SBR monitoring begins with collecting and observing leaves
from sentinel plots at regular intervals throughout the season (Fig.
4). For example, in Alabama and many other states, soybean sentinel
plots are sampled every 2 weeks prior to soybean flowering
(flowering signifies growth stage R1 [16]), then weekly thereafter.
Plots are primarily monitored by individuals trained in SBR identification
under the guidance of the state SBR coordinator. Because
SBR is difficult to detect at low incidence within fields, many individuals
collect leaves and confirm the disease under controlled
laboratory conditions. Leaves are examined under a dissecting
microscope (×100 magnification) following a 24- to 48-h incubation
period to promote sporulation. At this magnification, pustules
of P. pachyrhizi can be observed, confirming the presence of the
pathogen. Consequently, SBR can be detected when three to four
pustules are present on a single soybean leaflet, which can be difficult
to detect using traditional field scouting methods