Keep winter wheat T1 sprays at GS32 urges Bayer’s’ Tim Nicholson after many T0s were abandoned or applied late following cool and wet weather through much of March.
He says the focus needs to be on fully protecting leaf 3, and timing is essential for that. “It’s the first key yield producing leaf so protection through to flag leaf emergence is important. The correct timing is when leaf three has just fully emerged. Too early and you might only protect the leaf tip and any fungicide could run out of steam ahead of GS39. Too late and leaf three is exposed to potential infection ahead of application.”
That advice doesn’t alter for those that got T0 sprays on. “The T0 is designed to protect leaf 4 from Septoria spreading from the base, and strike at yellow rust if needed. If a T0 goes on late, the T1 should still go on at the conventional time. It is the chance to reset the programme,” he advises.
In his view azole + CTL still has a place at the T1, but not where a T0 was omitted. “For many weed control took priority, with black-grass herbicide efficacy compromised by CTL, and severe frosts removing yellow rust in many cases, the T0 was dropped. With Septoria present in the lower canopy an SDHI at T1 is inevitable. They are our best Septoria protectants, and offer some kick-back if needed.”
But he isn’t advocating any rate increases. “Aviator (prothioconazole + bixafen) applied at the 1.0 l/ha rate with CTL will provide robust activity and an 80% rate of azole to help protect the SDHI. Growers must heed azole rates, to reduce SDHI selection pressure as much as possible. Money saved at T0 can be reinvested at T1 to ensure products are used at appropriate rates,” he suggests.
To help growers identify leaf 3 emergence a video is online – https://cropscience.bayer.co.uk/leaf3
For those wanting to do this a sharp knife is essential but also is the need to identify main tiller. This is the widest one notes Crop Management Partners agronomist Richard Cromie, who is featured in the video.
Working back from the ear will allow growers to identify the emerging leaf once the main tiller is separated. “After separating the main tiller, split it in half from top to bottom cutting through the leaf layers. As you move down the tiller you should feel the nodes.
“Then gently lift everything out from the inside until you get to the top node in the plant. At this point you can discard the remainder of the tiller and then working from the ear, count backwards from the flag leaf to identify which leaf is currently emerging,” he advises.