From lost chemistry to the weather, potato growers face new challenges every season. In this series, Farmers Guardian follows four agronomists from Hutchinsons and Farmacy to see how crop management is changing around the UK.
Fife and Angus: Keith Brand, Hutchinsons
Principal crops: Ware (Fife area), seed (Angus)
The demise of linuron and other actives is prompting significant changes to herbicide strategies among Keith Brand’s clients.
Mr Brand says: “Linuron used to be the mainstay of many programmes, but we have had to move on given its withdrawal, and also because of the rise of weeds such as cleavers and grasses”
Some growers have switched into clomazone-based products to tackle cleavers, while others are looking at including products based on flufenacet and metribuzin for grass-weeds. Glyphosate is also an option being considered on ware crops, not those grown for seed, he says.
“Pre-emergence glyphosate is not something I have done before; there is an issue with timing but that risk applies to all herbicides to a certain extent, especially when growing varieties more susceptible to adverse effects. Pre-emergence means exactly that; you cannot go on when the crop is 5 percent emerged as some did in the days of paraquat.”
Earlier herbicide applications may mean a follow-up spray (e.g. carfentrazone-ethyl) is needed to control later emerging weeds.
“Two herbicide sprays are already more common in England, but it is something growers will do here.”
Although diquat has featured in herbicide programmes, Mr Brand agrees its loss poses bigger issues for desiccation where it is often applied in sequence with a carfentrazone-ethyl-based product.
The long growing season in Scotland and high blight risk, given suitable conditions, reinforces the need for robust spray programmes from the outset, Mr Brand adds.
“We will typically use the full quota of cyazofamid in a 12-spray programme, but always vary actives through the season and keep intervals tight, usually seven days. Last year was lower blight pressure, so some stretched to eight to 10 days, while in higher-risk years we have been down to five.”
Cheshire: Andy Goulding, Hutchinsons
Principal crops: Processing varieties for crisps and chipping.
The weather rather than product withdrawal has prompted changes seen to early season weed control among some of Andy Goulding’s growers.
Knowing linuron and diquat were likely to go, he has tried not to rely on them. On peaty, organic soils, metribuzin is typically incorporated into the seedbed, while mineral and organic soils also receive a residual and contact herbicide (metribuzin+ prosulfocarb) as close as possible to emergence.
He says: “But after two difficult dry seasons, some herbicides are being applied earlier – maybe a week to 10 days before emergence – to take advantage of remaining soil moisture.
He welcomes the arrival of the new aclonifen-based herbicide, Emerger, as a cost-effective alternative to metobromuron, with similar weed spectrum.
“The product is taken up by hypocotyl stems and shoots as weeds push through the surface, so does not rely on root uptake, which can be restricted in dry soil.
“Hopefully it will help with fat hen control which has been difficult in dry seasons. Bindweed is another important weed it should control well.”
For blight control, Mr Goulding’s approach is to “start strong” and never allow disease to establish in rapidly expanding crops, tailoring chemistry to variety, growth and disease risk.
Programmes generally begin with benthiavalicarb isopropyl and mancozeb, then he favours products with more systematic activity during the rapid growth period, such as Infinito or Zorvec if blight pressure is very high.
He advises some strong blight products may be weaker on Alternaria.
“Alternaria is a weak pathogen that usually targets stressed crops later in the season and affects varieties differently. If it is an issue, use difenconazole in co-formulation with mandipropamid, at first sight of disease.”
East Anglia: John Chamberlain, Farmacy
Principal crops: Processing, some salads, soft/set skin, baking potatoes.
From black gen soil in Cambridgeshire to heavier land near the Essex coast, John Chamberlain contends with variable growing conditions in the UK’s driest region.
He says: “Crops went into good conditions but there has been precious little rain to get them growing. Fortunately, about 95 percent of my potato area is irrigable, from river abstractions or winter-fill reservoirs, as water is vital in the early stages, especially in Essex where it can be very dry.”
Losing important chemistry, such as linuron and diquat, has created challenges for weed control and has increased weed costs, he says.
Until now, diquat plus metribuzin has been a favoured approach on black fenland, but more growers are now looking towards a residual herbicide plus Roundup Flex (glyphosate); an approach already used by some Essex growers to tackle grass-weeds.
“Glyphosate is very effective, but we must be conscious of the damage it can do and time application carefully. Many growers spray just as crops are emerging, but this is not an option with glyphosate.”
He also thinks the new aclonifen-based herbicide will be more cost effective than metobromuron, and controls grass-weeds.
For blight control, Mr Chamberlain recommends products based on cymoxanil and mancozeb earlier in the season, then stronger actives later.
“With fluazinam resistance active, assessing blight strains upon seeing active blight will help tailor product choice accordingly and avoid using products at risk from resistant strains,” he says.
In light of recent research, Mr Chamberlain reiterates the importance of early nitrogen and not waiting until tuber initiation or flowering to apply a top-up.
“AHDB work shows clear benefits from early nitrogen, with little need to split applications.”
In dry conditions, he says there may also be benefits from using foliar trace elements or plant-based amino acid treatments to boost growth where root uptake is limited, and is trialling this on-farm this year.
Cornwall: David Harris, Hutchinsons
Principal crops: First earlies, (including under plastic), early salad varieties, crisping and traditional maincrop for local chip shops.
A big issue across the potato sector is the loss of active ingredients, and for David Harris, the withdrawal of Mocap, (ethoprophos) is a particular concern given its effectiveness against wireworm.
He says: “With so much grassland in rotations and the loss of actives, wireworm can be a bigger problem than potato cyst nematode [PCN]. Many crops are short-season, so are out of the ground before PCN becomes and issue. “Wireworm damage may become more prevalent without Mocap, especially on salad or seed crops, so we are trialling alternatives such as Nemguard and fosthiazate on-farm this season.”
The withdrawal of diquat raises further challenges for weed control and desiccation, Mr Harris adds. Diquat has featured in many herbicide programmes on open ground crops, alongside other products based on prosulfocarb, metribuzin and metobromuron, so strategies will have to change.
Post-planting, pre-emergence Roundup Flex (not all glyphosate has approval for this use) is one option, although the crop risks require extreme care with timing. Sprays should be applied earlier than traditional residuals – about 10 days after planting – and may require a follow-up before crops break ground, he notes.
Diquat and cyazofamid mixtures have also been an effective desiccant for many growers, so Mr Harris suggests more will flail crops before applying an alternative desiccant, such as carfentrazone-ethyl or pyraflufen-ethyl.
“Many already flail to make lifting easier, but it is relatively slow compared with spraying when stopping a crop that has reached its size, and more expensive.”
Although Mr Harris has not experienced issues with fluazinam-resistant blight strains, he reminds growers to be vigilant and suggests reviewing fungicide strategies. He favours starting with products based on cyazofamid or cymoxanil and mancozeb, before moving to products such as Infinito (fluopicolide+propamocarb), Valbon (benthivalicarb+mancozeb) and Zorvec (oxathiapripolin) during the rapid canopy phase.
Some growers may want to save cyazofamid allocations for desiccation.