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Februarie 2016
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ON FARM LEVEL
Integrated pest control
The symptomless nature of certain infections by these fungi results
in infected grain passing unnoticed. The major economic implication
of Fusarium ear rot is the ability of these fungi to form mycotoxins
in infected maize. The most important being fumonisins which are
toxic to chickens, pigs and horses.
Horses are extremely sensitive to fumonisin and a level above
5 parts per million (ppm) in their feed will result in a fatal disease
called
Leukoencephalomalacia
. Guidance levels for fumonisins in
pig and chicken feeds are set at maximum allowable (safe) levels of
10 ppm and 50 ppm, respectively.
Research has also implicated this mycotoxin in causing human
oesophageal cancer, which is common in certain regions of Africa,
Europe, China and the USA.
Life cycle and epidemiology
F. verticillioides
is a ubiquitous fungus which is widespread
throughout the South African maize production area. The fungus
survives on crop stubble in or on the soil surface. The ability to in-
fect endophytically and symptomlessly, gives this fungus a further
survival advantage over other fungi. This fungus may overwinter in
seed in the pedicel, endosperm and/or embryo.
F. verticillioides
is transmitted by seed, air and insects. Seed infec-
tion levels of up to 100% have been recorded. The fungus has been
shown to grow systemically from the roots to the stalk, and into the
ear. Airborne spores are carried great distances by wind currents
and the small size of the spores enables them to be spread widely.
Insect transmission is primarily due to the stalkborers, Chilo partel-
lus and Busseola fusca. Stalkborers feed on infected tissue, move
to new plants or plant parts and continue feeding, while leaving the
fungal spores in their frass.
Under favourable environmental conditions, the fungal spores ger-
minate on the plant surface and infect maize stalks or ears directly,
or through wounds caused by hail, insects or birds.
F. verticillioides
is favoured by dry, hot climatic conditions such
as those prevailing primarily in the North-Western parts of the
South African maize-producing areas. Climatic conditions play a ma-
jor role in the severity of both Fusarium ear rot as well as mycotoxin
production.
Control measures
Due to the common occurrence of these fungi in nature, the use of
sanitation practices have not been very successful in disease reduc-
tion. With the use of climatic modelling, Fusarium ear rot and fu-
monisin predictions can be made for areas with favourable climatic
conditions.
These models still require confirmation and further research be-
fore being used. Recent research results indicate that timely con-
trol of stalkborers using insecticides or Bt maize helps to reduce
F. verticillioides
ear rot infections and fumonisins. The literature in-
dicates that hybrids vary in their susceptibility to
F. verticillioides
infections and fumonisin production.
Local hybrids therefore need to be screened before hybrid selec-
tion will play a role in controlling Fusarium ear rot and fumonisin
contamination levels. Research on hybrid screening and breeding of
resistance to fumonisins is on-going at the ARC-GCI.
5a and 5b: Fusarium ear rot symptoms observed in associa-
tion with maize stalk borer feeding channels.
6: Pink kernel discolouration symptoms not related to
kernel damage.
Ear rots in maize production
6
5b
5a