364 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



into leaf in the spring, and also a later spraying during the early 

 summer if the latter should be considered necessary or practicable. 

 He likewise urged the removal of all affected twigs and fruit spurs. 

 Professor Pierce stated that by following these recommendations 

 thoroughly it was possible to reduce the number of blighted nuts by 

 fifty per cent. Mr. E. G. Ware, of Garden Grove, while in charge of 

 a large walnut grove near Placentia, which belonged at that time to 

 Thum Brothers, carried on what was probably the most extensive and 

 most carefully conducted experiment along this line. For several 

 years he sprayed thoroughly with Bordeaux mixture, using large blocks 

 of trees and leaving unsprayed trees or rows as checks. Mr. Ware 

 came to practically the same conclusion as Professor Pierce, namely, 

 that the number of blighted nuts could be reduced about 50 per cent 

 by spraying with Bordeaux mixture just as the buds are swelling. 

 Neither of these experimenters was able to state any distinct increase 

 in the crop obtained by spraying, but it should be said that such a 

 measure of results is practically impossible in seedling walnut groves 

 on account of the extreme variation in the production of the various 

 individual trees. Mr. Ware also experimented with the application 

 of lime to the soil after Professor Pierce 's suggestion, with the idea 

 that this might produce a firmer, harder tissue in the growth of the 

 trees and thus render them less susceptible to blight. He believed 

 that some benefit was derived from such an application, using large 

 quantities of air-slacked or sugar-beet factory refuse lime. Other 

 growers have sprayed their walnut trees with Bordeaux mixture and 

 various other materials at different times, but it may be said in a 

 general way that such practice has never become common and for 

 several years it has been entirely discontinued. 



At the commencement of this work in 1905 plans were made to carry 

 on very thoroughly and systematic spraying experiments in order to 

 determine definitely the extent to which blight control could be accom- 

 plished by this means. In the spring of 1906 several large blocks of 

 good sized seedling walnut trees were obtained for this purpose in the 

 vicinity of Whittier and spraying operations were commenced. The 

 principal experiments were made with three different fungicides, 

 Bordeaux mixture, lime-sulphur, and a sulphur spray made by boiling 

 together sulphur and caustic potash. The work was done with a power 

 sprayer, and was carried on more thoroughly and carefully than any 

 grower would be likely to do such spraying and without regard to 

 expense. In one instance a large block of trees was sprayed with 

 Bordeaux mixture, using a 5-6-50 formula, in another a heavy lime- 

 sulphur was used, the spray being prepared by boiling, while in the 

 third the potash-sulphur spray mentioned above was used. It was 



