As wheat ears emerge in crops across the UK, Dr David Ellerton, technical development director at Hutchinsons emphasises the importance of careful planning of T3 sprays
The T3 ear wash spray serves three important roles which should be considered in any plans; controlling ear diseases such as fusarium and microdochium, topping-up foliar disease control and extending green leaf retention, explains Dr Ellerton.
“When deciding the T3 strategy, varietal disease susceptibility, the challenges from yellow rust this season, T2 fungicide applied, and a forecast of unsettled conditions, must be considered to ensure that crops maintain their full yield potential through to harvest.”
Dr Ellerton expects most T3 applications will be spread over the next fortnight or so, but stresses that decisions must be made on a variety and field-by-field basis.
He points out that if unsettled conditions prevail then the disease risk will increase, if it stays dry, brown rust could become an issue, particularly in varieties such as Crusoe.
“The season has been a roller-coaster for many, resulting in a wide range of growth stages that could make for trickier timing of the final fungicide most crops receive, he says.
“Relatively settled weather during May meant that most T2 applications were timely. However some wind and rain did mean that there were some cases where this was disrupted, particulary in later drilled crops.”
The first thing to consider is the level of risk with regards to mycotoxin reduction and specific control of fusarium. He recommends that growers carry out the carry out the AHDB mycotoxin risk assessment for DON on the AHDB Fact sheet.
“This is in order to complete section 5 of the Combinable Crops passport assessing the risk of breaching the limits of mycotoxins in grain.”
When deciding T3 product choice, weather at flowering is key, he says.
“If it’s warm and wet, this will favour the development of fusarium species, so products should contain prothioconazole or tebuconazole which give good control of fusarium leading to reduced DON.
“There is also evidence that products based on phosphites such as Advance 66 or Phorce, when applied at ear emergence can reduce DON.
“Cooler weather at ear emergence however, will promote microdochium nivale. Whilst not producing mycotoxins, it can have a significant impact on yield. In these conditions, include prothioconazole in the ear emergence spray."
While it is tempting to apply tebuconazole alone as a cheap disease control option, not only is it poor on microdochium, but it is also less effective on DON reduction than when applied in combination with prothioconazole, Dr Ellerton adds.
“Where aphids or orange wheat blossom midge are present, think about including the adjuvant Wetcit with the fungicide, which significantly aids pest as well as disease control. This is particularly useful where grain pyrethroid resistance is suspected or powdery mildew is present.”
“Whatever product is chosen, timing and dose are critical, and a minimum of 50% of the recommended dose of fungicide for fusarium control should ideally be applied as soon as the ears complete emergence and flowering is just starting (GS 63-65).
“Delaying the application, even if the T2 spray has only recently been applied, will seriously reduce efficacy, particularly once flowering is well underway - delaying application even for a few days will result in poor control of both Fusarium and Microdochium.”
“Generally, there is less need this season to consider possible topping up of the T2 flag leaf emergence, for extended disease control, particularly for Septoria tritici, as disease levels have generally been low (apart from yellow rust), and most T2 fungicides (mainly based on SDHIs) have performed well given dry, settled weather around flag leaf emergence,” says Dr Ellerton.
“However, there may be cases where earlier failure to control Septoria or severe yellow rust in a wide range of varieties has resulted in inadequate disease control at T2. This is of particular concern where no SDHI was included at T2 leaving the crop exposed to later Septoria infection, particularly if heavy rainfall occurs as happened in summer 2019.”
“Where the T2 spray included a robust dose of SDHI and achieved good disease control, product choice at ear emergence should include triazole-based products with specific activity on ear diseases (eg: prothioconazole +/- tebuconazole or fluoxastrobin), as well as reasonable control of some foliar diseases.
“Where the T2 did not include an SDHI and there has been some rain since, or where the flag leaf spray was delayed to cover both flag and ear, then the T3 should ideally include an SDHI such as bixafen or fluxapyroxad for Septoria. Also include an appropriate azole such as prothioconazole +/- tebuconazole or fluoxastrobin to cover the risk of Fusarium or Microdochium. Folpet could also be included where there is higher Septoria pressure.”
Yellow rust, which has been a major issue this season, may also influence choice of products at T3 with products containing tebuconazole being particularly strong options, he suggests.
“Strobilurins, such as fluoxastrobin or azoxystrobin, could also be considered for inclusion in the ear spray not only for improved control of rusts but also for Septoria nodorum and sooty moulds.
“They also have the benefit of increasing yield through improved green leaf area retention and improved reaction to stress conditions. However, as with SDHIs, it should be remembered that strobilurins can only be used twice in any crop fungicide programme.”
Begin AHDB mycotoxin risk assessment before applying T3 - cereals.ahdb.org.uk/mycotoxins