How to keep maize weed-free in a late spring

The window for weed control in maize could be tight this spring, so growers and contractors will need to be on the ball with herbicide spray timings and product choice to avoid competitive weeds robbing yield.

After a dry February, unsettled weather was a constant through March and the first part of April, hindering seed-bed preparation and drilling of spring crops, including maize.

See also: Why grain maize is key break crop in arable farmer’s rotation

Covering an area used to unsettled weather, Andy Roberts, senior agronomist at CAS, is expecting flurries of activity as and when the weather allows drills to move and says demands on sprayers for herbicide applications are going to be high.

Advising across south Lancashire, north Cheshire and into north Wales, he thinks this could lead to eyes being taken off the weed control ball in some maize crops.

But because the weed competition that robs young maize plants of sunlight, water and nutrients has such a detrimental effect on yield, every effort should be made to keep crops clean.

“You have got to help plants to get ahead of the weeds from the start, because once plants get stunted from weed competition, they never recover,” he stresses.

Pre-emergence spray

Jon Myhill, national agronomist for the Maize Growers Association (MGA), says the biggest weed concerns are fast-growing and competitive weeds such as fat hen, black nightshade, orache, mayweed and Polygonum species.

There are also reports of groundsel becoming a much trickier weed in maize crops in parts of the country, along with grassweeds such as blackgrass and ryegrass.

The potential workload pressures lead Mr Myhill to recommend a pre-emergence spray, to control or sensitise broad-leaved weeds ahead of post-emergence applications, where sprayer capacity allows.

Man squatting beside a seed drill

Jon Myhill says the biggest concern is fast-growing and competitive weeds such as fat hen © Jon Myhill

There are two main options, including straight pendimethalin products such as Stomp Aqua at a rate of 3 litres/ha, or the pendimethalin + dimethenamid-P product Wing-P, which is more expensive but has a slightly wider control spectrum.

Growers can also utilise S-metalachlor-based products Dual Gold and Camix, with the latter also containing mesotrione.

“Straight pendimethalin is cost-effective, but we do see Wing-P doing a better and longer-lasting job,” he says. “With plenty of cereals and sugar beet still to drill, I’d recommend everyone try to get a pre-emergence spray on to buy some time.

“It should also allow flexibility on post-emergence dose or let you use less-complicated mixtures that won’t risk knocking the crop,” he explains.

With plenty of moisture in soils at present, pre-emergence applications should work well, but Mr Myhill says even if soils begin to dry, growers should not put off getting a holding spray on.

“Damp nights are enough to activate the residual actives and they should still provide good results,” he says.

Close-up of young maize crop with weeds

© Blackthorn Arable

Holding spray

Mr Roberts believes some businesses might find it tricky to apply a true pre-emergence across the board, which he typically applies with liquid fertiliser straight after drilling.

However, this year he sees more of his clients applying fertiliser only to the seed-bed and following up with an early post-emergence herbicide spray at the two-leaf stage of the crop.

This first spray will include pendimethalin and he will add in pyridate-based Diva to bolster control of the broad-leaved weed species common in his area.

“That will hold things back and I’ll then monitor for further weed emergence and tailor the true post-emergence spray to weed spectrum present.”

A mesotrione product will form the base of his post-emergence herbicide sprays, with a nicosulfuron product such Fornet 6 OD added to strengthen grassweed control.

Maister is another option to add to grassweed control, but results with all ALS-inhibitor-based herbicides will vary depending on resistance status of the blackgrass or ryegrass population, notes Certis Belchim technical manager James Cheesman.

Three-way mix

He explains that the company’s trials over several years have shown good post-emergence success against a wide range of weeds with a three-way mix of mesotrione, Fornet 6 OD and Diva.

The pyridate adds good control of tricky species such as fat hen, groundsel, black nightshade, chickweed, annual mercury, common amaranth and orache.

Mr Cheesman says it has also proven a useful weapon against cranesbill – both cut-leaved and to a lesser extent dove’s-foot – which are a problem in arable rotations where maize is being grown for anaerobic digestion.

He warns that growers should be mindful of crop and weed size when timing post-emergence herbicides, with the best results coming from a well-timed application to small, actively growing weeds.

“There is a shading effect if you leave applications too late, as the crop canopy is big by the six- to eight-leaf stage and can compromise coverage and leave weeds uncontrolled.”

Mr Roberts says his post-emergence application timing will often be combined with foliar nutrition, with product choice informed by tissue testing ahead of the spray to cover any specific deficiencies.

This is combined with a biostimulant such as phosphite and any herbicides between the four- and six-leaf stages of the crop.

“However, growers do need to be mindful of label restrictions of each individual product,” he notes

Most post-emergence herbicides, including Fornet 6 OD, cannot be used after the eight-leaf stage of the crop, while Diva cannot be used before 15 May.

Don’t scrimp

Input costs, including herbicides, have increased significantly since last spring, which does raise the prospect of growers cutting back on weed control programmes to trim spending. However, Mr Myhill warns that this is a risky strategy in any season.

“You don’t need 100% control, but a robust programme to suppress weeds to the six-leaf stage of the crop is crucial to avoid competition.

“Herbicides are more expensive, but as weeds can have such a detrimental impact on yield, it’s important not to scrimp.

“Nitrogen input is the area where people could potentially save money if they wish to economise,” he notes.

Weed control in maize 2023

  • Prevailing wet weather is condensing spring workloads
  • Contractors and sprayers will be in demand across all crops
  • Use a pre-emergence herbicide where possible to supress early flush
  • Base post-emergence sprays on mesotrione, nicosulfuron and pyridate
  • Consider other options to bolster grassweed control where there is a concern
  • Apply as early as possible to small, actively growing weeds
  • Beware crop shading effect when applying late

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