Keeping tabs on variety ratings

A series of multi-year trials, which are a collaboration between Bayer and KWS, have been exploring the relationship between variety disease ratings and yield responses to fungicide rates.

In 2020/21, plots of the winter wheat varieties KWS Guium, KWS Dawsum, KWS Siskin, KWS Palladium and KWS Extase were drilled on September 30 and three different fungicide programmes were applied across the season (see table 1).

As well as tracking yield and quality responses, Bayer used its Crop Check rapid disease detection technology to monitor disease levels in the untreated plots throughout the season (see table 2) to determine how disease ratings were stacking up.

Gareth Bubb, commercial technical manager at Bayer, says: We did sampling on June 2 and nothing had septoria but Guium, which is not surprising given its 4.7 rating.

Later in the season the results from June 14 showed that Extase had the least amount of disease, followed by Palladium, and the highest amount was in Guium.

This is all as we would expect and it showed their variety scores were bang on.

We also looked at the association between higher yields and high green leaf area.

Extase had both of these over Guium.

This is because some varieties have inherently higher potential for yield than others, but some cant meet their yield potential because disease stops them from getting there as they dont have enough leaf.

However, even the treated trials saw cost-effective yield responses to fungicides with the highest resistance ratings.

Bob Simons, a crop consult ant working with KWS, says: Last year showed us that with moderate to high levels of disease, all these varieties responded to fungicide inputs.

With a variety like Extase, youre still going to get a response to using good fungicides.

Its decent ratings mean there is scope to economise on T1s but a strong T2 that includes rust protection is recommended.

If people are going to take advantage of its Group 2 status youd really be wanting a decent T3 as well.

There are opportunities for savings but dont try and overdo it because you could get caught out.

Highlighting last years problems in varieties with Cougar parentage, most noticeably in earlier drilled crops, Mr Simons adds: These issues were a combination of early drilling and then because of the difficult spring/summer, indecision in terms of what people used fungicide-wise, which were a bit low on rates in some instances.

With low disease levels in crops early on and not much rainfall, inputs were cut at T1 and the long interval between T1 and T2 left many ‘firefighting, says Mr Bubb.

If you put a low rate on something with inherent higher risk, you will be firefighting later on again.

Even if risk is low, I wouldnt be using straight azoles anymore, so even in a low input system you would need a reduced rate of Aviator.

In a higher risk scenario I would say one litre/hectare of Ascra at T1.

There is definitely scope to reduce fungicides, but I think people have different views on how low you can go.

In wider trials by Bayer exploring other commercial varieties, crop quality was also assessed, with significant responses seen in some varieties.

Mr Bubb says: We saw a massive difference in quality in Skyfall and Zyatt there were yield responses but the difference between treated specific weights and untreated were huge.

One of the things Ive seen year-on-year is Extase has a good yield response but no real difference between quality.

Its always very similar treated and untreated.

With this seasons high growing costs, Mr Bubb recommends broad spectrum control from the start to keep disease levels down, which can then be tailored later on depending on pressure.

Start off on the right foot if you dont get off to a good start at T1 youve already lost the battle when you get to T2.

Have a plan but be willing to adapt, he says.

Its too early to see where we are, but there are certain principles people should have in their head about how theyre going to achieve yield.

In wheat you want to keep it green as long as possible.

Try and maximise crops this year so youve got money in the bank going into next year.

Callows location in the west of England means septoria is the disease of focus at the site.

However, although yellow rust is relatively easy to control, there are still big yield responses to fungicides in trials on crops infected at the site because it is such a devastating disease, says Mr Bubb.

Revystar gave slightly better results than our lower input programme I would say thats too low for septoria but okay for yellow rust, but you will get more response from spending the same on a bigger programme.

At Bayers Oxfordshire trials site, the worst untreated yields were seen in varieties with low yellow rust ratings.

Mr Bubb says: The yield responses were not as high at Callow because they didnt have late season septoria and you dont have to spend a huge amount of money to keep on top of yellow rust.

If youre sowing later, think about yellow rust.

If youre sowing earlier you definitely need to be focused on septoria.

However, if youre using a good standard programme, you should be able to do both.

• Aviator bixafen + prothioconazole
• Ascra bixafen + fluopyram
• Savannah tebuconazole
• Firefly prothioconazole + fluoxastrobin
• Revystar fluxapyroxad + mefentrifluconazole