Arable News

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‘Wake-up call’ lessons must be learned

Chlorothalonil should play a major role in fungicide tank mixes this spring if growers want to get disease control programmes in wheat off on the right footing

Chlorothalonil should play a major role in fungicide tank mixes this spring if growers want to get disease control programmes in wheat off on the right footing. Dominic Kilburn gets advice. Prime Agriculture agronomist Bill Barr (pictured left) admitted that last season’s big wakeup call was the visual shift in the sensitivity of triazole fungicides to septoria in wheat crops. He stressed that although there had been plenty of warning, recent years of relatively low disease pressure had meant that the extent of the shift – leading to an increase in resistant septoria isolates and a reduction in eradicant control – had gone largely unnoticed.Bill advises on land in Bedfordshire and Northamptonshire, mostly on Group 3 and soft Group 4 wheat varieties for mills in the East Midlands, including supply to Weetabix, and also some barn-filling hard Group 4s.”Septoria is a big worry,” pointed out Bill. “Last year with the terrible conditions there was very little eradicant performance from the triazoles and so, for this season, everyone must be very proactive in getting sufficient protective chemistry on crops in time.”He said that rust in wheat crops is also of concern and, while he had planned to move his growers away from the rust-prone Oakley-type varieties last autumn, a lack of seed choice meant that there was more Oakley and Robigus drilled than originally intended.Speaking in mid-March, Bill said that with high levels of inoculum brought over from last season, it was no surprise that he was now starting to see yellow rust appearing in susceptible varieties.Cyproconazole or epoxiconazole plus chlorothalonil will be his starting point for a T0 – the chlorothalonil kicking off what will hopefully be a season-long programme of protection against septoria.Chlorothalonil will again be in the mix at T1 as continued protection against septoria will be key, and Bill suggested that there may also be the consideration of introducing SDHI chemistry at that timing – depending on cost or product and disease pressure at the time. “If you find yourself in a ‘fire brigade’ situation, and disease is out of control, then SDHIs are valuable tools to bring in at that stage,” he noted.Bill added that, potentially, with thinner crops in the field this season, and many that have been drilled late, it might turn out that septoria will not be so much of a threat as last season, but time would tell. Mildew, however, would almost certainly be a problem on account of late drilled crops and this would need addressing at T0 and T1.
SDHI fungicides did well last year, he continued, despite the perception from some growers that they didn’t perform as well as expected in protecting yield. “Yields last season were compromised anyway and if they hadn’t been used, the situation would have been a lot worse. “We used them at T2 and I am pleased we did as we got a good response from them.” In terms of SDHI choice, Bill said that it was very difficult to determine any difference in performance between Aviator Xpro (bixafen + prothioconazole) and Adexar (epoxiconazole + fluxapyroxad), but it may simply come down to price, or whether growers want chlorothalonil in the SDHI mix (Bayer does not recommend mixing chlorothalonil with Aviator, since it can be antagonistic).
“The new one from DuPont looks interesting although we need to see it more, and so the jury is still out on that one,” he added.Bill concluded with a key piece of advice ahead of disease control programmes this spring:
“With crops at variable growth stages this season, watch out for leaf emergence to determine applications and don’t assume calendar dates are the right times to spray.”Remember too – later drilled crops go through the growth stages faster and they will need watching carefully.”Agronomists are suggesting that chlorothalonil should play a key part in fungicide tank mixes this spring.Signs of septoria in the south
Richard Alderman of Crop Management Partners advises on land in Hampshire and Berkshire.Also speaking in mid-March, he said that early drilled wheat crops looked well, were not too forward and had tillered nicely. Later drilled crops were looking patchy in places, he added.With Southampton on the doorstep, a large area of Group 3 varieties are grown for export, while the presence of Rank Hovis’ mill at the same location meant that, traditionally, milling wheat featured prominently in rotations, although the poor weather last season had resulted in a slight move away from milling quality crops for this season, Richard said.He noted that there had been considerable signs of septoria in wheat crops in early March which reinforced the need for growers to include chlorothalonil in their programmes this spring. “Chlorothalonil should be playing a major role in this season’s disease control programmes to keep septoria at bay and they should try to include it where they can throughout the programme.”
While there was no sign of mildew as yet, he reckoned that Talius (proquinazid) at the T0 timing might be an option if required, however, if he could hold off until T1 in terms of mildew, then he would. “Mildew is really something to focus on this season, particularly with backward crops, and it’s very important to keep it out, before it becomes established, especially with susceptible varieties,” commented Richard.
“In the absence of mildew T0 could be a straight chlorothalonil plus a triazole if rust is a problem but that decision will be taken in view of what diseases we are facing at the time. “Potentially some of the backward crops may move rapidly through the growth stages, and timings between T0 and T1 may be short.  With one eye on crop potential, and considering what growers have already spent on slug pellets so far this season, we could even give the T0 application a miss, but it just depends on how fast they move and the disease pressure at the time.”Provided you can be timely on your T1 spray, backward crops at T0 is where you might save a spray this season, but only in the right situation. It’s something to consider,” he added.
Richard said his T1 will probably be based around a ‘Tracker-type’ approach, or prothioconazole and both with chlorothalonil, while, in very poor conditions and high disease pressure, he would consider an SDHI.”In 2012 if you walked into a crop treated with an SDHI you might have scratched your head and wondered what you had spent your money on, but then if you compared them with crops that hadn’t received a similar treatment, you can see why they were justified. They make a huge difference and bearing in mind triazole sensitivity, then SDHIs are important products and we need to use robust rates of triazoles in the programme to protect them,” explained Richard.He said he tried all three SDHI’s at T2 last season; Seguris (epoxiconazole + isopyrazam), Aviator and Adexar, but he’ll be sticking with the latter two in equal measure for this season, providing prices come into line.
Like Bill, Richard said that he was looking forward to seeing more of DuPont’s SDHI which he suggested would be worth exploring in more detail when it became available.

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