190r).] PUBLIC. DOCUMENT — No. ;^8. U 



cessful ill eradicating troublesome insect pests. Its prin- 

 cipal drawbacks, however, in groAving- lettuce, have been 

 due to its stimulating ctfects on the plant itself, which, 

 where proper precautions are not taken as regards tempera- 

 ture, etc., result in developing a more tender plant, with a 

 loose and less desirable head. A lettuce plant of this type 

 is more tender because it contains more water, and it is not 

 so desirable for the market. Moreover, such plants are in- 

 clined to be susceptible to Botrytis rot, if not properly 

 handled. . We learned ver}^ early in our experiments that, 

 on account of the stimulating effect brought about by grow- 

 ing plants in sterilized soils, it is necessary to hold the crop 

 back by maintaining lowx>r night temperatures. If a tem- 

 perature of from 8° to 10° F. lower than is customary at 

 night is maintained, so that the crop may develop no faster 

 than one grown under normal conditions, the result will bo 

 a crop possessing firm heads of equal texture and resisting 

 qualities to that grown under normal conditions. We have 

 repeatedly called attention to the necessity of this practice 

 in growing lettuce in sterilized soils, but this advice has not 

 always been followed. 



There has been a slight increased tendency for lettuce 

 })Uuits to become more subject to Botrytis rot when grown 

 in either sterilized soil or that treated by hot water, owing 

 to a more accelerated gro^vth, and the production of a head 

 of less firm texture. Botrytis rot is the principal disease 

 that most lettuce crops are troubled with at the present 

 time. However, it is not a very serious one with good 

 growers. There will be observed here and there a plant 

 affected with Botrytis rot in the best of houses ; the ideal 

 conditions, however, require that there should be none. As 

 to the loss by Botrytis rot by experienced growers, it is of 

 no practical importance, since the percentage will bo repre- 

 sented by a small decimal. Botrytis rot can, nevertheless, 

 be eliminated to a greater extent than it is, if lettuce growers 

 would follow certain precautions more carefully. In grow- 

 ing plants in sterilized soil, Botrytis rot can be reduced by 

 paying attention to proper temperature conditions at night, 

 or, in other words, by holding the crop within legitimate 



