A look at robust disease programmes for wheat

for the Farm Advisory Service

Winter wheat fungicide programmes pay back well in high risk situations and seasons, but less so in low risk disease years like 2018, where there was little foliar disease pressure.

Already for 2019, winter wheat crops in Scotland are carrying more disease overwinter than they were last year when crops were remarkably clean coming into spring. Septoria and yellow rust were noted before Christmas and mildew was also present in the variety, Leeds.

Planning fungicide strategies should start early and be tailored as the season progresses. Most major ag-chems have product in place already, so are not anticipating any disruption to supply if Brexit issues emerge.

We have some newer products, but we are also wrestling with emerging resistance issues in septoria so adjustments to programmes will be needed compared to previous years. The aim of a winter wheat programme is to protect the key leaf layers – the flag leaf in particular, but also leaves two and three.

Leaf three usually emerges at GS 32 and is targeted by the first spray (T1 spray). If managing septoria alone, there is less justification for a T0 spray applied before the standard T1 start to the programme.

However, yellow rust is a key driver of the need for an earlier treatment. Data for the UK Cereal Pathogen Virulence Survey shows that the rust races in 2018 were pretty stable, with no new major shifts so, in theory, varietal ratings should hold true and varieties with good resistance should perform as expected. Knowledge of how much rust is in the area and also past experience of high risk sites around the coast, will also help pinpoint at risk fields.

Slippage in fungicide efficacy for both azoles and SDHIs means a need for a careful reappraisal of what goes where in wheat programmes. The SDHI and azole market is now fairly crowded, with plenty of product choice.

Some of the newer offerings to the market, such as Ascra Xpro or Elatus Era, will fit well at the yield responsive flag leaf timing (T2) which may give a pragmatic reason for using older offerings at T1. With slippage in efficacy, there is some sense in compensating through dose and by ‘trading up’ to the most effective actives.

The use of multi-sites is crucial, though we are concerned that multi-sites are under threat of legislative withdrawals, but we do have then for 2019. In wheat, multi-site fungicides like folet, chlorothalonil and mancozeb could all have positions – with chlorothalonil having the best efficacy. Final fungicides in the wheat programme targeting the ear are still reliant on the azoles – with a space for alternative azoles to those used elsewhere in the programme.

Yield losses are highest in weak varieties and it is encouraging that Scotland has largely moved away from older, inherently weak varieties. The difference between a 5 rating or a 6 may seem small, but can make all the difference. Later sown crops will also be at reduced risk, so prioritise the early sown sites and weaker varieties.