18 MASS. EXPERIMENT STATION BULLETIN 305 



Soil, 3 inches deep in flats, in which lettuce seedlings were growing, was watered 

 only with solutions of copper sulfate (0.43, 0.57, 0.86, and LO gram per gallon), 

 applied often enough to keep the soil at or near the optimum moisture content 

 for growth. One month after treatment began, tip burn was severe on plants in 

 soil receiving only water, but there was no tip burn on plants watered with any 

 of the solutions of copper sulfate. At this time all plants were inoculated with 

 Bremia lactucae E. Kegel. Less infection (than the checks) resulted on plants 

 in soil which had received copper sulfate, but plants were injured by the treat- 

 ment. There was but little infection on plants in soil watered with 1.0 per cent 

 copper sulfate solution, but this treatment was very injurious to plants. 



Lettuce plants which had been watered for one month with these solutions 

 of copper sulfate were set in the field, after which they received no more copper. 

 They, too, were inoculated with B. lactucae, and the spread of downy mildew 

 on them during the summer showed that no lasting protection had resulted 

 from earlier applications of copper sulfate to the soil. 



The following materials (per acre) were applied to soil in pots: potassium 

 carbonate 1000 pounds, hydrated lime i]/^ tons, these materials together in 

 these amounts, and copper sulfate 250 and 400 pounds. Lettuce plants were 

 set immediately thereafter. These plants and untreated checks were inoculated 

 with B. lactucae 4 weeks later. None of the treatments significantly' affected 

 infection. Great injury to the plants was caused by 400 pounds of copper sulfate 

 and by potassium carbonate and hydrated lime applied together. 



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

 probability of developing varieties of tomatoes sufficiently resistant to tomato 

 leaf mold, caused by the fungus Cladosporiiim Julvum Cke., to prevent crop loss 

 appears promising. Selections have been made of the F^ and ¥ ^ generations 

 of the hybrids noted in the previous annual report (Bulletin 293, p. 17). The 

 red currant tomato, Lycopersicum pimpinellijoliiim Mill., which is immune to 

 the disease, has been hybridized with Success, Belmont and Break o'Day. Of 

 several tomato hybrids grown in the field, the following showed the highest 

 degree of resistance in the F., generation: Bewley II (Stonnor's M. P. X Up-to- 

 Date) with Norduke, Bewley IV (E S 1 X Up-to-Date) with Norduke, Bewley I 

 (Riverside X Up-to-Date) with Norduke, Norduke with Stirling Castle, Up-to- 

 Date with Norduke, and Maincrop with Norduke. The parents of these hybrids 

 possess considerable resistance to the disease, but they are not satisfactory 

 greenhouse tomatoes. Other hybrids with a susceptible and a resistant parent 

 showed no resistance in the Fj growing. 



A spray consisting of 1 ounce of salicylanilide paste (Shirlan H B) and 23^ 

 ounces of sulfonated oil spreader (Agral I), which is reported from England to 

 be very effective in controlling the disease, was used with very good results. 

 Spraying lacks the advantages of sulfur vaporization (see Bulletin 248). A patented 

 sulfur vaporizing apparatus, the "Suiphurator," was investigated and subjected 

 to certain improvements in construction. This ingenious apparatus gives promise 

 of replacing other methods of applying sulfur fungicides under glass. 



Eradication of Nematodes in Greenhouse Soils by the Use of Chemicals. 



(L. H. Jones.) Orthodichiorobenzene has not proved to be a practical substitute 

 for paradichlorobenzene when used with calcium cyanide for the eradication of 

 nematodes in ground beds. The poisonous effect on the plants persists longer 

 and, although more than half the tomato plants were free of nematode galls, 

 there was a greater degree of infection with orthodichiorobenzene than with 

 paradichlorobenzene. 



