Spray timing is critical in protecting oilseed rape crops from yield-sapping sclerotinia infections and a monitoring tool being restarted in the coming days will help growers make timely applications.
The Adas/BASF sclerotinia monitoring service, which kicks off later this month, enables growers to assess the disease risk in their area and then decide when to treat.
The sclerotinia fungus has an overwinter phase as resting bodies (sclerotia) in soil. The sclerotia germinate in spring and release air-borne spores once soil temperatures hit 10C.
These airborne spores latch on to rapeseed plants, which are at greatest infection risk from mid-flowering onwards, when petals begin to senesce and fall.
Therefore, risk is highest when sclerotial germination coincides with early flowering.
“The petals are the biggest source of sclerotinia infection, because if they are carrying spores when they fall and become stuck to wet leaves, the fungus uses the dead petal as a food source.
The infection then spreads from the leaf to the stem,” explains Adas research scientist Caroline Young.
Pale brown or white lesions on stems will show about two weeks after infection and gradually increase in size, choking off plant growth if lesions are on the main plant stem.
Dr Young says the disease is tricky to predict because high inoculum levels don’t necessarily translate into high infection rates, and local conditions can vary greatly.
“It can be pretty localised and it must be humid and warm for disease infection.
Monitor the crop when flowering starts and, in the absence of any information about spore levels in the crop, it’s best spray at early to mid-flower to protect the crop before main petal fall.”
The Adas/BASF sclerotinia monitoring service sees information pooled from sites across the country to indicate risk locally. Growers can enter their postcode and use the colour-coded UK map to gauge whether it is time to spray.
Weekly sclerotial germination assessments are made over a 12-week period, with each site supported by petal tests at first flower, early flower and mid-flower to establish disease pressure from airborne spores.
To use the online tool visit the Basf website.
The AHDB also offers a sclerotinia risk report based on data from 16 monitoring sites across the country, which can be found by searching “AHDB sclerontinia risk report” on the AHDB Cereals and Oilseeds website.
This is a three year project, now in it’s second year, looking at whether more detailed more detailed monitoring of inoculum levels and infection conditions can help growers hit the first fungicide spray more accurately.