Archive Article: 1997/09/20

20 September 1997


WHO said it was going to be a "low disease" year? Many agronomists did, early in the season. But agrochemical distributor Colin Myram of the Crop Care Group certainly didnt.

Results from the companys trial site near Bury St Edmunds show he was right. Fungicides have added over 3t/ha (1.2t/acre) to untreated yields on responsive varieties such as Riband.

In this region, wide-scale foliar disease arrived fairly late in the day. Early drought kept the lid on disease pressure at the start of the year. However, the sharp-eyed Mr Myram spotted low levels of yellow rust and septoria on his site early in the spring. Then the rain started in June, and disease took off.

"Timing was the most critical factor this year – with both the old and the new fungicide chemistry," says Mr Myram. "The traditional approach – the T1 mid April, a T2 mid May, and earwash mid June – has come out top."

The thinking with the new chemistry had been that the best strategy might be early spray timings, to exploit long-lasting protectant activity. But this has not proved the case at this site.

The other lesson learnt was that the new fungicides give the best results when mixed with partner triazoles. In this season at least, neither the strobilurins nor the plant activator were good enough on their own. And the yield response was only significant when full rates were used, says Mr Myram.

This must increase the pressure on the manufacturers for "more realistic" pricing of the new products, he comments. In other words, if the new fungicides are too expensive, then growers wont buy them.

That said, Mr Myram is pleased with "excellent" mildew control from early treatment with quinoxyfen (Fortress) and the strobilurin mix kresoxim-methyl with fenpropimorph (Ensign).

Cyprodinil (Unix in France) showed its mettle against eyespot, giving good yield responses – but was less visually effective against mildew. Some promise was shown by the plant activator SAR, which effectively "immunises" the wheat against disease. But more work is needed to investigate the varietal differences with SAR, suggests Mr Myram. Conventional triazole difenoconazole (Plover) and azoxystrobin cleaned up ears well.

Azoxystrobin and cyprodinil came up trumps against net blotch in winter barley, but the current best selling triazole, flusilazole (Sanction) continues to give good results. Once again, traditional timings were best with the barleys – a two spray sequence of early April followed by early March.


YELLOW rust, septoria and late mildew swept through the plots at the Horncastle trials site, Lincolnshire in June.

"Disease pressure was as bad as we have ever seen this late in the season," says Dr David Stormonth of distributor Brown Butlin.

"Some untreated wheats were completely defoliated by mid June."

When T1 sprays went through in April, the site was relatively clean. But by flag leaf emergence in May, "all hell had broken loose," remembers Dr Stormonth.

Three strategies were under scrutiny: a conventional triazole sequence at T1, T2 and T3; a strobilurin sequence (Amistar with Fortress) at T1 and T2; and a developmental programme which included the plant activator SAR and Amistar at T1, followed by a kresoxim-methyl/epoxiconazole mix at T2. The massive disease invasion gave the fungicides a tough test.

"Intriguingly, some varieties responded more to the strobilurin sequence than others. But were not sure why, as yet."

Wheats which appeared to suit the Amistar programme included Equinox, Rialto, Blaze, Madrigal, Chaucer and Caxton. Abbot and Raleigh were less responsive.

The results, averaged over all the wheats, are given in the table. Top performance in terms of gross margin was from the strobilurin sequence – and the figures are calculated using "sensible costings" for the Amistar.

"It was impressive just how clean Amistar kept the lower canopy and stems. And although there had been concerns that this product might keep ears green for too long at the end of the season, in fact crops turned very quickly, and there were no problems with maturity."

Fortress proved itself as an "exceptionally powerful" mildewicide, says Dr Stormonth.

In all, he is optimistic about the cost-effectiveness of the new chemistry. "The huge yield responses weve recorded are a reflection of the intense disease pressure. Treated and untreated plots were like chalk and cheese."


THERE was "phenomenal" net blotch control from Amistar on winter barley on this Brown Butlin site, says Dr Stormonth. "However, this product could need help tackling rhynchosporium – perhaps a little mbc should be added."

