Diseases

Diseases

Teagasc fungicide trials in winter wheat have given a yield response of approximately 3.0 t/ha with a good margin over fungicide costs and improved grain and straw quality.

A reasonable fungicide program will cost in the region of €190/ha. Crops Costs and Returns 2020 However this may be reduced by 20% for late sown crops, where disease pressure from Septoria and Eyespot is low and where disease resistant varieties are sown.

Integrated Pest Management (IPM) techniques should be used where possible. For more information on IPM visit: Integrated Pest Management

Septoria

• Septoria is the most important disease of wheat in Ireland.
• A good fungicide programme has delivered 3.0-5.0 tonnes per ha in Teagasc trials
• However some strains of septoria are now resistant to some of the main fungicides.

Mildew

• Mildew is most evident in dense, susceptible varieties on older leaves e.g. Avatar.
• It appears as white pustules on the leaf
• Mildewicideare very active on wheat mildew.
• Include a mildewicide with first fungicide i.e. Leaf 4 (GS 31) or Leaf 3 (T1

Eyespot

• Early drilled crops in a plough-based system are highest risk
• Assess crops for visual symptoms at gs 31 and treat at the T1 timing
• Average yield response to eyespot fungicides 0.4 t/ha (HGCA - high-risk sites)
• Min-till crops have a lower risk due to antagonistic factors in the cereal stubble.

Yellow Rust

• Outbreaks of yellow rust occur occasionally in certain prone varieties
• It has the ability to spread very quickly in dry conditions
• Where detected use a strobulurin +/- to control.
• Yellow rust can also be controlled at the Leaf 3 timing with the triazole and SDHI fungicides.

Winter wheat disease control strategy

Winter wheat spray timings, rationale & research results

Leaf 4

• Yield response: NONE - helps better timing of Leaf 3.
• Timing: apply with PGR/onto leaf 4.
• Recommendations: 1.5 l/ha multisite (+/- strob for rust; morph for mildew)
• Notes: No benefit from adding triazoles but increases risk of resistance occurring
• Add a strob if rust is problematic or mildewicide if mildew is prevalent.

Leaf 3

• Yield response: (2012-2014 Teagasc experiments 0.5 t/ha)
• Timing: Apply onto final leaf 3 fully emerged (~ gs 32).
• Recommendations: 1.5 l/ha multisite + 80-100 % (SDHI + triazole mix)
• Notes: Assess for eyespot and mildew also at this timing.
• Yield response: (2012-2014 Teagasc experiments 1.7 t/ha)
• Timing: Apply onto flag leaf fully emerged (~ gs 39). See table above
• Recommendations: 1.5 l/ha multisite + 80 - 100 % (SDHI + triazole mix)
• This is consistently the best paying spray in winter wheat trials

The importance of identifying leaf 3 for septoria control in winter wheat.

Find out how to dissect the plant to find leaf 3. Protect leaf 3 from disease and this ensures that leaf 1 and 2 as also protected. These are the key leaves for the grain, they need to capture as much sunlight as possible to convert into carbohydrates

Flag Leaf

• Yield response: (2012-2014 Teagasc experiments 1.7 t/ha)
• Timing: Apply onto flag leaf fully emerged (~ gs 39). See table above
• Recommendations: 1.0 l/ha chlorothalonil + 80 - 100 % (SDHI + triazole mix)
• This is consistently the best paying spray in winter wheat trials

Head spray

• Yield response: (2012-2014 Teagasc experiments 0.5 t/ha)
• Timing: Apply at start of flowering.
• Recommendations: Fusarium & Septoria active triazole (See table above).
• The yield response can be low in low disease pressure years.

For further information see Steven Kildea’s presentation at the National Tillage Conference 2015 available from here

Winter Barley Disease Control

While disease control is important in barley the response to a fungicide programme is not as big as wheat, typically 1.0.1.5 tonnes per ha. Teagasc trials from 2010-2012 show that a 3 spray program (< gs 30, gs 31-32 & gs 39-45) gives the best response from fungicides.

Rynchosporium

• Rynchosporium leaf scald is one of the most diseases in barley
• Developss in cool moist conditions
• Early sowing of susceptible varieties increases risk
• Triazoles e.g prothioconazole have good activity on rynchosporium.

Net Blotch

• Net blotch can be a very destructive disease of barley
• It can kill out tillers reducing yield as a result
• It is distinctive by its netted pattern on the leaf
• Strobulurins and triazoles give good control

Powdery Mildew

• Develops in warm humid conditions 12^oC +
• Can reduce yields by up to 10%
• Mildewicides give good control

Ramularia

• Typical symptoms of ramularia are small brown rectangular lesions surrounded by a yellow halo
• Typical symptoms of ramularia are small brown rectangular lesions surrounded by a yellow halo
• Ramularia develops when crops have been stressedRamularia is resistant to strobulurin fungicides
• Mulitsites mixed with triazoles give best control

The following graph is from trials carried out by Oak Park across the country in the last four years. It shows the yield response to different fungicide timings and spray combinations.

Key messages from the trial

• Trials from 2010-2013 show that the three timings; < gs 30, gs 31-32 & gs 39-45 give the best response from fungicides.
• The two fungicide applications (gs 31-32 and gs 39/45) gave the best response. However a higher yield response can be expected from the three fungicide applications where the disease challenge is high in early season.
• Applying the final fungicide at gs 39/45 out preforms applying a fungicide at gs 59, whether as a single application or in as part of a fungicide program.
• Waiting to apply the final fungicide until the head fully emerges gives a poor response to fungicides.

Tillering spray (T1): Early disease can cause tiller loss at a critical time for yield formation.

Spray crops with high levels of Rhyncho to protect new growth with a suitable product such as Prothioconazole (Proline) and include a non-Triazole as an anti-resistance strategy. A Tillering spray has given up to 0.33 t/ha response in SAC and Teagasc trials. Watch six row varieties and Hybrid varieties for brown rust at this early stage.

Stem extension (T2): A comprehensive fungicide mix should be applied during Stem Extension (gs 32-37). Best responses will be achieved when applying closer to gs 32. A PGR can be added to this timing

Flag leaf/booting (T3): At flag leaf to heading stage a broad-spectrum fungicide such as a Triazole + SDHI mixture would be appropriate. Include a multisite on all varieties.

Winter Oat Disease Control

There are two main diseases in oats namely mildew and crown rust.

Mildew

• Mildew is the most important disease in oats
• It can affect both yield and quality
• Variety selection can play an important role in reducing the risk
• Specific mildewcides give good control

Crown Rust

• Crown rust generally develops under warm conditions approx. 20^OC
• It infects the leaves, leaf sheaths and the panicles
• It can reduce yield by 10-20%
• Triazoles mixed with strobs or SDHI chemistry give good control

For more details about individual products, timings and mixes contact your local Teagasc advisor.

Oat Mosaic Virus

• Generally occurs when oat crops are grown too frequently
• Can cause losses of up to 50%
• No chemical control
• Carried by a soil borne parasite which infects the crop
• Cultural control methods such as crop rotation, 1 oat crop every 4-5 years to prevent build up in the soil, is the only way to control the virus.