296 THE PEANUT— THE UNPREDICTABLE LEGUME 



suspected in regions where the legume aphid is rare, appear to have been 

 eHminated from consideration. 



Several factors seem to influence the pathogenicity of the rosette virus. 

 These factors, obviously, may be efifective on the peanut plant or on the 

 aphid vector. The most important factors are : 



(A) Season. In Africa late plantings are more severely attacked by 

 rosette (24). Plants not infected during the first 8 weeks of the season 

 apparently remain uninfected (25). Rosette has been reported more 

 prevalent (27) and spreading more rapidly (24) in dry seasons. 



(B) Soil Moisture. Possibly many of the apparent seasonal effects 

 are actually effects of variations in soil moisture. An early report indi- 

 cated a greater degree of susceptibility to rosette during a rainy period 

 following a long drought ( 175) . If there is scant rainfall in the first month 

 of the growing season, rosette may be intensified (25). 



(C) Vegetative covering. Certain observations indicate that denser 

 vegetative coverings in peanut fields make for less severe rosette. Weed- 

 ing does not prevent the spread of infection, but weed covering between 

 peanut rows apparently results in reduced infection (27, 59, 135). Plants 

 on the border of a field are reported most frequently infected (59). 

 Whether these effects are independent of the effect of shading on soil 

 moisture is not clear. Possibly there is some effect of these dense vege- 

 tative coverings on the vector. 



Control. Some reports from Africa (25) have indicated that com- 

 monly grown varieties are susceptible. In the Gambia region, the Philip- 

 pine pink, a local section from Tennessee red, is regarded as resistant 

 (26) with the Philippine white either less resistant than the pink or not 

 resistant at all (26). 



From Gambia (6) and the Congo (7) it is reported that various con- 

 trol measures have reduced the incidence of rosette so that it is no longer 

 serious. The following control measures have been recommended in ad- 

 dition to the use of resistant varieties : 



(A) Seed treatment, insuring good stands and vigorous, drought- 

 resistant plants (64). 



(B) Early planting (142). 



(C) Rotation — the disease is reported more severe the second season 

 on the same land (135). 



(D) Close planting for greater covering of soil surface (142). 



(E) Roguing of volunteer peanuts (142). 



(F) Roguing of infected plants (112), 



