Eyeing up the risk

19 February 2000

Eyeing up the risk

Be warned: eyespot risk is higher than ever this year, according to some experts. So does that mean you need a dedicated eyespot spray? The jurys out…

A BIGGER wheat area, earlier drilling and a mild, wet winter all add up to the potential for more eyespot than usual. A greater area of second wheat, mostly at the expense of linseed and winter oilseed rape, could exacerbate the problem.

Chris Bean, UAPs technical director explains: "Crops drilled before the end of September are more prone to the disease because they have more time to become infected by wind-carried spores and there is still plenty of inoculum around in the form of infected stubbles and trash."

A rotational break doesnt appear to be as good a defence as it was once considered: "Weve found that first wheats are just as prone to the disease as second wheats," he says.

The potential may be there for eyespot, confirms ADASs Bill Clark. But hes not convinced that the threat will last the course. "The risk may subside; the severity of eyespot rests on the weather in March. Early spring moisture helps retain the wheat leaf sheath and allows infection to penetrate to the inner stem where it does the damage. But if conditions are dry those outer leaf sheaths can fall off – taking the eyespot infection with them."

He urges growers to check wheat crops from GS30 onwards: "Keep looking weekly until GS33. You should treat eyespot if the threshold of 20% of tillers with penetrating lesions is reached."

Mr Bean is more relaxed about the risk. "Foliar diseases, namely septoria, come first in my book; eyespot is very much a secondary disease and in the 25 years I have been in this business there have only been one or two years when it has been worth targeting it," he says.

He plumps for early treatment with strobilurin Landmark, which in UAP and SAC trials gives not only the all-important septoria control, but also very good activity against eyespot.

Convincing trials evidence for the Landmark/eyespot effect can be found from a UAP site near Minster, east Kent in both 1997 and 1998, says Mr Bean. Hereward, drilled after potatoes, suffered badly with eyespot. Landmark gave 70% lodging control, compared with 76% for Unix.

In the following year, Brigadier sown after peas demonstrated another bad eyespot attack with 90% lodging, despite a robust growth regulator programme. "The five plots that remained standing were the only ones that had been treated with Landmark, because it had significantly reduced the level of eyespot," recalls Mr Bean.

Last season UAP commissioned the Scottish Agricultural Colleges (SAC) to do a trial on an East Lothian site where eyespot is always a problem. The study compared Landmark to other fungicides, tank-mixed with the same amount of epoxiconazole as that present in Landmark, which rules out its effect.

Early timings were put to the test. Some treatments went on at T0 (GS30, ear at 1cm), and some at the more conventional T1 (GS32, second node) timing. At T0, the Landmark and Unix plus Opus plots easily had the lowest eyespot indices (assessed in early August). The azoxystrobin plus Opus plots had the worst eyespot, possibly because azoxystrobin is more active against sharp eyespot, present at a low level, allowing the other eyespot to dominate, suggests Mr Bean.

Broadly similar results were seen with the T1 treatments. However, theres a problem with eyespot – best control doesnt always translate into best yield response. And this was the situation here. At the T1 timing, however, Landmark gave both the top yield and the best eyespot control.

It has convinced Mr Bean. "Weve now had three successive years of trials showing that Landmark has good eyespot activity, and continental results confirm ours. So if the disease is not severe enough to justify a specific spray, the use of Landmark is a good idea, particularly as it also controls septoria and yellow rust."

Mr Bean believes that both components of Landmark contribute to its eyespot activity. That is corroborated by Steve Waterhouse, BASFs eastern business development manager. True, Landmarks eyespot control is more variable than that of Unix, at times it can be higher, as it was in the SAC trial, he says.

Not everyone is convinced that early Landmark is the answer for eyespot, albeit at low disease levels. For ADASs Mr Clark, Landmark stays in his second league of products for eyespot control, alongside prochloraz and flusilazole. "Unix is without doubt the best product for high infection. Eyespot control may be a useful attribute of Landmark, but not its main virtue."

So at lower levels of risk, the decision should rest on price, with Landmark, or flusilazole (Punch C) with Amistar as possible alternative strategies, he says. And although Amistar does have useful sharp eyespot activity, its such a sporadic disease that it is not worth targeting, he adds.

Dr David Stormonth of Farmacy clarifies the position. "All triazoles have eyespot activity, but whether it is commercially useful or not is another question. It all depends whether sufficient chemical is within the vulnerable stem zone of the plant. In many cases level of control is so insignificant, that no claim can be made."

For moderate risk situations, his favoured option is flusilazole. Low risk crops are not worth treating specifically for eyespot. "Epoxiconazole does have some activity against eyespot – but specifically for this disease is it of commercial value? Id suggest it would be marginal. If I thought eyespot was an economic threat, then Id go for cyprodinil – Unix – which is superior to prochloraz."

With grain at its current value, what really matters is a cost-effective broad spectrum treatment in the spring. The economic threat of eyespot has to be put into context.

Active ingredient Product Profile

Azoxystrobin Amistar No activity against common eyespot, but the only product to control sharp eyespot

Cyprodinil Unix De luxe eyespot treatment, and mildew activity

Flusilazole Punch C, Sanction Popular, cost-effective triazole, with reasonable eyespot plus some foliar control

Kresoxim-methyl Landmark, Mantra Strobilurin that may offer better some surprisingly (with epoxiconazole) good eyespot control – but not every time

Prochloraz Sportak family of Old stager with good eradicant eyespot activity products against both strains

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