TWO NEW products, Amistar and Proline, join Filan this year as effective sclerotinia fungicides.

That provides plenty of contenders for the flowering spray, but raises questions about likely returns.

Knowing whether the response to the latest products will outweigh the spray cost is not always straightforward, admits Masstock”s Clare Bend.

“With rape at 130/t, the 0.4t/ha yield benefit predicted from these fungicides represents a 2:1 return on investment.”

But sclerotinia risk must be monitored crop by crop and sprays targeted appropriately.

“They need to be used preventatively,” she says. “That means the flower petals have to be coated before they fall, so that if they do get wet and stick to the stems, there is protection against infection.”

There are sclerotinia forecasting systems, but Ms Bend believes it is too soon to comment on the risk this year.

“A number of factors need to come together. “Germination of sclerotia has begun and will increase with recent rain and warmer weather, but that is only part of the story.”

Wet weather at petal fall and field history are other key drivers. “Keep monitoring for another month.”

Typical yield boosts from Proline and Amistar are 0.4t/ha (3cwt/acre), making them similar to Filan in performance, though they vary in their strengths on other diseases.

“For all these fungicides, the response can be as much as 0.7t/ha in a high risk crop,” says Ms Bend.

If disease fails to materialise the treatments, costing 20-30/ha (8-12/acre), can seem expensive.

“A 0.2t/ha yield response – which is more likely in the absence of infection – is worth around 26/ha at current prices.”

Despite those reduced returns, using older, cheaper chemistry instead is inadvisable, she believes.

“If you are going through the crop, with the risk of wheeling damage, it is worth doing the job properly. There is no doubt the new fungicides are more effective.”

But data on them are limited. “We saw good greening effects with Filan last year, and very consistent results. It will be interesting to see whether we get a strobilurin greening” effect with Amistar and whether Proline lives up to Bayer”s promise to improve seed retention in the event of harvesting delays.”

Where light leaf spot remains a concern, Proline is the more obvious choice. “Neither Amistar nor Filan are very good on light leaf spot. But you can tank-mix with Charisma to boost their light leaf spot and alternaria activity.”

Applications at early-mid flowering often try to target alternaria as well, so good doses must be used, she advises. “Alternaria comes in at the end of the season, so you need persistence.”

For Filan, that means 0.5kg/ha, with Amistar it is 0.8 litres/ha (in a tank-mix) and Proline should be applied at a minimum of 0.5 litres/ha.

Spraying before early-mid flowering is an Amistar option, but only where crops are at low risk. “Syngenta has hinted at some timing flexibility by being able to go at yellow bud. But alternaria control may suffer if you do this.”

Lincs-based independent agronomist Bridget Carroll is unconvinced by the economics of flowering sprays. “They very rarely give a response much above their cost and nearly all are expensive products.”

Sclerotinia is largely a historical problem, unlikely to strike where it has not been a problem before, she adds. Crops should have been assessed post-flowering last year for the telltale “rat dropping” signs in the lower stems.

“Oilseed rape can look as though it has been badly affected, but yield losses aren”t high because the crop is such a good compensator.”

It will be vital to keep costs low if a margin is to be made at 130/t, she stresses. “If you haven”t encountered the disease before, spraying could be a waste of money. Check the risk warnings for your area before making a decision.”

Older products like Compass, Rovral and Ronilan are also worth considering, she suggests. “And carbendazim treatment is much cheaper, at around 4-5/ha. It may give you the insurance you need.”

fwcropsfwi@rbi.co.uk