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The suggested norm is to avoid planting sunflowers on infested
lands for a period of five to eight years. Under local production
conditions this may entail planting maize under monoculture for at
least five seasons.
Rotation will reduce stem rot more significantly than head rot.
Head rot can still develop from windborne spores blown in from
surrounding areas. Deep burial of sclerotia prevents them from
producing apothecia. One must however avoid bringing these buried
sclerotia to the surface in following seasons as they can then result in
the disease developing again.
Resistance to stem and head rot does occur. Sunflower hybrids
may be resistant to head rot and not stem rot and
vice versa
. No
sunflower hybrid is resistant and resistance is influenced by weather
conditions.
Local sunflower hybrids need to be screened and the mechanisms
of resistance need to be determined for significant progress to be
made for use in local management systems. Application of Benomyl
as a seed treatment is currently the only registered fungicide on
sunflowers in South Africa.
Researchers at the ARC-GCI in collaboration with the University of
the Free State are presently involved in the evaluation of various
biological control products and modelling of disease epidemics to
optimise fungicide sprays for use in South Africa. Control of broadleaf
weeds and volunteer sunflowers reduces possible inoculum increase
by reducing possible alternate hosts of Sclerotinia. Avoid planting
sunflowers next to infested fields that could be a source of spores.
Plant clean sunflower seed as infected seed may be a primary source
of inoculum in uninfected fields.
Why is it crucial to prevent the disease?
Reports from the Crop Estimates Committee and the ARC-GCI
survey shows that epidemics fluctuate yearly due to changes in
environmental climatic conditions. This indicates that in a dry
season the epidemics could be very low whereas in wet seasons
when conditions are favourable, epidemics can be devastating.
This disease is capable of wiping out the entire sunflower planting
on an individual producer’s fields causing total sunflower loss in one
season. The disease was so severe in the Lichtenburg area during
the 2013/2014 season that some producers had to spray chemicals
to dry their crops and stop the infection from progressing to the
rest of the sunflower head.
This was done so that they could harvest earlier. Others opted to
plough their crops down. The potential economic impact caused
by this disease is so severe that it could lead to producers
abandoning the crop thereby reducing the total area planted. This
will result in increased imports and sunflower prices and a risky
maize rotation crop.
For more information, contact Moses Ramusi at
ramusim@arc.agric.za.
Sclerotinia disease of sunflower:
A devastating pathogen
ON FARM LEVEL
Integrated pest control