Feb. i, 1921 Onion Smudge 709 



above 20 C. and remained between 20 and 27 for most of the time 

 until harvest. On July 2 a few scattered acervuli were found. A 

 slight precipitation was recorded on July 2, 2 inches on July 4, 0.02 inch 

 on July 5, and 1.17 inches on July 7. Following this rainy period there 

 was a marked increase in number of acervuli noted on July 10. A slow 

 rain fell during most of July 14 and part of July 15. On July 15 the 

 disease was prevalent above the bulbs on the unthickened portions of the 

 outer leaves which comprise the "neck." These infections were clearly 

 the result of spores spattered upon these portions from the bulb scales 

 by rain a few days previously. The rainy weather, which prevailed until 

 harvest, about August 10, resulted in continued spread and development 

 of the disease, so that the white sets were all badly spotted by the latter 

 date. Further observations showed that the development of the disease 

 in other fields followed closely that noted in the experimental plot. The 

 infection in practically all cases, however, was confined to one or two of 

 the outer dry scales, the fungus being unable to attack the fleshy scales 

 previous to harvest. On the yellow and red varieties the fungus was 

 very abundant on the uncolored portions of the leaves at the neck, but 

 the highly colored bulb scales remained entirely free from it. This has 

 been the usual observation with the colored types. 



IN 1916 



The month of July, 191 6, was extremely warm and dry as contrasted 

 with cool, moist weather of the same period in 191 5. The soil tempera- 

 ture mean passed 26 C. on July 2 and remained above that point for the 

 rest of the month. In fact, for a large portion of that period it was well 

 above 32 , the maximum temperature for growth of the fungus on potato 

 agar. No signs of smudge were found until July 8. The extent of the 

 disease at this time was very meager, only a few acervuli being noted. 

 It is probable that the dry weather preceding this date checked the 

 fungus, in spite of the fact that the soil temperature was favorable. 

 Aside from 0.03 inch precipitation on July 8, 0.45 inch on July 20, and 

 0.14 inch on July 31, no rain fell during the rest of the month. More- 

 over, the soil temperature was well above the maximum for development 

 of the disease. On July 13 but very little smudge could be found. 

 On July 22 no further development was noted. The moisture from 

 the shower of July 20 disappeared very rapidly from the upper 2 

 inches of soil because of the extreme heat. A rainy period occurred 

 on August 3, 4, and 5, and following this Macrosporium porri 

 and Phoma alliicola developed rapidly. Smudge increased but very 

 slowly, however, probably because of the scarcity of viable spores.. 

 Another heavy rain fell on August 9 and 10, and the weather then 

 remained clear until after harvest on August 23. At the latter date 

 the bulbs were examined carefully, and in general the sets were only 

 moderately infected. The disease was confined for the most part to the 

 portions of the bulbs below the surface of the soil, while the abundant 



