"310 MASS. EXPERIMENT STATION BULLETIN 24.7 



On the basis of this tinding, Mr. V. A. Tiedjens of the Market Garden 

 Field Station has made crosses of these varieties in an effort to deveh)]) 

 a mildew-resistant variety which will head well in winter, poor heading 

 being an objectionable characteristic of May King. At least one promis- 

 ing selection has been made. 



Eradication of Nematodes and Parasitic Fungi in Greenhouse Soils. 

 (L. H. Jones). It has been learned through clay pot studies that single 

 api>lications of calcium cyanide to amounts as high as 9600 pounds per 

 acre are ineffective in eradicating nematodes from a gall-infested soil. 

 However, wiien tiie soil is Infested with (mly the motile phase 1200 

 pounds per acre gives eradication. In an effort to determine the resistant 

 phase, work was centered u})on eggs of the "brown cyst" stage. The 

 longest case observed required thirty-nine days for such eggs to hatch. 

 By making three applications each of 1200 pounds ])er acre at weekly 

 intervals, it was found possible to eradicate nematodes in the soil when 

 all stages were present in galls of a half inch diameter. This method 

 was not successful in the dry hot days of summer. 



The problem was then developed on the hypothesis that if the hydrocy- 

 anic acid gas, which forms when calcium cyanide reacts with moisture, 

 can be kept in the soil a sufficient length of time the nematodes in all 

 stages will eventually succumb to its lethal character. Investigations con- 

 ducted in this Department have produced evidence that an acetic acid- 

 treated soil has some properties in common with a soil that has been 

 partially sterilized with steam. Acetic acid alone and in two repeated 

 treatments was ineffective on nematodes. Yet when it was used in con- 

 junction with calcium cyanide complete eradication was secured in two 

 applications, but this combination failed when only one application was 

 made. This method was successful in many experiments and was further 

 developed to reduce labor by dissolving the calcium cyanide in a dilute 

 solution of acetic acid and flooding the soil with the solution. No attempt 

 is made to describe the physical or chemical phenomena involved in the 

 use of these two chemicals for soil disinfecting purposes. 



It is felt that further progress on this method may be made b> sub- 

 stituting a dry chemical in place of the wet acetic acid. The development 

 of a dry chemical mixture that is effective in nematode eradication would 

 make it possible to eliminate this pest from large areas of land on which 

 the crop production is seriously limited because of this organism. 



Two other methods for nematode eradication were attempted. It was 

 found that by keeping the water-holding capacity above 80 per cent the 

 formation of galls on tomato roots could be reduced to almost none. 

 However, the plants do not grow well imder such conditions. It was 

 also learned that the nematodes were not destroyed by keeping the soil 

 flooded for a month. This was determined by evaporating some of the 

 water and growing tomato plants imder normal soil moisture conditions. 



A condition of extreme drought, on the other hand, gives complete 

 eradication. Galls were introduced into air-dry soil. Every half week 

 some pots were removed, watered and tomato seed planted. The nema- 

 todes did not survive more than two weeks under these air-dry condi- 

 tions. If the relative humidity is similar to that of a normal August, then 

 three weeks are necessary. Such an extreme condition of desiccation is 

 not practical for other than potting soils, flats, pots, greenhouse parts, or 

 tools, all of which may be sources of serious contamination. 



The Rest Period of Gladiolus. (L. H. Jones.) The particular object 

 in altering the rest-period of gladiolus is to produce out-of-season blooms, 