The developmental strobilurin mix of kresoxim-methyl with epoxiconazole did well against mildew.

Although barley crops were less badly hit by disease compared with the wheats, a two spray sequence was still required, says Dr Stormonth.

"At the barley T1 timing, cyprodinil is interesting, because of its eyespot activity. Its useful against rhynchosporium and net blotch – but its not the best.

"Of all the varieties, Regina looked tremendous – Fortress kept it extremely clean. It didnt lodge, despite being pushed with high nitrogen – though a growth regulator was used."


UNLIKE conditions down south, there was disease on the CSC CropCare site right from day one.

"The septoria pressure has been as bad as we have ever seen here," says Dr Keith Dawson. "On Riband the yield response has been the highest ever at 80%. But we havent had yellow rust – yet!"

With many plots yet to harvest, yield data is limited. But visual assessments showed the excellent protectant activity from kresoxim-methyl and quinoxyfen. "Both products gave about 70 days protection against mildew."

The best programmes were flusilazole with either the strobilurin kresoxim-methyl/fenpropimorph or quinoxyfen as an early spray, followed by kresoxim-methyl with epoxiconazole at flag leaf timing. This is due to good green leaf retention and better stress management by the plant, suggests Dr Dawson.

Cost-effectiveness calculations for this strobilurin must wait for yield results, but he expects to see benefits over and above those from disease control – even with costings including £70/t wheat prices. "But beware – weve only seen these yield benefits at the full rate."

Dr Dawson is concerned that manufacturers may be asking too high a price for the new chemistry. "Although strobilurins have been cost-effective in our trials over the past five years, the manufacturers must now take a more realistic view on fungicide prices."

With late maturity the rule in the north, any delay to ripening is bad news. But kresoxim-methyl has not extended maturity, reckons Dr Dawson. "Ripening was accelerated at the end of the season."

With barley, cyprodinil has shown its worth as a mixer product, adding good eyespot and net blotch control. Ensign and Fortress have both given "exceptional" mildew control.

"We may see a revival of Prisma and Pastoral – we can now control disease all season long with one well-timed early spray. And autumn mildew control, on light soils, has lasted through until April – its astounding. Flusilazole with kresoxim-methyl worked very well against rhynchosporium."

Dr Dawson notes a growth regulatory effect from kresoxim-methyl on the winter barleys. He speculates that this could be due to better rooting, through control of early mildew.

Spring barleys have benefited from fewer screenings and lower grain nitrogens following both quinoxyfen and kresoxim-methyl. "Dose rates and timings need more careful management on the spring barleys." Mildew has been "the worst for 15 years" on some varieties; both quinoxyfen and kresoxim-methyl have given up to 80 days control, he says.

"For growers, the key will be to use the best of the new products and mix with the old, for a least-cost formulation. The use of certain adjuvants also improves the new chemistry."


IN THE face of high disease pressure, the strobilurin Amistar gave a sterling performance at the Zeneca trials site near Kineton, says trials officer Mel Codd.

Brigadier was badly hit by yellow rust, first spotted in early April. With a range of Amistar sequences, yields were astoundingly three times greater than the untreated control.

Conventional high performance triazoles also did a good job – but Amistar was still ahead, out yielding the triazole programmes by 20-25%.

"However, a flag leaf spray of full rate Opus did have the edge against straight Amistar," says Mr Codd. "It highlights the superior kick-back of the triazoles."

The best Amistar sequences are where the strobilurin was put on as part of a T1 mix, with a full rate follow up at flag leaf mixed with flutriafol.

Septoria-prone Riband given early Amistar in March, at tillering (GS26-27), appeared to benefit – but with the other varieties the conventional T1 timing worked better.

On balance, Mr Codd reckons the traditional T1 timing is a safer option "because otherwise the gap between sprays could become rather too wide for comfort. With the very early treatment, a safer strategy might be to include more frequent, low dose sprays."

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