Fungicide resistance is underestimated, survey finds

Farmers Weekly recently conducted a survey, supported by BASF and Syngenta, on the knowledge and attitudes of more than 260 growers and 50 advisers relating to fungicide resistance and asked industry expert Bill Clark, commercial technical director at Niab Tag, what we can learn from the findings.

Farmers should be placing more importance on fungicide resistance management to ensure products currently on the market remain effective against crop diseases for as long as possible.

See also: Farmers fear azole ban could hit wheat yields

Farmers Weekly’s survey on fungicide resistance shows that growers think septoria is becoming much harder to control in their wheat crops, but half of them don’t believe that they are seeing disease resistance on their farm.

Fungicide resistance explained

  • Pathogens that cause disease in crops, such as septoria in wheat, can evolve resistance to fungicides through genetic mutations within the population
  • It can occur in two ways: Gradual, such as the decline of azole activity against septoria, or sudden, such as the breakdown of strobilurins to the same disease
  • All fungicides are susceptible to resistance development, but some are higher risk than others
  • Of common cereal fungicides, multi-site actives such as chlorothalonil are at the lowest risk, with azoles moderate and strobilurins and SDHIs moderate to high

This is a worrying disconnect, as fungicide resistance development is a reality. We have seen this with the strobilurin fungicide group and more recently the decline in azole efficacy for controlling septoria in wheat over a number of years.

There is much discussion within the industry on the topic of herbicide resistance in blackgrass populations and in many cases these problems have been created within an individual farm unit, but disease pathogens such as septoria have the ability to spread from farm to farm.

Fungicide resistance has to start somewhere and it could be down to one farmer using fungicides – such as the new-generation SDHIs – in an irresponsible way, allowing resistance to develop and spread to a neighbour’s farm.

It is therefore a collective responsibility to ensure that we are all adopting good fungicide resistance management strategies when controlling crop diseases to ensure that the products we have remain effective for as long as possible.

In other words, one farmer could ruin it for the rest.

While the decline of the two key azoles prothioconazole and epoxiconazole has been steady, strobilurins were rendered ineffective against septoria almost overnight.

The survey has also shown that only 55% of farmers believe that SDHIs are susceptible to losing efficacy due to disease resistance, which is a further area of concern as they are moderate to high risk and must be used responsibly.

Disease resistance to fungicide pie charts

On top of that, regulatory pressure from the European Union is increasing and there is a very real chance that important azoles could also be lost for good in an instant, much like the case of neonicotinoid insecticides, and this would be a disaster.

The hope that new super-eradicant or protectant products will come along is not going to be realised, so we are likely to see a dip in disease control and a negative impact on yield in the short term.

This highlights the importance of protecting what we have and the messages from manufacturers when using their products are correct. They only want the same thing as the farmer – effective disease control products.

Key survey findings

  • Growers not linking difficult disease control with fungicide resistance
  • The susceptibility to resistance of SDHI chemistry is grossly underestimated
  • Worrying proportion of growers/advisers not flexible on fungicide budget
  • Perception that new products will come to the market to control cereal diseases

Using fungicides less frequently, in mixtures and at the appropriate timing and dose will all help to prolong their effective life.

The other interesting and important aspect of the survey results is that 12-13% of growers and advisers set a fungicide budget at the beginning of the season and stick to it regardless. It is naive to think that you can do this.

In 2012, some growers spent more than £160/ha on disease control, but I also spoke with some that put on what they thought was their final ear spray, not knowing that a second spray was needed, and didn’t apply more fungicide as they had spent their budget.

Those crops could be ruined by not finishing the programme if disease rears up again. So despite 50-60% of growers and advisers budgeting £90-120/ha – which would be fine in a lower disease pressure year – flexibility is crucial to react to disease through the growing season.

Yellow rust was also highlighted as more difficult to control, but this must be seen in the context of recent favourable seasons and the rise of the more aggressive Warrior race, not resistance to fungicides.

Resistance in fungicide spray strategy pie charts

Strategy for defining fungicide strategy

Campaign to raise resistance awareness

An initiative from agrochemical giants BASF and Syngenta aims to raise awareness of the threat from fungicide resistance development and provide practical advice for the industry on how to form sustainable fungicide strategies.

Syngenta’s wheat campaign manager Melanie Wardle believes the Farmers Weekly survey results justify the need for the Take Ownership Now (TON) partnership campaign.

“Many growers believe they aren’t seeing resistance on their farm and, if that is the case, they need to make sure they are forward thinking and aim to keep it that way.

“We all want the best disease control possible and what works today might not work as well tomorrow, so providing growers with the information to ensure they are using products correctly is crucial,” explains Mrs Wardle.

Both companies have various key cereal disease control products in their portfolios, including new-generation SDHI active ingredients.

BASF’s Jonathan Ball says that there are various factors that could have a negative effect on the available chemistry, some of which are out of the industry’s hands – such as EU legislation and the rate of introductions of new active ingredients coming to the market slowing.

“In the 2014 season, disease control was good despite the high pressure. So the chemistry we have is still effective and with potential product losses and launching new products becoming increasingly challenging, we must keep it that way.”

Fungicide groups susceptible to disease bar graph


Cereal diseases on the rise bar charts

Resistance management and fungicides cost bar charts