400 Bulletin 266. 



of the fact that the number of spores capable of producing infection is 

 enormously reduced. Undoubtedly the good showing made by experi- 

 mental plat No. 3, sprayed only four times, can be attributed to this 

 fact, for some Rot was present and rains were of sufficient frequency 

 and duration after July nth to have allowed for abundant infection 

 and the complete destruction of the crops had spores of the fungus 

 been present in sufficient quantity. Should this peculiarity of the fungus 

 prove to be of constant occurrence, it will be possible to reduce the number 

 of applic ;ions of spray actually necessary to control the Rot. This 

 fact expl. ns the common observation that "after the seed gets hard" 

 the Rot s ops. The virtue lies not in the hardness of the seed but in 

 the habitf of the fungus, for as a matter of fact, berries may and often 

 do rot to I limited extent up to the time of picking. 



CONTROL. 



The work of control previous to 1908 had shown marked results 

 in favor of spraying and it was felt that certain facts were demonstrated 

 beyond question. These facts are stated below: 



(a). When Black Rot is prevalent in a moderate degree spraying 

 will completely control it. This was shown especially in the work of 

 1907. The plats of that year consisted of one acre each, sprayed with 

 mixtures of different strengths and some unsprayed. Wherever thorough 

 spraying was practiced, 87 to 95 per cent of the total weight of the 

 grapes produced on the plats was graded as firsts and shipped in pony 

 baskets. So effective was the spray that the owner of the vineyard 

 asserted that the grapes might all have been sold as first grade without 

 sorting. On the other hand, the unsprayed plats gave a smaller total 

 yield and only 66 to 70 per cent of this yield was graded as firsts. The 

 total yield on the unsprayed plats averaged about three-fourths of a 

 ton less than that of the sprayed plats. Commercially, the grapes 

 on the unsprayed plats were of little value. 



(b). Iron sulfate as a fungicide for controlling Black Rot is of little 

 value, scarcely better than nothing. The work with iron sulfate was 

 carefully and accurately done, yet the total yield of the plat was less 

 than that from plats sprayed with Bordeaux mixture and the spray 

 itself seemed to be ineffective in controlling the Rot, for only 78 per 

 cent of the total grapes picked was graded as firsts. 



(c). The different "stickers," such as resin sal soda or fish oil soap, 

 are of no practical value. 



(d). Burning the dingers from the wire of the trellis is a means of 

 destroying some of the winter spores. The cost of the work, however. 



