5 March 1999

This years mix of crop development and yield

potential poses a real challenge for cost

effective disease control. In this special feature

we consider the latest advice and examine the

newest product options, starting here with a

detailed look at making the most of strobilurin

fungicides. Edited by Andrew Swallow

Strobs okay

Early treatment pays

ON-FARM trials have turned strobilurin policy upside-down on a light-land farm in Cheshire.

"Our rationale is to take full advantage of the greening effects early on," says CWSs Mike Shapland. He is assistant manager at Weston Hall, near Crewe in Cheshire, where the light-loam soil can dry out rapidly in June.

That means putting most of the strobilurin on at T1, a lesson learned from Profarma Select Agronomy trials, which the farm hosts. Which strob will be used depends on the deals available.

"The trials have shown us that there is no significant yield difference here between kresoxim and azoxystrobin on the wheats, from full down to half rates. So it all comes down to price," he says.

Last year Mantra (epoxiconazole + fenpropimorph + kresoxim-methyl) went on wheats at 0.7 litres/ha at T1 and 0.3 litres/ha at T2. This season strobilurin rates will be kept the same, but products look set to change.

"We may well move from co-formulation to Ensign to give us more flexibility to juggle the triazoles," he suggests. T3 sprays are unlikely.

"We have no milling wheat, and do not feel even the strobs are justified on light land. Trials have shown that T3 sprays either have nil or a negative effect on gross margin."

Barleys are treated similarly to wheats, with strobs loaded towards T1. "We will probably use 0.5 litres/ha of Amistar plus 0.4kg/ha of Unix, and may not go back at T2. That can be a waste of money on our droughty soil."

Total spend on fungicides is anticipated to be £60-£65/ha on wheats and £50-£55/ha on barley.

Profarmas Craig Morgan endorses Mr Shaplands farm policy. "Our light land philosophy is changing from an equal strob split between T1 and T2 to delivering more strobilurin and less triazole at T1. But we would never use a strobilurin without any triazole."

That should cut T2 costs and boost margins, he adds.

Strob yield responses on the light land seem to be more than on heavier ground, with some plots at Weston Hall outyielding untreated plots by over 2t/ha and triazole-only treated plots by 1t/ha. (see table).

Heading for this strob table

GS30/31 GS37/39 Yield t/ha Response t/ha

Wheat Chaucer Untreated 8.16 –

0.6 Az + 0.25 Opus 0.8 Az + 0.25 Opus 10.14 +1.98

0.25 Opus 0.8 Az + 0.25 Opus 9.39 +1.23

Barley Fighter Untreated 4.97 –

0.4 Unix + 0.4 Az 0.4 Az 7.24 +2.27

0.4 Unix + 0.4 Az 0.25 Tilt 6.81 +1.84

Source: Profarma. Light land at CWS Weston Hall, Cheshire.


&#8226 More at T1, less T2.

&#8226 T3 treatment marginal.

&#8226 Good return barley and wheat.

&#8226 Responses more than heavyland trials.


&#8226 More at T1, less T2.

&#8226 T3 treatment marginal.

&#8226 Good return barley and wheat.

&#8226 Responses more than heavyland trials.

Weston Hall strobilurin trials

GS30/31 GS37/39 Yield t/ha Response t/ha

Wheat Chaucer Untreated 8.16 –

0.6 Az + 0.25 Opus 0.8 Az + 0.25 Opus 10.14 +1.98

0.25 Opus 0.8 Az + 0.25 Opus 9.39 +1.23

Barley Fighter Untreated 4.97 –

0.4 Unix + 0.4 Az 0.4 Az 7.24 +2.27

0.4 Unix + 0.4 Az 0.25 Tilt 6.81 +1.84

Source: Profarma. Light land at CWS Weston Hall, Cheshire.

STROBILURINS will boost margins on nearly all wheats this season, including late drilled crops, says ADAS cereal specialist Bill Clark. But only if growers and advisors understand how to use them, he warns.

"The key to using the strobilurins well is to understand the difference between eradicant and protectant activity. That sounds simple but many growers have not grasped it yet."

