POTATOES 169 



Potato beetles and flea beetles are kept in check by 

 spraying or dusting the plants with poisons. For example, 

 one part of Paris green is mixed with 20 to 40 parts of pow- 

 dered lime, air-slaked. It is put into a burlap sack and shaken 

 over the potato plants in early morning while the dew is on 

 them. This work should be started in early spring when the 

 adult potato beetles are coming out of their winter hiding 

 places to lay their eggs on the potato leaves. Killing old ones 

 early will prevent much damage by young ones a little later. 

 See the insect chapter for the life history of potato beetles. 



Spraying potato fields is a little more expensive than 

 the dusting method, but is usually the more desirable for 

 several reasons: (1) the poisoning can be done more thor- 

 oughly; (2) the poison when applied wet will stay on the 

 plants longer and may not need repeating so often; (3) the 

 spraying work may proceed in fields all day, while dusting 

 can be done only while the dew remains hi early morning; 

 (4) when spraying for beetles the farmer may also add Bor- 

 deaux mixture, and thus prevent the blight disease, at the 

 same time. 



The spray solution for beetles alone should contain 

 arsenate of lead or Paris green. If the latter is used a little 

 lime is added to make the spray cling well and to prevent 

 damage to the leaves by free arsenic. Use one-fourth to one 

 pound of Paris green and one pound lime to 40 or 50 gallons 

 of water (or Bordeaux). Keep well stirred while spraying. 



For spraying with arsenate of lead, mix two to -three 

 pounds of the arsenate in paste form with 40 or 50 gallons 

 of water or Bordeaux (see Appendix, Table III). 



Potato blight is often as serious an enemy of the main 

 crop as the beetles. In one sense it is more serious because of 

 the fact that when it makes a start in a field nothing can stop 

 it and the whole crop is likely to become affected. Preven- 

 tion spraying is the only practical remedy. Bordeaux mix- 

 ture is used for this. Apply it as early as you would begin to 



