Stem Rust In Wheat In North Canterbury

Press, Volume CIV, Issue 30937, 18 December 1965, Page 9

Stem Rust In Wheat In North Canterbury

Stem rust has appeared in wheat in North Canterbury, according to Dr. R. C. Close, of the Plant Diseases Division of the Department of Scientific and Industrial Research. The development of the outbreak will depend on weather conditions.

Stem rust can completely destroy wheat crops or else it reduces yields considerably and lowers the quality of grain, says Dr. Close. The rust attacks mainly the leaf sheaths and stems and when very severe is present on the stem just below the head, where it restricts the flow of water and food to the developing grain. In this way yield is reduced. In recent weeks the nucleus of a stem rust epidemic has been found in North Canterbury. On November 24 stem rust was present as a light infection on a Hilgendrof 61 crop at Waikari. In this locality in September volunteer wheat plants in the headlands were bearing active pustules of stem rust. Infection had carried over the winter on these plants, and, although they were disced under in October, infection had already spread to the autumn-sown crop.

Removal of volunteer wheat or its destruction by hardgrazing or thorough cultivation is essential to prevent stem rust overwintering. There is still the possibility that stem rust can come from Australia, but this certainly does not seem likely to happen this season. Oinihi Valley Stem rust was also found on November 24 at two localities in the Omihi valley. Both were in Hilgendorf 61 crops—one a light infection and the other severe. In this area, the rust had come from stem rust-infected wheat plants which had been growing on the road-side near Glenmore, about three miles south of Motunau. This volunteer wheat was there because part of a wheat paddock had been used in making the deviation. Active pustules were present on these plants in June, September and October. The site has since been cleared of wheat plants by members of the Federated Farmers.

These are two instances where stem rust has overwintered on volunteer wheat and these have almost certainly acted as source plants from which rust has spread to autumn-sown wheat. There are probably other instances where rust has overwintered on volunteer wheat, and all have contributed to the initiation of this potential epidemic.

In a limited survey, crops of Hilgendrof 61 infected with stem rust have been found at Glenmark, Broomfield and Balcairn. Although! most are light infections (pustules occurring on lower stems and leaf sheaths), some are severe with rust on the upper stems. Between now and harvest a serious rust epidemic could develop in the Omihi-Balcairn area. It all depends on the weather. If conditions are dry, then the rust will develop only slowly and little harm will result However, if conditions are wet then the air-borne

uredospores will be able to germinate on plants and cause an infection. Plants have to be wet for at least 12 hours for spores to infect Once infection has taken place, the fungus can grow within the plant irrespective of the weather. After eight to 14 days a new lot of spores are produced and these spread to adjacent healthy parts and plants. Each pustule is capable of producing 350,000 spores and thus with the right weather conditions the spread within crops and from crop to crop can be very rapid. Rust-resistant varieties are the obvious solution and work has started on this problem at the Crop Research Division. At the moment, both Hilgendorf 61 and Arawa are very susceptible, while Aotea is not as susceptible. Fungicides to protect plants against rust attack have been used and in a number of cases have prevented rust infection and the yield losses that occur. In these cases fungicides were regarded as

an Insurance against a possible severe rust attack. Noone can forecast the weather over the next few weeks, but as it is often wet during late December-early January it ia better to have protection against rust than run the risk at serious losses. The only fungicide suitable for protecting wheat plants is Dithane S3l, applied at 31b an acre in 10 to 12 gallons of water (aerial application). Unfortunately this fungicide is in short supply and even that available will not arrive until the week before Christmas. Thus only potentially high-yielding crops which are severely infected (i.e., 5 per cent of the stalks with rust pustules on the stem below the head) should be sprayed. In all cases, where crops are sprayed, an unsprayed strip of about one acre should be left so as to measure yield differences and assess the fungicide. Trials have been put down on the Hilgendorf 61 crops of Mr L. J. Stackhouse and Mr J. F. Wyllie at Omihi. In the first case there are blocks aerial sprayed with Dithane S3l, and with Antracol (a BASF product) as compared with unsprayed blocks. There is also a smaller scale trial comprising Dithane S3l with two new fungicides (four replications of each). At Mr Wyllie’s there are two strips sprayed with Dithane S3l, compared with one of Antracol, and unsprayed areas. If farmers in North Canterbury who contemplate spray-

ing would leave unsprayed strips then much useful information on the control of wheat stem rust by fungicides should be obtained this season. If a fanner is in any doubt about whether he has stem rust, samples can be sent to the Plant Diseases Division at Lincoln or the local Department of Agriculture who will assist in determining the severity of attack and the necessity for spraying.