14 TIMOTHY EUST IN THE UNITED STATES. 



considerable damage to the timothy crop from this })arasite become 

 necessarj'. Only one method at present known can be employed 

 against it with any promise of success, and that is the development 

 of varieties of timothy resistant to rust. To tliis end work has 

 been commenced. 



RESISTANCE OF VARIETIES OF TIMOTHY TO RUST. 



A fair opportunity was olfered to study the resistance of varie- 

 ties of timothy to rust and to make selections for rust resistance at 

 the Arlington Experimental Farm during 1908 and 1909, as the 

 disease was plentiful in tliose years. Mr. W. J. Morse, of the Office 

 of Forage-Crop Investigations, who had charge of timothy-breeding 

 work at that place, says in an unpublished report: 



By July 30 (1908) no timothies were found to be entirely free from rust. * * * 

 The rust resistance varied greatly, ranging from zero to 98 per cent. In some instances 

 a few small rust spots appeared on the culms and no rust on the leaves. Several selec- 

 tions made no growth at all, the rust appearing to stunt the growth. In other 

 instances the plants made some growth, but the production of seed was prevented. 

 In 1909 the rust attack at the Arlington Experimental Farm was even more severe 

 than in 1908, although the rust did not appear to any extent until the middle of May. 

 This seA'ere attack brought to light the fact that many of the strains marked "resist- 

 ant" in 1908 appeared to be much less resistant in 1909. It was noticeable, however, 

 that the relative resistance of the different strains was very little different in 1909 

 from what it was in 1908. 



In 1910 the rust attack on the same farm was not nearly so severe 

 as in the two preceding years. Under such conditions the distinc- 

 tion between resistant and nonresistant strains is not nearly as well 

 marked as when rusts are abundant. As a result many strains 

 failed to retain in their resistance percentages the same relative posi- 

 tion which they occupied in 1908 and 1909. Tliis corroborates the 

 experience of the writer that the value of rust-resistance figures 

 obtained in years when the rust is not abundant or at places where 

 the rust attacks are not severe is questionable and shows that the 

 notes taken at such times and })laces may often hs misleading. 

 Dependable data can be secured only either in "rust years'' or 

 in places wliere vigorous rust attacks occur or are artificially })ro- 

 duced every year.' 



In order to determine whether or not the figures on rust resist- 

 ance obtained in the field during seasons when rust is abundant are 

 com])arable to data secured where difl'erent strains are placed under 

 identical conditions and subjected to artificial inoculation, experi- 

 ments were undertaken in 1909 in the greenhouses at Washington, 

 D. C. Seed of various strains of timothies from the 1908 selections 

 at the Arlington Experimental Farm was planted in 4-inch pots. 



> Freeman and Johnson, loc. cit. 

 224 



