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Weather making spray timing ‘challenging’

14 June 2019

“It is essential that mycotoxin risk assessments are carried out for all wheat entering the food chain”

The rainfall over recent weeks started out as a welcome relief to earlier dry conditions – but, inevitably, the prolonged period of showers has knocked some spray plans awry.  In winter wheat crops, it has impacted on the ability to get the all-important flag leaf spray on in good time, but for the most part, delays were not too serious and initial plans were just deployed a little late.  Though, for some crops, the delays were longer.

Fortunately, disease levels in the majority of crops are still low so it is not the crisis it might have been if disease pressure was high.  It is always a judgement call to know what to do when spraying gets delayed, but in general, it is best just to get back on track with subsequent spray and

Winter wheat with fusarium (seen as pinkish) on the ear and hints of sooty moulds infecting where flowers have dropped away

not to make further compromises to the efficacy of later sprays by also delaying them.

The efficacy of the ear spray to protect against Fusarium is, though highly timing dependent and drops dramatically a few days after infection, so delaying this final T3 ear spray much beyond early flowering can compromise the protection it affords significantly.

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.  This risk assessment captures the main drivers of fusarium risk which are wet weather at flowering and then wet weather during grain filling and ripening.  The risk assessment should be started before flowering in the crop so that the risk rating of the crop can be factored into T3 fungicide plans.  A copy of the risk assessment is at this link //cereals.ahdb.org.uk/mycotoxins

A record of rainfall at flowering and over-ripening is one of the key pieces of information needed to complete the plan as this is the main driver of risk and accounts for almost 60% of the maximum risk score that would be possible.

Scotland is inherently at lower risk than the rest of the UK because many of the mycotoxin forming fusarium species like warmer temperatures.  Howeve3r, they do still occur here, so this doesn’t mean Scottish crops can’t exceed risk thresholds.  Trash is another risk factor so direct drilled crops are at slightly greater risk and following a maize crop adds significantly to fusarium risk – but that scenario is still relatively rare for most of the arable regions of Scotland, although more common in silage growing areas.

Continued protection against septoria rust and other foliar disease is also a factor in selecting head spray fungicides so the inclusion of an azole fungicide with good septoria efficacy is important, as is the inclusion of a milti-site.  The SDHI fungicides have less of a place in the ear spray as their spectrum of disease management fits best at stem extension and flag leaf.

Fiona Burnett SRUC, for the Farm Advisory Service

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