Potato Review

www.potatoreview.com POTATO REVIEW MAY/JUNE 2021 45 WEED CONTROL Pre-emergence weed control achieved depending on product or programme Average weeds (per m 2 ) Stomp Aqua (2 L/ha) Defy (3 L/ha) Sencorex Flow (0.58 L/ha) 350g active/ha = Artist rate) Gamit (0.15 L/ha) Praxim (2.5 L/ha) Artist (2 kg/ha) Emerger (1.75 L/ha) Emerger (1.75 L/ha) + Gamit (0.15 L/ha) Emerger (1.75 L/ha) + Defy (3 L/ha) Emerger (1.75 L/ha) + Praxim (2.5 L/ha) Emerger (1.75 L/ha) + Stomp Aqua (2 L/ha) Emerger (1.75 L/ha) + Artist (2 kg/ha) Weed Species Spring Barley (2) 1 6 0 0 100 0 100 100 100 Programme performance 100 100 100 100 100 Cleavers 4 9 0 0 0 1 0 10 60 40 95 100 60 65 90 Redshank (2) 2 4 25 0 20 1 0 0 60 85 95 70 100 95 100 Black- Bindweed 5 20 2 0 50 0 0 50 90 90 100 100 100 100 Fat Hen 1 1 20 0 70 0 5 70 70 70 100 95 90 95 Cranesbill (2) 8 1 45 1 2 43 7 5 60 3 0 10 10 10 50 Poppy (2) 1 7 95 3 0 75 3 5 49 95 95 90 95 95 100 100 Chickweed 1 1 9 90 5 0 60 9 5 95 80 100 100 100 100 100 100 Creeping Thistle 3 0 10 0 70 0 5 80 80 90 90 90 90 98 Sow Thistle 3 4 20 0 40 3 0 20 50 20 70 80 95 20 95 Charlock (2) 2 8 10 5 63 5 55 84 83 90 80 90 70 90 Common F- Speedwell 7 0 100 8 5 100 8 0 0 100 90 80 90 98 95 100 Source: Bayer, Hinxton, Cambs, 2020. NB. Trial conducted in dry conditions. Typical on-farm herbicide costs (£/ha): 2017 v 2020 2017 2020 Artist (2.5 kg/ha) 45 56.00 Gamit (0.15 L/ha) 14 9.25 Defy (4 L/ha) 24 22.60 Shotput (0.75 kg/ha) 14 19.01 Shark (0.33 L/ha) 15 13.60 Gozai (0.4 L/ha) (inc. oil) 15.78 Praxim (3 L/ha) 60 55.20 Emerger (1.75 L/ha) n/a 24.50 Titus (50g/ha) 26.04 Linuron (1.2 L/ha) 9 n/a Example programmes Shotput (0.75 kg/ha) + Shark (0.33 L/ha) 28 32.61 Shotput (0.75 kg/ha) + Shark (0.33 L/ha) + Gamit (0.15 L/ha) 43 41.86 Shotput (0.75 kg/ha) + Shark (0.33 L/ha) + Gamit (0.15 L/ha) + Praxim (3 L/ha) 103 97.06 Artist (2.5 kg/ha) + Emerger (1.75 L/ha) n/a 80.50 Artist (2.5 kg/ha) + Shark (0.33 L/ha) + Praxim (3 L/ha) 120 124.80 Source: industry sources such as Gozai or Shark, are limited to no more than 10% crop emerged. Any later and growth will be seriously checked,” said Eric. Which alternative herbicide? One consequence of this was to increase the pressure on the residual component of the programme. Concerns over the future of metribuzin in a programme are therefore not too far removed from the questions posed at the start of last season: Which of the alternative herbicide choices can be expected to give the greatest control? There is no suggestion that the focus of control should move away from residuals, rather the concern centres on how to construct a suitable programme. The answer is far more straight-forward than many might realise. “The central issue is one of weed spectrum to be controlled. Failure to understand the weeds present in the field will result in higher costs in the long-term,” says Mr Anderson. “On skirt or fenland soils where the variety is approved for metribuzin then it’s a no-brainer; metribuzin has the widest label covering annual-meadow grass and many broadleaved weeds. Adding Emerger will bolster control of chickweed and black-bindweed,” says Mr Anderson. Soil moisture status is another consideration. Emerger (aclonifen) is less affected by dry soils than Defy (prosulfocarb), “Care needs to be given to what products are used if unnecessary expense or false economies are to be avoided.” this may influence application timing. “Defy needs to go on later, typically as late as you dare and often as a standalone application. This has obvious cost implications and weed control in potatoes in now twice as expensive as it was two years ago,” Eric said. For some, there is still the suggestion that Praxim (metobromuron) has a place in the programme. Compared with Emerger, it has a smaller weed spectrum – just eight susceptible and one moderately susceptible weeds at the lower rate of 3 l/ha – and is more than twice the per hectare cost in 2020 (see table). “Emerger has the wider weed spectrum and is more cost effective with better activity against fat-hen, black-bindweed and common field-speedwell, but both will require the addition of Defy (prosulfocarb) to bolster control of cleavers,” he adds. After weed spectrum, soil texture and seedbed conditions are the considerations likely to influence programmes. “Cloddy seedbeds always impair the performance of residuals, but angled nozzles will help to improve coverage. A three-way mix of metribuzin + Emerger + Defy would be the basis of a pre-em spray in such situations,” he adds. Broadleaved weeds aside, annual meadow- grass can be a challenge and in such situations Artist ( flufenacet + metribuzin) will give the best control while Defy also has some control though is less effective in dry conditions. “Once annual meadow-grass passes two true leaves neither Gozai nor Shark will touch it. In cases where AMG presents a strong challenge then I would advocate Artist. This would also give good control of cleavers,” Eric said. Black bindweed