West: Help for agronomic decisions in May from Bayer

Crop Progress

Some dry weather towards the end of April gave a window for applying T1 fungicides in wheat. There was plenty of Septoria around, plus yellow rust in certain varieties.

Local CropCheck latent disease testing at the time showed leaf four awash with disease, with leaf three not looking so bad. But with latent infections, T1 likely required a decent product to give protection through till T2 sprays.

The dry weather also helped growers catch up with other jobs, and crops greened up and started to look happier.

Matt’s agronomy tips for May

What to do with T2s in higher and lower disease situations?

At the time of writing we’re still 3-4 weeks away from flag leaf sprays in wheat, so it’s impossible to predict the weather and therefore disease pressure.

If we get showery, warmer conditions between T1 and T2, then obviously diseases like Septoria will be cycling faster, and moving up the leaf architecture.

The flag leaf spray remains the most vital spray in the programme giving the largest returns on investment, and in high disease pressure situations choosing a suitably high performing product will be important.

Where Vimoy® (isoflucypram) + Proline® (prothioconazole) was not used at T1, that could fit the bill. Vimoy® , as well as being very good against Septoria, will also give excellent protection against brown rust, which might be beneficial especially in the more easterly parts of the southwest, and yellow rust. Prothioconazole will help against those diseases, while also adding early protection from Fusarium.

In exceptionally high disease pressure there’s also the option of using Jessico® One (fenpicoxamid) with Vimoy® , where neither active was used at T1. It’s probably the strongest combination on Septoria available. Adepidyn® is another contender, but from what I’ve seen in trials, while it keeps crops extremely green that didn’t always equate to a big difference when plots were harvested.

If Vimoy® + Proline® was used at T1, along with the option of competitor products such as Univoq® (fenpicoxamid + prothioconazole), there’s also Ascra® (bixafen + fluopyram + prothioconazole). At 1.2-1.5 L/ha it’s a very good T2, offering good Septoria and rust protection.

I’d also be considering Ascra if disease pressure drops away because of dry weather between T1 and T2, or for late drilled crops with lower yield potential. Septoria pressure in the west never completely go away, so keep doses around 1.2 L/ha.

Complete remaining winter barley T2s

Winter barley growth stages were all over the place, as we approached the last 10 days of April. In some crops awns were starting to emerge, while other crops were further behind.

Any remaining awns emerging sprays will be a priority for early May, with product choice depending on what was applied at T1.

Where Ascra® was used earlier in the programme, options for the second spray include Revystar® (mefentrifluconazole + prothioconazole) as that will offer some Ramularia control, or Siltra® (bixafen + prothioconazole) where wet weather diseases are more of a concern.

If Ascra® was not applied at T1, then it is a strong choice at T2 as it will cover both Ramularia and the wet weather diseases, such as Rhynchosporium and net blotch. In our trials the fluopyram in Ascra® is on a par with mefentrifluconazole against Ramularia. With winter barley having gone through a difficult season, and stress a key factor in the severity of Ramularia there’s potential for it to be a high pressure season.

One or two spray fungicide programmes in spring barley?

Spring barley drilling was late this spring, with the majority being drilled in mid-April or even later. Once established it’s likely to rush through growth stages once it gets hold of the nutrition in the seedbed.

I always recommend two fungicide sprays in the southwest because of the warmer, wetter conditions meaning disease gets going really quickly. Further east in the region there’s probably more scope for a one spray approach.

Where you’re using two sprays, the first should be targeted at when the crop is meeting across the rows. These crops will need to be kept healthy to retain tillers and maximise yield potential, and that can be achieved by using Ascra® , which as in winter barley cover all the main disease threats.

A second spray of Siltra® can then be applied when the awns emerge, two to three weeks later.

Will oilseed rape need a second flowering spray

Flowering in oilseed rape started pretty early because of the mild winter and perhaps as a stress reaction. With the variable growth in the crop it has been very protracted and still ongoing as this is written.

Where crops are still flowering strongly in May, and it’s been three weeks or more since any previous fungicide, then another fungicide application to protect against Sclerotinia might be required, if conditions are favourable.

That could be 0.5 L/ha of Aviator® (bixafen + prothioconazole) where the dual mode of action is helpful for disease control and resistance management, with the SDHI component bringing some plant health benefits.

Prepare for fast emergence of later planted potatoes

Weather windows have allowed growers to get on with potato planting. Where main crops are planted relatively late in April or even into May, prepare for faster emergence in warmer soils.

That will have an impact on weed control in that timings need to be spot on for some products, including Roundup® (glyphosate) if being used for contact activity. You need to be on the ball and watching for crowns emerging as you don’t want to be hitting those with glyphosate – it’s not quite the same as it used to be with diquat.

Another product that must be applied pre-emergence is Emerger® (aclonifen) – our advice is to spray it at least seven days before emergence. It gives control of a good broad spectrum of weeds. Mix with partners like Artist® (flufenacet + metribuzin) for extra grassweed activity or Sencorex® Flow (metribuzin) for increased broadleaf weed control on tolerant varieties.

Plan blight control strategies

With reports of resistance to CAA fungicides, such as mandipropamid and the Zorvec® OSBPI fungicide (oxathiapiprolin) in new blight strains EU_43_A1 and EU_46_A1 on mainland Europe, we’re going to need to be aware of the potential threat if those blight strains arrived in the UK.

Start planning how you would react to such a development, and consider how to follow the new FRAG-UK guidance around mixing modes of action and alternating chemistry.

Cultural control remains vital for preventing blight infections in the first place, so make sure all dumps and outgrade piles are destroyed as soon as possible, and control volunteers effectively from previous crops.

Weed control programmes in maize

Growers will be getting on with planting maize during May, and it’s a crop that benefits from good early season weed control as it doesn’t react well to competition.

Using a pre-emergence herbicide, such as pendimethalin, particularly if the weather stays conducive to residual herbicide activity, will buy a lot of time and means you don’t have to worry about post-emergence timing quite as much.

The ideal timing for contact herbicides, such as MaisTer® (foramsulfuron + iodosulfuron), is the 2-4 TL stage of the maize, when there will be lower interception of the spray by the maize crop, allowing it to reach the target weeds.

MaisTer® is a strong option for a range of broadleaf and grass weeds, particularly where you have difficult black-grass where it shows good control. Add a partner depending on weed spectrum you’re facing – we’ve been able to expand the range available.

Acknowledgements

Vimoy containts isoflucypram. Proline contains prothioconazole. Jessico One containts fenpicoxamid. Adepidyn contains pydiflumetofen. Univoq contains fenpicoxamid + prothioconazole. Ascra contains bixafen + prothioconazole + fluopyram. Revystar contains mefentrifluconazole + fluxapyroxad. Siltra contains bixafen + prothioconazole. Aviator contains bixafen + prothioconazole. Roundup contains glyphosate. Emerger contains aclonifen. Sencorex Flow contains metribuzin. Zorvec contains oxathiapiprolin. MaisTer contains foramsulfuron + iodosulfuron. Vimoy, Proline, Jessico One, Adepidyn, Ascra, Siltra, Aviator, Roundup, Emerger, Sencorex Flow and MaisTer are registered trademarks of Bayer. All other brand names used are Trademarks of other manufacturers in which proprietary rights may exist.

Use plant protection products safely. Always read the label and product information before use. Pay attention to the risk indications and follow the safety precautions on the label. For further information, including contact details, visit www.cropscience.bayer.co.uk or call 0808 1969522