Stressful Times For Potato Tuber Initiation

15 May 2025, UK: Potato crops have emerged to already face incredibly challenging growing conditions this season.

The combination of high temperatures and record low rainfall has put immediate stress on crops, with little potential for respite in weather forecasts.

The immediate high risk is that stress at the early onset of tuber initiation can result in plants setting fewer tubers, which will have serious implications for tuber numbers and size later in the season, warns Syngenta Technical Manager, Andy Cunningham.

If good growing conditions return over the coming weeks, plants can set further tubers, but that will impact on size grading and maturity at harvest, he adds.

“Under these conditions, biostimulants have an important role in uprating potato plant’s resilience to environmental stresses,” advocates Andy.

Syngenta research has consistently shown that Quantis has a significant beneficial effect when applied at the time of tuber initiation, along with Maxicrop biostimulants helping to restore healthy growth and mitigating stress through the growing season.

Trials have shown that even under normal growing conditions Quantis application at tuber initiation (above) produced a 6.5% uplift in tuber numbers and an 8% increase in overall yield, with further advantages in tuber numbers under dry conditions.

“Quantis has a significant beneficial effect when applied at tuber initiation, as well as been scientifically proven to help with ‘pinch points’ in the season, particularly around temperature stress.

“The temperature stress forecast in the Syngenta Portal App highlights the optimum timing for application on your farm.”

And, as this season progresses, the threat of restrictions on water abstraction or where scarce irrigation resources have already been eaten into, will inevitably mean some crops will be subjected to greater water deficits – and consequential stress – before the pumps are switched on.

“Potato plants that are already subjected to some degree of moisture stress are more likely to be susceptible to effects of temperature, light and nutrient stresses too,” he believes.

Andy advises combinations and sequences of Quantis and Maxicrop Triple biostimulants through the season will help to maintain healthy crop growth, which will be even more important given the difficult start.

Maxicrop Triple is derived from seaweed, to extract the plants’ natural ability to withstand high stress of repeated drying out and climatic exposure on the foreshore. It can help with growth and development, along with osmoregulation through drought periods and chlorophyl production.

“Including Maxicrop Triple now will make the crop more resilient to the conditions that we’re going through now. And then putting it on with every other blight spray, until these conditions improve,” he recommends.

Biostimulants can be readily incorporated into the blight programme through the season, he says. “But such is the importance of Quantis to counter temperature stress, that growers are advised to regularly check the temperature stress forecast on the Syngenta Portal App to highlight when best to include it in the spray programme.”

Nutrients dried up

Prolonged dry soils could now compromise the availability of applied nitrogen for the potato crop, just at a time when rapid leaf growth and tuber initiation demands high inputs. That’s especially the case where soil reserves have been depleted by the wet winter weather.

Including Vixeran biofertiliser in with early blight treatments and Quantis application at the tuber initiation will provide a quick fix of readily available N.

Warmer soils will help to initiate rapid development and colonisation of the nitrogen fixing bacteria in the roots and soil biosphere, where they will continue to convert atmospheric nitrogen into plant nutrients to resource the growing crop through the season.

Alternaria onset

Growers and agronomists are being warned to look out for early risk of alternaria, if the highly stressful growing conditions persist. Plant stress is commonly associated as a precursor of infection that allows the pathogen to establish and multiply rapidly.

Andy Cunningham reports that Syngenta Potato Power blight research continues to trial effective fungicides to target late (Alternaria) and early (Phytophthora) blight, particularly with the availability of mancozeb that has been valuable in reducing alternaria risk.

“Blight programmes may need to be tailored for the timing of specific alternaria products, such as Amphore Plus, this season,” he advocates. The Blight Forecast Tool in the Syngenta Portal App provides vital guidance to tailor the season long programme.

Research by Syngenta at the Eurofins trials site and Potatoes in Practice in Scotland this season is also looking at the role of biostimulants to minimise stress and enhance plant health of potato crops, that may have potential to improve natural resilience and risk of infections.

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