664 WEED FLORA OF IOWA 



* Matricaria inodora (Wild *Agrostis sp. (Bent grass) 



chamomile) Agropyron repens (Quack 

 Plantago major (Common grass) 



plantain) Poa annua (Low spear grass) 



Lychnis alba (White cam- * Veronica sp. (Speedwell) 

 pion) Myosotis sp. (Forget-me-not) 



^Euphorbia exigua (Spurge) Alchemilla arvensis (Parsley- 

 *Alopecurus agrestis (Foxtail piert) 



grass) 



Most of these species are troublesome weeds, and it may be added 

 that those marked with * were abundant. 



For an Iowa cultivated field on June 2, 1903, the following 

 weeds were found in one square rod. 



Name of weed. No. per sq. rod. 



Smartweed (Polygonum, pennsylvanicum) 



Hedge mustard (Sisymbrium officinale) 



Black beggar-ticks (Bidens frondosa) 



Prickly lettuce (Lactuoa scariola var. integrata) 



Pigweed ( Chenopodium album) 



Horseweed (Erigeron canadensis) 



Dandelion ( Taraxacum officinale) 



Foxtail ( Setaria) 



40,324 



3,060 



476 



204 



340 



7,412 



68 



136,000 



WEEDS AND CONTINUOUS CROPPING. 



Everyone has observed that continuous cropping increases the 

 number of weeds ; not only is this true for many parts of Iowa but 

 it is equally true for the older sections of the United States and of 

 Europe. A. D. Hall who reported on the crops grown in grain 

 land at Rothannstad* said: 



After continuous cropping for forty-seven years said weeds of all 

 descriptions occupy considerably more space after continuous crop- 

 ping than before. The relative proportion they bear to the grasses 

 and clover has increased from year to year. Such weeds as barnet, 

 hawkbit and black knapweed became abundant. 



Mr. Long gives the following list of worst weeds made by four 

 expert Scotch agriculturists: 



Arable Land. — Charlock, ranch, chickweed, spurrey, docks, 

 thistle, groundsel, coltsfoot, day nettle, red-shank, annual meadow 

 grass, bulbous oat grass (pearl grass), couch grass, fine bent grass 

 or black couch, and wild oats. 



*Jour. Roy Agr. Soc. 64 :-83. 



