How to avoid blackgrass spread at harvest

Careful harvest planning and practising good hygiene will help contain blackgrass to contaminated fields and avoid its inadvertent spread between fields and farms.

As they gear up for harvest, growers should build a map of blackgrass patches and get them tested for herbicide resistance, according to Ben Giles, commercial technical manager at Bayer CropScience.

“It is useful to know what you are dealing with to help you plan ahead. Once you know where any resistant blackgrass lies you can avoid contamination by combining these fields after the cleaner crops,” he says.

Mr Giles warns growers not to go from a horrendously bad blackgrass field to a cleaner field without thoroughly cleaning all machinery first. The same goes for baling.

See also: Blackgrass trial reveals host of weed control solutions

Although pausing to clean the combine during a busy harvest won’t be top of most growers’ priority list, it is an effective way of ensuring blackgrass seed is not spread across land and farms.

Where to find blackgrass seed hiding in your harvest machinery

  • Feed house
  • Auger
  • Header
  • Sieves
  • Axle and chassis
  • Wheels and tyres
  • Body panel gaps and ledges

John Deere’s territory manager David Purdy says machinery hygiene is too often overlooked at harvest time and any blackgrass problems can intensify as a result.

“As all growers know, blackgrass is very prolific and is the most problematic weed in arable farming.

“One blackgrass seed is enough to contaminate a clean field; it will produce up to 200 seeds and spread fast,” he says.

Mr Purdy adds that growers who are particularly struggling to control their blackgrass should not underestimate how much the spread of the yield-restricting weed is worsened during harvest if steps are not taken to remove it from all machines.

Heavy seed sticks to machines

Mr Giles says that blackgrass is a heavy seed so, rather than being airborne, it is mainly transported by machinery that moves from field to field – or in the case of contractors’ kit – from farm to farm.

“If you are chopping straw through patches of blackgrass, do bear in mind that you are going to be spreading the seed over a wider area of the field as the combine moves through,” he says.

When cleaning a combine after harvesting a block of crop with blackgrass, John Deere’s combine sales specialist Scott Mackenzie recommends using an industrial air compressor to blast off any weed seeds lurking on machinery.

He acknowledges that the process is time consuming, and that this can put growers off, but says that the task should become quicker and easier the more regularly it is carried out.

“The combine is potentially a catalyst for blackgrass so the key thing to remember is your basic husbandry and good practice.

“You need to be blowing the machine off really well. Although it is a pain to do routinely, it will keep blackgrass from spreading,” he says.

Mr Mackenzie estimates that an effective combine clean using an air compressor will take up to an hour and a half.

Keep blackgrass problems at bay

John Martin

John Martin ©Tim Scrivener

Dorset grower and recently crowned Farm Sprayer Operator of the Year John Martin says that even though he doesn’t have much of a blackgrass problem at present, he still takes precautions at harvest.

“We are entirely arable here so if we get blackgrass it is going to be a real problem and every farm around us already has it,” he says

For a relatively blackgrass-free farm like Mr Martin’s, the biggest risk is weed seeds being carried on site by contractors that may not have properly cleaned their machinery.

A few years ago he decided not to sell straw anymore because the risk of any blackgrass seed harboured in the baler and being spread in his fields was too high.

“Any machine that comes on to the farm must be clean and we have a zero-tolerance approach.

“At harvest, we use a leaf blower to clean the combine off before we go home every evening even though we don’t have much of a problem at the moment,” he says.

Throughout the year any individual blackgrass plants on Mr Martin’s 320ha farm are pulled out and small patches are sprayed with glyphosate, mapped on GPS and monitored from year to year to avoid the weed becoming established.

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