18 MISC. PUBLICATION 541, U. S. DEPT. OF AGRICULTURE 



Oospores, or resting spores, are produced in diseased leaf tissue and 

 have been found mixed with the seed. It has not been determined, 

 however, just how important a role they play in the life history of 

 the fungus. 



CONTROL MEASURES 



Although copper protectants are toxic to spores of the downy mildew 

 pathogen their use has not been found practicable under commercial 

 conditions. There is little evidence to suggest that the disease can 

 be controlled through development of resistant varieties of spinach. 

 Because of circumstantial evidence that the disease may originate 

 in a field through use of infested seed, it is possible that some measure 

 of control may be obtained by use of seed from a disease-free field. 

 Under Long Island, N. Y., conditions the most important method of 

 control found was reducing the primary inoculum by separating over- 

 wintered spinach from winter and spring plantings. 



(See ,17,2^,71,81, 121.) 



Heterosporium Leaf Spot 

 (Heterosporium variable Cke.) 



Heterosporium leaf spot, although widely distributed, is ordinar- 

 ily of only limited commercial importance. The causal fungus is 

 usually considered to be only weakly pathogenic and to attack plants 

 that are already of low vigor as the result of unfavorable environ- 

 mental conditions, infection of downy mildew, or other diseases. On 

 the market it is occasionally found as a conspicuous blemish of Vir- 

 ginia and Texas spinach. 



The disease may be identified by the presence of numerous small, 

 circular, light-brown, slightly depressed spots that average from one- 

 sixteenth to one-eighth inch in diameter (pi. 10, G).- They have 

 sharply defined borders and are evident upon both the upper and the 

 lower surface of the leaf. The pathogen appears as an abundant 

 olive-green to black sporulating mold that covers the older spots on both 

 leaf surfaces. Where spots are numerous they coalesce and the adja- 

 cent uninfected areas of the leaf may become yellowed and then turn 

 brown. Spots are most abundant on the older leaves. 



No specific control measures are known. 



(Sw 30, 65, 119.) 



White Rust 

 {Albugo ocddentalis G. W. Wils.) 



White rust is at times a serious disease of spinach in the Winter 

 Garden district of Texas where it first appeared in destructive form 

 in 1937. The disease has also been found in Oklahoma and Arkansas. 

 On the market, white rust is one of the important diseases of Texas 

 spinach. 



The pathogen develops within the leaf tissues and later produces 

 on the lower leaf surface numerous tiny blisterlike pustules (sori), 

 which are filled with whitish masses of spores (pi. 10, A). These 

 fruiting structures of the fungus in themselves serve to identify 



