Five insights into March agronomy in the west

Crop Progress

In comparison with other parts of the country, crops are looking fairly reasonable in the southwest and I get the feeling that growers and agronomists feel quite content.

That’s not to say there aren’t some fields that haven’t suffered in the wet weather, but even later drilled wheats have actually established reasonably well, helped by the mostly mild weather.

Most growers in the region now seem to be drilled up. You can find disease in some of the earlier drilled crops – the usual high volume of Septoria in the southwest and I’ve heard reports of yellow rust in Extase.

Matt’s agronomy tips for March

1. Weed control remains a priority

It looked like there was going to be a weather window at the end of January into the beginning of February to apply contact herbicides, but it soon closed with another bout of rain. So most growers as we approach the last week of February still have weed control to do.

It’s usually better to spray mesosulfuron-based products separately if possible, especially if you’re thinking of using tebuconazole as a T0 spray in wheat, because that can’t be mixed with any of our mesosulfuron range of products. Applying separately also helps maximise efficacy.

One complicating factor might be if it coincides with fertiliser applications. Ideally you would want the crop to grow away and recover before running through with a herbicide, because the growth resulting from the fertiliser could trigger more uptake of the herbicide and, especially with liquid fertiliser, cause a bit more scorch, which with this season’s crops is something to avoid.

In March, the full range of mesosulfuron-based products are available, including the 0.5 kg/ha dose of Pacifica Plus (mesosulfuron + iodosulfuron + amidosulfuron), which can be used to target bromes. It will also help against black-grass and Italian ryegrass.

For annual meadowgrass you won’t need such a heavy hit. Where it is overwintered and well-established 12g/ha of a mesosulfuron-based product should be sufficient, and lower in later drilled crops with lower weed pressure.

If you choose Atlantis Star (mesosulfuron + iodosulfuron + thiencarbazone) remember if you then need to follow up with another ALS / sulfonylurea herbicide for broadleaved weed control, such as metsulfuron or thifensulfuron, only winter wheat is allowed as a following crop. There’s differences in following crops with other mesosulfuron products so check labels carefully. The same applies to adding residual partners, where labels differ in what is allowed.

Another consideration is whether you’re going to follow the wheat crop with a cover crop or other SFI-type option in the autumn. We don’t have the data to support all the various cover crop species after mesosulfuron applications, so our default guidance on the label is to use deep tillage before the next crop to break up the herbicide layer. If you try to direct drill some kind of cover crop there’s no guarantee the herbicide won’t have some impact on establishment.

In winter barley, weed control options at this time of year are very limited. In our portfolio Chekker (amidosulfuron + iodosulfuron) is one option that might give some grassweed suppression, but the dose of iodosulfuron is low so results cannot be guaranteed to give the barley more chance to out compete the grassweeds, but it will deliver good broadleaf weed control.

We also have Emerger (aclonifen) approved for use in field beans and combining peas. It can only be used pre-emergence and should be tank mixed with another herbicide to broaden weed control and improve efficacy. In trials it lifts control of weeds such as black-grass, Italian ryegrass, charlock, chickweeds and poppies.

Finally, remember to use the correct dose of Roundup (glyphosate) when spraying off stubbles and any remaining cover crops. It’s easy to default to a standard 720g/ha of glyphosate for stubbles without considering whether you have other weeds that will require a higher dose.

Using a branded Roundup formulation will also contain all the surfactants and wetting systems to help get droplets past the hairy or spiny leaves of some of the more difficult weeds found in fields.

2. Assess disease risk in barley and wheat

Decisions around T0 fungicides are likely to be hotly debated this season with crops in very different states of growth and potential.

In winter barley in the southwest, very disease susceptible varieties – Maris Otter being the most extreme example – will likely benefit from a T0 spray to mop up as much Rhynchosporium and mildew as you can.

Early drilled, susceptible crops have had a lot of moisture and grown on in this mild winter, so could be lush and thick with higher disease pressure could also benefit.

T1s will likely be due in either late March or early April between late tillering and GS30/31. These will have even greater significance than normal in winter barley crops, especially ones that have struggled overwinter this season, with tiller retention vital for maximising yields. Preventing diseases will lead to fewer tillers being aborted through crop stress.

Our advice remains to build this timing around prothioconazole-based products. Siltra (bixafen + prothioconazole) remains a good choice with the bixafen bringing increased Rhynchosporium and net blotch control. Prothioconazole will boost mildew control and also has good activity against barley brown rust – remember wheat and barley brown rust are different pathogens.

For winter barley with more potential or higher disease burdens, Ascra (bixafen + fluopyram + prothioconazole) at 0.9 L/ha is probably the gold standard for T1. As well as increased efficacy against key diseases, we know that it also helps with physiological benefits, such as greening, stem elongation and stem strengthening which will also help with tiller retention.

In wheat there are fewer fungicides that fit with T0s than when chlorothalonil was available and the decision whether to apply one will depend a lot on circumstances.

Assess disease risk using variety disease resistance ratings. Yellow rust is an obvious disease to target at this timing with a tebuconazole or strobilurin fungicide. Susceptible varieties are most likely to benefit, including later drilled crops which research suggests are more at risk from yellow rust. It’s better to keep the disease out than rely wholly on a curative fungicide at T1.

Varieties with good disease resistance, especially to Septoria are less likely to need a T0. In the east of my region up on the chalks disease pressure might be lower too, allowing to get away without one.

There will be growers thinking a lower yield potential means at risk crops don’t need a T0, but a lower yield potential doesn’t mean they won’t get disease, so my opinion is it’s still worth protecting your investment.

3. Watch out for light leaf spot in oilseed rape

No one has been talking too much about oilseed rape during the winter, as drilling cereal crops have been causing the main concern. There’s been some reports of cabbage stem flea beetle larvae in some crops, and March is usually the month where that becomes make or break.

Assuming crops do have a viable future, again it’s when decisions should be made about investing to protect what you have. Light leaf spot historically starts showing in February through into March, and at a meeting in mid-February one agronomist said they were finding plenty in crops. The risk rises quickly as daylength increases and temperatures rise especially if no fungicide has been applied to the crop as yet, so you probably should be considering an application of Proline (prothioconazole) to keep on top of it through to flowering.

4. Weed control in potatoes

Potato planting continues in the southwest, with second earlies and some crisping varieties likely to be planted in March, where the early harvest helps spread workloads in factories.

With most earlier crops not in the ground for too long, nematodes are less of an issue than in more main crops regions. There are a few fields where potato cyst nematodes are beginning to show, and where Velum Prime (fluopyram), in conjunction with nemathorin could be considered.

For weed control, we have a decent range of options in Emerger (aclonifen), Artist (flufenacet + metribuzin) and Sencorex Flo (metribuzin). The latter will deal with a wide range of broadleaf weeds, the flufenacet in Artist helps with grassweeds, while Emerger is good tank mix partner for either to further boost and extend control.

Emerger works well in dry conditions and has a decent half-life, but does need to be applied at least seven days before the potatoes emerge so it does need planning carefully.

5. Research maize varieties

First maize varieties will be planted under plastic in March with the bulk of drilling in the following couple of months. While, unfortunately, at the moment we don’t have any data on our Dekalb varieties under plastic, they are worth considering if you have a favourable site for maize and you’re looking for a variety with high yields, good starches and MEs.

Find out more on our website: https://cropscience.bayer.co.uk/our-products/maize