CARBON DISULFIDE EMULSION 11 



acetic acid at less expense. Each was used in combination with carbon disulfide 

 emulsion, but only formaldehyde made an effective and compatible combination 

 (Table 3). Judging from the results shown in Tables 3 and 4, formaldehyde may 

 be regarded as having considerable nemacidal value, but acetic acid none. These 

 results appear to be confirmed by the reports of Watson (8, 9) to the effect that 

 formaldehyde when applied in the dosage ordinarily used for the control of fungous 

 diseases gives very good control of the root-knot nematode in seed beds in Florida. 

 Observations of its use in greenhouses in Massachusetts show that alone it does not 

 offer satisfactory control of nematode, although the results in Table 3 are excep- 

 tional. In some of the experiments a concentration of 1 gallon of formaldehyde in 

 combination with 1 gallon of stock carbon disulfide emulsion in 50 gallons of 

 water was employed; but successful control of soil inhabiting fungous para- 

 sites can be obtained at a concentration of 2/3 gallon of formaldehyde, as 

 has been brought out from the results of many tests at the Field Station. 



To qualify as a good nemacide, a chemical must be (a) effective in eliminating 

 the nematode as a crop loss factor, (b) harmless to the soil for plant growth within 

 a reasonable interval after application, (c) easy to apply, and (d) non-injurious 

 to man. Of over thirty chemicals tested by Newhall (6), many of which had 

 been previously considered in earlier investigations, none was entirely satisfactory 

 being objectionable chiefly on account of cost, inefficiency, and unsatisfactory 

 methods of application. Newhall found that pure carbon disulfide used at the 

 rate of 100 gallons per acre was almost as good as the best chemical treatment, 

 i. e., a mixture of napthalene flakes and Cyanogas, on the basis of plant yields. 

 He did not use carbon disulfide emulsion. 



On the basis of the writer's experience and that of most growers, the objections 

 to the chemicals used by Newhall should not necessarily apply to carbon disulfide 

 emulsion. However, carbon disulfide possesses that disadvantage of being harm- 

 ful to man. Prolonged exposure to the gas causes severe headache, dizziness, 

 and vomiting. It increases the heartbeat, and owing to this effect persons having 

 any heart weakness are cautioned not to use it. Otherwise, application is practical, 

 quicker, and under many conditions less expensive than steam sterilization. 

 The harmful features may be largely overcome by the exercise of certain precau- 

 tions such as shifting the help at the end of five hours, and taking care to provide 

 all the ventilation possible. 



Once an infestation of the root-knot nematode appears, its eradication seems 

 impossible no matter how efficient the soil treatment. In spite of the complete 

 absence of visible signs of root-knot at the end of a crop, sufficient potential in- 

 fection to cause a heavy root infestation and a yield failure on the succeeding 

 crop escapes the action of heat or chemicals (Table 7). Where the practice 

 is to grow two warm temperature crops such as cucuuibers or tomatoes each year, 

 the greenhouse beds must be treated before each crop, otherwise the root-knot 

 disease will render unprofitable any investment in the crop. For this reason, 

 it would be more economical in the end to install the permanent tile system of steam 

 sterilization if the greenhouse establishment is permanent and if steam is available, 

 since the expense for chemicals equals a substantial part of an investment in a 

 tile installation. If the use of chemical is objectionable on account of its harmful 

 effect upon men, then sterilization by the use of steam or hot water is advisable. 



Carbon disulfide emulsion appears to be the most satisfactory chemical nema- 

 cide yet discovered and should find particular use in greenhouse establishments 

 not equipped with efficient systems of steam or hot water sterilization, or where 

 the grower for lack of time finds it more practical and desirable to use chemicals 

 instead of steam or hot water. On the basis of the results here reported, many 



