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in control of Sclerotinia
I
n response to producers’ rising concern about the impact of
Sclerotinia diseases in grain fields, Grain SA and Bayer Crop-
Science joined hands to host three information days in differ-
ent production areas of the country to share more information
about this devastati g pa hogen.
An American view on Sclerotinia
At each of the events a keynote address was given by Dr Bill
Underwood, a plant pathologist from the Agricultural Research Ser-
vice of the United States Department of Agriculture (USDA-ARS)
who has been focussing on Sclerotinia and its effects on sunflower
in his research.
According to Underwood environmental conditions strongly in-
fluence disease development with little or no disease being ob-
served in some years. Disease inoculum can survive in the soil for
more than seven years and is difficult to eradicate once it has
established.
Fungicide applications are not very effective in controlling the dis-
ease and are affected by time of application as well as coverage.
Field trials done in the USA indicate that for most fungicide che-
mistries that exhibit efficacy against Sclerotinia, application at
R1 (initiation of flowering) is optimal. For most fungicides, adequate
coverage seems to be critical and it is important that the fungi-
cide must penetrate the canopy to cover the flowers. Reduced
ground speed, increased spray volume and pressure, and the use
of nozzles that produce fine to medium droplets can improve cover-
age and efficacy.
The core focus of the programme to which Underwood contributes
is to improve genetic resistance. ‘Be patient, we are working on it,’
Underwood encouraged producers. He mentioned that variation
for resistance exists within cultivated germplasm resources and in
crop wild relatives. ‘Resistance is however highly polygenic, hinder-
ing breeding efforts to incorporate resistance into agronomically
favourable varieties.’
A possible solution
No major resistance genes against the disease have been found
in hosts, only minor genes with quantitative resistance which only
provide varying degrees of tolerance in hosts. This is according to
Ms Nelia Rousseau (grower and channel marketing manager: Bayer)
who conveyed the news to attendees that a biological agent Con-
tans, which can be applied against the disease, has been developed
at Bayer. Contans (
Coniothyrium Minitans
) is a water dispersible
granule biological fungicide designed to control Sclerotinia sclero-
tiorum and Sclerotinia minor. Rousseau discussed the efficacy and
value proposition of the product amongst others.
Dr Chrisna Steyn (Department: Plant Sciences, University of the
Free State), a member of the newly established South African Scle-
rotinia Research Network (SASRN), confirmed that the university
is conducting cultivar evaluation to develop a model that will de-
termine the risk percentage of Sclerotinia development on crops.
However, with greenhouse and field trials not collaborating, the pro-
cess remains a challenge.
SASRN is a collective of local researchers working on Sclerotinia
and has been formed to prioritise production research, improve
collaboration amongst researchers and facilitate collaborative ef-
forts with international researchers. The network will be approach-
ing funding bodies and other stakeholders in an effort to increase
research outputs that will ultimately aid producers.
LOUISE KUNZ,
SA Graan/Grain
contributor
1: The Sclerotinia Information Day for the North West Province and Free State was held at
NAMPO Park near Bothaville on 22 September. Cobus van Coller (Grain SA Executive
member, on the far right) with the speakers: Dr Chrisna Steyn, Nelia Rousseau and keynote
speaker Dr Bill Underwood.
2: After the session, producers were given the opportunity to raise their concerns regarding the
disease to a panel of expertise, which included the three speakers and Dr Bradley Flett (right)
from the ARC-Grain Crops.
33
December 2017
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