Wednesday 28 September 2016

Timing is everything in fungicide application

Michael Hennessy

Published 29/04/2015 | 02:30

Extend: Keeping a barley crop as green as possible for as long
as possible might look good, but it may not add as much to the
bottom line compared to wheat Photo: Roger Jones
Extend: Keeping a barley crop as green as possible for as long as possible might look good, but it may not add as much to the bottom line compared to wheat Photo: Roger Jones
Last run: The vast majority of the work with winter barley crops should be done by now, with the number of grains per plant largely determining total yield. Photo: Roger Jones

Making fungicides pay is a combination of many factors. The most critical interaction is the timing of the spray application in relation to the growth stage of the crop rather than the specific fungicide product used.

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In this article I will explore how to best time applications to give the best returns from fungicides.

The increase in winter barley area has been quite dramatic over the past number of years.

Winter barley acreage was a little under 30,000ha in 2010 and is estimated to be close to 75,000 hectares in 2015.

The greening rules in the new CAP have had the effect of switching even more production from spring barley into winter barley.

These newer growers are on a bit of a learning curve in how to get the best from the crop.

As one grower remarked to me in the last week, "I didn't realise that all the inputs for winter barley were finished so early in the year".

To get your head around this, you need to understood plant growth stages and the critical timings to get the best from the crop.

Let's look at the lessons from recent years in terms of return for fungicide spend and how this informs us for the final decisions this year.

Barley growth habit

It is important to understand the differences between barley and wheat yield development.

Understanding the differences greatly informs the fungicide program and where it can go wrong. Over 65pc of yield in wheat comes from the flag leaf and the ear with the lower leaf two contributing 25pc to final yield.

This is why the total yield in a barley crop is predetermined earlier.

It is also usually limited by the number of grains available to store the carbohydrate, although this may be relevant in the case of six-row barleys. Up to now, most of the research has been in two row varieties.

Therein lies the biggest difference between wheat and barley - the maximum number of shoots need to be produced and retained until harvest to achieve a high yielding barley.

This is why keeping the crop as green as possible for as long as possible may not return more grain in the trailer, in contrast to wheat.

These factors influence the fungicide program as the potential return from timings are different between wheat and barley.

Teagasc research on winter barley fungicide programs has shown there is a significant increase in yield from three fungicide applications.

The first (T1) at the tillering stage, the second (T2) at growth stage (GS) 31-32 and the final application (T3) at GS 39-45, or awns at peeping stage. However, having a yield response and an economically positive response are two different things. The average return in trials from the T1 application has been small at 0.25t/ha, and some could argue that this is not economic. However, this must be examined further.

In the past three seasons there has been considerable disease pressure, specifically from rhyncosporium, in the early part of the season in crops, especially in the southern part of the country.

In the subsequent weeks after this fungicide application the dry weather conditions in these years did not suit disease development.

Although yield returns from the early fungicide were small, if the weather conditions stayed wet disease would have been more difficult to manage and a much higher return would have been seen this early treatment.

It is clear from many other trials that if disease is allowed to develop in barley at an early stage then tiller numbers will suffer and yield will be lost.

Responses

The same trial results show that the T1 application (GS 31-32) gives some of the best yield responses, making it one of the most important fungicide applications.

The reason for this is that this fungicide application reduces disease, and thus protects tillers, which is critical to maintaining yield.

In order for the final fungicide application to pay its way it needs to be applied before the head is fully emerged.

Applying the fungicide to the emerging awns will give maximum return.

This fungicide application needs to be applied preventatively (especially for Ramularia) to get maximum returns.

At this stage of the year there is only a final application to be applied to barley.

Generally barleys are quite clean and the job of the final fungicide is to maintain disease control until senescence. See page thirteen for more details on suggested barley fungicide programmes.

Michael Hennessy is a tillage specialist with Teagasc

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