Control Measures 213 



against them. On the other hand, if the potato crop is 

 alternated with other crops or can be grown in a three- 

 to iive-year rotation, these parasites depending upon the 

 potato for food will be starved out during the intervening 

 years. Unless such parasites are introduced again by 

 planting affected seed, or with manure containing these 

 organisms, or with infected soil washed or carried on to 

 the land, the potato crop planted in a rotation should be 

 comparatively free from them. 



This would be the case were it not the habits of some 

 organisms like Rhizoctonia to live on hosts other than 

 the potato, or of others like the scab organism to live 

 from year to year on dead organic matter in the soil. 

 However, a rotation aids in reducing these organisms 

 when they are troublesome, and for this reason, if for no 

 other, should be practiced when possible. 



Often there are a large number of missing hills in a 

 field caused by the decay of the seed tuber from attacks 

 of Rhizoctonia, or for other reasons, causing the total 

 yield to be materially reduced. This is especially true 

 when the tubers are planted in hills or at distances greater 

 than 18 inches in the row. When the tubers are planted 

 close together, a missing hill does not mean a complete 

 loss, because the neighboring hills, having more room for 

 growth, will produce a larger yield. Some farmers have 

 found it profitable to replant missing hills with tubers 

 that have been greened, i.e. left in the light so that they 

 have stubby green sprouts. Such tubers when planted grow 

 rapidly and are not much later than the ones planted first 

 and not greened. Greening potatoes is a good practice, for 

 such tubers will give a better stand than those not greened. 



There are diseases, such as early and late blight, that 

 occur under favorable weather conditions and do much 



