Wheat rust control on the way

Press, 9 November 1981, Page 2

Wheat rust control on the way

Supplies of the chemical to control stripe rust in wheat crops in Canterbury are likely to be available later this week. The advisory and development manager of Bayer New Zealand.- Ltd, Mr M. S. Moore, said at the week-end that supplies would arrive by air from Australia and Germany. The powder from Germany will have to be repacked after arrival. Staff would work round the clock doing this, he said. Mr Moore said the price for the supplies would remain the same in spite of the extra cost of transport. The supplies were expected to arrive soon enough to avoid the need to call on chemical held for use in other parts of New Zealand. . The chairman of United Wheatgrowers, Mr A. L. Mulholland, said at the weekend that the warm, dry weather late last week seemed to have slowed down the development of the disease, but there was some anxiety that the change in the weather again at the week-end could result in a rapid build-up. In this event it was felt that the German and Australian supplies might arrive too late. Because the disease is new to New Zealand there is uncertainty about its effect on wheat yields. Mr Mulholland said that if it reduced yields by more than 20 per cent it would be catastrophic. Next season he would like to see chemicals used to prevent the disease rather than cure it. He suggests an early warning system so that at the first appearance of rust spores crops could be treated immediately to halt further development of the disease. Overseas only one spray generally was applied, sometimes two. In New Zealand this season some people had sprayed their crops four times.

The prevalence of the rust this season has raised questions about the number of spray applications that farmers might economically make.

Mr B. L. McCloy, a farm advisory officer (agronomy) of the Ministry of Agriculture in Christchurch, thinks that on a good crop two sprays could be justified but possibly only one on light dry land. He said last week that the cost of application of the chemical — more than $4O per hectare to aerial spray autumn-sown crops — and the possibility of warmer weather lessening the effect of the disease might encourage some farmers to halt further spraying. Mr McCloy said that about 70 per cent of the main cropping area would be in susceptible varieties but he does not subscribe to some of the more pessimistic forecasts about the likely impact of the disease in Canterbury. Where a heavily infected flag died off prematurely for lack of spraying now, the yield could be reduced by at least 10 per cent and grains could be smaller, he said. However, Mr McCloy does not see the average yield of the crop in the province being seriously reduced. In a season when the crop earlier looked likely to be above average, he said that the yield could still be about the average of three or four tonnes per hectare. Some farmers are anxious about the effect of stripe rust on other crops. Mr Mulholland said that English information showed that barley, oats, and some ryegrasses were also vulnerable, although wheat was most susceptible. Dr J. Hedley, officer-in charge of the Ministry of Agriculture’s plant health diagnostic station at Lincoln, said that there were numbers of races of the rust in overseas countries, but at this stage it was thought that there was only one here that affected some varieties of wheat. However, other crops were being constantly monitored for any possible effects. Farmers’ meeting, page 10