PARASITIC WEEDS 95 



arvensts) is found en a variety ef weeds as well as *n clAver, 

 including deck, deg's mercury (Mercurialis perennis), s>w- 

 thistle, charlock, black nightshade (Solanum nigruni), nettle, 

 creeping thistle, wild lettuce, knetgrass, and mayweed. 1 



Didder seeds retain their pewer f germination for several 

 years, even when buried in the soil. The germination >f the 

 seeds is spread ever a lng period, the largest percentage 

 earning up during the first menth after sewing, while the 

 ethers appear later en in gradually decreasing numbers. 

 Seme e-f the seeds are " hard " and it is these which form a 

 dangere-us stock in the sail for several years after infection. 

 Although dedder seeds will lie dormant in the seil for se leng, 

 Italian investigators claim that they are net able te withstand 

 the action ef farmyard manure. If they are buried in a heap 

 f manure mest ef the seeds lese their pwer ef germinating 

 within abeut a menth, only a very small percentage retaining 

 their vitality ever ledger perieds. It is censidered, therefore, 

 that there is comparatively little danger ef spreading dodder 

 infection by means ef farmyard manure, provided the latter is 

 well made and properly treated. 



Eradication of Dodder. In this country clover dodder (C. 

 trifolii) is the species that causes most trouble. As prevention 

 is better than cure every effort should be made to sow seed 

 that is absolutely free from dodder seeds. With the excep- 

 tion of an American species (C. gronovii], which has extra 

 large seeds resembling in size those of clover, the ma- 

 jority of dodder seeds can be effectively removed from clover 

 and lucerne by screening with sieves of suitable mesh. A 

 large proportion, but not all, of the dodder seeds may also be 

 destroyed by dry heating, as they lose their power of germina- 

 tion at temperatures that are harmless to the associated clover 

 seeds. The most effective temperatures seem to be : 2 



149 F. for 2 hours. 



158 F. for 30 minutes or for I hour. 



167 F. for 30 minutes or for I hour. 



If infection does occur and the patches are observed before 

 they have spread too far, the affected part of the crop should 

 be dug up, covered with chaff, sprinkled with paraffin and 

 burnt on the spot. The dodder should not be torn out with 

 a rake, as this serves to spread the trouble. If infected plants 



1 D'Ippolito, G. (1913), Le Stazioni sperimentali agrarie italiane, XLVI, 

 pp. 540-549. 



2 Ibid. 



