Polymyxa betae is the fungal vector of beet necrotic yellow vein virus (BNY
VV), which is the causal agent of the sugar beet disease rhizomania. The wi
thin-season dynamics of the fungus are a crucial factor in the occurrence a
nd severity of rhizomania. Late infection of the host by viruliferous fungi
enables host resistance to the virus to develop and hence limits crop dama
ge. A previously published mechanistic model for the dynamics of Polymyxa b
etae is extended in this paper to incorporate the effect of temperature on
the germination of resting spores, and on the latent periods between infect
ion and the production of secondary zoospores and new resting spores. It is
shown that, for UK temperature conditions, the effect of sowing date on in
fection is greater than that of year-to-year variations in temperature asso
ciated with a single representative sowing date. The variation in inoculum
build-up predicted when temperature data from a range of soil types were us
ed in the model agreed with field observations, where higher levels of infe
ction are observed on sandy soils than on black fen peat soils. The differe
nce was most distinct when daily maximum soil temperature values were used
to drive the model rather than rolling 24-hour average values.