Disease cuts wheat yields

Press, 29 January 1982, Page 15

Disease cuts wheat yields

By

HUGH STRINGLEMAN

Take-all main offender, rust damage uncertain

The disease take-all has substantially reduced wheat yields at the Lincoln College cropping farm this harvest but it is too early to assess the effects of wide-spread stripe rust on the wheat yields of Canterbury. Mr Graham Tate, supervisor of the college cropping farm, said this week that wheat yield was down from 5 tonnes per hectare average over the last two harvests to only 3.5t/ha this year and that this substantial reduction was mainly due to takeall.

The effect of stripe rust, which has been a major bugbear to many Canterbury wheatfarmers this year for the first time, is much harder to gauge. Mr Tate said some pinching of grain on the cropping farm may be due to stripe rust but that the disease has had no effect on yield that could yet be measured. “We are harvesting a trial which could give us the answer to the effect of stripe rust but results are not yet available,’’ he said. Of much. greater concern was the take-all problem which will have major impli-

cations for future farm practice at the College.

Take-all has reduced yields to less than 2t/ha on some paddocks of the cropping farm, and it is significant that take-all has occurred in paddocks which had not been under cereals for some years prior to the present harvest. It had been a practice on the farm to undersow white clover with wheat to provide seed production in the following year but now an alternative to that would have to be found.

This is because one method of reducing the carryover of take-all is to burn stubble to reduce the straw debris in the soil where the disease can exist from wheat crop to wheat crop.

Mr Tate said the college would keep Canterbury farmers advised of any changes to the cropping farm’s practices to cope with take-all, but that early indications were that more stub-

ble burning was going to be necessary. Direct drilling after burning may also assist in reducing the menace. Almost all the wheat has been taken off the college farm and recent dry weather is also accelerating harvest throughout Canterbury. At the Wheat Research Institute results of testing for the first 1000 samples have indicated an average baking score of 19.1 for the 1982 harvest compared with 19.4 last year. This is not a significant difference, certainly on early indications. Under the baking quality test 12 is the minimum acceptable for milling grade and good quality wheat can expect to score around 20. Up to 10,000 samples of wheat for testing are expected this year, so that testing thus far is in its early stages. The over-all effect of

stripe rust on wheat yield will only be arrived at during the next few months by extensive “de-briefing” and consultation among officials of the Ministry of Agriculture and Fisheries, Department of Scientific and Industrial Research, Lincoln College and industry. The plant health diagnostic station of the M.A.F. at Lincoln College will be co-ordi-nating a series of meetings between all parties in early March and publishing a joint summary of the findings thereafter.

M.A.F. officers throughout Canterbury and Southland will be advised of the findings so as to give useful advice to farmers for the 1982-83 crop. The plant health station has just been advised from' Australia that another race of stripe rust has developed in that country, and that the

disease has been observed on barley and triticale. Until now the only stripe rust race found in Australia and New Zealand has been 104E137, but there are more than 60 races known in the world.

The presence of another race raises fears of stripe rust being. able to attack hitherto rust-resistant wheat varieties in Australia and New Zealand.

and savagely mauled a number of crops (including some barley varieties) ... and then it surfaced around Tamworth in N.S.W., across Bass Strait in Tasmania and in the following year it showed up north of Adelaide and in New Zealand," said the article.

"This season Queensland growers felt its bite. ’

"Australian wheat breeders are working flat out to develop and bolster resistance to the new threat, but the thing which scares them is the disease’s ability to rapidly mutate and attack wheat varieties which have previously been safe. “If stripe rust takes hold in the early pre-flowering period, yield losses can be savage. At the Horsham Research Institute in Victoria the 1979 Wimmera losses have been put. at 20 to 40 per cent of the otherwise expected yield.

Although the effect of the disease can be minimised by selection of wheat varieties which are resistant, large losses in grain yield can occur when a susceptible variety gets a substantial dose of disease or when a variety is attacked by a mutation of stripe rust for the first time.

Under the heading “Striped crop bandit” a recent issue of the Australian “National Farmer” newspaper said that there were fears that stripe rust, Europe’s worst crop disease, was preparing to take a bite out of the Australian grain harvest. “Stripe rust, first found in Australia in 1979, has now appeared in all States except West Australia, and many think the Nullarbor won’t keep it out for long,” the article said.

“Later trials have narrowed this to around 25 to 30 per cent.

“In the United Kingdom, stripe rust plunders between 5 and 15 per cent of the crop each year and for individuals growing susceptible varieties, half the yield can be lost.

“The disease first appeared in the Victorian Wimmera in a wettish year

“The only sure treatment for stripe rust is to grow a resistant variety such as (in Australia) Oxley, Condor, Banks or Cook.. “Victorian trials of aerial spraying with the fungicide Bayleton showed a definite gain in cases where the disease was caught early (only 5 per cent of leaf; area affected) on a susceptible variety. In this case up to 17 per cent of yield was salvaged. “Where the disease had got a strong hold (20 per cent of leaf area) it was found that spraying had little effect. “With spray costs around 525 a hectare, the farmer would have to be facing severe yield losses and have identified the disease very, early to profit on the spray outlay,” commented the paper. ■