Disease control advance

11 June 1999

Matching strobs to crop situation is top priority

Making the most of new and

existing cereal fungicides is

a key theme at a series of

open days being organised

by national distributor

Profarma. Edward Long

provides a preview

WHEAT growers must learn how to match strobilurin fungicides to soil type, variety and seed rate to reap maximum benefit.

CWS farm manager Martin Davies has used current materials for three seasons on a range of soils. In Profarma plots at Cockayne Hatley, Beds, the lessons he has learnt, plus those of three other CWS farm managers, will be demonstrated on 16 varieties.

"Growers who regard strobs as an instant way to boost yield will be in for a shock. They must be carefully managed or there could be trouble," says Mr Davies who farms 1430ha (3532 acres) in Herts and Beds.

"Some varieties on some soils are less suited to strobs than others. In a wet season a crop on moisture-retentive soil needs a low rate strobilurin treatment for disease control, but not a high rate to keep leaves green."

Experience on CWSs Cockayne Hatley Estate suggests disease-susceptible varieties such as Riband, Consort and Equinox are more likely to need strobs than varieties with better disease resistance. Quality types such as Rialto, Charger and Malacca are less likely to need them than barn-filling feed types.

Another worthwhile lesson from last year was that if strobilurin is used on the flag leaf and for the ear wash, plants on fertile soils could become top heavy and lodge.

The fungicide strategies of the four CWS farm managers are:

&#8226 Mr Davies used a little-and-often three-spray approach in 1998. But new Fungicide Resistance Action Committee guidelines suggest this is not safe, so 0.5 litres/ha Opus (epoxiconazole) and 1 litre/ha Bravo (chlorothalonil) was used for the T1 spray this year followed by 0.5 litres/ha Amistar (azoxystrobin) + 0.25 litres/ha Opus at GS 37/39. He plans to apply 0.3 litres/ha Amistar at GS59.

&#8226 Andrew Watts, who farms 1000ha (2500 acres) in Herts, is using a programme developed for his drought-prone land. The aim is to keep crops as healthy as possible before drought stress kicks in. Landmark (kresoxim-methyl + epoxiconazole) went on at 0.5l/ha at T1 and T2. "Cheap-and-cheerful" Plover (difenoconazole) at 0.2l/ha is earmarked for ear wash.

&#8226 Rupert Ashby, an assistant manager looking after 2000ha (5000 acres) in Essex, opted for the same Opus/Bravo combination as Martin Davies, but then applied a "hammer-blow" 0.75 litres/ha Landmark at GS 37/39 to provide insurance in case there are too few spray days to get round the farm. An ear wash spray of 0.3 litres/ha Amistar protects against sooty moulds.

&#8226 David Watson, who runs the 1600ha (4000 acres) Coldham Estate, near Wisbech, bases his strategy on evidence from Profarma Select Agronomy trials on the farm. With a wide range of breaks wheat can be drilled early, so has high yield potential. Main objective is to protect yield, but strobs do not deliver yield benefits on moisture-retentive soils, merely prolonging green leaf and delaying combining.

The T1 treatment comprises 0.5 litres/ha Opus + 0.2 litres/ha Erysto (quinoxyfen) for effective mildew control, followed by 0.75 litres/ha of Opus at T2 to protect yield. A 0.3 litres/ha dose of Amistar protects milling wheat ears.

Profarma demos

Open days take place at CWSs Cockayne Hatley Estate on 16 and 17 Jun, coinciding with Cereals 99, and 29 and 30 Jun to coincide with Sprays and Sprayers. As well as new fungicides, a strobilurin/N evaluation, and the CWS managers fungicide strategy comparisons, visitors will see five new hybrid wheats and trials to show how variety, seed rate and drilling date affect the choice of new and existing fungicides and pgrs.

Foil wrapped

New standard-setting triazole fungicide fluquinconazole from AgrEvo (as in Foil) performed as well as Opus in Profarma trials last year under Septoria pressure.

This season it is being used as a partner for Amistar. "Foil is supposed to be complementary, it helps Amistar to enter the plant so enhances its activity," says Profarma technical manager Craig Morgan. "In trials we are using it at just 0.6 litres/ha with either Amistar or Ensign. Last year when it was partnered by Ensign we saw some useful yield increases."

When 0.35 litres/ha Ensign (fenpropimorph + kresoxim-methyl) was used for both T1 and T2 sprays the yield of Riband was 7.58t/ha (3t/acre). Where 0.45 litres/ha Foil was added to both treatments yield rose over 12% to 8.55t/ha (3.5t/acre).

Foil is also claimed to be highly persistent. Disease assessments in Profarmas plots in July will show its worth for long-term control.

Disease control advance

STROBILURIN fungicides represent a huge advance for disease control over triazoles. But existing ones have weaknesses.

"Amistar and Landmark both have chinks in their armour and we expect new products to offer the prospect of broad-spectrum disease control to plug the gaps," says Profarmas Craig Morgan.

One new strob is coded product 279 from Novartis. It is effective against Septoria, rusts, and mildew, but it is still only a protectant so needs a triazole partner.

Also new is Du Ponts MC444, which is intended for T1 timings. It is not a strob but works on a similar pathway to provide protection from Septoria and eyespot.

A third new strob, which is at an early stage of development, is highly effective against Septoria and rusts, and possibly mildew as well. &#42

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