302 THE PEANUT— THE UNPREDICTABLE LEGUME 



Aspergillus rot is in part a pre-emergence disease and is most serious 

 in that aspect. The post-emergence aspects of Aspergillus crown rot 

 strongly resembles collar rot^^ of the southeastern United States. 



3. Texas Root Rot (Southwestern United States) 



In the southwestern United States Phymatotrichum omnivorum 

 (Shear) Dugg. causes a root rot of a number of plants. This root rot is 

 generally regarded as the most important plant disease in that area (31). 

 Peanuts have been reported attacked by this organism in Texas, Arizona 

 and New Mexico with greater losses on heavier soils. In one survey in a 

 Texas county, 7 of 11 peanut fields were found infected with losses of at 

 least 15 percent in most fields and up to 83 percent in some fields (75). 



Fine, brownish strands of the fungus cover the roots of infected 

 plants before above-ground symptoms are evident. Under moist conditions 

 spore mats appear on the soil above infected roots. These mats are 2 to 12 

 inches in diameter, are originally white and cottony but turn tan with 

 spore formation. The fungus forms rhizomorphs and pinhead size scler- 

 otia. The sclerotia are light tan, and become darker and warty with age. 

 The sclerotial stage has been called Ozonium omnivorum Shear. The 

 foliar response is wilting, with death occurring in a few days. The entire 

 root system decays and the plant slips from the soil easily. 



It is suggested (75) that damage to peanuts by Texas root rot in- 

 creased as a result of expanding peanut acreage to heavier soils as well 

 as to soils known to be infected. Chester (31) suggests the following prac- 

 tices for the control of Texas root rot: (A) Three- or 4-year rotations of 

 susceptible crops with highly resistant crops, such as grains; (B) avoid- 

 ance of susceptible perennials, such as alfalfa, and certain trees and orna- 

 mentals; (C) promotion of soil organisms antagonistic to Phymatotri- 

 chum omnivorum through the use of manure or other organic fertilizers ; 

 (D) clean cultivation to eliminate susceptible weeds. 



DISEASES OF MINOR IMPORTANCE 



Quite a few diseases of peanuts appear to be unimportant wherever 

 they occur. These diseases fall into two classes : (A) Diseases known to 

 be of minor importance, and (B) diseases which cannot be definitely 

 classified because they have not been extensively studied. 



All of these diseases may be important under abnormal environmental 

 conditions, thus such diseases should be regarded as potential threats. 



^ See page 269 for discussion of collar rot. 



