Trials are taking place to investigate alternative approaches to blight control, including the value that innovative options could bring to wider management programmes. CPM collates some of the findings.
“The future involves introducing novel tools, as well as nutrition, to help bolster baseline plant health.” DON PENDERGRAST
By Janine Adamson and Rob Jones
Compared with controlling foliar diseases in cereal crops, tackling late blight in potatoes is considerably more challenging when it comes to devising a robust management programme to last the season.
The list of dos and don’ts is complex – both FRAC guidelines and stewardship from manufacturers have to be adhered to, to help prevent the exposure of critical fungicide actives to the risk of resistance break-down.
And now, with popular multi-site mix partner mancozeb no longer available for use, growers and agronomists have to think even harder to devise an effective plan for late blight control.
However, with the industry fully aware of this impending situation, Agrii began scenario planning for life without mancozeb a few years ago, to see if the gap could be plugged, highlights the firm’s Don Pendergrast.
“But with a limited suite of registered active ingredients, this meant exploring novel fungicide solutions to understand the impact they might have on late blight control, as well as wider plant benefits,” he explains.
Trial work initially began in 2024 while mancozeb was still available for use, centred around the introduction of biostimulant, Innocul8 (peptides). Both applied alone and alongside a conventional fungicide programme, Innocul8 delivered impressive yield gains, says Don.
“When Innocul8 was added to a standard fungicide programme, it delivered an additional 2.3t/ha average in marketable yield. However, in the absence of mancozeb, the best treatments were those where Inoccul8 was included in the first two applications alongside the standard programme.
“Because it out-performed in terms of green leaf area, we believe this is what delivered the yield uplift – it seems Innocul8 underpinned the fungicides,” he explains.
With this in mind, Agrii developed a new protocol for 2025 to reflect the impending loss of mancozeb. Given the previous year’s results, all treatments featured early applications of Innocul8 in addition to a base fungicide programme, with the variable being different novel solutions.
These included Crusade (drift retardant), a new potassium phosphonates formulation, Privest (ametoctradin+ potassium phosphonates), other variants of potassium phosphonates and co-formulated products, a copper-based micronutrient, orange oil, and an upcoming plant extract awaiting registration.
The trial took place at Eurofins’ Derbyshire site and was drilled on 29 May. Despite being inoculated with blight three times due to the extremely low pressure season experienced last year, Don says it was in fact a wild strain of EU46_A1 that eventually infected the crop.
“The weather just wasn’t optimal for blight so it was only identified towards the back-end of the programme, from 14 August onwards. Of course, EU46_A1 is the strain with resistance to OSBPI fungicides such as oxathiapiprolin (as in Zorvec).
“Prior to this, what we did note was the benefit the biostimulants were having in the crop’s canopy development, but once blight did take hold, it moved reasonably quickly through crop.”
According to Don, because of the ‘odd’ season last year, it wasn’t possible to measure significant differences between the novel treatment plots, instead they saw more anecdotal and trend-based results. “Overall, the treatments that included Privest looked the best with a clear difference in general greening and health of the crop.
“But, this could have been because they were the only plots to not include OSBPI fungicides, which are vulnerable to EU46_A1. However, everything added in over the standard fungicide plus Inoccul8 treatment appeared to give a boost in performance.”
Don adds that in terms of stem lesions, the differences between products were very subtle. “What we did observe is that oil-based products such as orange oil and the adjuvant appeared to give greater control. This is likely due to better penetration and spread following the product’s application.”
He stresses that unfortunately, due to the extreme drought conditions, last year’s results will have to remain anecdotal. “Next steps will involve repeating the trial during more blight-typical years. We’ll also have to investigate the exact positioning of these products and application timings in order to maximise the flexibility they may offer.”
Despite the trial not going quite to plan, one factor that could be measured was the resulting residues of potassium phosphonates. “The maximum used in the trial was three applications and with this, we were well under the MRL at just 20mg/kg.
“This is something we’ll continue to evaluate during the trial next year, looking at the impact on residues of up to half of the treatments including potassium phosphonates.”
Even though the results have been mixed to date, Don believes they suggest there is hope for life after mancozeb and without OSBPI fungicides. “Instead, it’ll involve introducing novel tools, as well as nutrition, to help bolster the baseline plant health.
“Regardless, the aim with late blight remains getting in front of infection, as firefighting is very difficult with today’s tools. It’s critical that robust programmes are used to manage blight under decent pressure in the future,” he concludes.
