The Gray Bulb-Rot of Tulips 



15 



meanwhile being covered with tarred paper to prevent accidental transfer 

 of contaminated soil to them. The check plots were then covered and the 

 treated plots were planted, after which all plots were left exposed. 



On April 17, 1923, the junior author made the following report: " Plot 

 6 shows practically a complete stand — only two tulips are missing in 

 the entire bed. Plots 2 and 4 show about one-half a stand of tulips. The 

 control plots 1, 3, and 5 do not show more than three or four tulips in each.'' 

 (Plate VI). 



A short time later the senior author inspected the plots and found the 

 visual results even more striking than the report. 



It is evident that to effectively disinfect soil contaminated with this 

 pathogene, at least 1 pound of formalin (40-per-cent) must be applied to 

 every 6 square feet of soil. This makes the treatment rather expensive, 

 but it is effective and for small areas is not prohibitive. If the " bad 

 spots " are marked as soon as discovered and are promptly treated, it 

 should rarely be necessary to disinfect large areas. Since steam steriliza- 

 tion should be even more effective, a series of such treatments was made on 

 the same area in the fall of 1923. The experiment (figure 6) was laid out 

 as follows: The plots were the same as those used in the previous season's 



1*- IO -»!/ u jo- 



*1/U JO -J/U JO J/u- JO — -J/^ 



-f 



5" 



r* -Check-- -^ Scorned -Lftour \ Steamed I hour \ Steamed a houri 15 lbs. forma/in r Check - -m 



Figure 6. plan of the plots in the 1923-1624 control experiments 



(1922) experiments and of the same size and arrangement (figure 5). 

 Before treatment, contaminated soil from the check plots of the previous 

 year was thoroughly mixed with the soil in the other plots. Plots 1 and 

 6 were left untreated as checks. Plots 2, 3, and 4 were steam-sterilized 

 by the steam-pan method — plot 2 for one-half hour, plot 3 for one hour, 

 and plot 4 for two hours. Plot 5, along with isolation strip D, was treated 

 with formaldehyde solution, 15 pounds diluted in water at the rate of 1 

 to 50. Four plots were planted with healthy tulip bulbs (variety Moon- 

 light) on November 17, 1923. Plot 5 was not planted until December 3. 



On June 10, 1924, the junior author reported that the plants in check 

 plot 1 were badly injured by the disease. Of the 35 bulbs planted in this 

 plot only 13 plants came up, of which 11 showed evidences of disease; 

 8 of these plants bloomed. 



Fifty-two bulbs were planted in each of the steam-sterilized plots. Plot 

 2 gave a stand of 50 plants, of which only 4 showed disease; 27 bloomed. 

 Plot 3 gave a stand of 50 plants, of which 3 were diseased; 25 bloomed. 

 Plot 4 showed a stand of 47 plants, of which »> showed disease; 22 bloomed. 



