Adaptability in a T1 programme can help to set growers up for unpredictability in weather and disease pressures. CPM explores fungicide options and approaches as we move into the spring.

“A fungicide strategy should include as much diverse chemistry as is available.”

By Melanie Jenkins

Boots on the ground indicate that a reasonable amount of winter wheat has been planted in the early part of 2024, despite the tricky autumn and testing conditions.

And while growers had a few favourable weeks during late January and early February to plant late sown autumn crops, the wetter conditions since have likely instigated a switching point where growers start to look at spring cropping.

The good news is that crops are looking better than many might have expected, due in part to the recent mild spell, explains Syngenta’s Joe Bagshaw. “We’re at the stage where growers are looking to apply nitrogen and trace elements, but we’re still in a situation where it’s essential to manage crops on a field-by-field basis.”

Dr Tom McCabe, agronomy researcher and director at Prime Agriculture agrees, noting that the drier conditions in late January have helped crops to improve, bringing growers nicely into T0. “There’ll be some very good crops going into T1 and confidence levels have improved but keep in mind the context of your crop as there’ll be variability. Factors such as soil type, which usually wouldn’t make as much difference, have had a bigger impact this year and crops are far more varied than normal.”

And as far as inoculum level goes, yellow rust still appears to be the most high-risk disease. “The cold spell we had did knock it back but there remains high pressure to be aware of, especially in susceptible varieties. We’ve seen temperatures of 10-14oC and with moisture, yellow rust can cycle very quickly.”

According to Tom, the disease is notable for its unpredictability. “Although it can appear predictable, the disease can be elusive some years and in others it can arrive in January and be present the rest of the season. Currently, the feeling is to be reactive, but it should be taken as a serious concern because you don’t want to be chasing it. So the key is to get ahead of it using a planned programme for prevention.”

If yellow rust has been present in the crop, hopefully a T0 has been applied and then a T1 will be the most important spray for maintaining control, says Joe. “Elatus Era (benzovindiflupyr+ prothioconazole) is effective in this slot due to its performance against yellow rust. Looking at the AHDB dose response curves, the straight Elatus Plus (benzovindiflupyr) is outperforming newer products, with a 25% dose doing a better job than 100% dose of other chemistry.”

Tom also suggests including an SHDI and strobilurin. “You don’t want to be applying azole after azole – a fungicide strategy should include as much diverse chemistry as is available.”

If there’s rust in crops at all, Joe stresses treating it as a priority. “There are obviously some varieties with seedling resistance, so you wouldn’t expect to see rust early doors, but if a variety is seedling susceptible you might see the disease at T0 and T1. You can’t rely on adult resistance at these stages because it can take up to GS39 for it to fully kick in – it’s a gradual process and not a switch.

“Aim to control the disease before it becomes an issue as it can be too late if you wait until T2 – be proactive as it’s easier to protect against it than to try to cure it.”

In contrast to last year, septoria pressure is lower due to crop biomass being more modest, says Tom. “However, if there’s a strong growth period in the coming weeks this could change.”

Joe highlights that whatever the pressure, it’s still important to keep on top of septoria. “Looking at disease forecasting maps the risk was low as of mid-February but it’s pertinent to keep an eye on this as there’s potential for the weather between March and May to push up pressure, driven by the intensity and level of rainfall.”

The key window, based on work done with ADAS, is between 16 April and 15 May, he explains. “This period is where septoria inoculum spread, leading to later disease development, which is why at T1 it’s important to apply a persistent product protectively at leaf three. This will provide protection between T1 and T2 during that key window known as the firebreak.

“If you apply at T1 it’ll help to stop the spread of disease above leaf three which then protects 75% of the yield which is produced by the top three leaves and the ear – it’s about keeping the plant as clean and green as possible.”

Joe also advocates including a multi-site in the T1 slot. “Folpet is an important part of the programme in terms of efficacy but it’s also helping to protect the chemistry. Ideally, we’d recommend using 1-litre of folpet with Elatus Era at T1 to give you the best coverage between T1 and T2.

“Looking at the biokinetics of Solatenol (benzovindiflupyr), you can achieve 35-40 days of persistent protectant control which covers you between the key timings when applying robust rates of 0.8-1.0 l/ha. This can depend on the variety and a lot of growers have opted for those with strong septoria resistance. But those growing quality milling wheats have a lot less choice and rust can be a bigger risk for these too, so adapt your programme accordingly.”

Current data from disease risk maps indicates high levels of eyespot pressure, so including prothioconazole at T1 is important, says Joe. “Ideally, you’ll want 100g or more of prothioconazole to achieve any useful reduction in eyespot.”

The other disease that can be influenced with T1 sprays is take-all, he says. “Looking at inoculum maps there appears to be higher than normal pressure from this disease. So if you have second wheats or know you’re in a high risk situation, adding Amistar (azoxystrobin) at T0 or T1, or a split between the two timings, can reduce the risk by suppressing the pathogen and will helps crops to scavenge more nutrients from the soil. An early nitrogen application could also be helpful against take-all risk.”

Tom is an advocate of contact fungicides as a partner to all key chemistry at T1. “As you go from higher septoria pressure you want contact and therefore folpet plays an important role, but where there’s high yellow rust pressure the extra spend should be focused on controlling this.”

Joe highlights that the key with T1 is timing. “I frequently see people basing T1 on date, but it should be based on leaf emergence. Even the nodal growth stage doesn’t really matter at T1, you really want to be hitting leaf three at least 75% emerged, to provide protection for the whole leaf. This will put a firebreak in to stop disease spreading up the plant.”

This article was taken from the latest issue of CPM. Read the article in full here.

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