Soybean rust is caused by two fungal species, Phakopsora pachyrhizi,
the
aggressive australasian pathogen and Phakopsora meibomiae,
the weaker relative (found in the Caribbean).
Factors favourable for disease development
- cool temperature between 15-27° C (59-82 ° F)
- relative humidity 75-80%
- leaf wetness (6 or more hours), dew and rain
Disease symptoms
Initial symptoms of disease infection are observed on the lower portion of
the plant as small light brown spots (1-2 mm diameter) barely visible on
the underside of the leaves. As the spots get larger they become more visible
on both sides of the leaf veins while the overall plant begins to turn yellowish
color. Masses of spores, known as pustules, develop on the underside of the
leaf and will lead to further infections as they are spread by wind, rain
and movements of equipment and workers.
Depending on infection levels and weather conditions total defoliation may
take as little as 2-3 weeks making Asina Rust a serious and devastating fungal
pathogen.
