THE 2025 Hutchinsons Potato Trials Results day hosted at Worth Farms, Boston, recently, focussed on field trials results and practical research on PCN, crop safety with post-emergence herbicides, wireworm, catch crops, late blight and Alternaria.
Simon Faulkner of SDF Agriculture updated delegates on results from Hutchinsons’ PCN varietal resistance and tolerance trials assessing a mix of older and newer varieties with and without applications of a nematicide (fosthiazate).
The replicated trial monitored 26 varieties put forward by a number of breeders, with varieties for processing, packing, chipping and crisping, with Lanorma, Cara, Markies and Maris Piper as control varieties.
The background PCN level for the field was 20 eggs/gram, and on creating the plots, the plots were then re-sampled to identify eggs/g per plot, which ranged from 0.5-20 eggs/g of soil.
Results showed newer varieties exhibited better resistance. “Cara had the highest yield, but as it has no resistance, PCN numbers went from 7 eggs/g to 686 eggs/g despite an application of a nematicide, while some of resistant varieties saw a reduction from 12 egg/g to 0.5 eggs/g under the same conditions,” said Simon.
There were nine varieties which did particularly well, obtaining a pf/pi of <0.3 when no nematicides had been applied.
He reminded delegates that tolerance means a particular variety can still maintain growth even when under considerable pressure from PCN; so more vigorous canopies are an indication of potential tolerance.
“When a variety is resistant, it means that the nematodes multiplication is reduced or prevented, reducing viable numbers of cysts forming,” he said.
Michael Rodger of Richard Austin Agriculture said timing of post emergence herbicide applications is key to minimising damage and results from Hutchinsons’ herbicide crop safety trials across 26 new and established varieties, gave very different results from those in 2023
“Most of the varieties showed some form of chlorosis,” he said. “The difference between weather conditions was also telling, with some of the varieties which did not show sensitivity to metribuzin last year, showing symptoms of scorch this year.”
He put this down to strong sunlight and water-stress at the time of treatment, noting this crop damage can be seasonal. He also revealed that some of the crops hit by herbicides became more vulnerable to secondary infections such as Botrytis and Alternaria, amongst others.
“Crop safety is variety specific and knowing the susceptibility to herbicide damage of individual varieties, plus assessing any stress the crop is under, provides crucial data for basing decisions on which active to use.”
Also presenting the results of PCN trials, he revealed fewer PCN eggs per plot at the end of the trial from a number of varieties across the fresh-pack, processing, chipping and crisping sectors.
“We were not only looking at the PF:PI ratios, but also the relationship with yield in plots treated with nematicide and those left untreated as a measure of tolerance.”
Some of the varieties trialled showed different results last year from PCN trials done in 2023. “Results are very specific to soil type and initial egg counts; these trials were done on Lincolnshire silts, but outcomes can be very different on lighter sandy soils especially with regards to tolerance.”
Remedial action for wireworm needs to start at least three years ahead of planting a potato crop, advised wireworm specialist Martyn Cox of Blackthorn Arable. This implies that where potatoes are grown in the rotation is key to minimising wireworm damage, and growers should not be fixated on the autumn before potato planting, he said.
“Growing broad leaf crops two to three years ahead of potatoes, as these are less favoured for egg laying, is one of the options available for controlling wireworm. As some insecticides can reduce adult beetle activity if used when they are active in crops, this is another possibility, as is cultivating immediately soon after harvesting cereals and subsequently keeping fields free of vegetation for at least a month,” said Martyn.
He recommended avoiding cereal species in cover crops during high-risks parts of the rotation. “The pest has a five-year life cycle, and the key is to break it, which implies managing stubbles two to three years ahead of a potato crop.”
Click beetles prefer to lay eggs during May and June in land with some vegetation, so cereals followed by cover crops or left with weedy stubbles, provide a good source of food for the pest after hatching and into autumn, he said.
“There is a widely-held belief that cultivation will get rid of wireworms and although inversion cultivation when they are active in the upper profile can reduce a population, it will not get rid of them.”
