106 A PLANT-DISEASE SURVEY IN TEXAS. 



YUCCA. 



Blight {Cercospora floricola Heald and Wolf, 32). — This disease 

 produces on the yucca {Yucca rupicola Scheele) elongated grayish or 

 brownish patches, which become darker with age and spread over the 

 main scape, the flower pedicels, and the outer divisions of the perianth. 

 The creamy-white outer perianth segments may be completely covered 

 with the conidial tufts, which cause them to turn nearly black and to 

 shrivel more or less. (PL XIX, fig. 3.) The fungus may spread 

 over the whole segment from the tip downward. The perianth di- 

 visions may be attacked before the flower opens and the flower bud 

 completely blighted (PI. XIX, fig. 2), or the flower may expand to 

 full size and open in a normal way, but blight completely a little 

 later. In the locality where the disease was prevalent fruit formation 

 did not take place. 



ConidioiDhores in dense fascicles of many short, brown, continuous 

 filaments, 30 to 45 by 5 to 6 /;i; spores generally straight, cylindrical, 

 or slightly clavate, hyaline or faintly colored, 18 to 69 by 5 to 5.5 /u, 

 and one to five septate, commonly three septate. (PI. I, fig. 3.) 



Specimen collected: On Yucca rupicola Scheele — Austin, 1438 (type specimen). 



Leaf -spot {Pestcdozziella yuccae Karst. and Har.). — Grayish lenticu- 

 lar areas, 4 to 10 mm. in length, are produced on the leaves. Pro- 

 truding through the epidermis are dark pustules, the acerAiili contain- 

 ing oblong clear spores with four hairs at the apex. 



Specimen collected : On Yucca rupicola Scheele — Austin, 1530. 



Leaf -blight {Kellermannia yuccogena Ell. and Kellerm.). — The 

 affected leaves become straw colored, the dead area advancing do^^n- 

 ward from the tip or showing as a narrow zone along the margin. 

 The advancing edge of the dead area is generally bordered by a nar- 

 row zone of brown. Our observations indicate that this species of 

 fungus is not strictly parasitic, but that it finds its entrance first into 

 leaves which have been scorched by prairie fires. 



The pycnidia are very abundant on both surfaces, showing as 

 minute black specks, 345 to 500 /i in diameter. Spores hyaline, two 

 celled, 33 to 45 by 9 to 10.5 /*, each with a colorless appendage from 

 the end, 15 to 30 /a long. 



Specimen collected : On Yucca fllamentosa L. — Sabinal, 1988. 

 226 



