As featured in Arable Farming Magazine
Stimulating plant defences to boost septoria control
by Arable Farming Magazine April issue
Natural products that stimulate wheat plants’ own disease defences can complement varietal resistance and fungicide activity in fighting septoria. Martin Rickatson reports.
While recent seasons have seen new fungicide chemistry added to growers’ armoury and many have moved towards varieties with stronger resistance scores, early season septoria control remains a primary challenge, an issue exacerbated by the loss of cornerstone multisite active chlorothalonil.
But the key roles played in integrated disease management by genetic resistance and chemical protection need support to sustain them and stimulating the wheat plant’s natural defence mechanisms to help minimise disease’s impact and bolster the longterm efficacy of variety resistance and fungicides could help here.
That is the view of Dr Paul Fogg, crop production technical lead at Frontier.
The company’s trials over the past six years with naturally-derived elicitors – products that elicit a defensive response from the plant – have been sufficiently encouraging to lead Frontier to market a product based on the principle for 2022.
Dr Fogg says: “The loss of chlorothalonil and general pressures on conventional chemistry make inclusion of different approaches worth evaluating as part of integrated disease management.
“That’s particularly true of protecting the plant at its earliest stages.
By their nature, elicitors are protective, rather than curative, working by triggering the plant’s natural defence mechanism to fight off disease over the long term.
Their place in the programme is therefore at T0/GS30, or even in autumn.”
The company’s research focus in this area has been with laminarin, a seaweed-derived product which is in full commercial production.
“While laminarin is a naturally-obtained product, purified from the seaweed species laminaria digitate, we see it having a part to play in all agricultural systems, from conventional through regenerative to organic,” says Dr Fogg.
“It works by lowering the plant’s pH, via the accumulation of salicylic acid.
It’s this that triggers its natural defence mechanism, stimulating a systemic acquired resistance throughout the plant after being exposed to elicitors from virulent, avirulent or non-pathogenic microbes, or artificial chemical stimuli.
“It can take several days for resistance to develop throughout the host plant, but once this is triggered it has a long-term effect via three main defence pathways.
“The first of these is physical, via the reinforcement of the cell walls, making it harder for the pathogen to penetrate and providing a barrier to disease ingress.
Secondly, it stimulates the production of phytoalexins, which create a toxic environment for the pathogen.
“The third aspect is the production of pathogenesis-related proteins, which the plant produces in response to a pathogen attack.
In addition to their role in protecting the plant, these also provide a small element of curative activity.
It’s a unique mode of action, classified by FRAC as P4, with minimal risk of resistance.”
Manufactured by UPL, the product being marketed by Frontier is branded as Vacciplant and contains 37g/litre of laminarin.
A registered plant protection product, laminarin is EU-classified as a low risk substance and bracketed in Annex IV for residue detection, being exempt from tolerances for maximum residue limits.
The manufacturer points out that while healthy plants have strong cell walls that prevent pathogen ingress, compromised or diseased cells release the degraded products of the pathogen or the cell walls, which become elicitors.
Recognised by healthy neighbouring cells, these then activate their defences, but this is not a speedy process and can take up to 48 hours, putting the plant at significant risk of becoming overwhelmed by disease in high-pressure situations.
The laminarin active, being a natural plant extract, possesses a similar structure to the degraded products from damaged cells.
This then acts as an elicitor, which triggers the plant’s natural defence mechanisms to come into play before it actually comes under attack.
The protective message is disseminated throughout the plant’s cells.
“Initial trial work we conducted with the product produced results too interesting to ignore,” says Dr Fogg.
“When we compared laminarin against chlorothalonil and folpet at and before T0, its protective efficacy was comparable, particularly on septoria-susceptible varieties, with protection length of around three weeks.”
Dr Fogg acknowledges that yellow rust can often be a bigger worry in the early stages of crop growth, particularly on low-rated varieties.
“While the focus at T0 is commonly driven by yellow rust, most elicitors have activity only on powdery mildew and septoria.
“However, the latter is most commonly the bigger concern as the season progresses and it’s here the product offers greatest promise.
Elicitors offer a potential broad spectrum of pathogen control and there is further work to be done on disease targets and applications.
“Most of our trial work has been with applications at T0, but the earlier the product can be applied the better.
The latest approved timing is before GS31.”
UPL says its own 2019 and 2020 field trials showed signifi cant control of septoria in winter wheat from Vacciplant applied at T0, and makes claims for robust disease control comparable to folpet and now-unavailable chlorothalonil multisites at this timing, recording an average 0.3 tonnes/hectare yield benefit to a wheat crop.
Formulated as a soluble concentrate, recommended application rate for Vacciplant is 0.75 litres/ha, although full rate is one litre/ha at a water volume of 50-500 litres/ha.
Rainfastness is similar to that of other products and it has wide tank mix compatibility with conventional and other biological products, says Dr Fogg.
Price is described as comparable to other T0 inputs.
Frontier is continuing to screen the product’s efficacy across multiple varieties to understand its capabilities across a range of resistance ratings, but it is fully available from the company for spring 2022.
“Growers are moving towards more disease-resistant varieties, particularly with regard to septoria,” says Dr Fogg.
“But there remains a significant wheat area sown to lower-rated varieties and it’s here we think elicitors have a considerable value as an aid to disease control and resistance management.
“And within a single season, the protection they offer at T0 may afford some input flexibility later in the year,” adds Dr Fogg.