392 Agricultural Experiment Station, Ithaca, N. Y. 



grown in Fig. 68. It grows rapidly and is of very easy cul- 

 tivation. 



The most inveterate pest of the lettuce grower is the green-fly or 

 aphis. If it once gets thoroughly estahlished, the most strenuous 

 efforts are needed to dislodge it. The pest is most frequent in 

 houses that are kept too warm. The plants may be sprinkled with 

 tobacco dust, or tobacco stems may be strewn upon the ground be- 

 tween the plants and in the walks, and either treatment may be 

 expected to keep down the aphis. It can easily be kept out of the 

 houses by fumigating twice a week with tobacco. (See page 408). 

 Do not wait until the insect ajppears. Begin fumigating as 

 soon as the plants are first pricked off and continue until within two 

 or three weeks of harvest or longer if necessary. 



The rot often ruins crops of lettuce. The outer leaves decay, 

 often quickly, and fall flat upon the ground, leaving the central core 

 of the plant standing. Fig. 70 is a fair sample of a whole bench of 



70. — Lettuce plant collapsed by the rot (Boltrytis vulgaris). 



lettuce which we lost a few years ago from the rot. The plants 

 were about two-thirds grown and in good condition. The house 

 was rather over-piped for lettuce and we kept it cool by careful 

 attention to ventilation. It became necessary for the assistant horti- 

 culturist and myself to be absent three days in mid- winter. Careful 

 instructions were given a workman concerning the management of 

 the house, but he kept it too close and too wet and at the end of the 

 three days the crop was past recovery. 



This lettuce rot is due to a fungus {Botrytis vulgaris) which 

 lives upon decaying matter on the soil, but when the house is kept 



