ANNUAL REPORT, 1941 25 



foot) was applied to soil which had been steamed five days previously, there was 

 some injury, as compared with growth in steamed soil, and there was certainly 

 no improvement in growth as compared with growth in untreated soil. It is 

 concluded that the stimulatory effect of formaldehyde on growth is due prin- 

 cipally or wholh- to its freeing the plants of the retarding effects of parasitic soil 

 fungi, and it is concluded further that formaldehyde may be dangerous, as re- 

 gards its effect on some plants, if applied to soil recently steamed. 



Spergon (2.7 gm. per square foot) gave fair control of a root-rot of sweet pea 

 seedlings when applied to soil one day before seeding, and there was no injury. 

 But it gave no protection if seeds were sowed thirty days after soil treatment. 



Copper oxylate applied to the surface of soil after seeding failed to prevent 

 damping-off of any species. 



Semesan (1.1 gm. in 1.2 quarts water per square foot), applied to the soil sur- 

 face before seeding but not worked into the soil, was not injurious, controlled 

 damping-off fairly well although not completely, and increased by 27 to 100 

 percent the numbers of seedlings of marigold, Scabiosa, pansy, and sweet pea 

 which lived. Results were less good when the dry Semesan was worked into the 

 soil, fcr it was then apparently not sufficiently concentrated near or at the soil 

 surface. 



Chemical Soil Surface Treatments in Hotbeds for Controlling Damping-off of 

 Early Forcing Vegetables. (\V. L. Doran, E. F. Guba, and C. J. Gilgut.) Es- 

 pecial attention was given to the possible use of ammonium hydroxide and 

 ammonium sulfate as soil disinfectants. 



Ammonium hydroxide, 12 cc. per square f'oot of soil surface, controlled damping- 

 off fairlj' well and without significant injury to seedlings of beet, although seeds 

 were sowed within five days after soil treatment. However, 16 cc. ammonium 

 hydroxide gave better control although, for safety', it was necessary to wait about 

 seven days before seeding. 



Ammonium sulfate had little oi no fungicidal effect in acid soils, with pH values 

 of 5.0 to 6.0, but it had a decidedly fungicidal action in soil which, as a result of 

 the earlier use of hydrated lime, had a pH value of about 7.0. 



When ammonium sulfate and hydrated lime, one part of the former and two 

 parts of the latter by weight, were intimately mixed and this mixture (at the 

 rate cf 10 gm. ammonium sulfate per square foot) was worked into moist soil, 

 there was a strong odor cf ammonia and damping-off was well controlled. It 

 was, however, necessary on grounds of safety to wait more than five days after 

 soil treatment before seeding. 



Hydrated lime alone, applied to soil, usually increased the number of plants 

 which lived and reduced the severity of damping-off, but the disease was not 

 controlled to any such degree as it was by ammonium sulfate and hydrated 

 lime applied together. 



Control of Greenhouse Vegetable Diseases. (E. F. Guba, Waltham.) Ap- 

 proximately 30 percent of the greenhouse tomato growing area in the fall crop- 

 ping season of 1941 was planted to the Bay State tomato, developed for resistance 

 to Cladosporium leaf mold from hybrids of Lycopersicum pimpinellifoliiimX L. 

 esculentum. The new tomato was released for trial in 1939. In the fall cropping 

 season of 1940 a new physiologic form of the fungus, to which Bay State is com- 

 pletely susceptible, was noted at Swansea, Bristol County. In 1941, other in- 

 stances of the complete susceptibility of Bay State to the new form of Clado- 

 sporium were observed. Globelle (Ohio) and Vetomold (Ontario) likewise de- 

 veloped for resistance to Cladosporium, and derived from red currant, have 

 shared the same experience. The new physiologic form of the fungus is infectious 

 to L. pimpinellijolium (Jusl.) Mill, and L. hirsutum Humb. & Bonpl., causing 



