114 James G. Horsfall 



The two diluents, lime and talc, were tried alone to see whether they 

 were exerting any toxic effects. They were used only once, but this was 

 sufficient to demonstrate their non-toxicity, as shown in table 32. 



HELMINTHOSPORIUM LEAF SPOT OF ORCHARD GRASS AND RED TOP 



Helminthosporium leaf spot on red top appears first as small spots of 

 Dresden brown (Ridgway, 1912) surrounded by a salmon-colored zone 

 which fades into the normal green of the leaf. The spots are small at 

 first, but they rapidly elongate in the direction of the long axis of the leaf, 

 forming streaks which finally result in the death of the affected organ. 

 The fungus fructifies abundantly on old lesions, appearing as a black fuzz. 

 The development of the malady on orchard grass is less well known, but 

 the fungus was isolated once from yellowed areas on leaves of this suscept. 



The causal agent was identified provisionally as Helminthosporium 

 triseptatum Drechsler (Drechsler, 1923:686), since the spores were ahnost 

 without exception two- or three-septate. Drechsler believes that it is 

 a saprophyte. Spores have never been seen in culture on Leonian's 

 medium and they are rare on oat agar and potato agar, but they are pro- 

 duced abundantly on sterilized wheat kernals at room temperature. 

 The mycelium is black and otherwise characteristic of Helminthosporia 

 in culture. 



Conidia thus produced in cultures isolated from orchard grass were 

 germinated at the following temperatures: 3°, 9°, 15°, 21°, 25°, 30°, 35° C. 

 in duplicate tests. The percentage of germination ranged from 98.6 at 

 3° C. to 99.5 at 35° C. 



These counts which were made after forty-eight hours indicate that 

 temperature within this range really has little effect upon germination if 

 time enough be allowed. It is interesting, however, that the fungus 

 germinated well at 35° C, while the spores of most of the other fungi 

 investigated were injured at this temperature. 



The results of two fungicide experiments are given in table 33. 



Copper-lime dust appears promising for the control of this disease. 

 The average high germination in 3.6-per-cent copper-lime dust diluted in 

 lime is of interest, but standard 20-80 copper-lime dust probably would 

 have inhibited germination completely. 



