Ensure you get most important decision right
Ensure you get most important decision right
Flag leaf fungicide timings
are approaching and recent
rains have bolstered
septoria pressure. So how
should growers respond?
Over the following pages
we provide some timely
pointers, starting here with
a look at the basics
THE flag leaf or T2 spray in wheat is the most important fungicide decision a farmer has to make during the entire growing season, says ARC director Mike Carver.
"The aim is to protect the flag leaf because it makes the biggest contribution to the grain filling process. A crop gains as much as 0.2t/ha/day during grain fill."
Growers who took a risk and cut back on T1 sprays during the long dry spell must be very vigilant as crops approach T2, he advises. "It would be a shame to let disease in now. Crops have good yield potential and heavy rain between now and May 15-20 will change the situation overnight."
Fungicide choice
Flag leaf sprays should contain a strobilurin and a triazole, Dr Carver advises. The triazole provides the "kick back" or eradicant activity to control any disease already in the crop and the strobilurin gives the forward protection, keeping the flag leaf clean during the grain fill period.
"Use the strobilurin to protect the leaf for as long as possible. Which product you go for comes down to disease pressure and variety," says Dr Carver.
The newer strobilurins – pyraclostrobin and picoxystrobin – also have some kick back activity. "But picoxystrobin is a better barley product than wheat and not really a contender at T2. If you need kick back, look at pyraclostrobin, which also has the edge on brown rust. If you get delayed, these curative properties become more important."
Growers have to decide what balance of products is required. "The ratio of the two partners is determined by whether you need more kick back or more protection. Generally, the strobilurin should be included at half to three-quarter rate."
Spray timing
The introduction of more powerful chemistry has given some flexibility with spray timing, believes Dr Carver.
"The ideal timing is when the flag leaf is fully out on the main tillers, which usually occurs in the second or third week of May. In practice, spraying often has to start before and end after this time.
"Theres more leeway with products which have some movement, as they can be applied a bit earlier without any loss in activity."
Start with the highest risk varieties and aim not to let the gap between T1 and T2 extend beyond four and a half weeks, he advises. Where timings slip, reconsider the curative component of the spray.
"Theres a potential problem with early drillings. If youve gone early with the T1 spray, you may have too big a gap. But bringing the flag leaf spray forwards is a very risky strategy."
Dose rate
Much will depend on the variety and local growing conditions when deciding rates, suggests Dr Carver. "Its a false economy to cut rates back too much at T2. Aim to apply as much as 50% of the total dose at the flag leaf stage."
Where spraying gets delayed, be prepared to raise this and increase the curative component, he advises. "You should be spending half of your fungicide budget on the flag leaf spray. So that might be as much as £25-30/ha on a responsive variety." *
Recent wet weather means it is now vital to get T2 spray programmes right. Striking the right balance between strobs and triazoles is the key, says ARC director Mike Carver.
1 Yield protection At least half yield comes from flag leaf.
2 Strobilurin Provides forward protection. Newer strobs have some kick back activity.
3 Triazole Gives eradicant control.
4 Timing Aim to spray when flag leaf is fully out on main tillers. Some leeway with new chemistry.
5 Mind the gap Keep interval between T1 and T2 to 4.5 weeks. Any longer and leaf 2 is put at risk, so increase curative component.
6 Early drillings Use a T0 to hold off disease development rather than extending the gap between T1 and T2.
7 Rates Apply 50% of total dose at T2. Vary dose according to disease pressure.
8 Costs Be prepared to spend around £25/ha on flag leaf spray on responsive varieties.
9 Products New strob pyraclostrobin comes at a price. Amistar or Twist good alternatives, partnered with Opus or Flamenco.
10 Formulated products Beware paying for actives you dont need.