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ON FARM LEVEL
Integrated pest control
This fungus also infects various other cereals such as wheat and
barley, which may help the pathogen to overwinter, causing even
larger disease outbreaks the following season.
Fusarium gramine-
arum
species complex infects maize seed and infection levels of up
to 66% have been reported. Seed to seed transmission, however,
has not been clearly shown.
Transmission
Spores produced in spore bearing bodies (perithecia) on maize stub-
ble are transmitted via air currents. These spores infect the maize
silks and grow down into the point of the ear. The pathogen has also
been reported to be transmitted by birds and insects.
Climatic conditions
Graminearum ear rot severity is favoured by cool, wet weather
within three weeks of silking. This disease is common under irriga-
tion conditions in South Africa. Regions affected by sporadic out-
breaks of this disease are generally KwaZulu-Natal and Mpumalanga
and irrigation fields in the Limpopo and North West Province.
Economic importance
Graminearum ear rot is not as economically important as Fusarium
ear rot in South Africa, but appears to be on the increase and may
well become the most significant ear rot in South African maize
production.
Reports from certain areas where cool, wet, late season conditions
are experienced, imply sporadic and localised outbreaks of this ear
rot disease. In certain cases severe yield and quality reductions
were observed.
The major concern is toxicity, associated with this disease.
F. boothii
the ear rot infecting species of the
Fusarium graminearum
species
complex in South Africa, is known to produce a number of important
mycotoxins, which cause major problems for pig farmers especially.
These mycotoxins are zearalenone and deoxynivalenol and whilst
there are also levels of nivalenol found in maize ear rot samples to
date, we are not sure what the source of this mycotoxin is and how
it gets into the grain.
F. boothii
is a known deoxynivalenol producer and not able to pro-
duce nivalenol; which bodes the question of where does the nivale-
nol come from? Researchers at the ARC-GCI are presently working
on this anomaly.
Toxigenic symptoms in pigs range from hormone induced syndrome
caused by zearalenone, which reduces the reproductive perfor-
mance of the animals, to feed refusal due to high levels of deoxyni-
valenol and/or nivalenol. Cattle appear to be much more resistant
than pigs to the hormonal effects of zearalenone, whereas chickens
do not seem to be affected. The most conspicuous changes in pigs
due to zearalenone are enlargement of the uterus and mammary
glands, and atrophy of the ovaries.
Feed refusal is apparently as a result of the unpalatability of the
feed and may be reflected in decreased weight gains and slower
growth rates. Vomiting may occur in animals that consume small
quantities of infected grain. Maize containing more than 5% of
infected kernels should not be included in rations for pigs, although
it may be diluted with sufficient quantities of first grade maize.
Control measures
Crop rotation
Rotation of maize with non-graminaceous crops generally decreases
the incidence of Graminearum ear rot. Recent studies have shown
that the pathogens have the ability to colonise and survive on alter-
nate crop organic matter left in or on the soil. It still is important to
avoid crop rotations between graminaceous crops.
Stubble removal
As the fungus overwinters on maize stubble retained on the soil sur-
face, the removal of maize residues will reduce disease incidence
in the following crop season. Increased breakdown of organic mat-
ter will also reduce survival of the causal organisms. It is important
to note that where maize is produced in conservation agriculture
(CA) cropping systems; the retention of stubble is required which
can increase the risk of maize ear rots. However, adhering to the CA
principle of crop rotation will decrease the risk and is thus recom-
mended as a standard practice.
Cultivar selection
Reports in the literature indicate that hybrids vary in susceptibility
to the disease. Local hybrids are currently being screened for resist-
ance to this disease at the ARC-GCI.
For further information, the authors can be contacted
on 018 299 6100.
Ear rots of maize:
A continuous threat to food safety and security
8: Gibberella ear rot.
8