Field observations have suggested that infection of peanut by Meloidog
yne arenaria increases the incidence of southern blight caused by Scle
rotium rolfsii. Three factorial experiments in microplots were conduct
ed to determine if interactions between M. arenaria and S. rolfsii inf
luenced final nematode population densities, incidence of southern bli
ght, or pod yield. Treatments included four or five initial population
densities of M. arenaria and three inoculum rates of S. rolfsii. Fina
l nematode population densities were affected by initial nematode dens
ities in all experiments (P = 0.01) and by S. rolfsii in one of three
experiments (P = 0.01). Incidence of southern blight increased with in
creasing inoculum rates of S. rolfsii in all experiments and by the pr
esence of the nematodes in one experiment (P = 0.01). Pod yield decrea
sed with inoculation with S. rolfsii in all experiments (P = 0.05) and
by M. arenaria in two of three experiments (P = 0.05). In no experime
nt was the interaction among treatments significant with respect to fi
nal nematode population densities, incidence of southern blight, or po
d yield (P = 0.05). The apparent disease complex between M. arenaria a
nd S. rolfsii on peanut is due to additive effects of the two pathogen
s.