1712 



ENCYCLOPEDIA OP PRACTICAL HORTICULTURE 



blight affects the foliage only. The late 

 blight not only kills the foliage but often 

 causes the rotting of the tubers, both in 

 field and in storage. The two forms are 

 treated in the same way. Commence 

 spraying with Bordeaux mixture and 

 arsenate of lead before the disease ap- 

 pears, or about the second week in July, 

 and repeat every 10 to 15 days through- 

 out the season, making about six appli- 

 cations in all. The arsenate of lead is 

 added for the control of the Colorado 

 beetle and may be omitted If the beetles 

 are not present. Thoroughness of appli- 

 cation is of utmost importance in spray- 

 ing for blight, the aim being to cover 

 completely both upper and lower sides 

 of the leaves, and thus prevent the access 

 of the fungus. On large areas where the 

 horse-power sprayer is used this is al- 

 most impossible, but where the spray 

 may be directed by hand it is quite pos- 

 sible, and when applied in this way three 

 or four applications during the season 

 will suffice. It is claimed that ridging 

 up the rows after the last cultivation will 

 prevent the disease spores from reaching 

 the tubers and in this way reduce the 

 proportion of rotten potatoes. There 

 seems to be but little difference in the 

 varieties with regard to susceptibility to 

 disease. The earlier varieties, however, 

 often mature their crop before the dis- 

 ease appears. 



C. D. Jabvis, 

 Storrs, Conn. 



.til;. 



Brown Rot. See Black-Leg, this sec- 

 tion. J 



Canker. See Wart Disease, this sec- 

 tion. *^ 



Downy Mildew. See BligTit, this sec- 

 tion. 



Dry End Rot. See Dry Rot, this sec- 

 tion. 



Dry Rot of the Irish Potato Tuber 

 Fusarium tuderivorum Wilcox 



Symptoms 



The dry rot here described is a strict 

 tuber rot affecting mature tubers only. 

 Neither the stems nor the young tubers 

 are ordinarily in the least affected. Nat- 

 ural infection is known to occur solely 



through wounds produced in the process 

 of digging or subsequent handling. In 

 many cases this rot secures a foothold 

 through wounds made by scab-producing 

 animals of certain sorts, and perhaps 

 even through scab spots due to fungus 

 parasitism, though the latter method is 

 certainly very rare, if we may judge 

 from the laboratory experiments. The 

 fungus cannot invade the tuber either 

 about the "eyes" or through the normal 

 lenticels. 



The rotting is rather slow, and in gen- 

 eral within four to six weeks from one- 

 third to three-fourths of the tuber is 

 destroyed. The epidermis of the rotted 

 portion becomes slightly wrinkled and 

 usually has a characteristic bluish color. 

 On account of the rapid destruction of 

 the underlying tissues the surface over 

 these areas soon becomes distinctly de- 

 pressed (Fig. 1). 



The rot may make its appearance at 

 any point on the surface of the tuber, 

 though more commonly perhaps at the 

 bud end of the tuber. There is no watery 

 degeneration of the tuber unless other 

 organisms gain entrance, so that this is 

 in fact a dry rot. 



Fi^. 1. Dry Rot of Potato Tuber. 



