Crop Watch: Monitor oilseed rape crops for slug activity

Oilseed rape drilling was well under way this week and crops should be closely monitored for slug activity, our Crop Watch agronomists warned.

Monitoring for slug activity was a priority in rape crops, particularly those established by sub-soiling, said Lincolnshire-based Farmacy agronomist Philip Vickers.

“Early intervention is essential because damage to young plants will reduce plant populations and potentially crop yield.”

Due to concerns over metaldehyde getting into watercourses, best practice advice was not to exceed a maximum total dose of metaldehyde of 160g/ha between 1 August and 31 December. Using 1.5% pellets could help achieve this goal, he said, but he was also recommending growers used alternative effective products, such as ferric phosphate, especially on headlands near watercourses.

“It’s important to remember that metaldehyde has a six-metre no spread zone near a watercourse,” he explained.

Rape crops established by sub-soiling would be treated for broadleaved weeds at the expanded cotyledon stage, he said.

“We must also bear in mind the metazachlor limit, which is up to 1000g/ha of active ingredient applied one year in three.”

In Yorkshire, Arable Alliance agronomist David Martindale said this year a higher proportion of land was being established by a subsoiler seeder unit as confidence was “growing year on year with this technique”.

Seed-beds so far had been ideal for rape drilling, he said. “Pre-emergence herbicides have been applied to moist surfaces and with good seed-beds they should work well.”

Countrywide Farmers agronomist Neil Donkin from Gloucestershire said there were concerns about drilling rape following an application of sulfonylurea or DFF herbicides in the previous crop.

“Agrochemical manufacturers advise cultivations and thorough soil mixing to 15cm before rape is drilled, but many crops are sown without that,” he said.

“Usually we get away with it, but it has been an extremely dry year and residues are likely to be higher than usual.”

However, he said recent rain should give ideal conditions for applying pre-emergence herbicides in rape.

“Check that the seed is adequately covered by soil (15mm depth) before spraying,” he said.

“However, be wary of spraying if heavy rain is forecast as chemical washed down around the seed can effect germination.”

Hampshire/West Sussex AICC agronomist Tod Hunnisett said he expected rape crops to be up and away quickly due to the combination of moist seed-beds and some warmer weather.

“Before drilling starts in earnest I’m hoping to get a decent chit of grass weeds sprayed off with glyphosate,” he added.

Mr Martindale said Group 4 winter wheat feed variety Oakley was featuring prominently again in cropping plans this year after it performed well last season.

But he added: “With Oakley being so susceptible to yellow rust it is important to sow an area that can easily be covered by the sprayer to apply fungicides.”