flag leaf, says expert

3 March 2000

T1 is now as important as

flag leaf, says expert

Fungicide decisions in

wheat will be dominated

by one group of actives for

most growers this

season – the strobilurins.

Which, when, where, how

much, and with what are the

questions. Dalgetys Bob

Bulmer and ADASs Bill

Clark provide the answers. Andrew Swallow reports

STROBILURINS are changing the relative importance of spray timings. The T1 application is now as important as the flag leaf spray for many growers, says one leading agronomist.

"Traditionally the T1 spray has been seen as a Cinderella spray, but I think it is becoming more important than the T2," says Dalgety national technical manager Bob Bulmer.

"In the last two seasons we have seen intense rust and septoria pressure early in the season and this is where things have started to go wrong in the south. It is becoming crucial to get the T1 timing and mix right," he stresses.

Early-drilling adds to that argument, as the T1 to T2 interval is stretched. (see Table). Not only is good eradicant activity needed to clean up the crop, but a hefty dose of protectant is needed to carry the plant through to flag leaf.

"It drives you down the strob route. I would look at something like 0.6 litres/ha of Amistar plus a half-rate triazole."

However, such early reliance on strobilurins by growers aiming for milling markets, or in Scotland and the north of England, presents problems with keeping to FRAC guidelines (see p75).

For them a strobilurin ear application is needed to maximise grain quality and make the most of the long grain-fill period respectively, he explains. That would take them to three strobilurin applications in a season and contravene FRAC guidelines, which Dr Bulmer feels must be followed.

"We are taking a big risk relying too heavily on the single site action of the strobilurins, and with wheat at about £60/t we cannot afford to jeopardise their efficacy."

For such growers, Dr Bulmer suggests adding protective product chlorothalonil to the triazole at T1.

"You could take the Bravo option giving about 40 days protection. With it you are getting away from relying too heavily on the strobs and it is a relatively cheap input – £3/ha max," he says.

Strobilurin protection from T1 is particularly important in thin crops, he continues. The lower leaves, leaf 3 which is emerging at GS32 and leaf 4, can contribute a significant amount to yield in an open canopy and must be protected (see figure). Added to that, if infected with septoria, these lower leaves will act as a source of innoculum for leaf 2 and the flag leaf. (Fungicide Special, Mar 5 1999).

"Assessing green leaf area is more an art form than a science. Really it is deciding whether you have a thick or thin crop and most growers can do that intuitively."

At flag leaf, T2 timing, there should be no question about using a strobilurin on all wheats, says Dr Bulmer. "It is a bit of a no-brainer, as the Americans say."

But which strobilurin, at what rate, and with how much triazole needs careful thought.

"Amistar has the advantage where rusts are a real threat but if you are up against it with septoria I would use a high rate of Landmark. In between it comes down to how much strob you can buy for your money."

Novartiss strobilurin, if available, looks reasonable on everything, he adds. "But it is still going to need a triazole."

Whichever strobilurin is used, growers should aim to keep rates up at flag leaf.

"Use as much strobilurin as possible, say 0.8 litres/ha Amistar – not a full-rate as I cant see that 1 litre/ha gives any more margin, but I wouldnt want to go below a half-rate either."

Adding a triazole is essential, typically at half-rate. If the T1-T2 interval has been stretched to over 28 days due to weather, or early drilling, then the rate should be increased to provide more kick-back. "Growers have got to think back to what they did at T1."

Generally earsprays provide little in terms of yield unless growers are in the north (see panel). "They are treatments for quality and to tackle specific late-season disease risks, such as brown rust on Soissons or Rialto."

Tebuconazole (as in Folicur) is Dr Bulmers preferred triazole at T3. "It is very good on the fusariums, good on brown rust and has some mildew activity." Adding Amistar at about a quarter rate keeps sooty moulds out and retains green leaf area longer if the crop does not die of drought.

PROGRAM PLAN

&#8226 T1 sets up season.

&#8226 Strobs for all at flag leaf.

&#8226 Beware sowing date effects.

&#8226 Use T1 strob on thin crops.

REGIONAL PROGRAMMES

In Northumberland and Scotland Dr Bulmer suggests growers stick to a triazole at T1, reserving strobilurins for T2 and T3. "Save the strob for the flag and ear so you can milk the late maturation effect. There also tends to be less disease pressure at T1 due to the colder winters and the T1 to T2 interval is generally shorter." Aiming for 1.4 units of strobilurin, he suggests a 0.8 litre/ha + 0.6 litre/ha split between flag leaf and ear. "Time the ear wash as early as possible as fusarium can already be established by flowering in wetter regions. Going that early tends to push flag leaf timing back to GS37, which ties in with the non-strob approach at T1."

In the south-west, strobilurin responses have been questioned, but Dr Bulmer believes timing is the key. "Here, varieties hit their growth stages very early and disease develops early. I think growers might see a response if they used the strobilurins earlier, say GS31 rather than GS32. But then there is a danger of missing leaf 3, so again T2 would need to be at GS37, as soon as the flag leaf is visible." Alternatively growers could use Bravo early at GS30 with the pgr to damp down septoria, and stick to conventional timings.

Growth stage according to sowing date

Sowing date GS32 Days GS32-39

Sep 4 Apr 3 47

Sep 17 Apr 14 33

Oct 9 May 1 22

Feb 19 Jun 6 10

All Claire, grown at Dalgetys Throws Farm, Essex.

[GRAPHIC]

% YIELD CONTRIBUTIONS

Wheat growth stage according to

sowing date

Sep 4 Apr 3 47

Sep 17 Apr 14 33

Oct 9 May 1 22

Feb 19 Jun 6 10

All Claire, grown at Dalgetys Throws Farm, Essex.

Number one, two or three…which strob will it be?Dalgetys Bob Bulmer says drilling date and end-market are key considerations.

PROGRAMME PLAN

&#8226 T1 sets up season.

&#8226 Strobs for all at flag leaf.

&#8226 Beware sowing date effects.

&#8226 Use T1 strob on thin crops.

Regional

programmes

In Northumberland and Scotland Dr Bulmer suggests growers stick to a triazole at T1, reserving strobilurins for T2 and T3. "Save the strob for the flag and ear so you can milk the late maturation effect. There also tends to be less disease pressure at T1 due to the colder winters and the T1 to T2 interval is generally shorter." Aiming for 1.4 units of strobilurin, he suggests a 0.8 litre/ha + 0.6 litre/ha split between flag leaf and ear. "Time the ear wash as early as possible as fusarium can already be established by flowering in wetter regions. Going that early tends to push flag leaf timing back to GS37, which ties in with the non-strob approach at T1."

In the south-west, strobilurin responses have been questioned, but Dr Bulmer believes timing is the key. "Here, varieties hit their growth stages very early and disease develops early. I think growers might see a response if they used the strobilurins earlier, say GS31 rather than GS32. But then there is a danger of missing leaf 3, so again T2 would need to be at GS37, as soon as the flag leaf is visible." Alternatively growers could use Bravo early at GS30 with the pgr to damp down septoria, and stick to conventional timings.