Helicopter crop tour finds little rust and mildew but septoria threatens

Growers are warned not to be lulled into a false sense of security and unnecessarily slash disease controlling fungicide use early this season, despite crops looking cleaner than a month ago.

A few weeks is an eternity when monitoring key diseases in wheat crops, with any slight change in conditions having the ability to turn a season on its head.

Sometimes this can work in growers’ favour and the team on last week’s Crop Doctor helicopter tour witnessed this first hand, with prevalent over-wintered rust and mildew now almost non-existent at wheat trial sites around England.

Crop Doctor plant pathologists Fiona Burnett of Scotland’s Rural College and Jonathan Blake of Adas were on hand to rummage through plots in the North, West, South and East (see below) on 30 March.

The only yellow rust their expert eyes could find were a few drying spores on the variety Reflection, near Hereford, and some unhealthy looking flecks of brown rust on Crusoe at Long Sutton. Mildew was equally hard to spot all over, even on the susceptible Leeds.

See also: Cut fungicide spend by £50/ha with the right wheat variety

The arrival of a drier and cooler spell along with a run of frosts has helped dry out these three biotrophic pathogens, but Prof Burnett says septoria is a tougher nut to crack.

“The strong impression from the tour is that all sites are similar in terms of the presence of septoria inoculum. We know that you only need some for an epidemic, and there is certainly enough there to start a fire,” she explains.

Actives

  • Adexar – epoxiconazole + fluxapyroxad
  • Aviator – bixafen + prothioconazole
  • Bravo – chlorothalonil
  • Cherokee – chlorothalonil + cyproconazole + propiconazole
  • Fandango – fluoxastrobin + prothioconazole
  • Folicur – tebuconazole
  • Librax – metconazole + fluxapyroxad
  • Opus – epoxiconazole
  • Siltra – bixafen + prothioconazole
  • Tracker – boscalid + epoxiconazole

Mr Blake agrees and says his assessment was that septoria is of most concern and is present across drill dates and in every variety – with varying severity – on the second-to-last leaf to emerge.

Infection

“The pressure looked lower at some sites, but don’t be deceived. We had infection conditions in the days leading up to the tour, so there is latent infection there. It’s likely to express itself around the T1 timing,” he explains.

So what does this mean for disease control strategies?

The first disease-holding fungicide sprays will be on, or in the process of being applied at the time Farmers Weekly goes to press, so many will be looking ahead to the GS32 T1 timing.

With lowly grain prices at present, trimming costs will be at the forefront of many minds and Mr Blake says that this could still be achieved on more resistant varieties such as Graham, which scores 7 for septoria.

It should be noted that although cleaner in the trials, Graham still had septoria high up its canopy at the Cawood site in Yorkshire.

“Varieties like Graham give you time to adjust as the septoria infection efficiency is lower and as a result, disease progress is slower.

“If conditions are less conducive to disease [at T1], then an azole plus chlorothalonil mixture might still be enough, but that is a big risk on more susceptible varieties,” he explains.

This leaves the conundrum of whether to invest in the more expensive, but more effective, SDHI-containing fungicides at this earlier timing.

Watch the video of the Crop Doctor experts in Yorkshire:

 

Compromised control

Prof Burnett says that going in cheap at T1 as leaf three emerges could compromise early disease control, so starting high and making savings later could be sensible, but acknowledges that is hard to do as it compromises flag leaf and ear sprays.

“If you do use an azole plus multisite, remember that dose needs to be high to get the control you would want.

“If opting for two SDHIs, the most important thing is to ensure balanced mixtures with multisites are used and the appropriate dose to get the job done.

“We know septoria has adapted to azoles and is starting to adapt to SDHIs, so you don’t want to risk making resistance worse.”

With resistance in mind, she also suggests picking one of the most effective SDHI-azole products, such as Aviator or Adexar, for the flag leaf spray, using the other at T1 to alternate SDHI actives.

“Also, don’t be complacent with yellow rust, as there will be pockets of inoculum that can pop up again and exploit any gaps in the programme.

“Eyespot at Long Sutton was noteworthy too and you don’t often find it so readily. It has the potential to be another unwanted spin-off from the mild, wet winter,” says Prof Burnett.


NORTH

Stockbridge Technology Centre, Cawood, Yorkshire

It has been very wet in the Cawood area this season and that is reflected by the high foliar disease levels in both winter wheat and barley plots at the Stockbridge Technology Centre trial site.

However, for independent AICC agronomist Ben Boothman, who walks crops north of the trial site up to Scarborough, says that in commercial crops it isn’t “panic stations” just yet.

He observes that frosts through February killed off the yellow rust and mildew prevalent in his wheat crops and also helped to keep septoria in check, but it is there and his main disease concern at present.

Mr Boothman had not written any T0 tickets when the tour landed at Cawood, but as Farmers Weekly goes to press, his growers will be getting their first recommendations if required.

“Some of my mixed-farming clients are looking to save costs and will miss the T0, but those applying one will hold off until there is no more than a three-to-four-week gap to T1,” he adds.

In a normal year, Mr Boothman says many local growers would save applications of newer SDHIs for the flag leaf spray and use a Tracker-Bravo or Fandango-Bravo mix, but says Aviator has been a favoured T1 product for his bigger arable clients. “Librax will be my choice at T2,” he adds.

Winter barley is an important crop locally, with mixed farmers using the crop to feed cattle, and he says plants are looking better after soaking up first nitrogen and manganese applications.

