Septoria tritici The threat in wheat for 2013 www.cropscience.bayer.co.nz Photograph Copyright John Innes Centre
Don t get caught out by Septoria tritici this spring! There is a lot of talk at the moment about Septoria tritici and more uncertainty and concern about effectively controlling this disease. I know, because in late August I visited paddocks from Ashburton to Winton and the disease was present in every paddock. Even in June I could find it in a Bayer trial near to Fielding on the North Island, nowhere is safe from this aggressive wheat disease! A disease that can reduce your wheat yields by 3-4 tonnes/ha if left unchecked. Not surprisingly, talking to farmers while on my travels I learnt that there is a lot of worry about this mysterious disease that has suddenly become so common. Farmers were asking questions like Why is it here? What should I be looking for in my crops? How do I control it? When should I spray fungicides? What dose do I have to use? Farmers are right to have a healthy respect for the disease but this doesn t mean that Septoria tritici can t be controlled. It just takes the adoption of a strong effective fungicide programme using robust rates applied at the right time. Having dealt with Septoria tritici since the early 1980 s in the UK, I have learnt a thing or two about this disease. In this publication I have tried, with help from my colleagues, to pass on some of that knowledge: To outline the disease, the factors that encourage its development and how to control it using Proline and Twist two highly effective Septoria tritici fungicides from Bayer. Marketing Manager Arable Crops Septoria tritici what should I be looking for? Early in the season look for irregular or oval blotches on the lower leaves. Often, black spore cases (pycnidia) can be seen. Later in the season Septoria tritici lesions tend to be constrained by the leaf veins and are long and narrow Early in the season lesions are usually oval but later they tend to be in stripes. But in all cases the give-away is the presence of small, black spore cases.
Septoria tritici the threat for 2013 Following the last two years when Septoria tritici (also referred to as speckled leaf blotch) has been a major problem in many wheat crops, advisors and farmers are concerned about what Spring 2013 may bring. And rightly so, as Septoria tritici is an aggressive disease easily capable of reducing yields by several tonnes per hectare. Where has Septoria tritici come from? While the disease has flared up recently we shouldn t be surprised to find the disease in our wheat paddocks as it has been present in New Zealand for many years. When our ancestors domesticated wild grasses many thousands of years ago, to develop the crop we now know as wheat, they inadvertently provided Septoria tritici with a great new host to live on. Septoria tritici took full advantage of this, traveling with wheat around the world, until now it is a global problem in all wheat growing countries including New Zealand. While Septoria tritici is not a new threat here, it is also not a problem you will be faced with every year. Not only are some seasons much worse than others (with 2011, and especially 2012, being bad years for the disease) but some paddocks will be more severely affected than others. Unfortunately current indications point to 2013 also being a Septoria Year. To understand why this is, it is necessary to understand the key components that impact on the severity of any arable disease: the pathogen (the life cycle of the disease), the prevailing weather and the host (the crop variety). This is called the disease triangle. The Disease Triangle Aggressive Septoria tritici infection, Canterbury, 9th September 2013. Ensure you monitor your paddocks regularly to avoid getting caught out!
Septoria tritici understanding the disease triangle The life-cycle Septoria tritici needs living tissue to grow and therefore the disease s life-cycle starts when the crop emerges. Resting spores on the previous year s stubble release large numbers of small airborne spores which are capable of infecting the new season crop. The spores are released over a period of several months but with the main release period being March to May in New Zealand. The impact of this is that early emerged wheat crops are much more prone to Septoria infection than crops that emerge from mid-may onwards. Rain splash moves canidia up plant causing re-infection Primary infection results from canidia and ascopores Typical eye-shaped leaf spotting symptoms occur At end of season pseudothecia develop Overwinters as seed-borne mycelium and as pseucothecia on crop debris Illustration courtesy HGCA, United Kingdom Once the Septoria spore has germinated on the leaf and infected the plant (usually by entering via the stomata) the fungus grows invisibly within the leaf until it is ready to produce a lesion on the leaf, release new spores and complete the life cycle. Once the Septoria spore has germinated on the leaf and infected the plant (usually by entering via the stomata) the fungus grows invisibly within the leaf until it is ready to produce a lesion on the leaf, release new spores and complete the life cycle. The period that the fungus is growing within the leaf is called the latent period. During the latent period the infected leaf looks healthy with no visible symptoms of disease. For most of its life Septoria tritici really is the invisible killer. The prevailing weather The prevailing weather affects Septoria in two main ways: Rainfall and crop moisture play a key part in disease dispersal and spore survival. Secondly, temperature affects the speed the disease develops (in other words the length of the latent period). Both factors play a part in determining the severity of the disease epidemic you will face. Septoria tritici is a disease that thrives under cool temperatures and wet conditions, with moisture playing a key role, both with disease spread and also with the ability of the spore to infect the leaf. The most common way Septoria spreads within the crop in spring and early summer is by direct, leaf-to-leaf, contact. This is caused by wind physically rubbing infected leaves and non-infected leaves together. However, this needs to be in conjunction with a moist crop e.g. from a heavy dew, irrigation or rain, as Septoria tritici spores need a period of several hours with moisture to germinate and successfully infect the leaf. A less common way Septoria spores can spread is by being splashed around and up the crop canopy, by a process called rainsplash dispersal. As the term suggests this needs a period of fairly heavy rain** to do this.
