52 



James G. Korsfall 



probable that the germinating conidia exercise a solvent action on the 

 sulfur, as suggested by the work of Marsh (1929). 



If sulfur dust will eradicate clover mildew once it is established, it cer- 

 tainly should prevent initial infections. An experiment in protecting 

 seedlings was carried out in the following maimer in the greenhouse during 

 the mildew period of 1928. Soil of uniform composition was placed in 156 

 four-inch pots which were planted uniformly to medium red clover on 

 August 9. The plants had become well established by September 6, when 

 the first natural infections were visible. On that date the pots were divided 

 into two groups of 78 pots each. One group was dusted with Kolodust 

 and the other was left untreated as a check. Sixteen pots of heavily 

 mildewed clover plants equally spaced around the experimental pots 

 served, with other mildewed plants about the greenhouse, to insure an 

 ever-ready and a copious supply of inoculum, which eliminated the neces- 

 sity of applying conidia artificially. A subsequent application of Kolodust 

 on September 12 and another on September 24 kept the treated plants 

 practically free of infection. On October 9 the plants from each pot were 

 cut at the ground line, weighed green, and then weighed again after drying 

 for two weeks at 105°C. The data procured are given in table 17. 



TABLE 17. Effect of Kolodust in Protecting Clover against Erysiphe Polygoni 



in the Greenhouse 



Weight in grams, per pot 



Dusted 



Total 



Average 



Undusted 



Total 



Average 



Green plants 



Dry plants 



Water 



Water per gram of dry matter 



1 , 042 . 3 

 L62 83 



879.46 



13.36 

 2.09 



1127 

 5.39 



604 



106.73 

 597 . 26 



7.74 

 1.37 

 6.37 

 4.65 



Obviously the sulfur controlled the disease, because the dusted plants 

 averaged 1.73 times as heavy as the undusted when green and 1.53 times 

 as heavy when dry. That means that the dusted gave an average of one 

 and one-half times as much dry hay as did the checks. 



Differences in resistance have only been suggested thus far, but crosses 

 between resistant European clovers that are susceptible to anthracnose 

 and winterkilling and American strains that are resistant to the latter 

 two maladies and susceptible to powdery mildew might give desirable 

 plants that would be satisfactory from all points of view. Mains (1923 : 312) 

 states that individuals resistant to mildew exist even among native clover 

 varieties. Selections from these also should produce desirable strains. 



