Tips on cereal disease control for this April

Crop Progress

Up until mid-March, when this was written, it hadn’t been easy for growers to make decent progress with field work. Those who had managed to travel to get some nitrogen on and / or some weed control will have given their crops more of a fighting chance.

But there was plenty out there at that point where it hasn’t been able to travel despite some dry days as they were invariably followed by another downpour. Any barley, for example, which hadn’t had any nitrogen was starting to look a little unwell, and it’s just increasing the variability gap still further from where it was before.

My biggest concern is the lack of rooting on a lot of crops due to sitting with prolonged wet feet, whether it is oilseed rape, wheat or barley. If there’s a dry spell, especially on soil types like Cotswold brash, it’s not going to end well.

Ben’s agronomy tips for April

1. Rusts and mildew headline early season disease risk in wheat

There’s been quite a lot of mildew in some crops, which provides a small dilemma in whether to treat at T0 with a specific mildewicide or leave it in the hope that the weather or fungicides used at T1 deal with it.

Adding a mildewicide obviously adds cost, but if you have a mountain of mildew then it’s probable that one will be required as part of the programme at T0 or T1.

Most T0 sprays will revolve around rust control. You would normally only be thinking about yellow rust and indeed there was a reasonable amount of yellow rust in crops in early March, including in varieties like Extase.

But there’s also a number of reports of crops with brown rust infections after a mild winter, particularly Crusoe. Those old enough to remember back to the year Alchemy was infected with brown rust in March – I think it was either 2006 or 2007 – will know that it was extremely tricky to get on top of.

The other variety to watch is Champion, which I don’t think is particularly strong against brown rust. If you look at the Recommended List data, it has quite a wide range of responses to fungicides. Everyone thinks it is a low input variety, but there are one or two sites where it had much larger responses and they are likely to be places where it got brown rust late.

Controlling either brown or yellow rust at T0 equals decent doses of tebuconazole, plus or minus a strobilurin if you want to. Remember you cannot just apply a straight strobilurin alone – it must be mixed with another mode of action.

2. Do thin crops equal low spend?

Do thin crops automatically equal a lower spend on fungicides? The answer, as ever, is probably: it depends.

If you’ve drilled a crop in September and through no fault of your own thanks to the weather, it has become a patchy crop, Septoria doesn’t really care about that – it only cares when it was drilled, so the pressure could still be quite high even if it looks a bit ropey.

A thin crop might get slightly less Septoria for a given drilling date because leaves rubbing together or infections spread though rain splash are less likely, but the drilling date risk is still there.

So I think if you’ve got early drilled wheat that is not in a great state, there’s probably a small amount of capacity to save money because potential is restricted, but definitely not to the extent of cutting a fungicide bill in half – that would be a dangerous game.

Late drilled thin crops are a totally different scenario as both of those factors will affect the level of Septoria, so there’s more scope to cut costs.

The worst-case scenario is where you might need to spend a reasonable amount to actually reduce a loss, which is a very difficult conversation or calculation to make. But it could mean spending £150/ha on a fungicide programme to only lose £200/ha rather than £400/ha from a lower spend on fungicides. But I really do hope there won’t be too many of those crops around.

3. Timing T1 sprays could be tricky

With variable crops both between fields and in field, timing T1 sprays correctly is going to be a challenge this season. Variability in field caused where crops have been waterlogged or grown at slower rates means an assessment will need to be made of when a reasonable average of the field has leaf three fully emerged on the main stem.

I’d probably look at doing that in the best parts of the field as they will provide the yield for you. Dissecting plants remains the best and perhaps only way of truly seeing which leaf layer has emerged at this time of year.

There’s an even bigger stable of potential options for fungicides this year with the launch of our Iblon® range, but if something worked well for you last year it’s not unreasonable to expect it to do so again this year.

There is potentially higher rust risk this year in a number of varieties, plus Septoria and mildew, so that could lead you down the route of buying the highest dose of prothioconazole you can buy for a certain price point.

