298 The Spraying of Plants. 



rapidly, so that apparently in a few days a crop may be largely 

 reduced. It seems to require about a week for the disease to 

 become noticeable after infection takes place, the rapidity of 

 the later changes depending very largely upon the condition of 

 the weather. A warm, moist atmosphere is particularly favor- 

 able to the development of this fungus. 



Treatment. Although the black rot appears late in the season, 

 it is always safe to begin early in treating the vines. The cop- 

 per compounds, especially the Bordeaux mixture, have shown 

 themselves to be practically specifics against this disease. Ap- 

 plications should be made before the disease has appeared. In 

 the South, where the rot is a regular visitor, the treatments may 

 be commenced to advantage as soon as the first leaves have 

 fully expanded. The second application may be made after the 

 vines have blossomed, and the third from two to four weeks 

 later, depending upon the season. The Bordeaux mixture may 

 be used with safety up to the time when the berries are three- 

 fourths grown, but if used later than this, there is danger of 

 staining the clusters and reducing their market value. This 

 may be partially avoided by reducing the strength of the normal 

 mixture one-fourth or one-third; although not so effective as 

 the stronger mixture, the dilute form still possesses much value 

 as a fungicide, and it may be used to advantage. Or the 

 ammoniacal carbonate of copper may be used in its place, and 

 this is the fungicide very commonly employed when the later 

 applications are made. If the weather is favorable to the dis- 

 ease, appHcations should be made about every ten days after the 

 fruit is grown. Six or seven applications should practically 

 prevent the appearance of the disease, even in badly infested 

 districts. 



In the North, where the attacks are not so severe, the treat- 

 ments need not be begun so early. If the vines are thoroughly 

 sprayed about the first of July, and two additional applications 

 are made at intervals of two or three weeks, little trouble need 

 be anticipated from black rot. 



But everything depends upon the thoroughness with which 

 the work is done. It was formerly supposed that to spray the 

 clusters was injurious to them ; but this is a fallacy. The clus- 

 ters should be treated as well as the foliage, especially when 

 they are young, and if the practice can be continued without 



