PEANUT DISEASES 307 



Diplodia sp. and Macrophomina phaseoli are found on the same peanut 

 plant. 



Little is known about the parasitism of Diplodia sp. on peanuts. Lack- 

 ing other conclusive evidence it may be assumed that Diplodia blight 

 usually develops on nearly mature plants and results in little decrease in 

 yield and few deaths. The inoculum is probably soilborne. There may be 

 some carryover from seed-borne inoculum or seedling infection, but such 

 earl)' infected plants probably die before they reach the stage of maturity 

 at which Diplodia blight develops. 



Nematodes on Peanuts 



Three types of nematodes have been reported on peanuts, but only 

 the root-knot type has attracted much attention. 



Root-knot nematodes. Root knot was reported from peanuts in the 

 United States in 1931 (4) and 1943 (13), but only since 1946 has it been 

 given more than passing attention. Parasitic nematodes were noted on 

 peanuts in South Africa in 1926 (137) but apparently were considered 

 unimportant. 



Christie (33) inoculated Virginia runners with nematode populations 

 from alfalfa, cotton, peanuts and sweet potatoes. After 6 weeks there was 

 no development of nematodes on peanuts inoculated with sweet potato 

 populations, but those inoculated with alfalfa and cotton populations 

 showed nematodes in the larval stages. The peanut plants inoculated with 

 the population from peanuts showed numerous egg-laying females. From 

 this Christie concluded that the peanut as a host has a varying effect on 

 the development of dififerent nematode races. 



Wilson (164) noted populations or strains of root-knot nematodes 

 attacking peanuts readily in North Carolina, Mrginia and Alabama, and 

 evidently on the increase in Alabama. A similar observation regarding 

 southern Georgia has been received from J. H. Miller^^. Recently Chit- 

 wood (32) placed the root-knot nematodes in the species Meloidogyne 

 arenaria. 



Root knot on peanuts is very similar to root knot on other plants. 

 Typical galls are produced on the taproot, lateral roots, pegs and shells. 

 The symptoms are shown in figure 4. If infection occurs early the plants 

 are stunted and the margins of the leaves become necrotic. 



Root knot does not seem to have been a serious disease of peanuts in 

 the past. It looks as though the strain or strains of nematodes attacking 

 peanuts are now on the increase in three major peanut-producing regions 



^~ Personal communication. 