Ascra® (bixafen + fluopyram + prothioconazole) had a good year both commercially and in AHDB fungicide performance trials where it performed equally as well as Revystar® (mefentrifluconazole + fluxapyroxad) against Septoria. Looking at the cross year AFD data, Ascra’s efficacy seems to have held whereas Revystar looks to have come back towards it to a point now where there is dose parity, which puts Ascra in a good price position.

Univoq® (fenpicoxamid + prothioconazole) is still the strongest Septoria product and is also well-priced but I think most growers will save that for flag leaf (T2) sprays.

The other choice you could consider is Elatus® Era (benzovindiflupyr + prothioconazole) for the rust risk. The trouble is I think its Septoria weakness now outweighs its rust strength and in a programme there is very little to choose between this and the other T1 options on rust

Of course, if you want the best all-round disease control because you’ve got a reasonably early drilled crop that’s got some potential, then try our new toy, Vimoy® (isoflucypram). It provides excellent control of rusts and Septoria and seems to have strong greening benefits above disease control.

For most crops I think 1.0l/ha of Ascra will be a good combination of disease control activity and price, but in the relatively few where there is more severe rust or Septoria risk, or places where you’re not going to use Univoq through sprayer or buffer margin restrictions, I would consider using Vimoy .

And if it is because Univoq is a no go at T2 then I’d probably go either Ascra® at T1 followed by Vimoy at T2, or Revystar followed by Vimoy.

4. Broad-spectrum disease control for winter barley

Most winter barley crops in the Midlands will have a two- rather than three-spray programme that might be found further north.

There’s plenty of brown rust in hybrid barley varieties, but it is a different pathogen to brown rust in wheat and easier to control. Prothioconaozle is more effective against barley brown rust than wheat, for example.

If the wet weather in the first part of March has carried through into early April then that will equal Rhynchosporium and net blotch risk, and a requirement for a decent programme that will do a good range of diseases.

Our programme would include Ascra or Siltra® (bixafen + prothioconazole), which is competitively priced. Where you have a variety weaker against net blotch I would favour Ascra and then follow with Siltra, rather than a double Siltra.

If Ramularia is a risk, then you could swap them around and use Ascra at T2, which at a decent dose will do more against that disease than Revystar , especially at some of the low doses being suggested. But remember you can only use Ascra once in the programme so you have to choose.

5. Protect oilseed rape crops

Some oilseed rape crops have suffered since Christmas with cabbage stem flea beetle larvae exacerbating the poor rooting, so they hadn’t grown away or thickened up as much as you would like by mid-March.

There was also some light leaf spot around. That probably didn’t need treating before early flowering unless it was rampant, while I suspect less tebuconazole will be used this year around stem extension because growth won’t need to be restricted.

That could mean crops getting to early flowering without having had any fungicide, which could mean light leaf spot is difficult to control or will need something decent. Obviously there is one clear option from Bayer in Aviator® (bixafen + prothioconazole), which I would use at 0.75 L/ha.

Aviator will also help control Sclerotinia although it has been a while since we had an epidemic, and the flowering spray is more for light leaf spot and greening these days.

6. One or two spray disease control in spring barley?

The way things are going with drillings it looks possible that spring barley will become a one-spray rather than two spray programme disease control this season. With the likely amount of spring barley in the ground this season, you would imagine prices will not be high so that might be a sensible decision.

If you decide to head down that route I would suggest using a decent dose of Ascra® , around flag leaf emergence timing – you know, it’s that six hour window when the crop goes from flag leaf emerging to ear full emergence.

Acknowledgements

Ascra contains bixafen + prothioconazole + fluopyram. iblon contains isoflucypram. Revystar contains mefentrifluconazole + fluxapyroxad. Univoq contains fenpicoxamid + prothioconazole. Elatus Era contains benzovindiflupyr + prothioconazole. Vimoy containts isoflucypram. Siltra contains bixafen + prothioconazole. Aviator contains bixafen + prothioconazole. Ascra, Iblon, Vimoy, Siltra are registered trademarks of Bayer. All other brand names used are Trademarks of other manufacturers in which proprietary rights may exist.