Fungicide programmes for wheat

Focused on the main spray timings, use this information to design fungicide programmes to optimise control and manage fungicide resistance risks in wheat.

Resistance management should be considered throughout the spray programme.

T0: Consider alternatives to azoles, such as strobilurins and multi-sites (according to the target disease), or add a multi-site to protect the azole

T1: Mix azoles with multi-sites and, where disease risk merits it, add an SDHI, QiI or strobilurin (depending on the target disease)

T2: Mix azoles with multi-sites and SDHIs, QiI or strobilurin (depending on the target disease) for maximum efficacy and resistance management (note: only one QiI application is permitted per season).

T3: Add a multi-site to azoles for added septoria control and resistance management

Additional fungicide sprays should never be a default part of fungicide programmes. If there is a clear economic benefit, multi-sites and other non-azole chemistry should be preferred. However, be aware of timing restrictions on multi-sites.

Low levels of resistance in some popular varieties, as well as the unpredictability of disease, mean fungicide use is relatively high in wheat crops. However, such use puts selection pressure on pathogens, making fungicide resistance more likely to occur. These steps will help you maintain sustainable levels of control.

Autumn

Fungicide applications are rarely required in the autumn. However, early drilling followed by a mild autumn may result in high levels of rusts and mildew. For mildew control, use a mildewicide. For rust control, use a strobilurin.

T0: 2–4 weeks earlier than T1 (leaf 3 emerged)

A T0 fungicide is only economic when mildew, yellow rust or brown rust risk is high on susceptible varieties and where these diseases are active. Some sprays targeted at foliar diseases at T0 may also help control eyespot. However, if eyespot is the main target, a T0 may not be economic. Septoria tritici control at this timing is rarely associated with yield benefits, even in high disease pressure situations. However, it can insure against a delayed T1 in susceptible varieties.

For mildew, use a mildewicide. For rusts, use a strobilurin. For septoria tritici, where the spray is an insurance against a weather-delayed T1, use a multisite. Avoid using an SDHI or QiI at this timing to reduce the risk of resistance.

Do not use an azole, unless necessary. An azole will select for more resistant septoria isolates. If an azole is used, consider adding a multisite to protect it (within label recommendations on maximum dose, application number and timing). Adjust dose to reflect risk, using too high a dose is poor resistance management.

Late-sown disease resistant varieties do not require a T0 for the control of septoria tritici. For early drilled and susceptible varieties, applying a T0 for septoria risk should maximise the use of multisites and minimise the use of azoles. If rusts are the target, use a strobilurin.

T1: fully emerged leaf 3 (GS31–33)

Sprays at this timing can help protect the fully emerged leaf 3 – mainly from septoria tritici – and provide additional protection from other foliar diseases (including rusts and mildew) on leaves 2 and 4. It is also a key timing for eyespot control, but optimise the timing of the spray for the control of foliar diseases. Adjust dose to reflect risk, using too high a dose is poor resistance management.

The optimal time is as soon as leaf 3 is fully emerged. Usually, this coincides with GS32, but it can vary between crops. In very early sown crops, leaf 3 can emerge at GS33. In late-sown crops, it can emerge at GS31. Dissecting plants is the most reliable way to identify whether leaf 3 is fully emerged. Prompt timing is most important on septoria tritici-susceptible varieties (e.g. disease ratings 5 or less).

At this timing, base sprays of an azole plus multisite mixture. The addition of an SDHI, QiI or strobilurin may be useful depending on the target disease. Be aware that only one QiI application is permitted per season. The use of high-input programmes on septoria is unlikely to be economical in varieties with a high septoria tritici resistance rating, especially in late-sown situations (e.g. from late October). However, September-sown susceptible varieties (e.g. disease ratings 5 or less) may merit robust programmes. If yellow rust is the target, ensure the products chosen have good activity. If additional efficacy is required, consider adding an azole or strobilurin with good activity. Where the eyespot risk assessment shows a high risk, include a product with good efficacy against this disease (e.g. a prothioconazole or boscalid-based spray). If mildew levels are high, ensure products targeted at other wheat diseases have mildew on the label. In susceptible varieties, consider a specific mildewicide.

To manage resistance, use a balanced mixture (where possible) of an azole plus multisite. Only add an SDHI where disease risk merits it. Use the lowest dose possible to obtain the required control. However, ensure each component of the mix gives comparable levels of control (this will require a robust dose of azole in relation to that of any SDHI included). Maximise the use of multisites to protect the azole/SDHI. 

T2: flag leaf fully emerged (GS39)

This is the most important spray timing in wheat. It controls disease on the top two leaves, which contribute about 65% to yield. Yield responses to this spray timing are most likely to be profitable. The main target disease is septoria tritici, although rusts are also targets. Prompt timing is most important on varieties susceptible to septoria tritici (e.g. disease ratings 5 or less). Adjust dose to reflect risk, using too high a dose is poor resistance management.