Also taking place last year was a trial by Richard Austin Agriculture, which suggests that biostimulants have the potential to reduce the impact of late blight while increasing crop yields.
“Blight control is becoming increasingly challenging as new strains continue to emerge and resistance to some fungicides develops. This trial investigated how biostimulants such as Sirius (organo-silicate) and Trident Plus (copper/zinc/cobalt) could be used alongside a conventional fungicide programme to support crop performance.
“The results were encouraging in terms of yield and crop response, but further field-scale trials will be required,” states trials manager, Michael Rodger.
The 2025 trial featured Melody, with the biostimulants applied from July to October alongside fungicides Enervin (ametoctradin) and Privest. The best total yield was achieved through a mixture of Sirius and Trident Plus, which in terms of blight infection, displayed a comparable percentage to using Privest alone.
“Biostimulants may help to reduce the impact of late blight indirectly by improving plant resilience, rather than directly controlling the pathogen,” suggests Michael. “Silicon can strengthen plant cell walls and create physical barriers that make infection more difficult, stimulating natural plant defence responses so the crop reacts more quickly to infection.”
He adds that biostimulants can improve overall plant vigour, nutrient uptake and stress tolerance, helping plants to maintain growth and yield even under disease pressure. “Some products may also influence leaf surface characteristics, which can make conditions less favourable for pathogen establishment.
“When used alongside conventional fungicide programmes, these effects may support crop performance and contribute to an integrated approach to blight management,” he says.
The Sirius (0.5 l/ha) and Trident Plus (3 l/ha) treatment was applied between 2 July and 30 October with a spray interval of 7-10 days. Michael believes seeing both yield improvements and a reduction in blight using this rate of application makes biostimulants a sustainable and cost-effective option.
“A healthy, stress-free plant is more resilient to both biotic and abiotic stress, which may help crops better tolerate disease pressure when used alongside conventional fungicide programmes,” he comments.
Work has also been taking place to assess the use of biostimulants and their effect on bulking rates and final yields. Trials conducted by Dyson Farming Research (DFR) indicate that while biostimulants can be used to increase bulking in good growing conditions, significant results can also be achieved when they’re used as stress protectants in hot and dry weather.
The work involved various biostimulant products, each tested according to the manufacturer’s recommendations, across two sites at Nocton and Leadenhall, explains Dr Christine Jones, crop research scientist at DFR.
She says as drip irrigation was available at the site at Nocton Estate in Lincolnshire, stress in the crop was delayed until a particularly hot spell in mid-August when temperatures reached 30oC.
“So, we didn’t see any effects on the initial rate of bulking, which average about 7t/ha/week in treated and untreated plots, meaning there didn’t appear to be any growth stimulant effect in these conditions. But after that particularly bad stress period, the untreated plots more or less stopped bulking while the treated plots continued, albeit at a lower rate than previously.”
One product that appeared most effective was Biimore from Rovensa Next – obtained from the bacterial fermentation of sugar case molasses by a proprietary strain of Corynebacterium glutamicum.
In the DFR trials, Biimore was applied once at 100ml/ha when the potato plants were 10-15cm tall and stolons elongating, says Christine. While there wasn’t a visual difference above ground in either trial, regular yield digs indicated a different story underground once the crop became stressed, she adds.
At Nocton, that resulted in a 26% increase in total yield for the Biimore-treated plot versus control. Although there wasn’t a significant yield difference in the 40-80mm grade, Christine explains the trial plots were left growing for longer than in a commercial crop.
“A lot of the extra yield was bigger potatoes. Commercially, we’d have stopped the crop earlier if 80mm was the maximum size grade.”
At Leadenhall – a site without irrigation – the dry spring and summer weather hit crop growth much sooner, highlights Christine. “Stress started before the onset of bulking, with much poorer growth than we’d usually expect on the silt soils.”
This time, where Biimore was applied, there was a significant increase in the bulking rate of around 33% compared with control plots – translating into nearly 30% higher total yield.
“There weren’t any oversized tubers in this trial, partly because of the poor crop growth from early in the season, so there was also a significant increase in 40-80mm sized tubers.”
Biimore’s formulation has been designed to assist aspects such as potassium translocation, photosynthetic efficiency, sugar synthesis and cell wall construction, explains Rovensa Next’s Bruce Morton.
“All of these enhance tuber size and quality, but in these trials, we think it was the potassium boost that helped drive the bulking of the tubers. The product is really exciting in how it consistently delivers a yield response, not just in potatoes but other crops too,” he concludes.
This article was taken from the latest issue of CPM. Read the article in full here.
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