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Mad Soybean II – A problem of unknown cause
The research scientists of the Brazilian Agricultural Research Corporation
(Embrapa), a federal research organization from the Brazilian government - and
others research institutions, teaching and extension service specialists formed a
working group to search the possible causes of the Mad Soybean II problem. So
far, it is considered a problem of unknown cause. It is not possible to confirm that
Mad Soybean is caused by diseases or any other hypotheses. The problem is being
studied by several Brazilian agricultural research institutions.
The information provided below can clarify some aspects related to the typical
symptoms, management and control of the problem.
Mad Soybean II
The occurrence of soybean plants with green stem and leaf retention has been
reported in several producing regions in Brazil, with symptoms that differ in
some respects from those caused by attacks of stink bugs, by nutritional
problems or other physiological disorders. This new anomaly, of unknown
origin, is popularly called as "Mad Soybean II."
The high incidence of this problem occurs without distinction between soybean
cultivars, GMO or conventional, affecting the harvesting process, and may
cause reductions in productivity of up to 40%.
Several causes have been related to this problem, however so far nothing has
been scientifically confirmed.
Major Symptoms
Symptoms of this problem can be detected from the vegetative stage, usually
from V5-V6, starting with narrowing of the top leaves on plants, wrinkling of the
leaf blade and thickening of the veins.
Leaves with symptoms present a darker coloration and less pubescence as
compared to normal leaves.
The stems display deformity in the shape of "splines" (or edges) and thickening
of the nodes. The pods may present necrotic brown lesions, cracks, less
pubescence, rottenness and reduced number of grains. Typically, the pods
contain from one to two grains of larger size.
The affected plants present a high rate of flower and pod abortions, often
causing induction to new flowering and symptoms of super-sprouting,
resembling the male-sterile plants. This abortion process is more intense on the
top of the plants, decreasing toward the base, and it prevents the natural
process of plant maturation, staying green, even after applying desiccant
herbicides.
Management and Control
Until the causes of this anomaly and the mechanisms that trigger their
symptoms are fully clarified, there is no specific recommendation for the
management or for its control.
It is suggested that the farmers follow the soybean production technologies
derived from regional research meetings.
Legendas das figuras:
First symptoms: narrowing of top leaves.
Leaflet with typical narrowing symptom, thickening of the veins and wrinkling of
the leaf blade (left), as compared to a normal leaflet (right).
New flowering induction (super-sprouting) and stems with “splines” of soybean
plant.
Necrotic lesions and cracks on the pods.
Mad soybean plants after desiccation with herbicides.