May IS, igao 



Halo-Blight of Oats 



143 



less favorable for the spread of the bacterial blight. The total precipi- 

 tation in Wisconsin for June was 2.31 inches, or below normal, while the 

 average temperature increased from 58.1° F. in May to 63.9° in June. 



With this rise in temperature and decrease in rainfall reports came in 

 of improved conditions in the oat fields. The new leaves which came 

 out were unspotted, and by the last of the month all the fields had resumed 

 a normal color and appeared to have almost completely recovered. The 

 badly yellowed field near Monroe was visited again July 2. It had 

 resumed a normal green color throughout with no halo lesions on the 

 upper leaves and only scattered old lesions lower down. The stand was 

 thin and the plants smaller than in adjoining fields. Neighboring fields 

 were just heading out, but this field would be 10 days to 2 weeks late. 

 Other fields showing yellow spots were reported to have resumed a normal 

 color, but plants in spots previously yellowed were at least a week behind 

 the others in development. This change of weather conditions in June 

 came at an opportune time. Continued cloudy, rainy weather would 

 undoubtedly have destroyed many plants and reduced the yield. As it 

 was, reports for the two seasons of 191 7 and 191 8 show an increase per 

 acre for the whole State of 2.2 bushels in 191 8, but this increase would 

 undoubtedly have been more than doubled but for the presence of halo- 

 blight. Following the unusually severe bacterial blight of the early part 

 of the season, blasting of panicles was also unusually abundant and gen- 

 eral throughout Wisconsin oat fields during 1918. In extreme cases as 

 many as 25 to 50 per cent of the spikelets in a head were undeveloped. 

 Counts of 30 panicles in a severely blighted spot gave an average of 29 

 spikelets per panicle and 31 per cent blasting. Counts of 30 panicles 

 from a part of this same plot not severely halo-blighted gave an average 

 of 34 spikelets per panicle and 20 per cent blasting. 



On six panicles sent in from Lincoln County the numbers of normal and 

 blasted spikelets were as follows : 



a Top blasted. 



The blasted spikelets are mostly in the lower half- of the panicle, but 

 occasionally the upper half is blasted as in No. 2. 



All the experimental plots showed considerable blasting and numerous 

 empty spikelets. Counts of 36 panicles of Wisconsin No. 14 oats from 

 treated seed showed an average of 11 per cent of the spikelets blasted. 



