Severe eyespot in flat fields with first wheat

4 August 2000

Severe eyespot in flat fields with first wheat

UNEXPECTEDLY high levels of eyespot are a key feature in some of this seasons lodged wheats, according to several agronomists.

However, random distribution of flat fields suggests many other well known contributory factors have been at work. By identifying them now, growers should be better placed to avoid lodging next year, they say.

"There is certainly a lot more eyespot about," says Peter Taylor, Herts-based chairman of the Association of Independent Crop Consultants. "The mild winter was ideal for it and the wet April and May kept it going."

Bucks AICC member Andrew Cotton agrees. "We had 5in of rain in the last fortnight of April and another 3in in May." Growers not adjusting the content of T1 sprays often delayed by bad weather have been hard hit, he believes.

"I saw 200 acres of early drilled first wheat completely flat because it wasnt treated for eyespot." Neither did later sowing eliminate the disease. "I was horrified at the levels in one mid-October drilled crop after linseed. It was plastered.

"Even where we did get on with the T1, I was forced to go back with a T1.5 spray including Unix."

By and large growth regulators went on as planned. But growers trimming triazole fungicide doses might have unwittingly encouraged lodging, he adds. "Triazoles do have some growth regulatory effect."

Many more first wheats than usual are affected by eyespot this season, maintains Novartis Colin Mills. "Traditionally it has been a problem of second and third wheats, but the trend to early drilling means we seeing it much more in first wheats." Besides encouraging lodging it causes early senescence and so limits strobilurins late greening benefits, he adds.

Dalgetys Mike Jeffes is less convinced by the eyespot argument, believing inadequate overall disease control is equally to blame. Essex trials unaffected by eyespot have big differences in lodging related to septoria control, he notes.

Much depended on spraying disruption, he says. "If the base of the plant is dirty with septoria because you didnt get on with a T1, the stems tend to be thinner. If you then put on T2 and T3 you can end up with a healthy area on top of an unhealthy one. Couple that with slightly earlier drilling, the warm autumn and wet spring and it is not surprising there have been problems."

Given the tricky season it is a tribute to growers that there are so few flat fields about, says Mr Jeffes. He estimates only 2% of the UK is badly affected so far. "A lot of it is headland lodging from seed or fertiliser overlaps." Clearly, though, there are some fields where varieties ill-suited to early drilling, such as Soissons, were sown too soon.

Take-all is unlikely to cause flat crops. Although the disease reduces root mass and potential anchorage, correspondingly poor aerial growth means crops are lighter and so less vulnerable to lodging, says Mr Mills.

Early drilling is thought to have encouraged more eyespot, even in first wheats.

Seed treatment aid

Baytan (fuberidazole + triadimenol) seed treatment can offset some of the negative effects of early sowing, a Bayer BYDV trial in Sussex suggests. The chemical is known to slow emergence, says the firms David Bluett.

Lush Consort sown on Sept 7 at 100 seeds/sq m and treated with Sibutol (bitertanol + fuberidazole) or Sibutol Secur (with imidacloprid insecticide) was half and two-thirds lodged by mid July despite a robust pgr programme, he notes.

By contrast the area receiving Baytan Secur was only 4.5% lodged. "It has nothing to do with disease control. But we know Baytan produces fewer tillers and stronger plants with well-developed, well-anchored root systems."

Lodging action

The important point is to identify the underlying causes of lodging, stresses Mr Mills. If crops have brown elliptical lesions or a brown smudge or ring around the stem below first node and feel soft, eyespot is the likely reason. If roots have rotated or stems are broken above or below first node and lack signs of eyespot, agronomic factors are implicated, he explains.

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