As in the wheat, mildew was present, but has been halted by frosts. Mr Boothman says wet weather disease rhynchosporium is now the main threat, which could be seen in the Cawood trials, along with net blotch.

Although T0s are becoming more common in winter barley, those in a feed barley systems tend to miss it out and whether one has been applied will dictate his T1 recommendation, which is imminent.

“We will use a 0.5 litre/ha dose of Siltra where a T0 hasn’t been applied, but those that have used an earlier spray can use a reduced 0.4 litre/ha rate,” he says.


WEST

Callow, Herefordshire

The dry and cold February and early March has so far prevented a septoria explosion in the West, but unsettled weather this week will get the disease moving, according to Bayer’s regional technical agronomist, Richard Williams.

Septoria is always the focus in the wetter West and Mr Williams says a recently applied T0 of Folicur plus Bravo will help protect plots until the GS 32 T1 timing. “I’d expect T1 to arrive within three weeks,” he says.

Local AICC agronomist David Lines agrees the recent rains will help push the disease on, with wet weather over the Easter weekend conducive to the spread of the disease and the outlook unsettled.

Mr Lines says late-sown crops after maize or more resistant varieties won’t have T0 sprays, but where crops have potential, Bravo could be added to plant growth regulator and herbicide applications.

While he used two SDHI applications at T1 and T2 last year, this season’s T1 plans again depend on variety and potential.

“In later-drilled crops, where the pressure is lower, I’m likely to use an azole such as prothioconazole or epoxiconazole, plus Bravo. There is also the potential to use a lower rate of SDHI and top up the azole component, too,” he adds.

Mr Lines will make an effort to save money on varieties with better disease resistance at T1 and says he would like to see trials in the future that test these types to see what growers can get away with.

“You still need to look after them to get the yield and we don’t have a variety you can turn your back on and not spray, but with better resistance, there is no point in just using the same programme as on more susceptible ones,” he adds.

Watch the video of the Crop Doctor experts in Herefordshire:


SOUTH

Hinton Waldrist, Oxfordshire

AICC agronomist Sam Clarke reckons he won’t be taking any unnecessary risks by cutting fungicide spend drastically in the face of low wheat prices this season.

After the wet and mild winter, he is seeing plenty of septoria in his wheat crops across Buckinghamshire, Oxfordshire and Berkshire, with any early rust infections dealt with using an earlier spray where required.

“I make tweaks to programmes anyway, regardless of grain price, but doing anything drastic is a false economy. It’s all about margin over input cost – if you cut back and
lose yield, it is ultimately the wrong thing to do.

“If you gamble with Mother Nature, she usually wins,” he explains.

Mr Clarke front loaded his fungicide programme last year and at present his mindset hasn’t changed and he plans to use an SDHI at the T1 timing.

“On varieties with better resistance, I will question that. T2 is an easy decision [to use an SDHI], as you are protecting the engine room, but these earlier decisions are trickier,” he adds.

Mr Clarke says that eyespot is a concern locally, and where varieties don’t have the Pch1 resistance gene, the disease will need attention by using sensible chemistry with activity on the stem-based disease.

“Of the two main SDHIs, Adexar and Aviator, you have prothioconazole in Aviator, which has more activity on stem-based disease.

“Adexar is more driven by rusts and septoria, so Aviator is certainly better for eyespot control at T1,” he says.

Bayer commercial technical manager Jonathan Helliwell (inset, below) agrees that Aviator covers eyespot, and also mildew, but where timings are spot on, a primary azole such as prothioconazole with multisite chlorothalonil could also be a viable all-round option.

He says it has worked well in trials compared with an SDHI-azole product at the Hinton Wildrist site, where application timings are spot on and in a protectant situation for septoria.

However, if timings slip, he says the addition of an SDHI gives you a bit more flexibility and curative activity, but should be accompanied by a minimum 75% azole dose.

“The rate needs to be appropriate for resistance management going forward,” he adds.

Watch the video of the Crop Doctor experts in Oxfordshire:


EAST

Long Sutton, Lincolnshire

With very high yield potential on his deep silt soils near the Wash, Lincolnshire grower David Hoyles is using low risk varieties to keep his fungicide costs under control.

While his spend is typically in line with other growers at about £125/ha, he hopes to achieve between 12-14t/ha, so in relation to output his fungicide costs are low.

“I have chosen Evolution and Graham this year and if I can keep my costs similar to everyone else’s and yield in the top 5%, then I have saved money. If we had high-risk varieties, we would have to spend more,” he explains.

Mr Hoyles says that crops were drilled in the last week of September to the first week in October, except some late-drilled wheat after roots, and all established well.

He notes that through the mild winter crops didn’t stop growing and despite rainfall from October and February being just 180mm, 170mm below the 350mm average, damp sea frets helped septoria and yellow rust take hold.

Aided by cooler weather and a T0 of Cherokee, yellow rust has largely disappeared in what were the thickest and most forward crops seen on the Crop Doctor tour, with some carrying up to 1,100 tillers/sq m.

However, septoria is present in the Long Sutton trials and Mr Hoyles’ commercial crops and the disease will be his main number one enemy at T1.

“We usually opt for Aviator, but if the risk isn’t there I will typically use an Opus plus Bravo mix.

“If it stays dry we might look to do more of that, but as you need a higher rate of azole now to do the job, it might be a similar price to using Aviator. I will look at costs before making a decision on product choice,” he explains.

See also: Watch the video summary of the Crop Doctor tour