Sharp focus on eyespot

9 February 2001

Sharp focus on eyespot

This weeks crop enemy to

come under closer scrutiny

is eyespot, a frequently over-

looked stem base problem in

cereals which looks set to

cause extra yield loss in

crops this season

A PROBLEM of intensive cereal production, eyespot cost UK wheat growers £20m in lost yield last year.

In the past four years levels of the disease have risen sharply, with the average annual loss of £17m exceeding typical losses to septoria, says Nigel Hardwick of the Central Science Laboratory.

"The combination of cooler, wetter springs, together with poor varietal resistance and use of fewer eyespot sprays, have led to an increase in the disease," he says. "The introduction of the strobilurins may have had a contribution – growers are using them at the key GS31 timing, but they have little effect against eyespot."

Two strains of eyespot are at large – the rye type and the wheat type. The more damaging rye type is by far the most common. So where a fungicide is used it should have activity against both strains, he says.

Control is difficult for two reasons. It is hard to identify and fungicides often have limited activity because they do not get to the stem base, where the lesions are found.

The symptoms

Bill Clark of ADAS Boxworth believes that the serious yield losses seen last year were due to an interaction between eyespot and take-all. "On many plants, there were multiple lesions up the stem."

He adds that growers underestimate eyespot because they dont see it. Advice is to check crops two to three times in the next month (or between GS30 and 32), as GS33 is the latest that spraying can be done for control.

"Take samples and look at the stem base for signs of lesions," advises Mr Clark. "Pull up 25 tillers in a field and peel off the outer leaf sheath. If there is a lesion underneath, known as a penetrating lesion, then the situation may be severe."

Identification is not easy, so there is a huge underestimation of the need to spray, he adds. Decisions should be made by assessing risk and predicting whether crops are likely to develop the disease.

Spray thresholds

Spraying is advised when 20% of tillers are found to have penetrating lesions. But relying on thresholds alone to judge the need for treatment is dangerous, as there are other risk factors that have to be taken into account.

"The presence of the disease at stem extension is not the only factor affecting final eyespot levels," says SACs Fiona Burnett. "There are seasons where there is no eyespot in the spring, but it develops in the summer."

She suggests adjusting thresholds with other information, such as sowing date, weather and rotation (see panel right).

Mr Clark agrees that thresholds need to be adjusted with individual situations. He suggests that the 20% threshold should come down to 10-15% by GS33, which is the last chance to get control.

Control options

Growers can expect to see a yield response from effective fungicide treatment, Syngenta trials, for example, showing a 1.14t/ha yield increase when 0.5kg/ha of Unix (cyprodinil) was added to the T1 spray, giving an extra £56/ha after the cost of treatment.

Product choice is between Unix (cyprodinil), Punch (flusilazole), Sportak (prochloraz) and Landmark (kresoxim-methyl).

ADAS advice is to use Unix in a high-risk situation, with low-moderate risk fields receiving Unix, Punch, Sportak or Landmark.

SAC trials suggest neither a split treatment nor the addition of an adjuvant improved control when Unix was used at GS32.

This year

There will be two distinct crops this year, says Mr Clark. "Growers who managed to get drilled in September and October have a potential high risk situation. It has been mild and wet, so check these crops carefully."

Later drilled crops are at a much lower risk of eyespot. "If it is not present in the early crops, it wont be in these ones." &#42

Fiona Burnett (right), SAC: "If you are in an early sown or second wheat situation and the wether is conducive to eyespot, I would spray."

Eyespot lesions at the stem base reduce yield by restricting upward movement of water and nutrients. Check for symptoms at GS30-32, before yield is lost.

Bill Clark: "Just one field in 51 was treated for eyespot in an ADAS survey last year, despite yield losses of up to 34%."

Control of eyespot species and strains

– products compared

Species Type Triazole Prochloraz Cyprodinil

W-type W 1a + + +

1b – + +

1c – – +

R-type R 11s – + +

11p – – +

Key risk factors

&#8226 Sowing date

Early sown crops have a much higher incidence of the disease, as the fungus takes a long time to infect and develop. Temperatures of 10C are ideal for development.

&#8226 Rotation

Eyespot is a disease of intensive cereal production and the fungus can survive a number of years on the stubble. Second wheats are at greater risk, although more first wheats have been getting the disease in the past few years, probably from surrounding crops.

&#8226 Cultivations

As it is trash-borne, ploughing can help. As yet, there is no evidence to suggest that it is worse in min-till situations.

&#8226 Location

Although unable to say why it occurs, experts agree that there are some farms with high-risk fields.

&#8226 Weather

The weather has a big role to play in determining whether the disease develops. Moist, cool conditions in spring are ideal, as are mild winters. In a dry spring, the disease tends to disappear.

&#8226 Variety

No variety has higher than a 6 for eyespot resistance, but Shamrock, Hereward, Soissons and Brigadier are all high-risk choices.

&#8226 Seed rate

Thick, lush crops are more likely to suffer from the disease and will be more difficult to inspect.

&#8226 Soil type

Heavy soils favour eyespot by encouraging humidity and slow straw breakdown.

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