We spoke of the latent period earlier and one of the many challenges with Septoria is that the latent period can take a very long time to complete. Growth of the Septoria fungus is governed by temperature with New Zealand data showing that it takes between 350 and 450 day degrees* from the time infection takes place until lesions are visible. In Canterbury, in early spring, the latent period can take 2 months to complete. This means that a plant that is infected with Septoria today will not show lesions on the leaf until early November. While infections that take place in early summer develop quicker, the latent period can still take 4 weeks in late November and December. *To calculate day degrees take the maximum temperature + minimum temperature and divide by 2 (ignore minus temperatures just use zero) For example: maximum temperature 150 C, minimum temperature -20 C = (15 + 0) / 2 = 7.5 day degrees. **The rainfall required for the rainsplash dispersal of Septoria tritici spores has been defined as total of 10mm rainfall over a period of 1-3 consecutive days. The crop variety All varieties of wheat are susceptible to Septoria tritici and while some varieties are more resistant to the disease than others the reality is that all commercially successful New Zealand wheat varieties should be considered susceptible. Unfortunately this means that unlike some other diseases it is difficult to manage the risk of Septoria tritici through varietal choice. How to manage Septoria tritici? It can be seen from understanding the disease that the only practical non-chemical way of reducing the risk of Septoria tritici is to delay planting but this can carry a severe financial penalty. In 2012 FAR trials demonstrated that delaying planting from mid-march to mid-april resulted in an average yield loss of 1.8 tonnes/ha. In most situations delaying planting is not the right approach. What to use and when to apply your fungicide programme? For 2013 the products recommended by Bayer for the control of Septoria tritici are Proline at GS 32 followed by Proline + Twist at GS39 and GS55-59. Both Proline (from the DMI group of fungicides) and Twist (from the strobilurin group of fungicides) are very effective against Septoria tritici (and all other key arable diseases) and are from different chemical If Septoria tritici is present in the lower leaves then as long as sufficient moisture is present for Septoria spores to germinate and survive long enough to infect the plant Septoria tritici wil spread throughout the canopy groups. This means if they are used in mixture, the two fungicides will not only give a high level of disease control but also offer a strong anti-resistance programme. The key fungicide timings to control Septoria tritici are GS32 (second node), GS37-39 (flag leaf emerging to fully emerged) and GS 55 (ear emerged).
