DISEASES IN WHEAT

Press, Volume XCV, Issue 28257, 20 April 1957, Page 9

DISEASES IN WHEAT

SURVEY OF CROPS IN CANTERBURY

RELATIVE RESISTANCE OF VARIETIES

In the fourth season of the wheat disease survey of Canterbury being carried out by officers of the Plant, Diseases Division and Crop Research Division of the Department of Scientific and Industrial Research, 49 crops were inspected. There were 34 crops of Cross 7, seven of Dreadnought, five of Fife Tuscan and one each of Arawa, Hilgendorf and Yielder. On four farms—two with Cross 7 and two with Dreadnought—there were also crops of Arawa. These were inspected also, but the observations have not been used in preparing the following summary. Diseases found in more than half the crops were ear blight, loose smut, leaf rust, mildew, septoria leaf blotch and crown rot (fusarium).

There were fewer crops than in the previous season with leaf rust, stem rust and eyespot and more with septoria and take-all. This was the first season of the survey in which ear blight, in most cases caused by fusarium infection, was common. Blighted ears were found in 80 per cent, of the crops, including two of the Fife Tuscan and four of the Dreadnought crops. Four of the Cross 7 crops had a moderate to severe amount of ear blight, with shrivelled grain. Each of these had been sown early in May. One had been- fed off in August and the other three, which were not fed off, were among the five crops with the heaviest infection of eyespot or sharp eyespot. Several other crops of Cross 7 with a large amount of ear blight were seen during the season. These had all been sown early, and besides the ear blight had a moderate to severe infection of one or two of the following diseases:—eyespot, fusarium crown rot and take-all. In the earlysown Cross 7 crops of the survey, among eight sown directly after grass there were three with moderate or severe ear blight, while among 24 sown after a crop there was only one moderately affected crop.

Leaf Rust One third of the crops had a moderate or severe infection of leaf rust, although as in the previous season it is unlikely that the disease caused any damage. Fife Tuscan crops were infected more severely than Cross 7. There was a trace of stem rust in a quarter, of the crops. In many of them it was found only on late plants. The distribution and severity of mildew have not varied greatly over the last four seasons, twothirds of the crops being infected and about one-fifth being recorded as moderate or severe. Septoria leaf blotch was more widespread than in the previous three seasons. All the Cross 7 and Fife Tuscan crops, and none of Dreadnought, were infected. Most of the Cross 7 crops had a moderate or severe infection of the upper leaves, and some had severe stem infection, but it appeared that infection of the stems had occurred too late to cause appreciable damage. As for root diseases take-all was found in a quarter of the crops, a greater proportion than in previous seasons. Only one crop, grown after peas, had a moderately severe infection. Eyespot and sharp eyespot were each found in about one crop in six. Severe damage was caused by eyespot in one crop grown after grass, and by sharp eyespot in one sown down with grass and clover after brassicas. As usual, most crops had some crown rot (fusarium) but this season none was severely infected.

Stem weevil was found in a third of the crops, and hessian fly* in two-thirds. Army worm damage was seen in only four crops.

Two crops were in the areas affected by hail storms in December. One was estimated to have suffered 25 per cent, loss, and the other 5 per cent.

Effect of Weather The extent and severity of infection by some of the diseases may be related to the weather ?ver the last season. The prolonged drought in the autumn

would have allowed a good survival of phizoctonia infection in the soil, with subsequent development of sharp eyespot. Rust infection was widespread in the previous season, and would have carried over well in the mild winter. The weather in spring was mild, with frequent showers,

encouraging the spread and development of take-all and septoria. Drier conditions, with ivarm winds, in late spring and

early summer prevented extensive stem infection with septoria, and made damage by take-all apparent at the “white-head” stage. During the summer intermittent showery weather led to moderate to severe attacks of ear blight, particularly in heavy crops of Cross 7 sown after grass. The new wheat variety, Arawa, has more field resistance to mildew and septoria, and probably to

ear blight and root diseases, than Cross 7, and should produce healthier crops on the most fertile soils. Arawa is not as resistant as Dreadnought to septoria or mildew, so there is still a possibility of developing better disease-resistant varieties. The field work this season was done by Dr. H. C. Smith and Messrs A. D. Thomson and G. M. Wright, of the Crop Research Division. A recommendation of the Wheat Specialists’ Committee that this disease survey should now be discontinued and the results analysed and published has been accepted. The co-operation of farmers in giving information about their crops has been greatly appreciated by those scientists who carried out the investigations. '*