io COMMON WEEDS 



(c) Weeds hinder proper and thorough Cultivation. 

 When a cultivated crop is infested with a multitude 

 of weeds, proper and thorough cultivation is largely 

 hindered. " Singling" of root crops, earthing up of 

 potatoes, even ploughing, cultivating, and harrowing, 

 are all rendered more difficult and costly by their 

 presence. 



(d) Weeds harbour injurious Insects and Fungi. The 

 harm frequently done by weeds in sheltering insect and 

 fungoid pests is considerable. Besides merely acting as 

 hiding-places for insects, they may be intermediate host 

 plants for both insects and fungi. As examples of these 

 harmful weeds may be mentioned Charlock (Sinapis 

 arvensis), Shepherd's Purse (Capsella Bursa-Pastoris), and 

 Garlic Mustard or Jack-by-the-Hedge (Sisymbrium Alli- 

 aria), and other Cruciferse, which shelter Flea Beetles 

 (Haltica spp.), these, in due time, attacking turnips and 

 causing the infestation known as " fly." Cruciferous 

 plants also support the larvae of the Diamond-back Moth 

 (Plutella maculipennis). The Bean Aphis (Aphis rumicis) is 

 similarly found on Docks and Goosefoot, and the Stem 

 Eelworm (Tylenchus devastatrix) is largely supported and 

 spread by many weeds, as also are other species of Eel- 

 worms. The well-known fungus Ergot of rye (Claviceps 

 purpurea) occurs on hedgerow and other grasses, and 

 may thence pass to rye and other cereals ; the Rust of 

 wheat (Puccinia graminis) passes one stage of its life on 

 the Barberry ; Finger-and-toe of turnips (Plasmodiophora 

 brassicce) finds a host in Charlock and other Cruciferous 

 weeds ; while White Root-rot (Rosellinia necatrix] attacks 

 a number of weeds. Many other insects and fungi are 

 similarly sheltered by weeds, not only in the open, but 

 in corners of fields and gardens, in hedgerows and 

 ditches, and round buildings. 



It may be useful to give a list of a few of the more 



