Crop Watch: Act now on grassweeds

Stale seed-beds and grassweed control in oilseed rape and wheat are top of this week’s agenda for our Crop Watch agronomists.

In Lincolnshire, post-emergence oilseed rape herbicides needed to be applied as soon as possible after cotyledons fully expanded, said Farmacy agronomist Philip Vickers. “Metazachor with dimethenamid-p or quinmerac are suitable products depending on the weed spectrum.”

Blackgrass levels in early-drilled oilseed rape crops were starting to cause concern, and treatments were needed soon to ensure plants were not too large for following propyzamide applications, he added.

Soil tests he carried out this summer showed bad blackgrass patches tended to have low pH, poor soil structure or poor drainage. “Soil condition can often be overlooked with the flurry of activity at this time of year, but it’s time to dust off the spade, look at the soil profile and get some samples analysed.”

In Wiltshire, oilseed rape crops had received an insecticide seed dressing for flea-beetle control, said Dan Dines from Wessex Agronomy Services. “So far this has protected crops, but monitoring is required as activity starts to drop over time.”

Turnip sawfly larvae had been found in some turnip crops, so growers needed to watch for the pest in oilseed rape, he warned.

His recommendations for pre-emergence herbicide applications in wheat would be based around flufenacet and pendimethalin or diflufenican tank mixes. “There will also be more Avadex (tri-allate) used this year, which offers an alternative chemical group in the continued battle against resistance.”

Yorkshire agronomist David Martindale from Arable Alliance said wheat drilling would kick-off in earnest this week. “But, with most oilseed rape drilled in good time, more growers than usual started drilling wheat in the first few days of September.”

Oakley, Duxford, Grafton, Viscount and JB Diego were the most popular varieties, he added.

A flush of volunteer cereals had emerged in min-tilled crops which would need to be controlled with a graminicide. “Blackgrass, ryegrass and brome are also emerging thick and fast, which will affect herbicide choices.”

Most oilseed rape in Hampshire had been drilled and sprayed pre-emergence with Oryx (metazachlor + quinmerac) plus adjuvant Grounded, said Agrovista agronomist Swaran Bachoo.

“Where cleavers are expected to be a problem Cirrus (Clomazone) has been added at a low rate. Any rape crop not sprayed can still be sprayed post-emergence once most of the plants have emerged, but ensure heavy rain is not imminent since metazachlor-based products can affect germination of rape if it comes into contact – clomazone should not be sprayed post-emergence.”

In Scotland a large proportion of potato crops had already been desiccated, but some regrowth had been seen, particularly where the bottom of the stem and leaf was not completely killed or removed, said SAC’s Mike Inglis.

Recent rain had softened up ridges that were previously hard and dry, which would make harvest more straightforward, he said. “Hopefully, we won’t get too much more as it could cause problems in-store. “Monitoring of crop quality and issues at harvest will be crucial this year to ensure any difficult areas are highlighted and tackled early.”

Click below to read the full reports:

Crop Watch north: David Martindale
Crop Watch south: Swaran Bachoo
Crop Watch east: Philip Vickers
Crop Watch west: Dan Dines
Spud Special: Mike Inglis, Perthshire

See more