SALAD CROP PROJECTS 149 



14. Irrigating. — Lettuce, as previously stated, requires an 

 abundant and constant supply of soil moisture, and for this reason 

 the crop is often irrigated with the overhead system as described 

 in W : 132 for celery. 



15. Cultivating. — Lettuce requires thorough tillage, and wheel 

 hoes or horse cultivators should be used as often as may be neces- 

 sary to keep the surface of the soil in proper condition. 



16. Combating insects and diseases. — Lettuce is attacked by 

 such pests as slugs, millipedes, cutworms, plant lice, webworms, 

 and beetles. Most of these are only occasionally troublesome, but 

 at times may cause serious damage. Roots of lettuce are often 

 infested with small whitish, waxy lice (lettuce root louse) which 

 if abundant may arrest the growth of the plant. Ants usually 

 occur about such colonies and may carry the lice to the roots of 

 other plants. 



Drop is one of the most serious lettuce diseases in regions 

 where this crop is grown on an extensive scale. It gets its com- 

 mon name from the dropping of the leaves. The outer leaves 

 wilt and droop and soon the whole plant collapses and lies flat 

 on the ground. The disease works rapidly. At first whitish, 

 cotton-like growths of the fungus are noticeable and later small, 

 blackish, irregular bodies are definite signs of the disease. Prompt 

 destruction of diseased plants is recommended. It is well to 

 sprinkle the soil with Bordeaux in areas where diseased plants 

 have appeared and have been removed. Several other diseases 

 caused by molds, mildews, and bacteria may be troublesome. In 

 all cases attention to cultural conditions and sanitation are im- 

 portant factors in control. Leaving diseased plants in place or 

 using compost contaminated with diseased parts of plants are 

 practices which tend to spread diseases. 



1. What relation do ants bear to colonies of root lice among which they 

 work? CL:259. 



