16 FAEMEKS' BULLETIN 868. 



water from rain or heavy dews stand for some hours on the leaves that 

 the disease can gain a foothold. This is an miportant pomt to 

 remember in connection with spraying; it explains why all portions 



of the plant should be covered with 

 Bordeaux and why protection with 

 the spray before ram is needed. 



Soil and location. — Hollows or low 

 places in the fields, wherever mois- 

 ture remams longest, are most likely 

 to develop late-blight, and potatoes 

 on clay soils are likely to suffer more 

 from rot than those on sandy soil. 



Varieties. — Partially resistant va- 

 rieties of potatoes have been bred in 

 Europe, but these are not well 

 adapted to American conditions. 

 We are now developing our o^vn re- 

 sistant strams, but at present no 

 variety which meets the require- 

 ments for a standard commercial 

 sort can be recommended as disease 

 resistant. Select the best variety 

 for your locality and market, and 

 protect from late-blight by spraying 

 with Bordeaux mixture. 



PREVENTION OF LATE-BLIGHT TUBER-ROT. 



1. Spraying . — Tlie first essential 

 is to spray, as recommended on 

 page 18. 



Fig. 19.— Potato tipburn. ^^7-^, /»?•• t,- 



2. Date of digging. — It is unwise 

 to dig potatoes when the fu'st blight appears. The immature tubers 

 are not m condition to keep well and they become infected by 

 contact with the tops wdide being harvested. Consequently, the 

 potatoes should not be dug until a week or more after the tops are 

 entirely dead. 



3. Sorting and storage. — Immediately after harvesting, sort out aU 

 potatoes showuig any trace of dry rot and store the remamder in a 

 dry cellar or storage house, kept cool, as near 36° F. as possible. 

 Dry rot will not develop at this temperature, but in a wami place it 

 wdl be spread from tuber to tuber. 



No treatment with lime, formaldehyde, or other disinfectant is of 

 any value against late-blight dry rot. 



