Weeds major problem in lucerne

Press, Volume CXI, Issue 32660, 16 July 1971, Page 13

Weeds major problem in lucerne

Weediness is a major problem in lucerne stands. But for this factor lucerne would become much more popular. Much of the cause, however, lies in management, according to Mr F. C. Allen, of the Department of Agriculture field research section at Lincoln. Speaking to fanners at Geraldine last week, Mr Allen referred to a survey made by Dr I. D. Blair about 1965, in which farmers reported that they broke up their lucerne stands mainly because of an invasion of weeds. Mr Allen said part of the reason for lucerne becoming infested with weeds was because it was being grown under sub-optimum conditions. A farmer could not do much about site conditions, but management could bring conditions up to the optimum. Weeds must come from somewhere, and management standards could be raised by changing cutting and grazing times. Weeds seemed to be a secondary effect of management practices, and once established, could hasten the deterioration of the stand. The question of weed control was basically a question finally of economics. Mr Allen advised springsowing, because something could then be done, if the weeds became evident. Chemicals added to the cost of establishment. Preemergence sprays cost about 20 bales of hay. It was essential that sprays such as 24D8 and MCPB be applied early before growth started. A delay in spraying until growth started could result in a 75 per cent reduction in the crop, particularly with MCPB. Dr J. G. White, reader in plant science at Lincoln,

said the key to successful lucerne management was to fit the management of the farm into the growth pattern of the plant. He stressed the need to cut at the correct time, and referred to trials demonstrating how the appropriate cutting times reduced the problem of weeds. Five cuts at the pre-bud-ding stage yielded 92001 b of dry matter, with a weed content of 63 per cent; four cuts with 50 per cent of the crop in bud produced 11,2001 b of dry matter, with a weed content of 21 per cent; and three cuts at the 1 per cent flowering stage yielded 14,5001 b, with no weed content. “The message is loud and clear,” Dr White said. “Cutting too early leads to a significant decline in the stand.” He advised farmers to cut at the stage of 1 to 10 per cent flowering for maximum dry matter, freedom of weeds, and life of the stand. Discussing grazing management, Dr White referred to the work of the late C. E. Iversen, who found that under rotional grazing few weeds became established, whereas under set stocking they became well established. Plant survival after five years was 26 per cent as against 15 per cent for set stocking. Mr Iversen recommended bold grazing, but Dr White said the system did have some problems, particularly at time of heavy growth. The potential for lucerne had been shown to be very good, with yields of up to 24,0001 b of dry matter an acre on Wakanui soils under irrigation. But on predominantly lucerne farms, there were problems in feeding stock in early spring. In this respect, delayed lambing could be a factor in suiting lucerne growth. Dr White said he was a firm advocate of liming before sowing. The pH should be about 6 to get good no-

dulation and an assured growth. Once established, liming was not required unless the pH fell. It was better to spread molybdenum, sulphur, boron and potash. Asked about trial work with coated seed, Dr White said good results had been obtained in the Mesopotamia area where the pH was 5.6 to 5.7. But where liming had been adequate, he saw no need to use coated seed, although work by Dr R. C. Close this year tended to contradict this. Dr White said there was a case for using coated seed in the back country where transport made liming expensive, but he advised that if coated seed was used, it should be fresh —no older than three to four weeks. He referred to widespread failures in young lucerne two years ago. This was brought about not so much by the lime-coated seed, as to the failure of the inoculant on the seed. To a questioner who referred to subterranean clover being a. strong competitor of lucerne in Geraldine County, Dr White recommended drilling lucerne in spring when subterranean clover was not establishing itself. He added that where lucerne was being continually defoliated, light was allowed in and this proved ideal for the growth of subterranean clover. Asked about the value of cover crops, other than straw crops, Dr White said lucerne had been established with turnips and rape at Ashley Dene. Rape was a suitable cover drop,, providing no more than 2oz to 4oz of seed was drilled per acre. What is the optimum time for rolling? A member of the audience said, local farmers were getting wonderful strikes by heavy rolling straight after drilling. Dr White agreed, with one reservation—that there could be a problem if sowing and heavy rolling was followed by heavy rain.