T
he diseases known as corn
infections have caused sig-
nificant losses in certain re-
gions across Brazil since the
2015 growing season. Cur-
rently, the introduction of some mea-
sures indicated by researchers are re-
ducing the damages caused by these
infections, more common in the warmer
regions in the Country. “The control of
these diseases goes essentially through
preventive measures”, says Elizabeth de
Oliveira Sabato, researcher at Embrapa
Corn and Sorghum, in Sete Lagoas (MG).
According to Elizabeth, these infec-
tions could reduce the production of
grains per plant by 70 percent, in com-
parison to healthy plants, in suscepti-
ble cultivars. In her view, outbreaks of
the disease occurred in Western Bahia,
in Southeast Goiás, in Triângulo Minei-
ro and in the Northwest in Minas Gerais.
Some measures, as the elimination of
all stalks from harvested corn fields and
the use of seed treated to insecticides,
are put into practice by the farmers.
Elizabeth explains that corn infec-
tions are caused by mollicutes (spiro-
plasma and phytoplasma), micro organ-
isms that lack a cell wall and cause corn
stunt spiroplasma andmaize bushy stunt
phytoplasma. The pathogen is identi-
fied through laboratory tests. The infect-
ed plants have shorter internodes, fewer
roots and produce a smaller number of
grains. The mollicutes are transmitted by
the corn leafhopper (Dalbulus maidis).
Both affect the development, nutrition,
and the physiology of the infected plants,
reducing the production of grains.
Besides the mollicutes, leafhoppers
also carry from one plant to the next the
maize rayado fino virus. “Not all leaf-
hoppers are mollicute or virus carriers,
but one leafhopper alone could carry
the three disease-causing agents”, she
observes. The insect sucks sap from the
leaves of corn and lives, preferably, in
the cartridge of plantlets. The biological
cycle of the insect (egg to adult) is influ-
enced by the temperature but, on aver-
age, lasts for 25 days. In warm regions,
if there are cornfields available, several
generations occur throughout the year.
PREVENTION
A series of mea-
sures need to be implemented by the
farmers to keep these corn infections
under control, says researcher Elizabeth
de Oliveira Sabato, who gave 20 lectures
on the disease to farmers and techni-
cians in 2015 and 2016, and 10 in June
2017. One of the directives consists in
avoiding the establishment of cornfields
close to older corn fields where disease
outbreaks have occurred. It is also rec-
ommended to seed more than one corn
cultivar and treat the seed to insecti-
cides registered for controlling leaf-
hoppers. She also suggests synchroniz-
ing corn seeding with the period other
crops are planted.
In areas of high corn infection and
leafhopper outbreaks, it is recommend-
ed to interrupt temporarily the culti-
vation of corn to eliminate the diseas-
es and vector insects. Furthermore, the
farmer should not leave volunteer corn
plants in the field, as they could shelter
the insect and the agents that could in-
fect the next cornfields. The use of corn
cultivars with genetic resistance to in-
fections is an alternative that could di-
minish the damages caused by these
diseases. An option for preventing these
infections consists in avoiding late corn
seeding.
n
Several steps are necessary
tokeepcorndiseasesundercontrol, infectionsnormally
causedbymollicutestransmittedbymaizeleafhoppers
Infections could reduce by 70 percent the production of grains per plant
