Arable

T1 disease risk is in the balance Concerns around disease resistance to SDHI fungicides are challenging T1 product choice. For Crop Management Partners agronomist Richard Cromie (left), it is about balancing the future of the chemistry with current crop performance. “The best way to reduce ‘selection pressure’ is not to use them, but that isn’t an option. Against septoria, an SDHI is the most potent option we have.” He feels it is impossible to optimise winter wheat performance without an SDHI, and that is the primary objective for his customers. So it is about reducing risks. “The flag leaf timing is still the most responsive for yield, so you’re looking to preserve green leaf area. It’s obvious why you want the most efficacious products here, especially if they have some physiological properties. Even with an effective T1 you could still have some infection in leaves three or two. There isn’t any option here but an SDHI. At T1 the plant isn’t so developed and

septoria may be in a less curative situation. That offers the opportunity for an azole + multi-site,” he notes.

Variety resilience The combination depends on variety resilience and spraying capacity. “If you’ve got something like Graham or Costello the risk of something going very pear shaped is lower, especially if it is drilled later and the weather has played ball. Providing you can hit GS32 and fully protect leaf three, then an azole + chlorothalonil (CTL) has a place. “But outside this, keeping septoria out has to be the focus. Even with more resistant varieties I’d favour an SDHI if I had a concern regarding pressure or drilling date. Some varieties like Santiago end up high risk regardless!” Risk is also the deciding factor when choosing a T1 azole. He feels prothioconazole and epoxiconazole are similar on septoria, but epoxiconazole has the edge on yellow rust. Fusarium or eyespot concerns would take him to Proline (prothioconazole) or Aviator (prothioconazole + bixafen) + CTL.

Flails to give you the cutting edge

Mr Cromie wants all farmers to put the same emphasis on responsible fungicide use as winter wheat performance. “The trouble with septoria is it can blow in from over the hedge. It isn’t always possible to select resilient varieties, and those who direct drill will want to drill early to take advantage of warmer soils. It isn’t practical to expect everyone to apply best practice disease control cultural techniques. So, we do need to ensure our fungicide strategies are appropriate to the situation in hand.”

Effective control Bayer’s Tim Nicholson (right) agrees. In Bayer trials Proline + CTL still works well. “We’re still seeing effective control from three-quarter rate prothioconazole and CTL, but timing is absolutely critical,” he cautions. That can be seen from Bayer trials last season, where T1 applications were delayed in a number of plots to see what impact it had. Despite reduced septoria pressure there was a visible effect as crops approached flowering. “By the time we got to GS59 and ear emergence you could see the impact. The plots where we delayed T1 applications had less green leaf area (GLA).” To quantify the value of GLA retention, Bayer called in ADAS, which has measured GLA decline on plots of Santiago at Bayer’s Callow site for the past three seasons. That showed that for every day

GLA was maintained in the upper canopy it was worth up to 0.5t/ha/ day. “Even last season you could see the benefit of a robust, well-timed fungicide programme,” says Mr Nicholson. “When we looked at the data, plots treated with Proline + CTL at T1 and Aviator at T2 remained above 35 per cent GLA for an extra 13 days compared with the untreated plots, contributing an extra 0.37t/ ha/day. “Plots treated with Aviator + CTL at T1 and Ascra (bixafen + fluoxastrobin + prothioconazole) at the T2 held on to GLA for even longer. Here a minimum of 35 per cent GLA was achieved for 18 days over untreated plots. This equated to an extra 0.32t/ha a day and response over untreated of more than 5.5t/ha,” he says. “Some SDHI co-forms only provide a half rate of azole at their commonly used rate. It dilutes the protection of C the SDHI component and azoles are still doing something curatively.” M He believes that is a greater Y danger than using SDHIs twice in a programme. “Researchers haveCM suggested one reason for the MY stabilisation in azole performance is CY SDHI use, as one group protects the other. In certain situations an azole CMY + CTL isn’t realistic at GS32, and an K SDHI mix is the only option. When that is the case it is imperative they are used at appropriate rates,” he concludes. ■

In brief...

New powdery mildew fungicide for fruit and veg

• Front - rear - side or offset for tractors 10hp - 400hp • Mulchsysteme gives proven control of pests and weeds while stimulating healthy crop and pasture growth

www.slopemower.co.uk Simon Richard Ltd, Crown Tailrig, Bonchester Bridge, Hawick, TD9 8RA Tel: 01450 860774 Fax: 01450 860772 mail@simon-richard.co.uk www.simon-richard.co.uk

BASF is launching a new specialist fungicide, Charm, for the control of powdery mildew in strawberries (outdoor and protected), protected tomato, cucumber and pepper. Charm contains the SDHI active ingredient fluxapyroxad (Xemium) and the triazole difenconazole and offers built in fungicide resistance management. It is highly effective, moving the level of disease control achievable forward, says BASF. It is applied at 0.6-litre/ha in strawberries and 1-litre/ha in tomatoes and peppers. It has short Harvest Intervals – one day in strawberry, three days in cucumber and seven days in tomato and pepper. BASF’s Rob Storer says: “Trials

have shown excellent control of powdery mildew. This is a result of Charm’s rapid uptake, mobility and persistence. It moves into new growth and protects both new and older leaves. In five trials in strawberries in the field and in polytunnels, Charm gave better overall control of powdery mildew than the standards. For example the untreated had on average 12 per cent powdery mildew. Applications of Charm reduced this to 2.2 per cent after a week and 2 per cent after 14 days compared with the standard programme which reduced mildew to just 4 per cent after a week and 3.8 per cent after 14 days.”

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