Wheat growers could have more reason to spray for eyespot this season, as Paul Spackman discovers.

Early sowing and relatively damp, mild conditions last autumn/winter mean many crops could be at greater risk from eyespot, says Scottish Agricultural College plant pathologist, Fiona Burnett.

“There were reasonable levels of inoculum about after last year and so far we’ve had nothing that will reduce the risk. We’re not getting the hard winters we used to.”

Shropshire agronomist Bryce Rham says eyespot lesions started appearing in crops earlier this month. But the weather over the next few weeks will determine how bad any epidemic is. “The risk is there, but it’s a wet, warm April that will really kick it off, unlike last April, which was very dry and reduced the risk.”

Dr Burnett advises growers to assess eyespot risk (see panel) on a field-by-field basis and prioritise treatments accordingly. “Knowing your fields counts for a lot and past experience is also a big factor in identifying high-risk fields.”

With the increase in grain prices, she says treatment at lower thresholds can be more easily justified. “In the past growers would generally have treated at a risk assessment score of 29 points. But the higher prices we’re seeing justify treating at the lower 20 points threshold. This can be very easy to achieve, for example, if you are sowing early following wheat, that’s your 20 points. It’s for the grower to judge how much they think crops are at risk.”

Yield responses to moderate eyespot infection can vary considerably, from 0.5-1t/ha in wetter areas on heavy land to almost nothing on light land that burns off early, she notes.

“But with wheat over £150/t, you only need an extra 0.1t/ha to pay for £15-20/ha extra spend,” Mr Rham says. “It’s a whole new ball game.”

Product choice

When targeting eyespot, product choice is essentially a two-horse race between Tracker (epoxiconazole + boscalid) and Proline (prothioconazole), although Unix/Kayak (cyprodinil) can play a part, Mr Rham says.

“I can’t see any justification for not using Proline or Tracker at T1 because of the stem-based activity they both have. Unix/ Kayak is too expensive and doesn’t really control anything other than eyespot, apart from mildew.”

He believes Tracker slightly has the edge in bad eyespot situations, whereas Proline is stronger where rusts and septoria are also present. “I tend to recommend Tracker on cleaner varieties such as Gatsby, Alchemy and Soissons, and Proline on dirtier septoria varieties like Consort, Napier and Einstein.”

Dr Burnett also says there is little to choose between Proline and Tracker. But being Opus-based, Tracker is a good option on eyespot-susceptible varieties and can fit nicely into the T1 slot. “It tends to be used at 1 litre/ha for septoria, which will also do a good job against eyespot. If you are growing something like Robigus, which is fairly weak against yellow rust, it might also be worth choosing Tracker.

For consistent eyespot control with Proline she advises growers to use rates above 0.5 litres/ha. “You really need to be looking at 0.6-0.8 litres/ha.” In high eyespot risk situations, she says there may be some merit in tank mixing Proline with Unix.

Mr Rham says using prochloraz at T0 can also give some useful early eyespot activity. “I tend to only be going with low rates of 200g/ha, which is not enough for proper eyespot control, but it is doing something.”

What the points totals mean:

  • 29+ points: Fungicide treatment likely to be cost-effective
  • 20 points: Lower threshold for very risk conscious
  • 36+ points: Higher threshold for more risk tolerant

Eyespot risk assessment

To determine the risk of eyespot developing in a crop growers can calculate an accumulated risk score by using risk tables available at www.hgca.com/publications or www.sac.ac.uk/consultancy/cropclinic/

Assign points to each crop for each risk factor at the start of stem extension.

SAC and HGCA are in the first year of a three-year project that aims to better understand the yield response between different varieties and situations. “We’ve got a pretty good understanding of the risk factors, but we still don’t really know why at some sites plants compensate for the disease better than others,” Dr Burnett says.

The project will also look at the effect of higher grain prices on treatment thresholds and it is planned to use the results to update the existing HGCA “Determining eyespot risk in winter wheat” model, available at www.hgca.com.

Accumulated risk score

Factor

Level

Risk points

Sowing date

On/after 6 October

Before 6 October

0

5

Eyespot infection at growth stage 31-32

7% or less

More than 7%

0

10

Cumulative rainfall (mm) in March, April and May

170mm or less

More than 170mm

0

5

Tillage

Minimum tillage

Plough

0

10

Soil type*

Light

Medium

Heavy

0

1

5

Previous crop

Non-cereal

Other cereal

Wheat

0

10

15

*Add a further 5 points for brash and limestone soils
Source: HGCA