Tune strob choice as runners line up for T1

- 14 April 2000 https://www.fwi.co.uk More in News Tune strob choice as runners line up for T1 - 14 April 2000 >More in News

Tune strob choice as runners line up for T1Sprayers are lining up, ready for the off at T1 on wheats across the nation. As growers place their orders with suppliers, ADASs Bill Clark has

some 11th hour tips on what to back. Andrew Swallow reports

IT is neck and neck in the race to be the best strobilurin, according to a leading independent scientist.

Working out exactly which will prove to be the best bet means tuning strategy to individual circumstances, says ADASs Bill Clark.

"The choice of which strob to go for will depend on the disease control you need, local prices, and how technical you want to be – particularly with your choice and dose of triazole."

The simple answer for septoria-prone crops such as Consort or Riband is straight Landmark, (epoxiconazole + kresoxim-methyl) he says.

"It does not really matter which strobilurin, so long as you use at least a half rate. But the triazole has to be epoxiconazole to get the best Septoria control."

Current pricing makes Landmark the cheapest strobilurin plus epoxiconazole option, so not only is it the simplest, is also the most profitable option where Septoria is the main aim, he says

(see table).

But on more Septoria resistant varieties, such as Equinox or Madrigal, applying a half-rate of strobilurin as Landmark can be unnecessarily costly. A straight strobilurin plus alternative

triazole, or a lower rate of epoxiconazole, will be more economic, he says.

"If you have got a mildew or rust susceptible variety you could be wasting money on the Opus in Landmark," he warns. Switching to the stand alone strobilurins also allows growers to tune

that part of the equation to the variety profile.

"Twist is stronger on Septoria, and Amistar better on rusts. This year Twist offers mildew control too, but with mildew resistance around how long that will last depends on how the industry

uses the product."

Where any mildew is seen in the crop, Mr Clark advocates adding a specific mildewicide such as Patrol (fenpropidin) or Torch (spiroxamine). While Twist (trifloxystrobin) plus Opus, or

straight Landmark may control mildew, it is no defence against resistance, he warns.

"Using straight Landmark was what got the Germans into trouble."

But Twist is weak on rust, so where rust is a concern, the strobilurin should be Amistar (azoxystrobin) or Landmark. "Yellow rust is not even on the label for Twist," he says.

"And the triazole does not need to be Opus, which eases the decision away from Landmark. It is relatively easy to control rust with low doses of triazole, a quarter to half-rate depending on

the level of rust in there. Keep the strob at half-rate.

"The truly systemic nature of Amistar will help protect new leaves against rust," he adds.

No matter how clean the crop, no strobilurin should be used alone because of resistance risks. Very low level mildew resistance would quickly escalate and net blotch resistance is also a

real risk. "We have to take the risk seriously."

"In practice most of the yield response comes from T1 and T2 timings anyway, except for Scotland, where strobilurin earsprays are more valuable."*

Strobs on SeptoriaMargin over cost (£/ha)

Three doses of:

0.6 Az + 0.6 Opus600

1.2 Tf + 0.6 Opus610

0.6 Landmark650

1999 ADAS results @ £65/t.

Septoria susceptible varieties.

Spring 2000 chemical prices.

OCT/NOV DRILLED EQUINOX

• At GS30-31, leaf 3 tip visible.

• Yellow rust a significant risk.

• Septoria protection secondary aim.

• Two options:

Spray now: 1/2 rate Amistar plus 1/4-1/2 rate of tebuconazole, metconazole, cyproconazole or epoxiconazole. Systemic nature of Amistar protects emerging leaf 3.

Wait for leaf 3 fully out: 1/2 rate Landmark.

• At flag: Three-quarter rate strob. Amistar plus 1/4 rate triazole cheapest? May need half-rate triazole if yellow rust present – Landmark back in equation.

• Similar strategy for: Madrigal, Reaper, Rialto.

EARLY DRILLED CLAIRE

• At GS31-32.

• Septoria pressure negligible.

• No rush unless mildew rampant.

• Spray at GS32-33, Leaf 3 fully out.

• Use half-rate Twist plus low rate triazole with mildew activity eg, cyproconazole. If mildew established, add specific mildewicide, or mix Landmark and Ensign (fenpropimorph +

kresoxim-methyl).

• Possibly delay T2 to ear emergence but must monitor disease. Decision as T1 but three-quarter rate strob.

• Similar strategy for: Hereward.

OCT/NOV DRILLED CONSORT

• At GS30-31, leaf 3 tip visible.

• Less Septoria visible but inoculum still there.

• Two options:

Spray now: 1/2 rate Opus + Twist: vapour action protects emerging leaf 3.

Wait for Leaf 3 fully out: 1/2 rate Landmark, but may need extra Opus to eradicate established Septoria.

• Flag leaf: three-quarter rate strobilurin + minimum half-rate Opus. Do not delay beyond GS39.

• Similar strategy for: Savannah, Charger.

EARLY DRILLED CONSORT

• Already at GS31-32.

• Leaf 3 near full emergence.

• Spray ASAP, but with what?

• Opus at minimum half-rate: Septoria established on lower leaves so must assume all leaves infected.

• Half-rate of any strobilurin, but Landmark likely to be most economic.

• NB persistence not an issue – flag leaf out in 4-5 weeks.

• At flag leaf: Opus again + three-quarter rate strob. Twist an option for GS37 timing as vapour action should help protect emerging flag leaf.

• Similar strategy for: Riband & Savannah.

Strob decisions. Septoria levels are likely to steer strobilurin fungicide choices in many

cases.

Septoria is clearly visible on leaf 5 of this Sept-drilled Consort. The adjacent leaf 3 (top)is sure to be carrying infection after last weeks heavy rain, warns ADASs

Bill Clark.

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