10 August 2001


When it comes to weed control, across-the-board cost cutting can be risky. Andrew Blake asked three AICC members how they plan to economise safely this autumn


RESISTANCE is uppermost in Peter Taylors mind when deciding where he can trim herbicide inputs to autumn sowings.

"It may seem obvious, but you have to know what you are dealing with and the status of the weeds. We have a lot of resistant blackgrass round here, there is wild oat resistance not far away, and I suspect there may be more resistant ryegrass about than we think.

"If you know you have resistant weed populations you really cannot afford to cut anything very much."

Some farms in his Suffolk/Cambs area are still fortunate enough to be able to adopt relatively cheap IPU/trifluralin programmes for autumn weed control in cereals. "They can work well on blackgrass and annual meadow grass.

"Elsewhere, where we think we have susceptible blackgrass but know from experience that we need a bit more control we tend to use Hawk/IPU. On farms with a bit more of a challenge Hawk/Lexus works quite well. But on those with full-blown resistance we need Lexus/Stomp."

Depending on the choice, outlay can be anything from about £15/ha to £35/ha. "But in most cases we will have had to use a pre-emergence beforehand, either Avadex or maybe the new Crystal, formerly AC210."

One way to trim that initial expense is to substitute trifluralin or Prebane (terbutryn) as the pre-emergence spray. "But that always pre-supposes that you are going to be able to get on with the main treatment within six weeks," he warns.

Wherever possible stale seed-beds burnt off with low rates of glyphosate are worthwhile investments, Mr Taylor believes. "The risk is that the weeds dont always germinate in time if it stays dry."

Adjuvants have little to offer in cheapening autumn weed control, he believes. "But you definitely need an adjuvant with Lexus to boost its contact activity."

Likewise there is little scope for reducing doses in his area. "You cant afford to mess about when you have blackgrass. If the weeds are really small we might come down to a two-thirds rate with Hawk, but otherwise we are usually thinking about increasing rates."

In oilseed rape newcomer Aramo (tepraloxydim) could prove more economic than other graminicides, he believes. "Where high rates of Laser or others are used against difficult blackgrass, Aramo looks to be more cost-effective. But if you have resistance, Kerb is really the only option because of its alternative mode of action, and for the best results you need a reasonably full rate."

If broad-leaved weeds are a target then metazachlor-based products also offer an alternative mode of action against blackgrass, he adds.

AUTUMN weed control in the West Midlands is relatively straightforward and cheap, according to Shropshire-based Bryce Rham.

"We are very lucky and its purely a factor of where we are. For us, blackgrass is not an issue, although I do have one farm with fully resistant ryegrass."

Main targets in the area, where many farms have rotations with sugar beet and potatoes, are annual meadow grass, pansies, poppies and speedwells.

"You can make things awfully complicated if you are not careful," says Mr Rham. "In wheat we tend to look at 1000-1500g/ha of IPU with 20-30g of DFF early post-crop emergence if we have pansies." For late sown wheat after beet or potatoes the IPU can safely be dropped to 500g, he notes.

On light land where poppies threaten, 20g/ha of DFF with 400g/ha of pendimethalin (as in 1 litre/ha of Stomp) has proved a very successful and cheap alternative provided the weeds are small. "It costs about £11/ha. I might be tempted to cut the Stomp to 0.75litres, but thats getting greedy.

"I tend to use a bit more Stomp in winter barley because its kinder to the crop than to wheat."

His only other consideration may be to add a quarter dose of Quantum (tribenuron-methyl) to deal with groundsel which pendimethalin and DFF do not control. "Groundsel is becoming a bigger problem round here."

Cleavers, wild oats and ryegrass treatments can safely be left till the spring, he believes.

Resistant ryegrass was unexpectedly well controlled (95%) by Hawk (clodinafop-propargyl + trifluralin) this year. "But I suspect it is going get harder so I am looking a other options."

Avadex (tri-allate) is ruled out. "Its difficult to get decent seed-beds on that farm. So I am looking again at chlortoluron as soon as we can post-emergence, followed probably by Hawk plus IPU in the spring. If there is anything left in the worst patches I might use Monitor. I had a free trial this year and it gave 98-99% control. But as a sulfonylurea it is not a beet farm product. You need a three-year interval between applying it and growing beet."

Mr Rham has only one client with oilseed rape. "I tend to use pre-emergence trifluralin followed by a low dose of Butisan or Kerb depending on the particular weed problems."

Adjuvants do not figure in his autumn plans. "In general the good ones are quite expensive, and Id rather spend the money on extra active ingredient."

EARLY drilling almost inevitably means higher weed control bills. Thats the warning from North Yorks-based Patrick Stephenson.

Good meadow grass and broad-leaved weed control in October sown cereals can cost as little as £7/ha (£2.80/acre), he notes. "If you drill very early you could be looking at £16/ha for the same thing. Ideally, Id like to lock all my clients in a cupboard until at least the end of August."

Another worry this season is the build up of grass weeds after many sprays were delayed or missed altogether last autumn, he notes. "Although I am in a mixed farming area we do have some resistance in both blackgrass and ryegrass. There are some real messes out there this season."

Autumn cereal growers unaffected by resistance and determined to sow early will be urged to adopt the SAC low dose approach of DFF or pendimethalin mixes applied before the weeds chit. "We have used the equivalent of 1 litre/ha of Panther or 2.5 of pendimethalin for three seasons and find it works remarkably well. With extra-early drilling we are moving into new territory and changing quite a few things. "With sunlight levels still relatively high then the sulfonylurea Quantum comes into its own as a possible alternative against broad-leaved weeds," he explains. "At only £4-£5/acre it starts to look attractive.

"For later sowings never underestimate the flexibility of having trifluralin in the system," advises Mr Stephenson. "It increases weed sensitivity. In Ardent you have a formulated material with DFF to mix in with IPU for a very rounded product for non-blackgrass sites."

For resistant blackgrass the starting point has to be Avadex or the cheaper Prebane, he says. "There may also be scope with Crystal to substitute trifluralin for pendimethalin in the early post-em treatment as the partner for Lexus."

As elsewhere chlortoluron is re-emerging to tackle resistant ryegrass, he notes. "But we hope Crystal will give us another tool."

Where resistance is not a problem an early strike is the key. "Catch meadow grass before it tillers and you can be fairly confident that 1000g of IPU will do the job. Once it has tillered a flame-thrower is more appropriate."

Almost all of Mr Stephensons winter rape will receive trifluralin, preferably incorporated to minimise losses to the air, as the first weed attack. "Beyond that we look to Butisan or Katamaran, but again treating when the weeds are small is key to controlling costs." &#42



Cheaper with oats

"If you really want to cut your autumn herbicide bills, grow a vigorous crop like oats," says Bryce Rham.

"I dont spray them before the spring because they are so competitive and I am convinced that autumn herbicides cane them. Sibutol Secur seed dressing means we dont usually have to spray against BVDV, and bar slugs there is no need to go through the crop at all until then."

See more