereal crops, but it could be suppressed at least until after harvest by spraying with hormones. According to Mr , Rankin the weed content of a pasture is the main factor in determining which paddock should be ploughed for witner feed. As the

pasture ages, Californian thistle, there potential threat of nodding thistle. When the pasture runs out, browntop sweet vernal, and Yorkshire fog with moss " cropped, and sown to grass & and remains in grass until weeds necessitate ploughing again.

Nodding ThisHe Results of experimental work on nodding, thistle in Ashburton County were given by E. Delahunty. The trials were conducted over three years and in each year “there has been a heavy strike of thistle seeds in autumn, and effective control of the thistle, with thistle-free plots in the following

summer, has been obtained by a spray application in April-May of light rates of several hormone weedkillers. Winter spraying of thistles has been unsuccessful, but September spraying has controlled the thistles on most occasions”. The recommendations were to apply i lb of MCPA, MCPB, or the amine salt of 2,4-D to seedling thistles, preferably in April or September. MCPB should be used where there were young clover plants, but this material was less effective during, cold weather. If there were thistles in the rosette stage, the rate of application should be increased to nearer to 1 lb per acre. More mature plants could not be controlled with light rates of hormone weedkiller. Sweet Brier The paper on sweet brier presented by A. R. Dingwall, J. G. Richards, and R. C. Schofield was of particular interest to South Islanders. The authors stated that the encroachment of sweet brier “has been much more marked in the South than in the North Island, and especially so in the favoured environments of open tussock grasslands east of the Main Divide. Today it occurs in all South Island counties and is viewed with concern in many inland parts of Marlborough, Canterbury, Otago, and Southland. The Rabbit Destruction Council’s successful ‘killer’ , policy removed a significant form of biological control and has been partly responsible indirectly for the brier’s conspicuous advancement in recent times, but sweet brier has also gained ground in areas where rabbits have , never been a problem”. The authors outlined the effects of various methods which have been used to control sweet brier, both in practice and experimentally grazing by animals, burning, cutting, grubbing, coverage or basal spraying with hormones, and dust or pellet basal applications of urea chemicals such as fenuron. Their recommendations were that “landowners faced with the seriousness of this problem would ■ be well advised to take immediate action. . . . Where improvable grassland is threatened by invasion oversow and topdress or otherwise improve competitive ground cover and grazing control. Maintain constant vigilance and grub out any brier seedlings immediately they appear. If brier is already invading, with seedling and scattered small plants apparent, -preferably grub or alternatively ‘spot’ spray with 2,4,5-T--diesel oil mixture. Follow up wherever possible by improving, ground cover and controlled grazing. “Where scattered plants have grown beyond the convenient grubbing stage remove by mechanical pulling or by basal treatment with either 2,4,5-T spray or fenuron pellets, whichever is the more convenient.

“When infestations are already firmly established on a relatively large scale and individual plants are readily accessible to treatment, spray basally with the 2,4,5-T-diesel oil mixture. Under similar circumstances, but where plants tend to form individual thickets rather than distinct and separate crowns, use fenuron pellets in preference to basal spraying. Surface. trash that interferes with basal treatments should be removed by grazing or burning before chemical control .is attempted. “Where infestations are strongly established and difficult to penetrate either burn off or open up the area with a light spray of 2,4,5-T applied aerially in summer. Follow up with winter basal spray or spring pellet dressing according to the general nature of the brier plants concerned. In waste places that are accessible or when dealing with exceptionally large plants or thickets bulldozing or mechanical rooting and subsequent chemical treatment of any reviving plants would be appropriate. : “For rugged, inaccessible areas where aerial application is the only feasible method of attack fenuron pellets could be used. Seed dispersal from these difficult areas could be prevented by a midsummer, application of 2,4,5-T in fuel oil, applied aerially, every second or third year.”. Crop Weeds The results of experimental work on weeds in .peas and maize were given by T. M. Patterson.. In pea trials MCA at 15 lb per acre gave control of weeds except fathen and grasses. A mixture of MCA at' 10 lb and MCPB at i lb per acre did not damage the peas and gave better weed control than either MCA alone at 15 lb, or MCPB at 1 lb. In the maize trials simazine gave excellent weed control. In one trial simazine . plots gave . a yield ,of 141 bushels of dry shelled maize per

acre, compared with 64 bushels on the unsprayed plots. The weed control' obtained with 2,4-D, though good, was inferior to that obtained with simazine, and the yield was 133 bushels. The higher yield obtained with simazine than with 2,4-D was not sufficient to warrant the additional cost of the simazine. Further trials will be conducted with lower rates of some of the newer chemicals related to simazine, which should be more toxic to the grass weeds which resist 2,4-D. In a paper on. the control of weeds in brassica crops M. S. Foreman discussed . the. differences ■ between the methods' used in the North and South Islands. Post-emergent applications of MCA gave good control of willow weed (Polygonum persicaria) and Prince of Wales feathers or redroot (Amaranthus retroflexus) , which were the main weeds in the North. How? ever, in the South Island, MCA was unsatisfactory where spurrey (known as yarr in the. South) and fathen were troublesome. • Of the • pre-emergent treatments CIPC was the most promising, and it “can play a valuable part in the control of spurrey and many other weeds in the South Island; where band spraying is possible the control of fathen. does seem within reach”.. However, CIPC was not recommended in the North Island, where owing to the higher soil temperatures it caused too much crop damage. Ratstail The paper prepared by D. A. Newman described recent work on control of ratstail with dalapon. Trials at Paeroa, Pukekohe, and Dargaville showed that very good kills of ratstail were obtained with low rates of dalapon without causing- too much damage to the better pastures species such as ryegrass and clovers. It was stressed that it was important to follow up by promoting a quick ground cover of good pasture and forming a tight

