534 SPECIAL PLANT PATHOLOGY 



Pea {Pisum sativum, L.) 



Pod-spot {Ascochyta pisi, 'Lih.). — The horticulturist, who attempts 

 to grow the garden pea, will find that the leaves and pods become 

 spotted with conspicuous, circular, sunken spots 3 to 6 mm. in diameter, 

 which are dark bordered, pale in the centers and slightly pinkish when 

 mature. Pycnidia are associated with these spots and out of their 

 porous opening under favorable conditions the spore masses may be 

 seen issuing. When the leaves are affected, it is usually the lower 

 leaves which become diseased first, and such soon die. If the stems 

 are attacked, the spots sometimes penetrate through the woody part. 

 Different races of peas differ as to their susceptibility. The variety 

 Alaska is slightly affected, while the varieties American Wonder, 

 French June and Market Garden are frequently badly diseased. 

 According to Stevens, the pycnidia consist of angular cells, 5 to 7/1 with 

 a rounded ostiole and reddish-brown surface. The conidiospores are 

 constricted slightly at the septum, are oblong and measure 12 to i6m by 

 4 to 6ju. The mycelium perennates in affected seeds, reduces their 

 power of germination and carries the fungus over to the next crop. 

 Selby has indicated that healthy peas may be grown by spraying with 

 Bordeaux mixture, and it has been suggested, that a two years' rotation 

 of non-susceptible crops lessens the prevalence of the disease, if another 

 pea crop is raised. 



Peach {Amygdalus persica, L.) 



Leaf Curl (Exoascus deformans (Berk.), Fckl.) (Fig. 192). — This 

 disease is called by the French Cloque du pecker, by the Germans 

 Krauselkrankheit and by Americans and English peach leaf curl. It 

 is widely distributed through America, Europe, China and Japan and 

 in Africa and Australia, so that it is practically cosmopolitan. 



The disease is most prevalent and most disastrous to the leaves and 

 tender shoots of the peach, when the spring months are damp and cool, 

 for records show that such conditions prevailed during April of the 

 year 1893, 1897 and 1899, when peach leaf curl was especially abundant 

 in Ohio and New York. Warm and relatively dry springs seem to be 

 unfavorable to its occurrence. The susceptibility of the host plants 

 differs to a marked extent, some being susceptible, others less so. 



The presence of the disease may be detected when the leaf buds 

 unfold, for the coloring of the young leaves is heightened, and as they 



