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.
