Flag leaf spray a tricky balancing act this year
Flag leaf spray a tricky balancing act this year
Almost half the yield
produced by a September or
October drilled wheat crop
comes from the flag leaf.
Even later drilled, thinner
crops get one-third of their
yield from it. That makes the
flag leaf spray one of the
most important agronomic
decisions in the cropping
year. We provide some
timely advice
TIMING of the flag leaf fungicide spray is a compromise. "It is targeted at both the flag leaf and leaf 2, which together account for 60-70% of the final yield," says ADAS fungicide expert Bill Clark.
Keeping those two leaves alive should be the cereal growers priority, so light interception is maximised. "During grain filling, the crop is capable of gaining 0.2t/ha/day. Many people underestimate the importance of leaf 2 in this process."
For that reason delaying the flag leaf spray is not advisable. "It leaves leaf 2 at risk, especially from septoria. And although it might control any flag leaf disease, the contribution made by leaf 2 can be as much as 30%. So remember that there are two targets with this important spray."
Identifying the timing
The right timing for the flag leaf spray, or T2, is when the flag leaf is fully out on the main tillers, says Mr Clark. This years unusual season and variable crops could make that trickier than usual to assess.
"Wait until the flag leaf is out completely. Dont be tempted to spray when you first notice the flag leaf emerging."
T1 sprays have been difficult to time this year, with a wide range of drilling dates leading to a mismatch of growth stages. "So the timing of the flag leaf spray will be more important than ever."
His advice is to look at crops at GS37, in early May, one week before the flag leaf timing. "Youll be able to tell whether the T1 spray worked or not by looking for disease on leaf 3 and 4.
"If leaf 3 has been lost, which may reduce yields by 8%, you should assume that leaf 2 is already infected. Where T1 has been poor, be more alert to timing and dose rate with the flag leaf spray."
Spraying delays
If the gap between T1 and T2 is too wide, leaf 2 will be put at risk, warns Mr Clark. ADAS trials have shown that delaying T1 by ten days results in a yield loss of 0.75t/ha, whereas delaying T2 by the same length of time loses 1.2t/ha.
"With a responsive variety like Consort, thats equivalent to 0.1t/ha/day. So if you are stuck, the best thing to do is start with the high risk varieties. Timing is more important than product choice."
Fungicide dose
Aim to apply 50% of the seasons total fungicide dose at flag leaf, he recommends. "You need at least half of the total dose at this stage.
"If you do get delayed, you need to increase the eradicant activity of the tank-mix. That means using more triazole than originally intended.
"Dont stick to your original rates if you are held up by a week. The dose must go up and you might need to change products."
Fungicide choice
A strobilurin is an essential component of the flag leaf spray and should be applied at between half and three-quarters rate.
A good triazole is also required, especially on the septoria prone varieties. "Choose from epoxiconazole, tebuconazole, metconazole, fluquinconazole and cyproconazole," says Mr Clark. "Leave the cheaper, older triazoles to the other spray timings."
Choice of strobilurin is between three active ingredients – kresoxim-methyl, azoxystrobin and trifloxystrobin. "There wont be a big price difference between them, and they are all co-formulated with triazoles to make life easier."
He believes Landmark (kresoxim-methyl + epoxiconazole) is a good option for responsive varieties. "With a less responsive variety, go for Twist (trifloxystrobin) or Amistar (azoxystrobin) and adjust the ratio of strobilurin in the programme."
Where spraying has to start early and the flag leaf is not fully out, Mr Clark says there is a case for using Twist. "The mesostemic movement of the product means that it goes up the canopy. So it gives you more flexibility if you have to get going before the ideal timing."
Costs
The total fungicide programme will cost between £50-55/ha on a Consort-type variety. "So expect the flag leaf spray to cost around £25/ha," says Mr Clark. "Of course, varieties like Claire and Shamrock should only cost £35-40/ha in total, so the spend at flag leaf will be in the region of £18/ha." *
Big differences in crop development will make flag leaf spray timings trickier than usual this year. But this is the spray that will give the biggest yield responses, so be sure to get it right, says ADAS disease expert Bill Clark.