Weeds in the Poaceae and Cyperaceae families prevalent in sugarcane fi
elds were evaluated as potential hosts for the root rot pathogen, Pyth
ium arrhenomanes. In greenhouse studies, bermudagrass, broadleaf signa
lgrass, browntop panicum, barnyardgrass, large crabgrass, goosegrass,
itchgrass, johnsongrass, Italian ryegrass, and purple nutsedge became
infected when grown in steam-treated soil infested with P. arrhenomane
s. However, the extent of root colonization, symptom severity, and gro
wth reductions varied among species. Symptom severity and root coloniz
ation by P. arrhenomanes were less when weeds were grown in sugarcane
field soil in the greenhouse than when weeds were grown in Pythium-inf
ested, steam-treated field soil. Levels of root colonization by P. arr
henomanes in both experiments were greatest for johnsongrass and itchg
rass and lowest for browntop panicum, goosegrass, and Italian ryegrass
. For weeds collected from sugarcane fields, frequencies for colonized
plants were moderate to high, but the extent of root colonization by
P. arrhenomanes was low for all except johnsongrass. The results indic
ate that weeds can serve as hosts for P. arrhenomanes and may play rol
es in the epidemiology of Pythium root rot on sugarcane.