10 MASS. EXPERIMENT STATION BULLETIN 292 



of the nematode. It is shown (Table 8) that where the smaller infested roots were 

 left in the soil and carbon disulfide was used at the rate of 1 gallon per square foot, 

 83 per cent of the roots were infested as compared to 68.2 per cent where the roots 

 were removed. Considered on the basis of the degree of infestation, it could not 

 be shown that the removal of the smaller roots improved the efficiency of the 

 treatment in this experiment. 



Nevertheless, judging from the results with carbon disulfide emulsion in 

 commercial practice, the removal of the infested roots and the decay of the smaller 

 roots and attached galls appears to be desirable as a matter of insuring greater 

 efficiency of the chemical. According to Jones (5) galls attached to roots require 

 more time to decay than detached galls. The rate of decay of galls is increased 

 with increases in soil moisture and temperature. In view of this fact, it is desirable 

 to keep the greenhouse beds moist by daily waterings, and as warm as possible 

 between the interval of removing the old plants and the time the chemical is 

 applied. The results of the writer's experiments show good control of nema- 

 tode with carbon disulfide emulsion applied three weeks after the removal of the 

 old planting without introducing the needed moisture and temperature conditions 

 to hasten decay of the roots in that interval. One more week elapsed before the 

 new planting was started. Good control of nematode was obtained when one day 

 elapsed between the removal of the old crop and the application of carbon disulfide 

 emulsion (Table 8) but this was influenced measurably by the rate of application. 



Nematodes exist as deep in the soil as the roots extend, and it is not uncommon 

 to find lettuce, cucumber, and tomato roots 30 inches deep in the subsoil. In 

 Florida, the root-knot nematode may be found at a depth of 36 inches, according 

 to Godfrey (4), and in greenhouses they occur fully as deep. Any treatment used 

 to sterilize the soil must be applied with the object of reaching the majority of 

 nematodes or the effectiveness of the treatment will be greatly diminished. The 

 thoroughness of wetting the- soil with chemical has a significant influence upon its 

 eiifectiveness as is borne out in Table 6 where it is shown that two applications 

 of carbon disulfide emulsion applied a week apart gave complete control, while 

 after one treatment 95.71 per cent of the roots were free from infestation. A 

 greater volume of chemical in one application is also more effective, for 1.4 gallons 

 of diluted carbon disulfide emulsion per square foot yielded 78.57 per cent roots 

 free of infestation, as compared to 66.66 per cent from 1 gallon (Table 5); and 2 

 gallons gave 92 per cent clean roots as compared to 31.6 per cent from 1 gallon 

 (Table 8). In no instance, however, when the rate of application was 1 gallon per 

 square foot, was nematode a factor in crop loss. At that rate of application, 

 increases in gross income of $90.08 to $\01A2 (Table 2) and of $71.44 to $79.04 

 (Table 3) were obtained per 100 plants above that of the same number of plants 

 in the control plots. 



The yields from the use of carbon disulfide emulsion were essentially similar 

 to those where efficient steaming was practiced, and this, in general, was correlated 

 with the degree of control of the root-knot nematode. Since a concentration of 

 1-50 of carbon disulfide emulsion applied at the rate of 1 gallon per square foot 

 has given good control and has restored normal yields, this formula is recommended 

 for those growers who desire to use this chemical. 



Carbon disulfide emulsion has given satisfactory results when tested under 

 commercial conditions of culture for combating nematode. Its use, however, 

 has given no control of soil inhabiting plant pathogenes; neither according to the 

 writer's experiments, has it manifested any killing effect on weed seeds. For the 

 control of soil-borne plant pathogenes in greenhouses, the use of formaldehyde has 

 heretofore received some recognition. Doran (2) has shown a similar value from 