Eradicant activity is essential at both T1 and T2 timings, whether disease can be seen or not, he stresses. That means adding a triazole, and maybe a morpholine if mildew is present, depending on the choice of strob.

At T1 the aim is to protect the emerging leaf 3 and clean up leaf 4. In crops developing normally that is at growth stage 32, but in late drilled crops leaf 3 can come through earlier. "An agronomist worth his salt should be able to identify it," he says.

If leaves 3 and 4 are kept clean then they cannot act as a source of septoria inoculum for the all important leaf 2 and flag leaf. (see Fig.) In thin crops leaves 3 and 4 can contribute a significant amount to yield too.

"It is a self-fulfilling prophecy that thin crops yield less, because growers often spend less on them. It is even more important to keep the lower leaves clean in a thin crop," he stresses.

Even in apparently clean crops a straight strob is not recommended. "It would have no effect on disease on leaf 4, and we cant tell if leaf 3 is free from septoria either. Both may be green even if infected, hence we have to use an eradicant, ie. a triazole. A morpholine is not sufficient as it only has 4-5 days kick-back, to a triazoles 14 days plus."

At flag leaf timings, eradicant activity is again required to clean up the very important leaf 2 which will have emerged unprotected 10 days earlier. Leaf 3 should still be carrying some protection from T1 strobs if growers did not go too early.

Epoxiconazole is the best triazole, but tebuconazole, cyproconazole and metconazole are nearly as good and price could mean these are a better partner product for some growers, says Mr Clark.

Rate of triazole at both T1 and T2 can be tuned to the variety and season but strob rates must be maintained for maximum margins. Growers should apply 1.5 units in a three-treatment programme, with some strob at each timing and the largest dose on the flag leaf.

Even in a dry year, rates should be kept up as greener crops will benefit more from greater light intensity of dry sunny weather.

At T3, an azoxystrobin earwash has proved very effective against sooty moulds and is preferred to Landmark (Kresoxim-methyl + epoxiconazole) despite an extension in the latters approved timing.

However, for other timings there is little to separate the yield responses from the two strobilurins, so long as a quality triazole is included.

Whatever the choice, variety should have no influence on the strob component of the mix. Over two years and 35 different varieties ADAS has been unable to establish a differential varietal response to strobs over triazoles.

"We have checked every strobilurin trial for a consistent variety/strob interaction and we cant establish a link. Therefore there is a reasonable argument for using strobs on all varieties," he says.

Optimum nitrogen rates are unchanged by strob treatment, though protein dilution may mean a late foliar urea is worthwhile for possible borderline milling wheats.

Typically growers can expect 1t/ha (0.4t/acre) yield boost from a strob programme over a triazole only approach. Even at £70/t for wheat, that is about double the extra fungicide cost.

Only on the most drought prone, marginal wheat land, might a non-strob programme be more cost effective, he concludes.


&#8226 Triazole essential at T1 & T2

&#8226 Landmark – fool-proof formulation

&#8226 Az – Technical expertise needed

&#8226 1.5 Units of strob for program

&#8226 Typically +1.0t/ha yield over triazole.


Where to use

&#8226 Response greatest in winter wheat, then winter barley, then spring barley.

&#8226 Variety trends not clear. Soil type interaction? Value of response tends to

be greater in traditionally responsive varieties.

&#8226 Similar responses on light and heavy soils in E Anglia.

&#8226 First cereals better effect than second – but did severe take-all mask


How to use

&#8226 T2 usually best single timing in wheat; T1 in barley.

&#8226 T1 + T2 sequence most consistent benefits in wheat.

&#8226 Consistent benefit from extra azoxystrobin at T3 in wheat.

&#8226 Higher dose usually brings better return.

&#8226 Lower doses may suit lower response situations.

&#8226 Minimum half dose at each timing.

&#8226 Must mix Amistar with partner product at T1 + T2.

&#8226 May be disadvantages with mixing strobs.

How to choose

Winter wheat

&#8226 Landmark stronger curative action + better on mildew.

&#8226 Amistar stronger on sharp eyespot + ear diseases.

&#8226 Alternating strob may be better than one product sequences.

