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Autumn switch point for fungicide choice

Disease Control
23.09.2021
Microscopic microdochium developing on leaf

Autumn disease control programmes are typically the most important timing to protect turf quality. Yet conditions frequently pose the most challenging decisions for greenkeeping skills.

It is a timing that needs to be got right, advises Syngenta Technical Mananger, Glenn Kirby. As growing conditions slow going into the winter, any disease scarring or turf loss could prove slow or impossible to recover – affecting surface quality right through the season.   

Removing dew from autumn green    

It’s a period when surfaces can remain damp for an extended time each day - which is conducive to the microdochium pathogen - combined with temperatures that are still warm enough for rapid disease development.

Historically reports and disease models indicate microdochium nivale is most active at temperatures of 0 to 6⁰C.

However, more recent research*, published in the International Turfgrass Society Research Journal, indicated conditions are optimal for its development at higher temperatures and humidity, of up to 20⁰C and 60 hours of leaf wetness.

microdochium developing on leaf

The research showed that at 60 hours of leaf wetness, microdochium patch spread on bentgrass species affected 10% of surface area at 8⁰C, 12% at 12⁰C and over 25% at 16⁰C. But at 20⁰C it reached more than 45% of the area in the duration

That work suggests preventative fungicide programmes may need to be weighted towards earlier timing when temperatures are warmer, particularly when conditions are wet.

The decision making for greenkeepers is made more difficult by fluctuating weather conditions, which through the autumn period can be quite warm by day and cold at night, or increasingly periods of extended high temperatures later in the season.

Referencing local historical disease risk data with weather records, available for more than 10 previous seasons on the Syngenta Turf website, gives a strong picture of when infection periods are likely to occur for any specific course.

Web button historical weather data

Furthermore, coupling that to the growth potential, indicated by Growing Degree Day calculations, can help to refine both the timing, application interval and the product selection for a more proactive approach to preventing disease.

Understanding the mode of action of any fungicide is essential to ensure it’s use at an appropriate time.

Fundamentally, systemic products that are taken up into the leaf require active growth to move around in the plant’s vascular system, to target points of disease infection. Contact products, however, remain on the outside of the leaf and protect the plant from infection getting into the leaf.

Whilst plants are actively growing, the systemic Heritage has the advantage of recycling and replenishing the disease protection in new growth.

With a contact fungicide on a growing leaf, some of the protection would be cut off and removed with each mowing.

microdochium developing on leaf

It therefore makes sense to target purely systemic products when GDD indicates plants are actively growing, and the only primarily contact product, Medallion TL, when growth is slow over the winter. For any individual course, the timing in the season when that occurs is going to be different- and need to be tailored each season to the prevailing conditions.

The greater challenge is the September to November window, when growing conditions can be variable – when a mix of systemic and contact actives in a single fungicide application could be the most appropriate strategy.

That could be achieved through a single co-formed Instrata Elite, mixing systemic and contact products in a FR321 one-box solution, or a combination of both approaches to protect turf over a longer period.

GDD indicator of turf growth

Reviewing GDD data for two contrasting sites last season, on the south coast of England and North Yorkshire, for example (above), highlights the conditions for a dual contact/systemic is similar – only the timing and duration will be site specific. Furthermore, repeating the study for previous years, shows the pattern is similar, only with greater or lesser seasonal variation.

The other highly important indicator from the GDD analysis, is that the site on the south coast could be expected to see more growth later in the season resulting in faster depletion of the fungicide application, along with warmer temperatures more conducive to microdochium pathogen development.

Web button GDD calculator

In this situation, it would likely prove necessary to require shorter intervals between applications in the south coast scenario, according to seasonal disease pressure, compared to a course in Bingley, for example. 

The key is that Syngenta research has consistently shown targeted application ahead of infection periods maintains better surface quality from a reduced number of treatments, compared to routine applications or treatments after symptoms have broken out.

Identifying the right product at the right time, along with accurate application to get it in the right place, will help to achieve better results right through the challenging autumn season.

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