Potato Review

www.potatoreview.com POTATO REVIEW MAY/JUNE 2022 19 BLACKLEG Again, tuber calcium concentrations were increased very significantly where the product had been used, mirroring the results in previous work. Risk factors So, what does this mean in practice? Mark says the potential effects in a commercial situation marginal and those effects may be greatest in a year where conditions are conducive to disease spread and all other known risk factors all align. Those risks would be planting a susceptible variety; a seed source with known blackleg incidence; and a site that requires early irrigation or for scab control. “Of the six trials I’ve been involved in, the effects all happen to be in one year, with the other three years seeing no blackleg, no rotting, but increases in tuber calcium. “In 2021, we’ve had plants that succumbed, but they succumbed less where we’ve applied this product. If you are in a high-risk PROACT – WHAT IS ITS MAIN INGREDIENT AND HOW DOES IT WORK? ProAct contains about 1% Harpin αβ , which consists of 4 active domains from naturally occurring harpin proteins produced by plant pathogenic bacteria like Erwinia amylovora which causes fire blight in top fruit like apples and pears. Commercially, harpin is produced via an industrial fermentation process using specific bacteria. Harpin does not act directly on a pathogen or pest, so is not a plant protection product. Instead, it is said to activate a natural defence mechanism in the plant, protecting against infection or infestation. Healthy plants treated with ProAct will absorb and bind more silicon and calcium in their cells. The effects of higher silicon and calcium concentrations continue after harvesting, resulting in increased storage and shelf life. situation, then it can work, but where you haven’t those three risk factors together, I’m not sure it will provide a cost benefit.” Both Mark and Stuart stress the need to apply ProAct early if using the product, as it can only provide a preventative effect against blackleg infection. As plants are very small and the product is absorbed through foliage, exploring the possibility of band spraying to target leaves more accurately early in crop development may optimise uptake and cut cost. Overall, Stuart believes there can be an effect on blackleg, but more work is needed to ensure growers get amore consistent return from its use. “It would be good if we can somehow find the relevant criteria on when and where ProAct should be used to give growers a much better chance of achieving success,” he adds. Matt Audley, technical sales manager for Plant Health Care, says the work conducted by Stuart andMark over recent years highlights the often small but meaningful benefits of biostimulants. He says the company’s UK data, along with studies from around the world, confirms that Harpin αβ has a consistent effect on calcium localisation. “In high-risk situations and difficult environmental conditions, this Harpin αβ - calcium effect can reduce the damage caused abiotic stresses and diseases like blackleg. “ProAct is not a miraculous cure- all product, but by delivering subtle improvements in plant health and tuber quality, ProAct users are gaining a good return on investment,” he adds. DOES PROACT OFFER ANY OTHER EFFECTS IN POTATO? Other metrics that were assessed in the 2021 trial by Mark Stalham Potato Consultancy included canopy development and duration, stem survival, tuber number, tuber yield, graded yield, and shape. There was an average total tuber yield increase of 4% across the trial, but this was not significant at a 5% probability level. No statistically significant effects were found on canopy development and duration, stem survival, tuber number and tuber shape. However, in other trials, like work in Poland in in 2019, ProAct has returned an average 5% increase in total tuber yield. This is around a 4:1 return on investment, depending on market prices There was also no observed impact of ProAct on skin set, bruising, weight loss, sprouting or levels of black dot in 2021. The same can be said for internal rust spot (IRS) and hollow heart, despite ProAct significantly increasing tuber calcium concentrations. It should be noted that incidence of IRS and hollow heart was low in control plots, so any effect on the calcium deficiency linked conditions can’t be ruled out completely. Mark Stalham Matthew Audley Stuart Wale