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Don't Under estimate the value of T3 sprays: May 12th

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Cutting back on the T3 ear wash fungicide before properly assessing disease risk could compromise your entire wheat disease control programme, leading agronomy firm Hutchinsons says.

Relatively low disease pressure so far this spring combined with lower grain prices is leading many to look for potential cost savings, with the T3 spray often regarded as an obvious target, especially as fungicide spend shifts to the earlier timings.

But technical development director David Ellerton says it is impossible to predict disease pressure on the ear until very close to ear emergence and growers must be prepared to tailor fungicide programmes to prevailing conditions nearer the time, rather than making premature plans to cut back.

“Generally disease pressure so far has been lower than last year which was exceptional particularly in terms of Septoria, but we are now into a spell of more unsettled weather and things can change very quickly, as we experienced in 2012. Up until mid-April [2012] we were in a drought, yet it turned out to be a very bad year for both foliar and ear diseases with many growers powerless to do anything about it with a serious lack of spraying opportunities.

“Lack of late disease control on the ear risks both yield and quality and can undo all the hard work and investment of earlier sprays.”

Kent-based agronomist James Short agrees, adding: “Given how unpredictable our weather can be, every season potentially has a sting in the tail, so it is foolish to risk compromising the considerable investment in crops to date by not putting a T3 on.

“There is obviously a lot of focus at T3 on managing fusarium risk in quality wheats and varieties with premium potential, but all crops will benefit if disease pressure builds. There may be some flexibility on products and dose rates for straight feed varieties though.”

In high disease pressure situations, such as 2012, the yield benefit from a T3 spray can be up to 0.75t/ha, although Dr Ellerton acknowledges its contribution to both yield and quality may be much lower under less severe pressure.

“There may well be scope to cut back on later sprays, but only do so according to disease risk at the time. The idea of taking a protectant approach to septoria with the T0 and T1 spray is identical to the concept of using the T3 to protect against sooty moulds or Fusarium/Microdochium, whether you’re growing for feed or milling.”

Target Disease and Milling

Fusarium ear blight, Microdochium nivale and sooty moulds are the three main targets for ear wash fungicides, although there may also be a need to top-up foliar action depending on disease pressure and the effectiveness of the flag leaf spray, Dr Ellerton says.

Weather during June and July, has the biggest impact on the type of ear diseases most likely to develop, with cool, wet conditions favouring Microdochium, while Fusarium (and associated mycotoxins) thrives in warm, wet weather.

Rusts can also be an issue at this stage. Warm weather often initiates late brown rust infection while yellow rust prefers cooler conditions and can infect the ear of susceptible varieties. This is something to be increasingly vigilant for due to the emergence of the aggressive, fast-developing Warrior race, he notes.

Timing of the T3 spray is not as growth stage specific as the T1 or T2 applications, but still requires close attention.

“You must wait until the ear is fully emerged and apply fungicides just before rain is due. If it stays dry you can afford to leave the ear exposed a little longer, but once it rains spores will start germinating and disease will take off, so make sure you allow enough time to get around and treat all crops in time.

“Remember that applying the T3 too soon could mean it runs out of steam early and may require a follow-up (T4) to protect crops during the grain filling period. If that does happen, it’ll be a repeat of similar products, but don’t forget to check the harvest intervals and cut-off dates for latest application.”
 
david ellerton says it is impossible to predict disease pressure on the ear
 
Product Choice and Timing

Dr Ellerton says an effective SDHI-based flag leaf spray should sufficiently control most foliar problems, allowing growers to focus T3 products on specific ear diseases.

Prothioconazole-based fungicides are most effective against Microdochium and will also do a good job against fusarium and top-up septoria control, he says.

Metconazole and tebuconazole are less effective against Microdochium, but are strong against Fusarium and sooty moulds, while tebuconazole is also his favoured option for controlling late yellow rust.

Prothioconazole-based ear wash sprays are also the preferred option for Mr Short, who says products containing prothioconazole in mix with fluoxastrobin or tebuconazole offer better protection against rusts than straight prothioconazole.

He favours a slightly earlier T3 application before flowering to protect grain quality in ears and top-up disease control on the flag leaf.

Strobilurin-based products are another option at T3, offering control of sooty moulds and both types of rust, as well as for green leaf retention, although they generally have limited efficacy against Fusarium and Microdochium, adds Dr Ellerton.

“Tailor product choice or combinations of products to disease risk at the time and the weather. Unless we end up in a prolonged drought and know for sure it will stay dry, then it’s probably worth playing it safe and at least applying a dose of a relatively cheap fungicide at T3.”

*Growers are also advised to assess the risk of mycotoxins by using the HGCA risk calculator. This risk can be reduced by use of appropriate ear fungicides. See http://www.hgca.com/mycotoxins