EXPERIMENT STATION WOKK WITH INSECTICIDES. 255 



harmless when carried out under conditions which have l)een detor- 

 niinod by experiments as necessary in the use of this remedy. Tlie 

 only objection against the remedy for use in orchard work is that of 

 expense. 



The California Station" has carried on elaborate tests with this 

 methotl and fumigation has been generally adopted in orchard work 

 throuirhout that State in the treatment of citrus trees for scale in- 

 sects. In citrus orchards the lime-sulphur wash and oil compounds 

 have certain obvious disadvantages which do not attach to fumiga- 

 tion. In a recent study carried on by the California Station meas- 

 urements Avere obtained of over 2,000 trees fumigated by 30 diifer- 

 ent men of extensive exi)erience in this work. The amount of the 

 materials used in fumigation were obtained for each tree. X study 

 of the data thus ol)tained indicated that practical experience of 

 orchardists has not resulted in a satisfactory solution of the amount 

 of materials to be used. A great variation in this respect was noticed 

 in the })ractice of ditl'erent fumigators and this variation demon- 

 strated clearly that the process of fumigation allows a wide margin in 

 the amount of materials between effectiveness against scale insects and 

 danger to the plant. In the estimation of the cubic contents of tents 

 placed over orchard trees a consideral)le degree of skill must be exer- 

 cised, since otherwise the estimated cubic contents nuiy vary greatly 

 from the facts of the case. Mon'over, it must be remembered that 

 fumigation tents are never gas tight. The odor of the gas is always 

 evident outside of the tent, even when the heaviest canvas is used. 

 The station carried on a number of chemical experiments to determine 

 the rate of the leakage of gas from the tents and found that the loss 

 in this way was rapid and of givat imi)ortance. In fact, it was so 

 great that it is considered desirable in making u}) the doses of chemi- 

 cals to be used to alh)w for the leakage as well as for (luantities 

 sufficient to jiroduce the recpiisite density of the gas within the tent. 

 The ell'ect of moisture was also studied. It was found that the gas 

 was so readily absorbed by wet tents as to disappear from the air 

 witldn llie tcul much more rapidly and completely than when the 

 tent was dry. This ])()int was also considered of sufficient importance 

 to enter into the estimate of the amount of nuiterials required. 



In Maryland ** some of the pioneer work of fumigation in the East- 

 ern States was done. The use of both sheet and box tents was shown 

 to b«' practicable in orchards, and fumigation of nursery stock in 

 sjiecially |)re|)ared houses was successfully done. The best results 

 were ol^tained from the use of 0.2 gram potassium cyanid per cubic 

 foot of inclosed space. 



irMlifornlM Stii. Rnl. I.TJ. 

 «>Marylaua Sta. liul. 51. 



