BUREAU OF PLANT INDUSTRY. 201 



worthless. It has been found that this trouble is caused by high soil 

 temperatures at the soil surface when the flax plant is from 1 to 4 

 inches high. 



The parasitic flax canker previously reported in North Dakota 

 and found during li)'20 in fiber flax in jSIichigan is caused by a fungus 

 belonging to the genus Colletotrichum. This disease is known to 

 occur in fiber-flax sections of Ireland and Holland, where it some- 

 times becomes important as a seedling blight. 



Control measures have not yet been determined for either of these 

 diseases. 



BARLEY " SCALD," AN IMPORTANT DISEASE IN THE WEST. 



For several years a disease of barley, becoming known as "scald," 

 has been destructive, especially in certain parts of California, Ore- 

 gon, and "Washington. The disease destroys the leaves, reduces the 

 size of heads, and causes shrinkage of kernels on affected plants. It 

 is caused by the fungous parasite Rhynchosporiuiyi secalis. 



Investigations carried on in cooperation with the California Agri- 

 cultural Experiment Station indicate that certain selections from the 

 barley varieties ISIariout and Tennessee Winter show resistance to the 

 disease, while all other varieties under experiment were very sus- 

 ceptible. 



THE NEMATODE, OR EELWORM, DISEASE OF WHEAT. 



Distribution and crops attacked. — The nematode, or eelworm, dis- 

 ease of wheat and r^'e has been found in 52 counties in Virginia, 10 in 

 West Virginia, and 1 in Georgia, and is thought to be present in some 

 counties in Xorth Carolina and in southeastern Ohio. Losses as high 

 as TO per cent of the wheat crop have been reported from farms in 

 Virginia. In several cases rye was found to be damaged equally as 

 much. Emmer and spelt also are very susceptible to the disease. 

 Repeated efforts to inoculate various varieties of barle}^ and oats have 

 met with very little success, so that these cereals may be regarded as 

 practically immune. Corn and the various grasses commonly groAvn 

 have been found free from attack and may be safely used in the rota- 

 tion. 



Sjiread. — The principal and only important method of spreading 

 this pe.st is by means of the galls in the seed. In the soil the organ- 

 isms are imablc to travel laterally more than 4 inches unless carried 

 by the washing of soil water. Vertically, however, they have been 

 found capable of infecting wheat at a distance of 10 inches. This 

 makes deep ])loAving ineffective as a means of control. 



Control. — Experiments conducted at several points in Virginia on 

 badl}" infested land prove that the organism is killed in the soil in one 

 year by sowing some crop which it can not infect. Land badly in- 

 fested in 1918 was sown to grass in tlie fall, and wheat was sown 

 again in the fall of 1919. The resulting crop in 1920 was entirely 

 free from infection. Among the half hundred varieties of wheat 

 which have been inoculated with this disease only one (Kanred) has 

 been found to show any appreciable degree of resistance. Less than 

 1 per cent of this variety was infected, while the other varieties 

 showed infection varying from 20 to 90 per cent. However. Kanred 

 is a hard winter wheat, not suited at all to the region where the 

 nematode disease prevails. 



24435— AGB 1920 34 



