INSECT AND FUNGOUS ENEMIES 189 



In planting potatoes, a tuber or piece of a tuber is used for 

 the " seed." There has been considerable difference of opinion 

 as to the proper size of the seed piece, but it is now quite generally 

 conceded that a piece weighing about two ounces and containing 

 at least two good eyes is a very satisfactory size for planting. 

 The objection to extremely small pieces is that they do not con- 

 tain sufficient food material to give the plant a strong start, 

 especially if the weather should be unfavorable. The chief ob- 

 jections to extremely large pieces are that their use may result 

 in the production of a large number of stalks and many small 

 tubers, and also that their use is extravagant in case the price 

 of seed is high. 



Tillage. — After potatoes have been given the first early tillage 

 with a harrow as suggested above, they should be cultivated at 

 intervals of a week or ten days until the tops have grown so large 

 that they seriously interfere with the tillage. If beating rains 

 threaten to cause crust formation, more frequent tillage may at 

 times be necessary. The aim should be to preserve a surface 

 mulch that will prevent excessive evaporation of moisture from 

 the soil. 



*' Straw Potatoes." — In some parts of the country it is the 

 practice to grow potatoes without any tillage after planting. A 

 heavy mulch of straw is substituted for tillage, to conserve the 

 moisture. The potatoes are planted as early as possible in the 

 spring, and the straw is spread to a depth of about four inches over 

 the entire field as soon as the sprouts appear at the surface of the 

 ground, or even before. If a hard rain should pack the soil before 

 the straw is apphed, one cultivation is given; otherwise it is not. 

 The straw not only conserves the moisture, but it also keeps dowTi 

 weeds and protects the potatoes from the sun. " Straw potatoes " 

 are allowed to mature, rather than being harvested green. They 

 are considered of superior table quality, and sell at higher prices 

 than other potatoes in some markets. 



Insect and Fungous Enemies. — Potatoes are almost invariably 

 attacked by the Colorado potato beetle, and frequently also by the 

 flea beetle. In many localities they are likewise subject to attacks 

 by two fungus diseases, known as the early and the late blight. 

 The former causes a premature ripening of the crop and lack 

 of size in the tubers; the latter often causes the tubers to rot either 

 in the field or in the storage house. Both can be controlled by 

 proper spraying with Bordeaux mixture. The spraying should 



