OBSERVATIONS ON SOME VINE DISEASES IN SONOMA COUNTY. 



17 



In regard to the effect of soil fertility on the Red-leaf disease, some 

 evidence well worthy of experimental control was obtained. In Sep- 

 tember, 1903, in a cursory examination of the vineyard in which the 

 experiment plot is situated, it was noted that the foliage in a " block " 

 of old Mission vines which were much larger and at least ten years older 

 than those in the experiment plot, showed very generally the discolora- 

 tion of the Red-leaf disease. These old Missions were given a good dress- 

 ing of stable manure during the winter of 1903. In 1904 they were 

 kept more or less under constant observation. On September 16th of 

 that year we noted that the old Missions, which the previous year 

 showed the foliar characters of the Red-leaf disease so markedly, were 

 still healthy. 



r 



TESOJ.VMD SPOT/HI rm rcon swjwre 



B -.vine arwwni \ira HORDE/NX mxruw 



vires unrrareo^rai UTT K> 

 wrnuss. 



, W, TrSo W } B W, W t W 5 B W 6 B W, 



FIG. 3. Table showing the average production (in pounds) of the vines, both sprayed 

 and unsprayed, at the South Sonoma Experiment Plot. 



From these observations one would surmise that fertilizing, with 

 stable manure at least, would have a certain action in controlling the 

 Red-leaf disease. If, moreover, coupled with these observations, it 

 were found that the soil was at all deficient in one or all of the plant 

 foods, then our surmise would become a plausibility, if not a certainty. 

 We had, therefore, the soil (an average sample) of our experiment plot 

 analyzed, and with the following result : The soil was found to contain 

 less than 0.05 per cent of phosphoric acid, which is quite low for a 

 productive soil. When we couple with this deficiency of phosphoric 

 acid the fact that the grapevine consumes more of this nutrient than 

 most fruit trees, it is not rash to assume that fertilization will greatly 

 help the vines to at least withstand the Red-leaf disease. 



