MICHIGAN ACADEMY OF SCIENCE. 125 



CUCUMBER DISEASES. 



.Micliij^an ijs uia* of tlio most im]>ortniit cuounibor-fjrnwinp,' states. 

 TluMi' an' at least '2Ty() salting' stations in liie lower |>eninsnla. For 

 a nunibei* of vears the eiuunibei* diseases have been doinj; much 

 dnmajie. In fact in 1912, I made the statement in a popular article 

 that ('ucnnd)ei' Diseases were so serious that the crop was in ])re- 

 carious condition. Last year at the majority of stations the 

 profitable picking- season was on an average only one-half of the 

 possible length. Three diseases Avere responsible for this shorten- 

 ing* of the ])icking season, Downy Mildew, White Pickle, and Scab. 



Doivnji Mihh'ir. Downy Mildew is caused by the fungus Psciido- 

 peronospora cuheiisis (B & C) and in 1905 was reported by Orton 

 in the yearbook as causing an epidemic in Michigan. It has been 

 found in various localities since that time. From observations for 

 several years it seems safe to say that given hot, moist weather in 

 August an outbreak of Downy Mildew is to be expected. Last year 

 it occurred too late to do its usual amount of damage. 



WMte Pickle. White Pickle (PI. VII B) is a new disease which 

 has never been reported in the literature of plant diseases. Atten- 

 tion was first called to the disease in 1912, Avhen specimens were 

 sent from Grand Rapids. The disease shows first as a distinct 

 mosaic of the leaves, accompanied by shortening of the main shoot-s. 

 The restriction of growth of the shoot and leaves gives the impres- 

 sion of leafiness to the diseased runners. In the last stages, the 

 leaves are dwarfed. The most conspicuous effect is produced upon 

 the fruits. These become excessivel}^ warty and roughened. These 

 warts show ripening effects before the rest of the pickle, hence one 

 commonly finds a small green cucumber with very conspicuous yel- 

 low warts upon it. Pickles borne upon plant's in the last stages of 

 the disease do not show the excessive wartiness, but remain small, 

 pale, bitter fruit, hence the name, "White Pickle." 



Observations made in 1913 and the testimony of the growers indi- 

 cated that the disease was infectious, since the history of the dis- 

 ease in the fields always indicated a progressive attack. Although in 

 many ways the appearance of the plants and fruits suggests a stig- 

 nionose, and although plant lice Avere common on the diseased 

 plants, they were not in great abundance, nor were they more pre- 

 valent in the fields affected than in the unaffected fields. 



\\'heu the disease started in a field the loss soon became total. 

 The disease appeared in well-drained as well as in low situations, 

 in sand and in clay, on loamy soil which had not grown cucumbers 

 as well as in fields Avhere the crop was repeated. It had been 



