The right weeds at the right time

Identifying the priority weeds for each field and hitting them early is vital for effective control, according to experts.

“Unlike cereals there aren’t many options for spring weed control in oilseed rape, so if you don’t control them in the autumn your options are very limited,” says ProCam’s David Ellerton.

“You need to know the field and the likely problems and tailor what you do accordingly.”

Cleavers and poppy are among the most competitive weeds, while mayweed, charlock and chickweed can cause problems if they get established early in the autumn, he says.

Populations of cranesbill have also increased in recent years, largely because many herbicides do not give effective control of the weed.

But before going down the pre-emergence route remember their effectiveness is reduced in dry seed-beds, warns Hutchinson agronomist, Ben Atkinson.

“I personally prefer to go very early post-em, which fits well with putting flea beetle sprays on as well.”

Pre-emergence products such as Treflan can also break down quickly in bright sunlight, he notes.

Targeting grassweeds

Weed resistance and tolerance concerns mean growers looking to control grassweeds should not rely on fop and dim chemistry, Dr Ellerton says.

Kerb or Carbetamex are his preferred choice but waiting for the right conditions is vital.

“You have to wait until it’s cool and moist enough, which can be into November or December.”

Silicon wetting agents, such as Silwet, can improve the efficacy of Kerb, Mr Atkinson adds.

Prior to Kerb it could be worth using trifluralin or a graminicide to take out volunteers and small grassweeds, Dr Ellerton says.

“A sequence means you’re not relying on the fops and dims against bigger weeds although you could be exposed to a range of broadleaved weeds, such as cleavers, mayweeds and sow-thistle.”

If conditions are good, Treflan can give useful activity against blackgrass and broadleaved weeds, notes Mr Atkinson.

Targeting broadleaved weeds

Springbok is new for broadleaved weed control this season, Dr Ellerton notes.

“It is a very specific product, likely to be similar in price to Novall and Katamaran.

If you’ve got more poppy, cranesbill or shepherd’s purse, the dimethenamid provides a boost over basic Butisan and possibly gives extra control of charlock and sow thistle.”

The cost of Springbok means it should be targeted at serious cranesbill or shepherd’s purse problems, or even aimed specifically at bad patches in fields, Mr Atkinson says.

Where cleavers are the main target, Katamaran or Centium work well, but are limited to pre-emergence use, he says.

“Alternatively, Galera gives good suppression of cranesbill and cleavers, particularly in the spring.”

A potential alternative to Springbok is Makhteshim-Agan’s Fox, which gained off-label approval for use as a post-emergence in oilseed rape last year.

“It can be good against cranesbill and charlock although results were a bit hit and miss this year, possibly because the cranesbill had grown a lot.

There are also some issues around its effect on the crop.”

Newly available pre-emergence product Jouster is also good against poppy and cranesbill, Dr Ellerton says.

“It is a cheaper product and is probably best used in tank-mix with trifluralin or clomazone.”

Napropamide, which is not a new active, is also available as AC650.