Oct. 1. 1920 Fusarium-B light (Scab) of Wheat and Other Cereals 29 



coming of rains and cloudy weather there was a marked increase in the 

 number of blighted heads only a week after the rain. This was shown 

 very plainly in experiment 22, one of the inoculation experiments in 

 1 91 8, 



At 7 o'clock in the afternoon, July 2, 191 8, 60 wheat heads in one of 

 the Wisconsin Experiment Station plots were sprayed with a suspen- 

 sion of Gibber ella saubinetii ascospores and left uncovered. 



On July 8, 1918, 12 heads, or 20 per cent, showed signs of first infec- 

 tion. Several days later there came a slight rain and the sky was cloudy 

 for over a day. By the twentieth of the same month 28 heads, or 45 

 per cent, showed symptoms of blighting. 



On the other hand, an experiment, which differed from the fore- 

 going only in that the heads were kept moist artificially (see inocu- 

 lation experiments, p. 25), showed 70 per cent infection on July 7, 

 1 91 8. The number of the infected heads did not increase after the 

 rainy and cloudy weather that followed. All controls in both experi- 

 ments remained healthy. This case, which is one of several, shows 

 that in the absence of proper weather conditions there is much less 

 infection than when the weather is favorable. In experiment 20, in 

 which the heads were kept moist, all the heads that were successfully 

 infected showed infection within six days, and the coming of rain in this 

 experiment did not increase the number of infected heads. 



Not only does rainy and cloudy weather favor blight infection but it 

 is also necessary for spore production, as already pointed out in this 

 paper. 



CULTURAL CONDITIONS IN RELATION TO HEADBLIGHT 



Even though they were well developed and still apparently healthy 

 and normal, the plants which were in shady places or overgrown by 

 weeds were attacked by headblight and noderot to a much greater 

 extent and by a greater number of the species of Fusarium than were 

 plants which had a normal amount of sunlight. This was especially 

 evident in one of the Wisconsin Experiment Station plots where a small 

 area sown with barley and wheat was allowed to be overgrown by weeds. 

 The blight infection on this plot was so abundant that in some small 

 areas practically all the plants were infected. In general, the whole 

 field had an average of 10 per cent of infection as compared with 5 per 

 cent from neighboring clean fields. Another interesting fact was that 

 nine different species of Fusarium, two of which have perfect stages, 

 were isolated from blighted heads gathered from this small plot cover- 

 ing not over 200 square yards. Gibber ella saubinetii was the most 

 common and most destructive species. 



Lodging of the fields also gives a marked increase of headblight infec- 

 tion. This was brought out especially well in a wheat field located two 

 miles northeast of Madison, Wis., where the head infection among the 



