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 
larve. 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 high, and insufficient attention is given to 
