38 MISC. PUBLICATION 44 0, U. S. DEPARTMENT OF AGRICULTURE 



The tall varieties of peas grown in California and Washington for 

 the market seem to be more susceptible than the varieties grown 

 chiefly for canning. In experimental tests the American Wonder. 

 Perfection, Canners Gem, Dwarf White Sugar, Little Marvel, Wis- 

 consin Early Sweet, Surprise, and several others have proved resistant 

 to common mosaic. 



The pea aphid, Moxvosiphum (Illinoia) pisi (Kalt.), carries the 

 virus from plant to plant in the field. The isolation of pea fields from 

 related leguminous plants, such as clover, that may harbor the 

 disease, and the development of resistant varieties should prove 

 effective control measures. 



(See 132, 11$, llfi, 157, 158.) 



POD SPOT (BLIGHT) 



(Mycosphaerella pinodes (Berk, and Blox.) R. E. Stone) 



Pod spot, also known as ascochyta blight, is one of the most com- 

 mon and most serious diseases of the pea and is found to some 

 extent wherever peas are grown. All varieties of field and garden 

 peas are affected and some closely related plants, such as vetch, are 

 susceptible. All parts of the plant may be attacked. The disease 

 is not only a factor from the production point of view but is also 

 a direct factor from the point of view of marketing, because the 

 lesions disfigure the pods and open the way for infection by sec- 

 ondary organisms. 



This disease is characterized by long and sometimes girdling 

 lesions on the stem. Grayish-tan circular spots are formed on the 

 leaves. On the pods the lesions are rather sharply depressed and 

 circular, varying from one-eighth to one-fourth inch in diameter 

 (pi. 10, A). These spots are pinkish to tan in color, and in older 

 stages may show small, black fruiting bodies (pycnidia and some- 

 times perithecia) in their centers. Deep lesions frequently pene- 

 trate the pod wall and discolor the seeds within. The old spots 

 probably do not enlarge in transit although incipient lesions may 

 develop, and spots invaded by secondary organisms sometimes enlarge 

 during transit. 



Besides the pycnidial stage of Mycosphaerella pinodes (Ascochyta 

 pisi Lib.) there is a related fungus, Ascochyta pinodella Jones, 

 which causes pod spots and blight and which may be confused 

 with the disease caused by the first-named organism. These fungi 

 are carried through the winter as dormant mycelium within infected 

 seeds of the previous year or by fruiting bodies (perithecia) in dead 

 vines. Young plants become infected and in turn produce abundant 

 masses (pycnidia) of summer spores. These spores are disseminated 

 and cause new infections, if warm wet weather prevails. Later 

 in the season the perithecial fruiting bodies are developed in stem 

 and pod lesions. 



As the causal organism is carried through the winter on diseased 

 plants, all vines insofar as possible, should be burned. Seeds also 

 serve to carry the fungus through the winter. Western grown seed 

 is to be recommended because it is usually free from infection. Crop 

 rotation should be practiced in some regions. 



(See 101, 111, 113, 121. />'. 149, 150.) 



