The Take-all Disease of Cereals and Grasses 31 



influence on the severity of the disease in Oregon, and that it appears 

 probable that only in certain especially favorable seasons will the disease 

 result in serious crop damage. Guerrapain and Demolon (1913) con- 

 clude that high autumn temperatures promote the infection of seedlings 

 in France. Dombrovski (1909) and Mangin (1914) state that high 

 humidity of the soil favors the disease. Robinson (1907) believes that a 

 dry summer followed by a wet winter affords the most favorable conditions 

 for fall infection. Brittlebank (1920) reports that water-logging of the 

 soil before harvest, with a subsequent drying, favors the development of 

 the disease. 



Observations made during the present investigations seem to cor- 

 roborate in general the foregoing statements regarding the effect of climatic 

 factors. In most of the infested wheat fields examined there was little 

 apparent difference in the amount of infection on high and low ground, 

 although in a few fields the infection appeared to be much heavier on 

 the lower and wetter soils. In the 1922 test plot an inoculated check 

 row in water-logged soil had a higher percentage of badly diseased plants 

 than did the rows on drier soil. 



Varying climatic conditions which occurred during the springs of 1921, 

 1922, and 1923 brought about marked differences in the amount and 

 severity of take-all. As shown in figure 3, the spring of 1921 was 

 warm and wet during March and April, while May and June were excep- 

 tionally dry. Under these conditions there occurred a higher percentage 

 of extreme stunting, combined with a premature dying of the infected 

 winter-wheat plants. 



The spring of 1922 differed from that of 1921 in that it was cooler or 

 rather later, and in May, and especially in June, there was greater rain- 

 fall. Under these conditions about 40 per cent less plants were found to 

 be diseased in the infested fields than in 1921. The plants that were 

 affected died later and the amount of stunting was much less. 



The spring of 1923 was abnormally late, cool, and dry, with the low 

 rainfall continuing until harvest time. Under these conditions the disease 

 was far less severe than in either of the two preceding years. This 

 decrease in the severity of the disease is shown by the fact that in 1923 

 the disease appeared two weeks later than ever before, and 70 per cent 

 less plants were found diseased in 1923 than in 1922; also, in 1923 there 

 was less dwarfing of the affected plants than in any previous year. 



Thus the weather conditions which seem to favor the disease are 

 abnormally high temperature and rainfall in the early spring (March and 

 April), followed by dry, hot weather from the period of jointing until 

 harvest. Springs in which abnormally high temperature and rainfall 

 occur seem to be less conducive to the development of the disease if during 

 May and June the rainfall is abnormally high and the temperature is 

 normal or below. 



