MARKET DISEASES OF FRUITS AND VEGETABLES 27 



The lesions also open the way for attack by saprophytic or weakly 

 parasitic organisms in transit and in storage. 



The pathogen, Phytophthora phaseoli, overwinters as dormant my- 

 celium or as oospores in affected seeds or in trash in the field. If 

 moist moderately cool weather prevails the fungus produces spores 

 that are disseminated by insects, wind, and rain. At times, the spread 

 of the fungus is largely accomplished by bees visiting blossoms and 

 carrying the spores from one plant to another. 



For control of this disease the use of clean seed is recommended, 

 and also the burning of bean trash, which may harbor the fungus over 

 winter. Spraying with bordeaux mixture may be advisable in some 

 localities along the Atlantic coast. 



(See 79, 94, 100.) 



POD BLIGHT 



(Diaporthe phaseolorum (Cke. and Ell.) Sacc.) 



Along the Atlantic seaboard pod blight of the lima bean occasion- 

 ally causes lesions on the pods and may penetrate to the seeds, ren- 

 dering both unsightly. Pod blight generally does not become severe 

 until late in June or early August, when the vines are nearly full- 

 grown. Young pods rarely show lesions. 



In the early stages the lesions consist of circular or oval spots of 

 darkened tissues; later, they become studded with minute gray ele- 

 vations that soon break the skin of the pod and emerge as black 

 pustules or fruiting bodies (pycnidia) (pi. 8, B). In advanced 

 stages the entire pod may become diseased and covered with pycnidia. 



The causal fungus overwinters in seeds or in bean trash. Under 

 warm moist conditions it produces pycnidia, from which the spores 

 are exuded during wet weather to be later disseminated by wind, water, 

 or other means. The leaves of the plant are attacked first and usually 

 have a good growth of pycnidia available by the time the pods be- 

 come old enough to be susceptible. Young pods are not attacked. 

 The fungus enters readily through wounds and the first symptoms 

 of disease appear about 4 days after inoculation. 



Because the pathogen apparently overwinters and is carried into 

 the field on seed, it is recommended that only disease-free seeds be 

 planted. 



(See 95.) 



RHIZOPUS SOFT ROT 



(RJiizopus tritici Saito, and R. nigricans Ehrenb, ex Fr.) 



OCCURRENCE, SYMPTOMS, AND EFFECTS 



Under favorable conditions for infection practically all kinds of 

 vegetables are subject to rhizopus soft rot. It occurs in vegetables 

 from all regions, and although it is rarely of any significance in the 

 field, during transit and marketing it often causes very serious losses. 

 It is much more important on beans than peas but sometimes occurs 

 on the latter. All varieties of pod and shelled beans may suffer from 

 this decay if they are moist in transit and if moderately high tem- 

 peratures prevail. 



