PEANUT DISEASES 271 



periment Station, with fresh isolations of all fungi from collar-rotted pea- 

 nuts. In two tests one set of plants was wounded by tearing off cotyledons 

 and ripping through stems underneath the soil surface. 



With the exception of R. solani there was no indication of patlio- 

 genicity for any fungi or bacteria. Even the severely wounded plants de- 

 veloped to maturity after inoculation. Most plants inoculated with R. 

 solani died, but the necrosis was typical for R. solani infection and in no 

 way resembled collar rot as observed in the field. In 1948 with isolates of 

 fungi from collar rot of runner peanuts Wilson'' found some indication of 

 parasitism for Diplodia sp. 



From inoculation tests no specific fungus can at present be connected 

 with collar rot of peanuts. There are, however, several possible explana- 

 tions for the disease, the most likely of which are: (A) The disease is 

 due to a fuiigus not yet isolated and identified; (B) the disease is due 

 either to R. solani, a parasitic Fusarium sp., or to a parasitic bacterium 

 and the true pathogen is obscured by a succession of saprophytic fungi ; 

 or (C) an involved complex operates in peanut fields in which mechanical 

 injury, chemical injury, insect and nematode injury, and "light" parasitic 

 infection all provide dead tissue in which ordinarily saprophytic fungi 

 thrive and eventually destroy living tissue. A similar complex has been 

 suggested as associated with a root rot of tobacco and small grains (70), 

 and it has been indicated that peanut root rot may, under different con- 

 ditions, result from a wide variety of fungi (111). 



Control. Collar rot has been observed as frequently and to as great an 

 extent in fields planted with treated seeds as in those planted with un- 

 treated seeds. There have been instances in which injury from seed treat- 

 ment has been suspected as a factor in the development of the disease. At 

 present the only recommendations for control are : ( A) Use of seed stocks 

 carefully selected to eliminate damaged or broken seeds; (B) use of care 

 in treatment of seeds to avoid injury from seed treatment; (C) close 

 spacing of seeds to insure good stands even if some plants are killed by 

 collar rot. 



DISEASES OF THE GROWING SEASON 



Cercospora Leajspot 



Importance. Because of frequency of occurrence Cercospora leafspot 

 is generally regarded as one of the most important diseases, or perhaps 

 the most important disease of peanuts. Although it has received more at- 



' Unpublished data, Alabama Experiment Station. 