Where does yield come from? In a well-managed wheat crop such as the one illustrated then most the crop s yield potential, around 90%, is manufactured by the top two leaves and the ear. These are the leaves that intercept the most light and so it is critical to keep these leaves and the ear free from disease for as long as possible. Certainly throughout the grain fill period until the crop starts to naturally senescence. This is achieved by applying effective fungicides as the flag leaf emerges and as soon as the ear is emerged. Ear Flag Leaf 20% 45% 90% This doesn t mean that disease control on leaf three isn t important. While this leaf only delivers 10% of the crop s yield, by protecting this leaf from disease infection, you are providing the foundation for successful disease control later in spring. The reasons for this are explained below but it is worth noting that it is always easier to keep a crop free from disease than it is to control disease once it is well established. Final Leaf 2 Final Leaf 3 25% 10% The GS32 application At GS32 final leaf three (counting from the top of the plant) has just emerged. It is important to keep this leaf protected from disease for two reasons. This leaf is responsible for 10% of your crop s yield but more importantly in a few weeks time this leaf will be at the same physical level in the crop canopy as final leaf two and also the flag leaf as it starts to emerge. This means that leaf three plays a key part in direct transfer of disease from the lower part of the canopy to the upper leaves: Leaves that provide most of a crop s yield and which are so important to protect from disease. Any disease present on leaf 3 wil be directly transferred from this leaf to the upper leaves. A bonus from this application is that usually at GS32 final leaf 2 is starting to emerge and so at least part of this leaf gets fungicide protection. Septoria tritici infection. South Canterbury. Late August 2013
Proline 0.4 L/ha Proline + Twist Proline + Twist The GS37-39 application At GS37-39 the flag leaf is emerging or has just emerged and the flag leaf is responsible for nearly half of your crop s yield. So we have to keep this leaf free from Septoria tritici for as long as possible which means applying a fungicide straight away. A bonus is that this fungicide will also provide a level of disease control on leaf two. In fact a combination of the protection provided by the GS32 spray on leaf two, coupled with the protection provided by a timely flag leaf spray, will ensure that all of the top three, yield delivering leaves are protected from disease. The GS55-59 application At GS55-59 the ear has emerged. This fungicide application is mainly aimed at protecting the ear from disease but it also acts as a top-up for the flag leaf against Septoria tritici. This is particularly useful when the second spray was applied before the flag leaf was fully emerged. Untreated crop showing Septoria tritici symptoms. Leaf loss will limit yield potential. Bayer trial. South Canterbury 2012. It is worth noting that during the grain till period a wheat crop that has been protected from disease will be adding 0.2 t/ha yield per day! Treated wheat crop protected from Septoria tritici. Bayer trial. South Canterbury 2012. When to use Proline WHEAT Best use guidelines to control Septoria tritici Proline 0.6 L/ha Proline + Twist 0.6 + 0.25L/ha Proline + Twist 0.6 + 0.25L/ha 0.4 + 0.25L/ha 0.4 + 0.2L/ha GS 29 30 31 32 37 39 49 58-65
Why should I worry about disease resistance? Many will know that in Europe Septoria tritici is resistant to strobilurin fungicides and that DMI fungicides are less effective than they used to be. Many factors have led to this situation, not all of which apply to New Zealand, but it is true that what has happened in Europe could happen here. We need to try to prevent this happening in New Zealand while we still have a chance to do so. The key actions you can take are as follows: 1. Use fungicides mixtures. Apply two or more fungicides that are active against Septoria tritici with different modes of action. For instance mix a DMI such as Proline with a strobilurin such as Twist or an SDHI fungicide such as Seguris Flexi. 2. Alternate DMI fungicides. For instance use Proline as your first and third DMI fungicide but with Opus as your second DMI. 3. At T1 mix DMI fungicides. Proline + Falcon is a stronger anti-resistance approach than applying Proline alone. 4. Where practical use cultural techniques. Delay planting and bury the previous year s stubble, especially for second and subsequent wheat crops. 5. Use robust rates of fungicides and pay attention to fungicide timings. Call toll free: 0800 428 246 www.cropscience.bayer.co.nz Proline and Twist are registered pursuant to the ACVM Act 1997 Nos. P7250 and P7437 and are approved pursuant to the HSNO Act 1996, Nos. HRS001661 and HSR002437 respectively. Proline, Twist and Falcon are registered trademarks of the Bayer Group. Opus is a registered trademark of BASF Ltd. Seguris is a registered trademark of Syngenta AG. BAYER UTE CARD is a trademark of the Bayer Group. For more information on Bayer CropScience products, contact the following Bayer CropScience Regional Sales Managers: Phil Bertram Upper North Island 021 426 825 Marc Fox Gisborne/Hawkes Bay/Nelson/Marlborough 021 426 823 Jeff Smith Lower North Island 021 426 824 David Parker North and Mid Canterbury 021 760 794 David Weith Mid and South Canterbury 021 426 096 Daniel Suddaby Otago and Southland 021 426 822 Colin Dunstan Seed Treatment Specialist, South Island 021 323 147 Bayer CropScience 2013. Download the new Crop Solutions App from the Apple App Store or Google Play Store