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April 2015
Control measures
Stubble reduction
Control measures include reducing surface stubble by means of
grazing, baling or ploughing-in of surface maize stubble on fields
where high Diplodia levels have been identified. Since the
S. maydis
survives on maize stubble and survives poorly in soil, any manage-
ment practice that reduces levels of infected surface stubble will
reduce inoculum concentrations in the field.
The removal of stubble for a single season and then resorting back
to stubble retention practices only reduces diplodia ear rot for that
specific season. Where stubble is present the following season,
the risk of Diplodia ear rot will increase to its original level, should
weather conditions be favourable for it.
Crop rotation
Crop rotations reduce Diplodia ear rots by reducing inoculum levels
in two ways. Firstly, a non-host for the fungus will not allow the fun-
gus to persist for the season where maize is not grown. Secondly,
a greater period (a season or two) between maize cropping allows
for a natural breakdown of maize stubble, which again reduces the
survival of the fungus. Leguminous crops such as soybeans, dry-
beans, groundnuts and cowpeas are very good rotational crops.
Other rotational crops that reduce Diplodia ear rots are wheat and
oats. Sunflowers do not significantly reduce Diplodia ear rots under
experimental conditions, but the reason thereof has not yet been
determined.
Early harvesting
Early harvesting will reduce Diplodia ear rots as it reduces time
available for the fungus to grow on the ear. The fungus (
Stenocar-
pella maydis
) can grow on maize ears in the field until an 11% grain
moisture content is reached.
Late or winter rains keep ears wet and increase the chance for
fungal growth. In certain cases it would pay to harvest early at
higher moisture levels and artificially dry grain. This possibly ex-
plains why Diplodia ear rot is not a major problem in the USA where
maize is harvested early and dried artificially.
Hybrid resistance
Selection of hybrids is very important in the control of Diplodia ear
rots. However, it appears that there is widespread confusion regard-
ing the resistance and use of resistance. None of the hybrids on the
market are resistant to Diplodia ear rot at all, however, some get
more ear rots than others under specific climatic conditions. This
reaction is affected by different climatic conditions which is impor-
tant to consider when selecting resistant hybrids.
1: Diplodia ear rot in a white maize ear.
2: Diplodia ear rot in a yellow maize ear.
3: Diplodia ear rot starting at the ear base.
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