Martyn said those identified in arable soils are three Agriotes spp.: A. obscurus, which is present throughout the UK; A. lineatus, is also present, but to a lesser extent; A. sputator which is common in East Anglia but fades out around the Humber. Other species commonly damaging crops belong to the genera Athous, others including Hemicrepidius are regularly found in some soils, they can damage potatoes but do not appear to damage other crops. Adrastus pallens can be very common and even large numbers do not appear to damage potatoes at all.
Talking about the Agriotes life-cycle, he explained that the oldest larvae pupate in July-August for two to three weeks and the new adults remain underground until the following spring. Once they become active, they emerge in April, lay eggs in May and June, then die, living for less than a year.
Factors that indicate higher risk include grass crops and cereals, land with good soil moisture retention, lower-lying more humid areas, also near to other areas of permanent grass such as irrigation reservoirs and river banks, he said, adding: “Wireworm can build up without your realising it, and in early August a crop may be past salvaging.”
Hutchinsons is one of the sponsors of the Fight Against Blight, and its Technical Root Crop Manager Darryl Shailes spoke about work done at the James Hutton Institute last year, when outbreaks of blight strain EU_46_A1 were identified very late in the season for the first time.
“The resistance found in Europe is due to their blight control strategies and the tendency to block spray,” he said.
He said EU_46_A1 has the ability to become insensitive to OXTP and CAA group of fungicides. The samples taken in the UK were tested for the resistance genes at JHI and found to have the gene for resistance to OXTP but not CAA’s – something growers need to consider when devising blight strategies this year.
He emphasised the need to alternate different modes of activity, not only to control blight but to manage resistance and noted that last year there was a high number of outbreaks of blight across all the potato growing areas. Collected data showed EU_36_A2 to be the dominant strain in England.
“36 is so aggressive that it completely dominates the populations in our blight trials even when they are inoculated with other strains. We should all be Blight Scouts to report infections and send samples to Fight Against Blight. It is the only way we know what is going on, and the results when reported promptly, can help you manage the populations more effectively.”
Whilst keeping blight out the crop is the best strategy, Darryl offered tips for late blight control which include:
• Good hygiene to reduce inoculum sources
• Following an effective anti-resistance strategy
• Alternating different modes of activity
• Avoiding the use single actives
• Maintaining a maximum of seven-day intervals
• Reducing intervals once blight is active
• Using a mixture of curative and contact actives
• Unsure sprayer is set up to avoid misses.
The licence for blight control active mancozeb has now been withdrawn in GB; sales are no longer permitted, and growers are now in the use-up period. However, Darryl revealed that the EU court has overturned the decision to withdraw the licence for mancozeb in the EU, as apparently there had been a reliance on out-of-date scientific data.
“Nobody knows whether this will have any effect on it coming back into use in Europe, or here in GB, but there have been a few emergency approvals applied for in Europe,” said Darryl.
He observed that the loss of mancozeb will also have an effect on Alternaria control, “Mancozeb has had a good effect on Alternaria in the background when used for blight control.
“This will now need to be managed with other products based on triazoles such as prothioconazole + fluopyram, the newly approved mefentrifluconazole and products based around difenoconazole.”
Reducing PCN levels remains a priority for many growers, and in 2024 trials were undertaken by Hutchinsons with the aim of building better understanding of how to get the best results from growing DeCyst-Prickly (Solanum sisymbriifolium) and DeCyst Broadleaf (Solanum scabrum) as cover/trap crops.
“However, we were not able to get it to grow very well and had to destroy it early because it was outcompeted by weeds.
“This was a good reminder that a catch crop is a crop and needs to be treated as such. Creating good seedbeds, drilling at the right seed rate at the right depth, with about 70kg/ha of N, and effective weed control are all key.”
“Aclonifen has just been approved under an EAMU so will be very useful going forward. However, in 2023 one of our growers trialled the DeCyst Broadleaf and got a very tall, lush crop, resulting in a massive reduction of PCN in that particular field.”
The results from the storage appraisal trials will be presented on May 21st at the SPoT Store open event at Fleet Lodge Farm, Holbeach courtesy of Lincolnshire Field Products with Adrian Cunnington and Simon Faulkner.
