FUMIGATION OF CITRUS TREES. 



31 



The inaccuracy of such a method is at once apparent. Measure- 

 ments made after many estimators have shown that the most careful 

 are very irregular in their scheduling. No one has been found who 

 does not at times vary as much as 50 per cent in dosage estimates 

 for trees containing exactly the same cubic contents after being 

 covered with tents. 1 This variation in the scheduling of an indi- 

 vidual fumigator is not all, but the general average dosage used 

 by one man has 

 frequently been 

 one-fourth to one- 

 half more and 

 sometimes even 

 twice that used by 

 another for the 

 very same insect. 



This chart of dos- 

 age for the trees in 

 an orchard is taken 

 into the field at 

 night. Before dos- 

 ing a row of trees 

 the common meth- 

 od is to first meas- 

 ure out the dosages 

 for the trees in this 

 row into small cans 

 and pitchers, which 

 are placed in a 

 hand tray, as shown 

 in figure 8. This 

 tray is then carried 

 from one tree to the 

 next down the row. 

 The water is carried in a pail and measured at each tree. The 

 instruments used for measuring the water have been found to varj r 

 all the way from graduated dippers to quart pitchers or old tin cans. 

 Under this old method the general results secured by a few of the more 

 careful and expert fumigators have been fairly good. However, the 

 work in the majority of cases has been irregular and poor. This old 

 system is rapidly sinking into disuse, being replaced by an improved 

 procedure which has resulted from the present investigations. 



Fig. 8.— Man carrying tray and water bucket as practiced under old 

 system of fumigation. (Author's illustration.) 



» See Bui. 79, Bur. Ent. 5 U. S. Dept. Agr., pp. 23-24. 1909. 



