I 



16 BULLETIN 1332, IT. S. DEPARTMENT OF AGRICULTURE 



Perennial phlox. — Same dosage as for iris. Keep in the dip for 

 from 9 to 18 hours, depending on the amount of soil present on the 

 plants. 



Sedum. — Same dosage as for iris. Dip for a period of from 15 to 

 18 hours. 



Peony. — Dosage, 0.5 cubic centimeter carbon disulfide per liter 

 of water. Dip for a period of 15 hours. 



Care should be taken that the temperature of the dip does not fall 

 below 65° F. at any time during the treatment. At the end of the 

 period of submergence the plants should be removed from the dip, 

 the latter discarded, and the plants, after draining, kept for 48 hours 

 in a room at 70° F. Care must be taken that the plants do not dry 

 out before or after the dipping. Plants so treated are then ready 

 for shipment outside the quarantined area 10 and not oefore. Any 

 chilling subsequent to the treatment should be carefully avoided, as 

 it may lengthen the time required to kill all the larvae. 



COMMERCIAL EXPERIENCE WITH THE METHODS 



During 1922 and 1923 the writers treated by the above methods 

 approximately 10,000 Japanese iris, 10,000 perennial phlox, 1,000 

 sedum, and 15,000 peony, valued in all at $10,000. There have 

 been to date no complaints from the quarantine officials or con- 

 signees. 



SUMMARY AND CONCLUSIONS 



Plants of the nature of Japanese iris, phlox, sedum, etc., have 

 a matted root system, while peonies are hollow-rooted. It is impos- 

 sible to eliminate larvae of the Japanese beetle which may be present 

 in these roots by such means as removal of the dirt, by washing or 

 by other ordinary methods. The experimental work here outlined 

 was therefore conducted for the purpose of evolving a chemical dip 

 in which such plants could be immersed for definite periods of time, 

 to make sure of killing any larvae present, and with no resulting injury 

 to the plant. 



The results of the work indicate that oil of wormseed (American) 

 and carbon disulfide are the best materials to use for this purpose. 

 These substances, when added to a hydrophile colloid and water, 

 are both capable of forming stable emulsions the toxic principle of 

 which is retained indefinitely. 



Oil of wormseed {American) . — The primarily active ingredient of 

 oil of wormseed is ascaridole, (C 10 H 16 O 2 ). Other ingredients of the 

 oil are also toxic in varying degrees. For greater certainty the con- 

 centration of the dip is figured in terms of ascaridole rather than in 

 terms of wormseed oil. 



When Japanese beetle larvae, with no soil present, are immersed 

 for six hours in a wormseed-oil dip the concentration of which is 

 equal to 0.5 cubic centimeter of ascaridole to 3 liters of water, the 

 larvae are killed, provided the temperature of the dip is maintained 

 between 65° and 70° F. The experimental results clearly indicate 

 that the temperature of the dip is the limiting factor in the success 

 of this method, and under no circumstances must it be allowed to 

 fall below 65° F. during the course of the treatment. It is advisable 

 to maintain it at 70° F. 



i° No injury has occurred as a result of the wetting received by the plants. In two series of experiments, 

 plants were taken out of the dip and immediately packed in damp moss. One lot was placed in cold storage 

 for two months and the other next to a hot stove for several weeks. The first lot was normal when removed 

 from storage, whereas the second lot made 6 inches growth in the moss. 



