34 BULLETIN 550, U. S. DEPARTMENT OF AGRICULTURE. 



Table 23. — Relative efficiency of different times an<T numbers of applications. 





Treatments 



common to 



all plats. 



Years 

 tried. 



Num- 

 ber of 

 vine- 

 yards. 



Num- 

 ber of 

 plats. 



Infested grape berries. 



Time and number 

 of applications. 



Best 

 plat. 



Adja- 

 cent 

 check. 



Poor- 

 est 

 plat. 



Adja- 

 cent 

 check. 



Aver- 

 age 

 of all 

 plats. 



Aver- 

 age of 

 all ad- 

 jacent 

 checks. 



Two applications 

 after blossoms 

 have fallen and 

 when grape ber- 

 ries are touch- 

 ing. 



Two applications, 

 same as above, 

 including only 

 plat adjacent 

 to that sprayed 

 3 times. 



Three applica- 

 tions, 2 same as 

 above; third 5 

 weeks after first. 



One application 

 when grape ber- 

 ries are touch- 

 ing. 



One application 5 

 weeks after fall- 

 ing of blossoms. 



Arsenate of lead, 

 3 pounds paste 

 or 1J pounds 

 powder; laun- 

 dry soap, 1 

 pound; Bor- 

 deaux mix- 

 ture (3-3-50), 

 applied with 

 "trailers." 



do 



1915, 

 1916 



1916 



1916 

 1916 

 1916 



7 



1 

 1 



1 



7 



1 



1 



3 

 1 



P.ct. 

 0.89 



1.57 



.68 

 5.25 

 19.97 



P.ct. 

 50.43 



79.72 



67.52 

 23.39 

 55.53 



P.ct. 

 8.43 



1.57 



.68 

 33.95 

 19.97 



P.ct. 

 75.16 



79.72 



67.52 

 75.16 

 55.53 



P.ct. 

 4.12 



1.57 



.68 

 18.71 

 19.97 



P.ct. 

 50.03 



79.72 



do 



67.52 



do 



51.29 



(i) 



55.53 







1 



1 Same as above, except arsenate of lead, 2^ pounds, and resin fish-oil soap instead of laundry soap. 

 FACTORS DETERMINING THE TIME AND NUMBER OF APPLICATIONS. 



The time and number of applications are determined not only by the 

 seasonal history and habits of the grape-berry moth, but also by the 

 development of the grape itself. Fortunately the times for spraying, 

 most favorable in relation to the pest and also in relation to the crop, 

 are nearly coincident. It is probable, therefore, that the vineyardist 

 will find it most convenient to time his operations entirely by the 

 development of the fruit. 



The first spraying probably destroys the largest number of first- 

 brood larvae, for it is applied just before they begin hatching in num- 

 bers. Besides these, it also destroys some larvae which hatch before 

 the blossoms fall and are feeding in the cluster, but have not entered 

 a grape berry. Following this application the grapes grow very rap- 

 idly^ and the larger part of the berry surface does not long remain 

 covered. But as at this time the majority of the larvae enter the 

 berry at the stem end, where the spray always collects, compara- 

 tively few escape. 



The second application is made after first-brood hatching begins to 

 decline, but it is effective against the second brood also. As soon as 

 the berries begin to touch, the majority of larvae begin entering at 

 the points of contact instead of at the stem ends. Spray which is 



