BUREAU OF PLANT INDUSTRY. 175 



disease which had been previously known but evidently had been 

 increasing in its intensity for several years. It had made such 

 headway in the clover fields of Idaho in a short time as to lead to 

 the suspicion that some unusual agency was at work. Attention was 

 at once given to the possibility of the transmission of the disease 

 through the seed, with the result that it was shown that clover seed, 

 even when recleaned, carries a considerable number of nemas, and 

 in the case of the Idaho seed in particular it Avas shown to carry 

 four different species of nemas, one of them belonging to the genus 

 Tylenchus, namely, the well-known Tylenclius dipsaci, or Tylenchus 

 devastatrix^ the cause of a serious disease of bulbous plants and 

 about 20 other crop plants, among them red clover. A general 

 examination disclosed the fact that some living larva3 of this par- 

 ticuhir species occurred in clover seed 9 to 10 months after it was 

 harvested. 



WHITE-PINE BLISTER RUST. 



White-pine blister-rust infection on Ribes is general in the New 

 England States and northeastern New York. Many widely dis- 

 tributed incipient pine infections are beginning to appear as a result 

 of heavy Ribes infection in 1915 and 191C, but the disease has not yet 

 liad time to produce severe damage to pines on a large scale. In- 

 fested ai-eas vary in size from a few pine trees within a hundred 

 feet of infecting Ribes to 50 per cent of the pines within a radius of 

 half a mile from diseased bushes. 



It, appears that in many regions the plan of protecting white-pine 

 tini])er by the systematic eradication of Ribes will prove to be an 

 economically sound policy. 



In this campaign cooperation is maintained with the New England 

 States and New York. The work is devoted almost entirely to per- 

 fecting cheap and effective methods of destroying wild Ribes, to 

 practical demonstrations of these methods on local control areas, 

 and to the encouragement of effective local eradication of Ribes in 

 cooperation with towns, associations, and individuals. 



Experience thus far gained on demonstration and local control 

 areas has proved that under normal conditions at least 95 per cent of 

 the wild Ribes on a given area can be removed at a cost ranging from 

 5 cents to $1.50 per acre. It is too early to draw absolute conclusions 

 as to the effect of Ribes destruction on the demonstration control 

 areas during the past two years, but there is a noticeable lack of re- 

 cent infection of pines on these areas, while on adjacent areas where 

 Ribes have not been removed there is a steady increase in pine 

 infection. 



Intensive studies of infection centers have been made to obtain 

 data as to the distance to which the disease may be carried from 

 Ribes to pine. The limit of 1,700 feet, which is in use at the present 

 time, is an arbitrary one, based on data now available. 



Various chemicals and sprays are being tested in the hope of find- 

 ing a cheap and practical means of killing wild Ribes. The results 

 obtained. indicate that dip oil, fuel oil, and possibly sodium arsenite 

 can be used economically to destroy dense growths of Ribes where 

 the cost of hand pulling is excessive. 



