The agronomy diary

AGRONOMY DIARY A natural defence against late season disease

Rob Saund ers

Elicitor products offer a useful addition to late season disease control programmes, when traditional fungicide options can be limited by strict harvest intervals. Hutchinsons agronomist Rob Saunders explains.

Controlling key foliar diseases like Powdery and Downy mildew during late summer into early autumn is often made more challenging given the various label restrictions on final fungicide applications before harvest.

Depending on the product, harvest intervals are usually at least 21 days to one month, but can be up to 63 days for those containing mancozeb. This potentially leaves vines exposed to disease infection during that period, a situation that is easily compounded if weather favours disease build-up, or if canopies are too dense, and/ or ripening and picking is delayed. Once defoliation occurs, vines lose the ability to convert sunlight into sugar, jeopardising quality and the ability of vines to lay down reserves for next season.

It is during this period when there is little or no cover from traditional fungicides that elicitor products, such as Fytosave, could offer a significant advantage to growers. With no residues or lengthy harvest intervals, they provide a low-risk way of protecting crops in conventional and organic systems.

Preventative action

Elicitors are based on components that essentially mimic microbial attack (e.g. by a Powdery mildew pathogen) when they are detected by receptors in the plant cells, tricking vines into activating various natural disease defence mechanisms.

Fytosave for example, uses two naturally occurring complex carbohydrates called COS (Chito-oligosaccharides) and OGA (Oligogalacturonans). These provide a double alarm signal to stimulate the plant’s defence mechanisms.

COS is detected by cell membrane receptors as a “foreign” molecule from a pathogen, while OGA is detected as coming from damage to the plant’s own cell walls. The double biochemical alarm works quickly (within 30 minutes of application) and spreads systematically around the plant, activating three main responses: 1. Thickening cell walls by depositing more cellulose and lignin, thereby providing a physical barrier to disease attack 2. Increasing peroxidase production to generate oxidising chemicals that are toxic to attacking fungi 3. Increasing salicylic acid production to manufacture more anti-fungal toxins.

Because of this action, elicitors must be used preventatively, before any disease symptoms are visible. They do not have a direct effect on plant pathogens, so are not something growers can turn to where curative action is required to tackle disease already present.

The recommended approach is to begin using elicitors earlier in the season, around pre-flowering, however the natural defence process can be initiated at any point in the growing season, providing no disease is present.

It typically takes three initial applications to fully build up the plant’s defence mechanisms with a product like Fytosave, so depending on disease pressure, it may be necessary to support the elicitor with conventional fungicide chemistry to prevent mildew coming in during this “build-up” period.

Once natural protection has been established, it should be maintained with regular follow-up applications throughout the remainder of the season up to harvest. Treatment intervals are typically every 7-10 days, although this varies according to the product and disease pressure. Always check the recommended intervals between applications and maximum number of treatments allowed on the label.

In very high disease pressure situations it may be necessary to again support elicitors with conventional fungicides, and generally there is good tank mix compatibility with the main options to allow this.

Managing resistance

The benefits of an integrated approach such as this can be two-way, as elicitors help reduce the disease pressure that traditional fungicides are exposed to. However, because they do not act directly on the pathogen, they are not subject to the same resistance risks as that chemistry, therefore provide a useful resistance management strategy.

With the important multisite mancozeb being lost from the armoury and metalaxyl resistance becoming more widespread within UK vineyards, growers must support and protect remaining chemistry, so elicitors could be a useful addition to foliar disease programmes, this season and next.

EDUCATION Changes to staff

> Ana Dogic, Sarah Midgley & Deepika Koushik

With the students either taking a well-earned break or working in vineyards and wineries across the country, this month we decided to focus on two important changes to staff in the Plumpton College Wine Division.

Ana Dogic (left) is leaving us after a little over 12 months. Ana took over the reins from Sarah Midgley, who took some time away on maternity leave. We would like to thank Ana for her excellent contribution to the winery and for teaching practical winemaking to our students. Ana brought energy and expertise to the Wine Division and will be sorely missed by both students and staff . We wish Ana all the best as she pursues an exciting opportunity in the UK wine industry with her partner.

Sarah Midgley (middle) after giving birth to young Elliot, has returned to the Wine Division in a part-time capacity, and we are delighted to welcome her back. Sarah will focus on winery sustainability courses and guidelines, mentoring and targeted development activities for UK winemakers. Sarah commented: “I am very much looking forward to getting stuck into my new role which will also allow me to use my winemaker knowledge and teaching skills.”

Sarah and Ana are pictured with Deepika Koushik (right), who we welcome as the new winemaker at Plumpton College. Deepika was awarded an MSc (Viticulture and Enology) from the University of California, Davis, an MSc (Applied Biotechnology) from the University of Westminster (high distinction) and has taught undergraduate students microbiology in India and the USA. Her winemaking experience includes stints in the Russian River Valley in the USA and Burgundy, where she was awarded the Confrérie des Chevaliers du Tastevin Award (2019). In addition to this, Deepika was the recipient of the INSPIRE Scholarship for topping her State in HSC level (equivalent to A levels) exams in India and was the recipient of the Mrs Ferooza Easwaran Golden Jubilee Prize for securing the highest grade in Microbiology (2013-2014). Deepika commented: “I am passionate about viticulture and oenology and I have a strong understanding of the science at its core and an appreciation for the tradition that comes with creating wine.”

The UK wine industry is one of the fastest-growing and most successful in the agricultural sector. So if you're interested in pursuing a career with a wealth of exciting opportunities, consider one of Plumpton College's degree courses, apprenticeships, or part-time courses. With the fi nest facilities and courses available in the UK, you'll be able to gain all of the knowledge you'll need to be successful in this highly competitive global industry.