Soyaccountsfor23%ofthe
incomefromagricultureand14%
oftheCountry’stotalexports
Inor Ag. Assmann
Asian soybean rust is no stranger to
most Brazilian soybean farmers. The dis-
ease fears no frontiers and is considered
to be the main barrier to the crop in the
Country. Caused by an airborne fungus
known as Phakopsora pachyrhizi, carried
by the wind, it has a high damage poten-
tial, occurring in most Brazilian soybean
growing regions, and also in Paraguay
and Bolivia. According to agronomist
Cláudia Vieira Godoy, researcher at Em-
brapa Soybean, one of the aggravating
factors is that the rust may occur at any
development stage of the crop.
“It occurs most commonly at soybean
canopy closure, due to the high moisture
content and scarce solar radiation on the
lower leaves, where the disease tends to
start”, she explains. The phytopatholo-
gist also clarifies that in late seeding, due
to the big amount of fungal inoculum
produced in the first seeding, the dis-
ease may start in the vegetative period.
Among the diseases that attack the crop,
Asian soybean rust is the one that most
reduces the productivity rates – on av-
erage, 40% in fields where no fungicides
are applied, with chances to reach 80%.
The control of the disease is through
the integration of measures, like sani-
tary gaps, periods of 60 to 90 days with-
out any soybean at off-season. The target
consists in reducing the fungal inoculum,
which overwinters in living plants. Oth-
er regions, according to Cláudia, should
seed the crop at the beginning of the rec-
ommended period, with early maturing
cultivars, so as to stay away from the peri-
ods when the incidence of the Phakopso-
ra pachyrhizi fungus is more severe; the
option for cultivars that bear resistance
genes and the application of fungicides.
The Ministry of Agriculture, Livestock
and Food Supply (Mapa) has registered 120
fungicides for keeping the soybean rust
under control, but the efficiency of these
chemical products has been reduced by
the selection of fungal isolates less sus-
ceptible r resi tant to these chemicals.
The scientist understands that the speedy
adaptation of these compounds puts the
control of the disease at risk. Over the next
years, the resistance of the fungi could ad-
versely affect the productivity rates of Bra-
zilian soybean fields, mainly because of the
rust, the disease with the biggest damag-
ing potential”, she comments.
FightagainstAsiansoybeanrust isstillachallengefor
research,mainlybecauseof thestrongresistanceof
thefungustothepesticidesexistinginthemarket
Restless
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