TAKE-ALL” OF WHEAT

Timaru Herald, Volume CXXXVII, Issue 19314, 15 October 1932, Page 6

TAKE-ALL” OF WHEAT

"FOOT-ROT" DISEASE. (By The Wheat Research Institute.) Wheat in New Zealand suffers from at least seven fungus diseases—two rusts and two smuts, which will be dealt with later on, and three diseases kind that are called “foot rots.” These three all attack wheat at about ground level and may cause the early death of the whole plant, or may allow it to come to maturity and produce empty heads, commonly recognised as “white heads.” Only one of the three is dealt with here. Effect of Take-All. The most widely recognised, if not the commonest of these foot rots is what in Australia and New Zealand is known as Take-All. It can frequently be observed in winter by the different colour of more or less circular patches a few yards across where the wheat is not thriving. The plants look stunted, and are easily pulled from the ground. If Take-All is the cause of the trouble the part between the seed and the surface of the soil is black and sooty, and apparently dead. By this time of year the patches are usually recovering, the rapid spring growth enabling the plants to stave off the disease for a time. If the spring is dry and growth poor, the plants reach a foot or so in height, and then gradually die off, leaving low circular patches in the field at harvest time. If the spring rains are good and growth rapid, the affected plants may produce heads, but they usually dry off early and produce no grain. Straws examined at this stage sometimes show for an inch or so above ground level, the same black sooty appearance that is to be found below ground in the seedling stage. This sooty growth contains the seeds or “spores” of the disease, and many of these spores reach the ripening grain of healthy neighbouring plants, either through the action of wind or in the threshing mill, but the majority of course remain on the straw and are ploughed in with the stubble. How the Disease is Carried. It has been fully proved that TakeAll can be carried on the seed, and therefore t is unwise to use seed from a crop that has been badly infected. For this reason crops with Take-All are not accepted for certified seed by the Department of Agriculture. But it does not at all follow that if clean seed is sown, the resultant crop will be healthy. While some spores get on to the seed, most of them are ploughed into the soil, and will infect a new wheat crop sown in the same field. Thus i* is universally recognised that Take-All tends to be worse in wheat after whfat after wheat, although of course the severity of the attack depends on whether the soil conditions have been favourable for the survival of the fungus during the autumn. A clear proof of the infection through the soil was afforded at Lincoln a few years ago. A field of wheat with a little Take-All was cut with a rather long stubble, and after harvest an attempt v/as made to burn it. As is usual, the burn was rather patchy. The stubble, part burnt, part unburnt, was now ploughed in, and the field sown with wheat again. Next year Take-All was serious wherever the stubble had not been burnt, while, wherever the fire had travelled the crop was clean. The spores had been burnt with the stubble and so had not affected the soil. Take-All After Grass. But if this were all the story, clean seed after any other crop than wheat should give a clean crop, whereas it is well known that wheat after grass is sometimes severely affected, especially on the Downs in South Canterbury. There is no doubt that Take-All lives on certain other plants, as well as on wheat, especially on barley or long twitch, and on perennial rye, and that these plants can infect a crop sown after them. It is probable that wheat sown after rape, turnip, peas or potatoes, has a better chance of escaping Take-All, than if sown in other positions in the rotation, but observations have not been sufficiently extensive to make sure of this, and exceptions to it certainly occur. Extent of the Damage. Mr J. W. Calder, of Lincoln College, who has made many observations on these foot-rot diseases, is of opinion that most of the Take-All affection occurs in these definite spots, and that the white heads often found scattered throughout a crop are caused not by Take-All as is commonly believed, but by other less known foot-rot dsieases.

Even although this is the case the total damage caused by Take-All must be very serious, for in certain localities and in certain seasons it is no uncommon thing to find half a wheat field hardly worth reaping, and there are small patches in nearly every field in the country. There is no doubt that Take-All is with us all the time to a certain extent, and that when the conditions of soil moisture and temperature are suitable the disease multiplies and spreads. It would appear that the most hopeful method of combating the disease is by some kind of rotational practice. Plant breeding could help, but the disease is so irregular in its appearance that selection of resistent strains is rarely possible; attempts have been made to secure an outbreak of the disease by sowing infected seed, but the disease did not develop because the soil conditions were not exactly right. Unless the disease appears regularly, selection against it is hardly possible. Seed treatment is useless because of the infection in the soil; and so the only hope of checking Take-All is to adopt those rotations that are found to give the wheat the best chance against the disease.