Apply this spray as soon as most flag leaves on the main tillers have fully emerged (GS39). Dissecting plants may be required to confirm that it is the flag leaf. Use mixtures (azole, SDHI, QiI, strobilurin, multisite) to ensure good control of septoria tritici and rusts. In addition to maximising efficacy, the use of mixtures is also essential for resistance management. Use the lowest dose possible to obtain the required control, but ensure that each component of the mix gives comparable levels of control (this will require a robust dose of azole in relation to that of any SDHI or QiI included). Inclusion of a multisite helps to protect azoles, SDHIs and QiIs from resistance. As well as providing better resistance management, inclusion of a multisite can also improve septoria tritici control.

T3: GS59 or GS63–65

At GS59, use a T3 spray to top up foliar disease control on the top two leaves or, at GS63–65, to control fusarium/microdochium ear blight. A spray at GS63–65 also gives additional top-up control of foliar diseases, although it is not as effective as a spray at GS59. Consider the relative importance of foliar disease and ear blight to decide which timing to use. If no T3 spray is planned, it is important not to delay the T2 spray. Delaying the T2 spray to allow part of the ear to emerge will lead to poorer foliar disease control on the critical flag leaf and leaf 2.

Sprays applied around GS59 can help maintain canopy size and prolong its duration by protecting leaf and ear green area against foliar diseases. It is only usually required for brown rust, where it is seen. At this timing, septoria tritici control is usually only needed in the north and west of the UK, where it is often wetter, with an extended growing season. A spray at this timing is not effective for controlling ear blight.

Fusarium and Microdochium species cause ear blight. Dry weather throughout flowering results in a low infection risk and a spray is unlikely to be cost-effective. If the weather is wet or forecast to be wet during flowering, the spray can be beneficial. The optimum time to spray is at early-to-mid-flowering (GS63–65). Sprays are not effective once flowering is complete. As well as reducing yield loss, the control of ear blight at GS63–65 also helps to reduce mycotoxins produced by Fusarium species. Where fusarium mycotoxins are not a major concern (e.g. resistant feed wheats), this spray is not usually required. 

For ear disease control, use an azole or azole-based mixture with specific activity against ear diseases and a minimum of a three-quarter dose of azole. Azoles also have brown rust activity. On septoria tritici-susceptible varieties, ensure the azole is also active against septoria tritici. Add a multisite for added septoria tritici control and resistance management (within label recommendations on maximum dose, application number and timing – folpet cannot be used after GS59, but mancozeb is an acceptable alternative and can be used until full flowering). Consider adding a strobilurin, where grain filling is likely to be prolonged or where brown rust risk is high.

Other timings

Do not use pre-T0, T1.5 and T4 spray timings, because they rarely give a yield benefit and can increase selection for resistance. In exceptional circumstances, a spray at one of these timings may be required. Use a multisite or non-azole to reduce resistance risk. Always take account of any timing and total dose restrictions. Sprays at these timings indicate that the long-term management strategy needs to be changed. In particular, look more carefully at other measures, such as rotation and variety choice.

The main diseases to consider in spring wheat are septoria tritici and – particularly at earlier spray timings – mildew and rusts. Compared with winter wheat, the gaps between fungicide timings are shorter. As less persistence is required, lower doses are an option.

T1: GS29–31

Use a multisite plus azole, possibly with the addition of a mildewicide for mildew and/or a strobilurin for rusts.

T2: GS37

Use a multisite plus azole, possibly with the addition of a mildewicide for mildew and/or a strobilurin for rusts.

T3: GS51–61

As per winter wheat, a T3 may be required for fusarium control, if it is wet during flowering. An azole is an appropriate choice, possibly with the addition of a strobilurin in high brown rust situations.

Fungicides that have multisite modes of action – folpet and mancozeb – are at lower risk of resistance and have no recorded instances of resistance in cereal foliar diseases.

Use multisites as a cost-effective mixture partner to protect higher-risk single site-acting fungicides (e.g. azoles and SDHIs) at each application timing.

Plan the programme to maximise use of the most effective multisite options – i.e. make full use of total maximum doses and application numbers (without exceeding them).

Although the use of the chlorothalonil (CTL) is no longer permitted (since 20 May 2020), it is essential to use other multisites, as part of a highly effective anti-resistance and disease management strategy.

As folpet and mancozeb have lower efficacy than CTL, higher doses are required. In fungicide performance trials for septoria tritici (2012–14), half rate of CTL (Bravo) gave about 70% control and a full rate of folpet (Phoenix) gave about 40% control (protectant situation).

Cereal chemistry changes demand a new approach to disease management. Fiona Burnett (FRAG and SRUC) describes how to weave fungicide options into programmes to protect efficacy and maintain sufficient disease control.