396 WEED FLORA OF IOWA 



them. When a field is badly infested it requires special treatment 

 for a season and close attention for a number of years. One of 

 the most effective methods is to plow lightly immediately after 

 the hay or grain crop is removed and follow with frequent use of 

 a broad-shared cultivator. Late in the fall plow again, somewhat 

 deeper. In the spring give frequent cultivation, so as to prevent 

 the development of any leaves and thus weaken the roots to the 

 greatest possible extent. About the middle of June or first of 

 July sow rape in drills at the rate of about iy 2 lbs. per acre. 

 Cultivate between the drills as soon as possible and repeat at short 

 intervals until the rape completely covers the ground. Some hand 

 hoeing may be necessary to keep all the thistles down. This should 

 pretty well exterminate the pest but if some plants still remain 

 when the rape is cut or pastured off, the field may be fall plowed 

 and put into hoed crop the next season, when special attention can 

 be given to any small patches that may appear. Buckwheat is 

 sometimes used instead of rape for a smothering crop." 



Prickly Lettuce (Lactuca scariola L. var. integrate, Gren. & Godr.). 



Description. — Tall, erect herbs, glaucous, green, 2-5 ft. high, 

 simple or branched except the lower part of stem which has stiff 

 bristles; leaves glaucous, green, smooth except the midrib which 

 is beset with weak prickles lanceolate to oblong in outline, with 

 spinulose, denticulate margins, occasionally sinuate-toothed; flow- 

 ers pale yellow. The leaves of L. scariola are pinnatifid and more 

 prickly ; trichomes multicellular. 



Distribution. — Prickly lettuce was introduced into Massachu- 

 setts about 1863 from Europe. It is quite widely distributed in 

 northern Africa and Europe and has become frequent throughout 

 the northern Mississippi valley to the Pacific coast. It is com- 

 mon everywhere in Iowa particularly along roadsides, highways 

 and in gardens. The L. scariola is becoming more frequent in 

 Iowa, in Ames, Des Moines, Boone, etc. 



Extermination. — The weed is easily exterminated from culti- 

 vated fields and in waste places by cutting off young plants below 

 the ground. Where the stem is cut off below the surface of the 

 ground it will give no trouble, but in meadows and lawns where 

 the plants are cut off above the ground the weed will continually 

 reappear, producing from 3-6 branches. The following excellent 

 suggestions are made by L. H. Dewey : 