Winter barley

&#8226 Amistar stronger, especially if net blotch present.

&#8226 Landmark may be cost effective, especially where mildew present.

&#8226 No advantage with strob sequences.


&#8226 Ensure adequate pgr where Landmark/Mantra used.

&#8226 Scope to trim pgr where Amistar used.

&#8226 In low N cases Landmark can improve uptake + therefore yield.

&#8226 In high N cases Landmark may boost yield above plateau.

&#8226 May need more N for following crop.

&#8226 Use higher rates and alternative modes of action to minimise risk of

resistance developing.

Now fine-tuning messages emerging

ALTHOUGH consultants have just one year of field experience with strobilurins, compared with 15 for triazoles, management advice is emerging.

Key to improving advice is identifying where the best returns were achieved last year, says David Ellerton of distributor ProCam.

Helping in that process is the companys computerised Crop Management Survey of over 17,000ha (42,500 acres) on 70 farms. Last year almost a third of the fields received a strobilurin.

Results confirm manufacturer claims for yield response. In winter wheat yield rose 11% over conventional treatments, worth an extra £72/ha after additional spray costs. Winter barley showed a 9% lift, worth £50/ha.

But those figures mask huge variation, stresses Dr Ellerton. "We need to see where the top 25% of responses were achieved and target those situations this season."

The best opportunities lie in crop choice, rotational position, spray timing and product choice (see panel). Varietal responses are less easy to pinpoint. Links with nitrogen, pgrs and harvest date also need considering.

Interactions with lodging need particular attention, says Dr Ellerton. "Landmark does seem to increase lodging, whereas Amistar does not." Zeneca work suggests that may be due to improved internode stem diameter and thicker stem walls where Amistar is used.

"They say that where an alternative strobilurin was used both ratings were lower and lower than where a triazole was used. So we may need to beef up our pgr use with Landmark, whereas with Amistar we may be able to cut back on pgr."

Identifying varietal opportunities is less easy. NIAB trials show responses ranging from 0.77t/ha to 1.61t/ha in wheat and 0.17t/ha to 0.83t/ha in winter barley. "Those are twofold and fourfold differences, respectively."

CMS data for wheat would seem to echo the NIAB results, with Brigadier and Soissons giving big gross margin responses, but Spark, Rialto and Consort returning far less or even giving a negative return. "But other trials disagree. It is very difficult to predict," warns Dr Ellerton.

In winter barley the picture is even more muddied. NIAB data shows Pipkin giving just 3-4% yield response, yet CMS figures show Pipkin turning in 1.22t/ha extra yield.

"Variety may be interacting with another factor, such as soil type." CMS data shows strob responses on heavy soils average £41/ha and £39/ha on light soil. "But some varietal responses do differ significantly between different soil types.

"Perhaps this helps explain why varietal responses are all over the place. We have asked Zeneca and BASF to look at their pioneer farm data to see if there is an explanation, but so far they have come back with nothing."

Harvest delay

Strobilurins may delay harvest in some seasons, warns Dr Ellerton. That is confirmed by Danish work showing stem moisture content when grain is at 12.5% moisture was 31% after strob use, compared with 25% following a triazole and 15% untreated. "For high risk situations it may pay to use low rate glyphosate to ensure timely cutting, especially where a milling or malting premium is at stake."


Strobilurin use on barley is a completely different story to wheat, says Mr Clark. Growers can adopt a wait-and-see approach, using strobs more like a conventional fungicide. Yield effects are less, but azoxystrobin in particular is brilliant on net blotch. As varietal disease resistance ratings are not so reliable for this disease, Mr Clarks advice is to spray if the disease can be seen. T1 timings should be slightly earlier than for wheat, at GS 30-31, and a half-rate Amistar should give very good and persistent control. To tackle mildew, rhynchosporium or eyespot then a morpholine or triazole mixer must be added. The T2 timing at GS40-45 is the most important as it protects the emerging awns. Again a half-rate azoxystrobin is recommended if net blotch or brown rust is present or expected. Reduced screenings, bolder grain, and higher value produce mean malting crops are most likely to merit the extra strob spend on barley.

on all wheats – ADAS