Initial epidemic area is strongly associated with the yearly extent of soybean rust spread in North America.

Hosts of soybean rust () are sensitive to low temperatures, limiting this obligate parasite in the United States to overwintering sites in a restricted area along the Gulf Coast. This temperature sensitivity of soybean rust hosts allowed us to study spatial spread of epidemic invasions over similar territory for seven sequential years, 2005-2011. The epidemic front expanded slowly from early April through July, with the majority of expansion occurring from August through November.

Landscape heterogeneity and disease spread: experimental approaches with a plant pathogen.

Understanding landscape effects on disease spread can contribute to the prediction and control of epidemic invasions. We conducted large-scale field experiments with wheat stripe rust, which is caused by a wind-dispersed rust fungus. Three landscape heterogeneity variables were altered: host frequency (mixtures of susceptible and resistant plants), host patch size (different plot sizes), and size of initial disease focus (attained by artificial inoculation).

Aerial dispersal and multiple-scale spread of epidemic disease.

Disease spread has traditionally been described as a traveling wave of constant velocity. However, aerially dispersed pathogens capable of long-distance dispersal often have dispersal gradients with extended tails that could result in acceleration of the epidemic front. We evaluated empirical data with a simple model of disease spread that incorporates logistic growth in time with an inverse power function for dispersal.

Long-distance dispersal and accelerating waves of disease: empirical relationships.

Classic approaches to modeling biological invasions predict a "traveling wave" of constant velocity determined by the invading organism's reproductive capacity, generation time, and dispersal ability. Traveling wave models may not apply, however, for organisms that exhibit long-distance dispersal. Here we use simple empirical relationships for accelerating waves, based on inverse power law dispersal, and apply them to diseases caused by pathogens that are wind dispersed or vectored by birds: the within-season spread of a plant disease at spatial scales of <100 m in experimental plots, historical plant disease epidemics at the continental scale, the unexpectedly rapid spread of West Nile virus across North America, and the transcontinental spread of avian influenza strain H5N1 in Eurasia and Africa.

Velocity of spread of wheat stripe rust epidemics.

ABSTRACT Controversy has long existed over whether plant disease epidemics spread with constant or with increasing velocity. We conducted largescale field experiments with wheat stripe rust at Madras and Hermiston, Oregon, where natural stripe rust epidemics were rare, to test these competing models. Data from three location-years were available for analysis.