Spring herbicides feel blackgrass pressure

Multiple flushes and high populations of blackgrass have put autumn herbicides under excessive pressure and there is now too much surviving blackgrass in many winter wheat crops.


That is the view of Hutchinsons’ technical manager Dick Neale, who warns growers not to expect too much from spring applications and to consider their options carefully.


A large proportion of planned residuals were applied to wheat in the autumn with many fields receiving stacked residuals, although some later drilled crops and those following roots have not had anything applied yet, he says.


These crops still have the option of half-rate Liberator (0.3 litres/ha) up until the end of March plus pendimethalin or prosulfacarb if they are applied within the label growth stage.


“Residuals have performed well, but they are not coping with the blackgrass populations from September and early October drillings.”


With at least 93% control needed just to stand still with resistant blackgrass, residuals should not be exposed to populations more than 100 plants/sq m, yet growers are still presenting 400-500, he explains.


Spring strategy


This means many fields will enter the spring with high populations of blackgrass and the decision whether and how to treat is one that growers need to evaluate carefully field by field, looking not only at the current situation, but back to previous control strategies.


About 25% of winter wheat has already been sprayed with Atlantis, because blackgrass emerged rapidly in early drillings, forcing agronomists to go in with a contact product. The results have been variable, he reports.


Atlantis is adding only 2-3% control on top of stacked residuals within Hutchinsons’ trials at Brampton. This isn’t reflected across the board, but is on an increasing number of farms with many growers now only achieving 30-40% from their Atlantis applications.


“Atlantis has gone on much longer than we dared hope it would, but it is reaching the point of serious decline.”



Getting the most out of Atlantis



  • Medium-fine spray quality
  • Apply to a dry and drying leaf
  • Apply at least two hours – ideally three – clear of rainfall or dew coming down
  • Avoid using air induction nozzles
  • Hawk or Defy nozzles are a good choice
  • Use a maximum forward speed of 12kph
  • Ideally soil temperatures greater than 5C for four to five days, then hit after seven days



Actives



  • Liberator – flufenacet + diflufenican
  • Unite – pyroxsulam + flupyrsulfuron
  • Defy – prosulfocarb
  • Atlantis – Mesosulfuron + iodosulfuron
  • Othello – Mesosulfuron + iodosulfuron + diflufenican
  • Kerb – propyzamide
  • AstroKerb – propyzamide + aminopyralid
  • Spitfire – fluroxypyr + florasulam
  • Eagle – amidosulfuron
  • Carbetamex – carbetamide
  • Galera – clopyralid + picloram
  • Centurion Max – clethodim

Economics


For this reason, Mr Neale is urging growers to look at what control they are realistically going to get this spring and assess whether any additional spending will be cost effective and reduce seed return enough.


Most growers are recycling blackgrass populations within the top 15cm of the soil, so they have to look back and see what products have done well in the past three years and those that have failed. If Atlantis has consistently disappointed then growers cannot expect too much if planning to put it or any other ALS herbicides on again, he explains.


But where do growers draw the line? The major yield depression comes from a fairly low population pressure with just 12 plants/sq m causing a 5% yield loss in the crop, explains Mr Neale.


“If established in September, 12 plants can deliver 180 heads/sq m while 12 November establishing plants may only produce 96 heads and that’s 10,000 seeds/sq m difference in potential seed return.”


Yield loss is not proportional to blackgrass population, so even if growers are able to reduce numbers down to 50 plants/sq m, they may not be significantly addressing the yield impact and certainly not the seed return.


Growers have to calculate if they can live with significant yield reductions and can pull back other inputs and still make a profit. “There is no point soldiering on to see what happens.”


Instead, Mr Neale would prefer to see growers planning long term how they can reduce their blackgrass burden in subsequent crops using stale seed-beds, later drilling and spring cropping thus reducing the burden on residual chemistry where the bulk of control needs to come from in future.


Sprayed off


For independent agronomist Sean Sparling, the picture is similar across his Lincolnshire farms. He agrees that growers need to draw the line somewhere and on farms that have already had multiple residual applications and a history of Atlantis 
failing, these crops will be sprayed off.


“You have to judge on an individual field and field history. The thing you should never do is keep ploughing ahead. It is false economy if you have a problem ending up with 200 or 400 heads/sq m.”


But where populations are reasonable and there isn’t target site resistance to Atlantis, Mr Sparling believes there is an argument for persevering with that crop, glyphosating off the worst areas in the field and treating the rest.


In these cases, where blackgrass is the main target Mr Sparling would choose Atlantis plus Defy, leaving Unite for situations with brome or mixed grassweeds.


But Mr Sparling urges growers to make sure that conditions are suitable for applying Atlantis (see above) emphasising that the more variables you get right the better the chance of control.



Oilseed rape


Opportunities for grassweed control in oilseed rape are all but over with the end of February cut-off for Carbetamex just under three weeks away.

Residuals have performed well this autumn with Kerb working slowly despite having been applied in good conditions on shallow rooted blackgrass, says independent agronomist Sean Sparling.

Centurion Max has worked very well on some farms and although there is still the opportunity to apply in the spring before stem elongation, applying on bigger blackgrass will put the product under too much pressure in terms of resistance.

“Clethodim will run out in two to three years because it is a dim.”

For Hutchinsons’ Dick Neale broad-leaved weed control will be centred on Galera for poppy, mayweed, thistles and groundsel and bifenox for charlock control if required.

But for those growers who had a weed spectrum suited to AstroKerb, a follow up with a contact herbicide will not be necessary given the increased poppy and mayweed control from the product this season. “Speed of control has been phenomenal.”

However, there will still be a number of broad-leaved weeds that growers will not be able to do anything about, such as hedge mustard and shepherds purse, he says.


Broad-leaved weeds


Broad-leaved weed control will almost certainly have been addressed where multiple stacked residuals and Atlantis have been used. Where growers are not focussing on blackgrass there are myriad things to choose from including Spitfire, spring sulfonylureas and Eagle.


“These should be the least of your worries,” he says.


On lighter land annual meadow grass is becoming more difficult to control at the traditional timings because we are running out of product choices, especially contact herbicides, reports Mr Neale.


“We still have Othello, which is very good, but we have to think long and hard about its use. If growers fall into the trap of overdoing Othello, resistance will develop.”


Read more: Early weed control key to spring cropping success