191 1.] Identification and Eradication of Weeds. 461 



early summer, when the cultivated crops on which it preys are, 

 for the most part, absent from our fields, did it not find weeds 

 like charlock to supply it with food ; and similarly the turnip- 

 gall weevil is often found in the roots of charlock. Then, 

 again, the microscopic fungus that causes finger-and-toe finds 

 a congenial habitat in the roots of this plant, which may thus 

 do much to carry the disease over the years that separate two 

 turnip crops." 



In two cases quoted by Schultz* the presence of charlock in 

 cereal crops caused the loss of one-third to two-thirds of the 

 crop, the yields on charlock-infested plots and on plots from 

 which the weed had been eradicated being as follows : — 





With Charlock. 



Without Charlock. 



Approximate Loss 

 due to Charlock. 





Bushels per Acre. 



Bushels per Acre. 



Per Cent. 



I Oats 



45 



6 7 



33 



2. Oats 



24-8 



76-5 



67-5 



Charlock occurs on almost all soils, particularly, perhaps, on 

 light calcareous loams. Brenchley found, f that between Har- 

 penden and Bedford it was characteristic of clay soils, being 

 " frequent" on clay and heavy soil, and also on chalk, but 

 "occasional" on sand and light loam. 



Not only is charlock a strong and rapid grower, but it 

 produces a large quantity of seed (according to Nobbe, J up 

 to 4,000 seeds on a single plant), the seeds ripening quickly, 

 and being easily shed from the pods. 



Seeds. — The seeds of charlock (Fig. 1, a) are spherical, or 

 slightly compressed, almost smooth and finely pitted or 

 dimpled, and to ^ F in. (1 to 1*5 mm.) in diameter. 

 When ripe they are dark brown or black-brown to nearly black 

 or blue-black, but when not quite ripe they are reddish to 

 brown. When chewed, the seeds have a sharp biting taste, 

 like mustard. Harz says that 1,000 large seeds weigh i'478 

 grams. They ripen quickly, are rich in oil, and possess con- 

 siderable vitality, lying dormant in the soil for many years, 

 especially when they lie at considerable depths in the soil. 



Arb. der Dent. Landw. Gesell. : Ackersenf und Hederich, Gustav Schultz, 1909. 

 t Join: Bd. Agric, April, 191 1, p. 18. 

 X Dr. Fr. Nobbe, Handbitch der Samenkimde, 1876. 



