LETTUCE 225 



to the roots of fall lettuce. If the beds are sterilized with 

 steam after manure has been applied, there should be no 

 trouble from this enemy. 



The white fly is found sometimes on lettuce, but 

 seldom in numbers large enough to cause any consider- 

 able damage to the crop. 



The green cabbage worm is sometimes a pest of the 

 fall lettuce crop. When it appears in numbers large 

 enough to cause concern, fresh pyrethrum, one part 

 mixed with six parts of flour and dusted on the plants 

 when they are moist, will be found effective in killing the 

 larvae. Pyrethrum when exposed to the air soon loses its 

 poisonous principle and thus becomes harmless to human 

 life. 



Snails feed on lettuce and they may appear in soils 

 which have not been steam sterilized. Air-slaked lime, 

 dusted on the soil and plants, is recommended to check 

 the ravages of snails. 



Cutworms may also feed on lettuce growing in soil 

 which has not been sterilized with steam. They feed at 

 night and may be killed by placing paris green or other 

 poison on lettuce leaves which are scattered over the 

 ground where the crop has been cut and left for a few 

 nights. In beds in which the plants are not ready to 

 harvest, poisoned bran mash will prove effective. Paris 

 green is mixed with dry bran until the latter is slightly 

 tinted. A sweet solution is made by mixing one quart of 

 molasses with ten quarts of water, and then mixed with 

 enough of the poisoned bran to make a mash. A table- 

 spoonful of the mash, which the cutworms prefer to 

 lettuce, is placed at frequent intervals on the beds. 



Diseases. There are several diseases of greenhouse 

 lettuce, but the most serious is known as the drop 

 (Sclerotinia libertiana Fckl.). It is most likely to appear 

 during cloudy weather when the temperature of the 

 house is too highland insufficient attention is given to 



