Great threat of barley blotch

11 June 1999

Combat disease by washing out your wheat ears

By Andrew Swallow

RECENT wet conditions mean disease pressure is high on emerging wheat ears. An ear-spray is justified even after a robust flag leaf application, say experts.

Timing such sprays will need more attention than usual. "We are seeing a big spread of ear emergence and flowering could span 5-6 weeks. Growers must adjust timings accordingly," says John Garstang, of ADAS Boxworth.

The most forward crops are well into flowering already, and time is running out for fusarium control. Even following a robust 75% to full-rate strobilurin application at flag-leaf, a triazole such as tebuconazole or epoxiconazole should be applied at early flowering, says Mr Garstang. Adding mbc can improve control.

Only where flag-leaf sprays were delayed until after ear-emergence, and crops are clean despite that delay, could the ear-spray be omitted, he adds.

On disease-prone varieties, such as Brigadier and Consort, work by Masstocks Wilts-based Crop Technology shows yield response to an ear-spray can be over 1t/ha (0.4t/acre). Even with relatively resistant variety Hereward in dry conditions a 0.25t/ha (0.1t/acre) response was seen.

"This year the late season disease pressure is comparable, if not greater than last season," says technical manager Clare Bend. "There have been a number of splash events and septoria will have spread up the plant. And wet conditions at flowering mean the Fusarium risk on susceptible varieties is high," she warns.

On disease susceptible varieties eradicant activity, plus protection, is needed with the ear-spray, she stresses. "Although Amistar alone has given excellent control of sooty moulds and a clean bright sample at quite low doses, it has few curative properties."

In the trials at Thornbury, Bristol, 0.2 litres/ha of Plover (difenoconazole) plus mbc gave higher yields than Amistar at 0.5 litres/ha, even following two robust Landmark (epoxiconazole + kresoxim-methyl) applications at T1 and T2. For fusarium-prone varieties, such as Charger, tebuconazole plus mbc may be appropriate, she adds.

North of the border, ears are just emerging on the forward wheats. Disease pressure is fairly low, but there is no room for complacency, warns SACs George Barton. &#42

Midge warning

Orange blossom midge levels are the worst since 1993, when the pest first hit epidemic proportions. "It is pretty bad in recognised hot-spots," says ADAS Bridgets entomologist Jon Oakley. Sheltered, moist areas where wheat is grown regularly are most at risk. Check fields on mild, calm, evenings.

Lightning strike or something more serious? Agronomist Seumas Foster (right) and farm manager Duncan Lee spotted these scorch-like symptoms in Charger winter wheat at Littlecote Farm Partners Ashridge Farm, Beedon, Berks last week. "We had seen something similar in Hants 10 days previously," says Mr Foster. "Both followed severe thunderstorms, so lightning seems a logical explanation." Samples have been sent to the Central Science Laboratory in case something else is to blame. Or if you know better drop us a line or fax 0181-652 4005.

Dodge mycotoxin woes

IS your on-floor grain drying and storage up to scratch? New information from Home Grown Cereals Authority-funded research shows how growers can avoid mycotoxin problems.

In a survey of 24 on-floor grain stores from Kent to north Lincs last year, eight samples contained the mycotoxin ochratoxin A.

Contamination occurred where grain was held at over 19% moisture for several weeks, leading to the growth of a mycotoxin-producing species of Penicillium mould, say joint project leaders Robin Wilkin and Keith Scudamore.

Ochratoxin A has been linked to serious illnesses in animals and man, prompting the EU to seek a maximum limit for food products, including raw cereals, says Mr Wilkin. The limit could be as low as 4-5ppb.

"The good news is that the survey showed there is no inherent risk of mycotoxins developing in on-floor stores. But it is important for growers to manage their stores well to prevent contamination."

Mycotoxins are produced if there is significant growth of the correct strain of mould, with serious fungal growth starting above 16% moisture and 10C. The toxins are extremely stable and almost impossible to clean out of contaminated grain, adds Mr Wilkin.

He urges growers to ensure their stores are up to the job now, in readiness for any changes to grain quality standards in future. &#42

Great threat of barley blotch

LEAF blotch syndrome, which last year wiped an estimated £6.5m from the value of northern spring malting barleys, is all set to do the same again this season, warns Keith Dawson of CSC CropCare.

The newly-emerging disease complex, thought to be caused by saprophytic fungi encouraged by pollen falling on poorly waxed leaves, was first noticed in 1997. Last year it ran riot in Scotland and Ireland and current weather means the risk is high again.

Last year the condition hit yield, screening levels and nitrogens and had a big effect on crop profitability. With much more spring crop drilled this season, giving a more competitive market, and over 90% of the area sown to susceptible varieties there is a real threat to the industry, Dr Dawson believes.

He discounts Irish suggestions that last years damage was caused by sudden sun scorch after a prolonged dull period. Scotland did not generally experience the same hot spell, he says.

CSC trials highlighted leaf blotch losses of up to £180/ha (£73/acre), with varieties Chariot, Derkado, Optic and Chalice hardest hit. Prisma was much less affected.

The trials also showed that certain fungicide programmes can help, but with three main provisos.

"Firstly only strobilurin fungicides offered any significant control."

Secondly and critically the spray timing had to be before pollen covered the leaves and disease symptoms appeared.

"Thirdly the use of certain adjuvants, such as Arma, enhanced the strobilurin effects and minimised cost." &#42

Do you want GM crops grown on UK farms – or not? That is one question the on-going media frenzy about GM crops persistently over-looks. Now you can make your voice heard through farmers weeklys "GM Crops – Have Your Say" initiative. Turn to p62 for our simple questionnaire.

&#8226 Beware mycotoxin risks.

&#8226 Start drying grain over 18% mc immediately.

&#8226 Aim for below 16% mc a month.

&#8226 Avoid damp surface layer.

&#8226 Monitor moisture at many points in bulk.

&#8226 Cool below 10C to cut mould growth.

&#8226 No visible mould no guarantee that mycotoxin free.

&#8226 Act immediately if problems – consider high temp drying.

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