The risk of Sclerotinia in oilseed rape is strongly linked to weather conditions around early flowering as well as crop rotation. Clare Bend, Technical Manager for Masstock, outlines important practical advice about this damaging disease and its effective control.
"High temperatures and humidity in the early spring will stimulate germination of sclerotia which may produce apothecia at the end of April or early May. Low soil moisture inhibits germination, but too much moisture may wash the spores directly from the fruiting bodies into the soil and so prevent infection. High temperatures and changeable humidity are ideal for the spread of disease. Rainfall is needed to stick the petals to stems which then act as a substrate for the spores to enter the stem," explains Ms Bend.
In Masstock trials on Sclerotinia, it was clear that fungicide dose rates should not be reduced. "If you are going to travel through the crop at yellow bud to full flowering, some damage to the crop is likely to occur. In order to offset that, dose rates should be maintained so that yield response is maximised. In our trials the products tested (Filan, Priori Xtra, Amistar and Proline) gave a margin over fungicide cost of £30 to £40/ha when used at full rates. Where rates were reduced by 20%, the margin over cost was cut to a maximum of £20/ha, with three out of the four products at reduced rates actually giving the farmer a net cost, rather than a net gain. So my advice is if you are going to do it, do it properly," advises Clare.
Diane Heath, Oilseed Rape Product Manager for BASF agrees. "When it comes to Sclerotinia, growers should not compromise on either the fungicide or the dose rate used." MORE……………
"When Filan was launched, it greatly surpassed the then existing fungicides. Recent trials show that Filan is also much stronger on Sclerotinia than azoxystrobin. A Filan treatment reduced Sclerotinia infection from 71% on the untreated to less than 2% and boosted yield from 2.9 t/ha in the untreated to 5.1 t/ha, an extra 2.2 t/ha. Azoxystrobin left 19% disease infection and produced a yield of only 4.5 t/ha. Filan produced an extra 0.6 t/ha compared to azoxystrobin," explains Diane.
"Having chosen the right product, it is equally important to use an appropriate dose. In six trials, Filan applied at 0.5 kg/ha gave 0.6 t/ha extra yield when compared with the untreated. This was a margin over treatment cost of £58.50/ha. When the dose rate was reduced to 0.4 kg/ha, the yield increase over the untreated was 0.47 t/ha but the margin over cost was reduced to £45.40/ha. The 0.5 kg/ha recommended dose rate should be used where there is a high risk of Sclerotinia, where persistence is required for Alternaria control and to give the best greening effects," says Ms Heath.
When choosing a fungicide for Sclerotinia, Clare Bend looks for a product that has good activity on the target disease, is easily tank-mixed with pyrethroids and has an ability to lift yield in absence of disease. "Filan is probably still the best product in a high risk Sclerotinia situation and good greening and yield benefits are seen from its use."
