The Importance of Early Season Disease Control in Barley

Grain yield in cereals is determined by three factors:
1. Number of ears per m2
2. Grains per ear
3. Average grain weight

Number of ears per m2 X Grains per ear X Average grain weight = Yield

Multiplying the three factors together gives us the yield of a cereal crop. Increasing grain weight in cereals has only a small impact on yield. There is a strong relationship between grain number/m2 (number of ears per m2 X grains per ear) but only a weak relationship between average grain weight and yield.

Thick crops of barley are essential for high yields

There is significant opportunity to increase the number of ears per m2 in barley and the number of ears per m2 has a strong impact on yield as shown in figure 1.

Figure 1: Relationship between ear number per m2 and yield in spring barley at Kildalton, 2009

The number of grains per ear is dependent on the number of fertile spikelets on the ear central stem. In barley, each spikelet has only one floret while wheat has two to five florets. Therefore, while it is possible to achieve some compensation for low ear numbers as crops with lower tiller numbers produce more grains per ear, the scope is limited in barley with this ability 30-50% less than in wheat.

Key point: Wheat has a higher ability to compensate for ‘thin’ crops than barley. ‘Thick’ crops of barley are essential for high yields.

Therefore to achieve a high yield in barley it is important to maximise tiller production during early canopy growth and to maintain as many of these tillers as possible until harvest. This article focuses on the importance early disease control in maximising tiller numbers but there are a number of other important practices in maximising tiller numbers including:
• Good seedbeds
• Early sowing
• Sowing rates
• Early nitrogen applications
• Growth regulation (primarily in winter barley)
• Pest control

Disease control
The wet weather diseases Rhynchosporium and Net Blotch are the biggest disease threats in Ireland and have the greatest potential to reduce yield. Other leaf diseases to look out for are Mildew, Ramularia and Brown Rust.

Ryncho and Net Blotch are the disease threats in Ireland

Winter Barley
Recent UK research has shown larger increases in yield from early fungicide applications than previously thought with early spring and even autumn applications sometimes economically justified. These responses are attributed to additional greening in early canopy formation resulting in increased light interception, higher numbers of ears per m2, higher grain numbers per m2 and ultimately higher yields.

Subsequent trials carried out by Teagasc at sites in Cork and Carlow in 2010 (see table 1), have shown early spring disease control resulted in higher responses than previously thought. Traditionally fungicide programmes in winter barley favoured a higher spend later in the season however this work suggests an increased spend earlier in the season may be more profitable.

The above results suggest the first fungicide should be applied during late tillering rather than the traditional GS 31-32. While these results are from one year, further work in Ireland and the UK supports the need for early disease control and is consistent with the need to promote tiller survival to maximise yields. In reality every year is different and there will be different responses to fungicide timings but on average commencing your fungicide programme early is likely to be economically justified.

Key point: A three spray fungicide programme with the first fungicide being applied no later than late tillering is likely to deliver the greatest return on investment in winter barley

Recommendations
• Target the first fungicide application in winter barley early in the season during late tillering (before GS 30). It may be necessary to apply the first fungicide even earlier than this where disease threatens tiller survival.
• Applying three rather than two fungicides through the season allows greater flexibility and is likely to deliver a higher return on investment.  Suggested timings (flexibility required depending on the season):
T1 GS 25-30 (Late tillering)
T2 GS 32-37 (Stem extension)
T3 GS 37-49 (Flag leaf just visible to first awns visible)
• As the T2 timing above typically delivers the greatest yield response; the greatest proportion of the fungicide spend should occur at this timing (circa 40%).

Spring Barley
Given the slightly surprising positive responses from earlier than normal fungicide applications in winter barley, Teagasc conducted extensive trials on fungicide timings in spring barley in the last couple of years. The results of these trials can be seen in figure 2.

Figure 2: Yield response at different timings in spring barley in Teagasc trials

The results in figure 2 show a slightly higher yield response to applying a fungicide early during late tillering compared to the traditional GS 31-32. As with winter barley every year is different and there will be different responses to fungicide timings but on average commencing your fungicide programme slightly earlier is likely to be economically justified. Interestingly, another result of this trial work showed that there was no advantage to applying more than two fungicide sprays in a season.

Key point: A two spray fungicide programme with the first fungicide being applied no later than GS 31 is likely to deliver the greatest return on investment in spring barley

The first spring barley fungicide should be applied no later than GS 31

Recommendations
• Target the first fungicide application in spring barley circa GS 30. It may be necessary to apply the first fungicide earlier than this where disease threatens tiller survival.
• There is no advantage to additional fungicide applications above the traditional two sprays.  Suggested timings (flexibility required depending on the season):
T1 GS 25-31 (Late tillering to early stem extension)
T2 GS 37-49 (Flag leaf just visible to first awns visible)
• As the T1 timing typically delivers a strong yield response; it should make up a significant proportion of the total fungicide spend (circa 40%).

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