sward to discourage the influx of ratstail seedlings. The recommendations Were: 1. Topdress adequately. 2. Spray with 2-| to 3 lb of dalapon per acre in 15 to 20 gallons of water. 3. Topdress and oversow or undersow the area within a fortnight of spraying. Drilling seed is preferable to oversowing where practicable. 4. Graze the resulting new pasture -in a manner which encourages quick : establishment of cover. Conference Prizes '-. Each year prizes are awarded for the best papers at the Conference.

Points are given for the value of a paper, audience interest, discussion, and punctuality and timing in the submission of a paper. The winning paper this year was that by E. Delahunty on “Control of Nodding Thistle”. A. R. Dingwall and co-authors gained second place with their contribution on “Control of Sweet Brier”, and -T. M. Patterson’s paper on “Weed Control in Peas and Maize” was third. In recent years the quality of the papers has risen considerably and has now reached a high level in both technical value and presentation. Many speakers use two projectors and are thus able to show’ illustrations of the effects of two treatments simultane-

ously, which makes it easier for the audience to compare the results. Field Trip The type of farming in the district was explained to the visitors during a field trip one afternoon which included an inspection of local weed trials and the Winton Experimental Area. Visitors met Mr J. Grant of Bayswater who for 13 years held the world’s record with a yield of 112 bushels of wheat per acre. Next Conference It was decided at the annual general meeting to hold the next conference at New Plymouth in July 1961. It was also announced that the executive had decided to award a prize in alternate years to the student from Massey or Canterbury Agricultural College who presented the best thesis on a subject relating to weed control. The officers elected for the ensuing year were: President, F. C. Allen, Christchurch; past-president, J. N. Fitzgerald, Wellington; vice-president, F. B. Thompson, Hamilton; secretary, L. J. Matthews, Wellington; treasurer, M. E. Williams, Wellington; committee, A. C. Burgess, Palmerston North, P. S. Ferens, New Plymouth, M. S. Foreman, Christchurch, P. B. Lynch, Wellington, G. R. Moss, New Plymouth, and R. L. Taylor, Nelson.

F.B.T.

Photographs by Elmwood Studios.

Papers and Speakers

“Weeds of South Otago and Southland”, A. R. Rankin, Fields Instructor, Department of Agriculture, Invercargill. “Control of Sweet Brier”, A. R. Dingwall, Fields Superintendent, Department of Agriculture, Christchurch, J. G. Richards, Farm Advisory Officer, Department of Agriculture, Oamaru, and R. C. Schofield, Department of Agriculture, Timaru. “Control of Spurrey”, R. L. Taylor, Research Chemist, Farm Chemicals Company, Port Mapua. “Brassica Weed Control in South Otago”, R. C. Stephen, Farm Advisory Officer, Department of Agriculture, Balclutha. “Chemicals and Application Techniques for Weed Control in Brassicas”, M. S. Foreman, Chief Technical Officer, J. H. Barbour and Son Ltd., Christchurch. “Adjuvants as an Aid in Increasing the Efficiency of Weedkillers”, W. M. Houlker, Technical Advisory Officer, Agricultural Division, Shell Co. of New Zealand Ltd., Wellington. “Aquatic Weed Control”, L. J. Matthews, Principal Scientific Officer (Weeds), Department of Agriculture, Wellington. “New Aspects of Vegetation Control”, G. J. Wills, Technical Representative, Ivon Watkins Ltd., Dunedin. “Total Weed Control”, R. K. Ward, Scientific Officer, Department of Agriculture’s Rukuhia Soil Research Station, Flamilton. “The Tolerance of Plants to New Chemicals”, F. B. Thompson, Principal Scientific Officer, Department of Agriculture’s Rukuhia Soil Research Station, Hamilton. “Weed Control in Peas and Maize”, T. M. Patterson, Technician, Department of Agriculture’s Rukuhia Soil Research Station, Hamilton. “Application of 2,4-DB to Mature Lucerne”, F. A. H. Meeklah, Technician, Department of Agriculture’s Invermay Research Station, Mosgiel. “Weed Control in Lucerne”, T. G. Sewell, Farm Advisory Officer, Department of Agriculture, Gore. “Residual Effects of Chemicals”, A. Thompson, Technician, Department of Agriculture’s Rukuhia Soil Research Station, Hamilton. “Crop Production in Chemically Killed Turf”, S. N. Dawes, Scientific Officer, Department of Agriculture, Wellington. “Thistle Identification”, A. J. Healy, Assistant Director, Botany Division, Department of Scientific and Industrial Research, Christchurch. “Control of Nodding Thistle”, E. Delahunty, Farm Advisory Officer, Department of Agriculture, Ashburton. “Eradication and Replacement of Ratstail”, D. A. Newman, Farm Advisory Officer, Department of Agriculture, Dargaville. “Control of Cutty Grass (Carex spp.)”, F. C. Allen, Technical Officer, Canterbury (N.Z.) Seed Co. Ltd., Christchurch. 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.