40 MASS. EXPERIMENT STATION BULLETIN 183. 



but not all of it. The 8 per cent, killed all of it. The death point con- 

 centration lies between 5 and 8 per cent., but such a high concentration 

 is hardly practicable in the rose house, and the exact point was not de- 

 termined. 



Copper Sulfate. — Concentrations of 1, 2, 3, 4, 5 and 10 per cent, were 

 used at the rate of 2 gallons per cubic foot. The 5 per cent, seemed 

 hardly to check the fungus, but 10 per cent, proved entirely effective. 

 Such a high concentration seemed prohibitive for application to soil, and 

 no more accurate determination was made. 



Lime-sulfur. — This mixture proved to be worthless, even when applied 

 at a concentration of 1 part of commercial product (32° Baume) to 10 

 gallons of water, and at the rate of 2 gallons per cubic foot. 



Dry Sulfur. — Finely ground suKur flour was added to the soil and 

 thoroughly stirred in. First, 10 grams per bottle were used, and when 

 that proved to be ineffective 10 grams more were added, etc. All results 

 were negative, even up to the rate of 7 pounds of sulfur to a cubic foot 

 of soil. This test was performed at a laboratory temperature of 19° to 

 24° C. Perhaps if higher temperatures had been used the sulfur would 

 have been more effective. Dry sulfur seems to be worthless at the tem- 

 peratures tested. 



Soot. — There is an idea prevalent among florists that soot has fungi- 

 cidal value, but plant pathologists seem never to have made any extensive 

 experiments with it. The same method and rates as for dry sulfur were 

 tried. At the rate of 4 pounds per cubic foot soot did not kill the fungus, 

 but at the rate of 7 pounds no growth of the pathogene occurred. 



Of all the chemicals tried, formaldehyde seemed to be the only one 

 which would give control at concentrations which could safely be used 

 on the soil. 



Greenhouse Tests with Formaldehyde. 

 The greenhouse tests on the use of formaldehyde were begun before 

 the laboratory tests were completed, and at a time when it appeared 

 that a concentration weaker than 1 pint to 25 gallons would be sufficient. 

 As a result, the tests on a large scale were made with a concentration of 

 about 1 pint to 40 gallons, but, on the other hand, more solution was 

 applied per unit of soil. Two houses, each capable of growing more than 

 1,000 rose plants, were thoroughly soaked with the solution. One of 

 the houses contained raised benches; the other, ground beds. Both had 

 previously grown diseased roses. The soil was replaced by soil from 

 outside the houses before sterilization. In the light of what we now know 

 of the habits of Cylindrocladium, it is safe to assume that this soil was 

 infested, because soil from the benches in previous years had been thrown 

 out near it. After soaking the soil thoroughly the houses were closed. 

 Fumes of formaldehyde were so strong in the closed houses that it was 

 not possible to remain in them. After the soil had dried sufficiently both 

 houses were planted with roses which had been potted in soil sterilized 



