Chemistry protects genetics and genetics protect chemistry

Septoria tritici is the most damaging and the most prevalent of wheat diseases. The UK is particularly vulnerable because of our mild winters and maritime climate. There are, however, tools available to growers which enable them to reduce the impact of this disease on their crops: wheat breeders are now producing varieties with improved levels of Septoria resistance and Revysol®, BASF’s new azole fungicide consistently out-performs competitors irrespective of Septoria disease pressure, pathogen insensitivity or wheat variety.

Wheat Breeder, Bill Angus said, “Whilst I’m full of praise for the chemistry and genetics sectors as both are incredibly important and have been very successful it is crucial that growers do not rely solely on varietal resistance or solely on fungicides because doing so is likely to result in a more rapid breakdown of both. We need growers to be aware that chemistry and genetics work synergistically.

Because wheat breeders have stepped up to the mark and produced varieties with AHDB ratings of ‘7 & 8’ for Septoria resistance, growers can mistakenly think that this is a panacea for reducing costs. If they do that, they’ll reduce their yields and they will reduce their grain quality. I think the idea that Septoria resistance will replace chemistry is madness. Fungicides do more than just control fungi – they keep the photosynthetic ‘factory’ open for longer – and more biomass equates to more grain yield.

If you apply less fungicide, there will be less persistence which means that you get to a certain point, in a wet summer when the persistence of the chemistry runs out and there isn’t enough genetic resistance to take it all the way through to harvest. There is no genetic immunity to Septoria – just degrees of resistance. Future strategies should revolve around optimising fungicide use by variety.”

Ear diseases are also often prevalent in wheat crops and Mr Angus said, “If growers do not put enough fungicide on, ear diseases will not be controlled, so not only do you end up with less yield, but you end up with less good grain as well.”

What plant genetics do is give growers more ‘freedom to operate’, allowing more flexibility in terms of spray regimes. They allow growers to get it wrong and still ‘get out of jail’. That was not the case with older varieties where growers were penalised because the disease would reappear, and control would be lost.

The adoption of more Septoria resistant varieties should be part of a grower’s integrated approach to controlling the disease.”

Field trials led by Julie Smith, Principal Plant Pathologist ADAS, investigated the performance of BASF’s new azole Revysol® using a range of varieties at different ends of the resistance scale. Dr Smith said, “ “There was a benefit to applying Revysol® irrespective of the wheat variety, the disease pressure or the septoria population, although when it came to disease control and yield benefit these were biggest in the more Septoria susceptible variety.”

Resistance mechanisms in Septoria carry some similarities to yellow rust in that there are major gene and multi gene resistances.

Mr Angus said, “As with yellow rust major gene resistance has the potential to be overcome but unlike yellow rust resistance which can collapse in a couple of years, with Septoria it is likely to be a slower process rather than a rapid degradation of resistance. Septoria tritici is a population and there are different evolutionary populations in different parts of the country. I would expect major gene resistances to be overcome in a period of about 5 years.”

Revysol® is a trademark of BASF plc.Revysol contains mefentriflucanazole. Use plant protection products safely. Always read the label and product information before use. For further product information including warning phrases and symbols refer to www.agricentre.basf.co.uk Ensure all warnings and restrictions on all labels are adhered to.