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Winter Wheat, June 2019

14 June 2019

Crops are growing away from earlier leaf scorches and stresses, some arising from T1 sprays when temperatures were still fluctuating wildly. The weather continues to challenge best-laid plans and some T2 flag leaf sprays were delayed by rain. Disease levels are fortunately still low, but we do have reports of yellow rust in some crops where spray intervals allowed its ingress. You may need some adjustment to the ear spray recommendations below if rust is active in a crop, but in general, the azole-based T3 will give good rust protection which can be augmented by the use of ‘double azole’ products which add a second azole to your base azole.

Where flag leaf sprays were a little late it is still usually better to spray T3 ear sprays in a timely manner as efficacy is very much compromised a few days after infection with Fusarium and michrodochium species. Infection risk peaks after a rainfall event during flowering, so when flowering coincides with a dry spell there is some scope to delay ear sprays a little, but in wet weather (as at present) the risk of infection early in flowering is high and delaying will significantly reduce the efficacy. That can seem hard if the flag leaf spray has only recently been applied but delaying the ear spray and layering one compromise on top of another is unlikely to help.

Fungicides applied to the ears of wheat have a dual purpose as they top up earlier foliar disease management but also help to reduce the risk of ear diseases. The ear diseases themselves split into two camps – those that limit yield and those that can limit yield but also cause quality issues through the potential production of mycotoxins. It is essential that mycotoxin risk assessments are carried out for all wheat entering the food chain. The risk assessment is available online. This should be started before flowering so that you can include the risk in your T3 fungicide plans (a nice example of IPM practice)

It captures the main drivers of fusarium risk which are wet weather at flowering and then wet weather over grain filling and ripening. A record should then be kept of rainfall at flowering and over-ripening as this is the main driver of risk and accounts for almost 60% of the maximum risk score that would be possible. We are at inherently lower risk in Scotland because many of the mycotoxin forming Fusarium species like warm temperatures, but many do occur widely in Scotland so we shouldn’t be complacent. Trash is another risk factor so direct drilled crops are at slightly greater risk.

To cover off septoria management then the inclusion of an azole with good septoria efficacy applies. But there is the option of boosting rust, fusarium and microdochium protection by mixing in other azoles. Sooty moulds can look bad but are less damaging to yield. The addition of a strobilurin still has some effect on sooty moulds so they have a place in the T3 choices, although sooty moulds are seldom worth specifically targeting.

In making decisions about ear sprays, check latest application dates carefully and also any other restrictions that apply when the programme for the crop is considered – such as the two application limit for strobilurins, SDHIs and for specific actives such as chlorothalonil.

close up of wheat crop

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