122 SPRAYING CROPS 



the spores being produced only in the later stages of 

 the disease. It winters over in the spore stage on 

 the dead vines. 



Remedies A number of experiments have shown 

 that these diseases may be prevented by spraying with 

 the Bordeaux mixture, provided the seed potatoes used 

 are free from infection. To be sure of this, seed 

 should be obtained from regions where blight and rot 

 do not occur upon potatoes, or from fields which were 

 sprayed the year before. Then spray from two to four 

 times with the Bordeaux mixture, making the first ap- 

 plication when the vines are about one-half grown, or 

 earlier if signs of the disease appear, and repeat the 

 application when it is washed off in about a fort- 

 night usually. Add half a pound of London purple or 

 Paris green to each barrel of the mixture whenever the 

 Colorado beetles threaten injury. While the best 

 results are most likely to be reached when the seed is 

 not infected, very satisfactory ones are obtained from 

 spraying crops from ordinary seed. 



The beneficial effect of treatment with Bordeaux 

 mixture, as it resulted in some experiments by Profes- 

 sor Jones, of Vermont, is shown on page 121. The 

 treated vines yielded marketable tubers at the rate of 

 291 bushels per acre, while those untreated yielded 

 only at the rate of 993^ bushels per acre. 



Br.ozvn Rot Besides the two maladies already 

 discussed, there is a form of blight and rot called 

 "brown rot," due to bacteria. This occurs on tomatoes 

 and egg plants as well as potatoes, and is worst in the 

 south. There is no spotting of the leaves as in the 

 preceding blight, but the first symptom is a sudden 

 wilting of the entire top, which is soon followed by 

 the shriveling and blackening of the leaves and stems. 

 The disease passes from the stem to the tubers, causing 

 a browning of the interior, which is soon followed by 



