Rampant rust, stresses and greening highlight the need for cereal flag leaf protection
Combined effects of rampant rust infections and drought-stressed plants are providing a double whammy reason to consider protecting all-important cereal flag leaves with a strobilurin fungicide this season, experts are urging.
In crops where the flag leaf timing hasn't been reached, rust levels may even require an interim fungicide to prevent infections spiralling out of control.
According to Syngenta cereal disease specialist, Matt Pickard, the flag or top leaf is the most important one to protect in wheat crops, contributing up to 45% of final yield.
Against that, however, he says rust infections seem to be everywhere this season, with brown rust on both susceptible and resistant varieties, and yellow rust even reported on crops with a resistance rating of nine.
"Yellow rust can deplete yield by up to 50% and brown rust by up to 30%," explains Mr Pickard. "Therefore both are important to control. Added to that, the dry April has left crops very short of moisture and susceptible to stress.
"As well as providing protection against rusts, we know a strobilurin fungicide can boost green leaf retention and has been shown to reduce stress symptoms in cereals.
"Just this spring we announced results of a research programme on barley with Amistar and Amistar Opti where there was a trend to the strobilurin-treated plants performing better under drought stress. With the pressures that crops are under this season, these results could have come just in time."
North East based farm business consultant Robert Sullivan of Strutt & Parker agrees that a strobilurin treatment on flag leaves is justifiable this year.
In particular, he sees the ability of strobilurins to improve crop greening as being a key driver for using one – mixed with a suitable dose of triazole fungicide according to disease pressure.
"We always use a strobilurin at T2 because we see the greening effect as useful," explains Mr Sullivan. "Amistar Opti is the most cost-effective way of getting a strobilurin plus Bravo into the plant.
"It's the first year I've seen brown rust up here when crop walking. Crops are under pressure from lack of moisture," he adds.
By combining a strobilurin with triazole fungicide in a tank mix, Matt Pickard says growers exploit the benefits of each type of fungicide against the different life cycle stages of rust growth.
Amistar is most effective against spore germination, together with early stages of fungal development in the plant and spore production, he says, while triazoles and morpholine fungicides are most effective at stopping the fungus spreading through the plant.
"Where rust is easily found before flag leaf sprays are due, growers may need to consider a low-cost holding spray of a rust active triazole such as Cherokee plus morpholine to damp down infection," explains Mr Pickard.
"Alternatively, where flag leaf timings have been reached, then consider a rust-active strobilurin, such as Amistar or Amistar Opti, but keep the dose suitably high to provide maximum duration of protection, and add either a rust-active triazole or rust-active triazole plus morpholine according to the level of curative action required."
