14 CRANBERRY DISEASES. 



the pycnidia of the scald fungus (PL II, fig. 1, &, and PL VI). This 

 form of the disease is called blast, as already described. 



The disease also affects the leaves, occasionally causing an irregular 

 reddish brown spot, covering a portion of the leaf, and bearing 

 pycnidia or perithecia of the fungus. These spots are of very infre- 

 quent occurrence. Where the disease has been severe for a number 

 of years the plants are completely killed, and the dead, brown leaves 

 still hanging to the vines are usually covered on the under surface 

 with the minute fruiting bodies of the parasite (PL II, fig. 1). 



Cuttings the first year or two after planting and before fruiting 

 are sometimes seriously attacked by Guignardia vaccinii, which 

 causes the leaves to turn yellow and fall and finally kills the plant. 

 Some of the other cranberry fungi are also associated with this 

 injury, but the greater part of the damage is apparently due to the 

 scald fungus. 



THE FUNGUS (GUIGNARDIA VACCINII, SHEAR) CAUSING BLAST 



AND SCALD. 



Scalded or rotten berries so rarely show any fruiting forms of 

 fungi that it is necessary to determine their presence and identity 

 by careful microscopical examination and cultures. A microscopic 

 study of the softened tissues of scalded berries at once reveals the 

 presence of an abundance of fungous hyphse. These hyphse when 

 transferred to culture media grow readily and frequently produce 

 the fruiting forms of the fungus. This fungus, Guignardia vaccinii 

 Shear, 24 which has been found upon blasted berries, upon the leaves 

 of scalded vines, and isolated in numerous cases in pure cultures 

 from scalded fruit, has been grown in the laboratory for several 

 years. 



Whitson, Sandsteri, Haskins, and Kamsey 16 state that the cran- 

 berry scald in Wisconsin is caused by an unnamed species of Rosel- 

 linia. We have never found any fungus of this genus associated 

 with cranberry scald or any other disease of the cranberry in Wis- 

 consin or elsewhere. The only cranberry fungus which at all resem- 

 bles Rosellinia is Anthostomella destruens Shear, which has been 

 found only once in our investigations, and then in New Jersey. The 

 true scald fungus (Guignardia vaccinii} has, however, been found in 

 Wisconsin berries. There are two stages thus far known in the 

 course of its development, a pycnidial and an ascogenous stage. 



Pycnidial form. The pycnidia are minute, black, membranous, 

 globose receptacles, 100-120^ in diameter, provided with a minute 

 apical, sometimes slightly prominent ostiole, or mouth. When oc- 

 curring on the leaves they are situated beneath the epidermis, usually 

 on the under side, and are slightly erumpent, with the minute ostiole 

 no 



