Glyphosate stewardship and other advice for growers in East Anglia this March

1) Glyphosate stewardship is ever more critical

News of Italian ryegrass resistance to glyphosate – now confirmed in three cases with a fourth population showing decreased glyphosate sensitivity – highlights the need to pay even more attention to glyphosate stewardship principles.

These guidelines help make sure glyphosate is used appropriately so we don’t increase the risk of resistance developing in weed species, while also maximising control from the active.

Practically this starts with walking fields to make sure species are correctly identified, whether that is cover crop species or weeds in a stubble. Many cover crops will have been sprayed off in February or before, but if weather has prevented it so far, remember the general rules that if there is large vegetative biomass or woody species, you’ll need a higher dose of glyphosate active per hectare. The same applies if you have species with a complex deep root system.

This is due to glyphosate’s contact activity, which needs to be translocated around the plant – if you only have a small dose, it physically won’t get through the entire plant.

If sprays are delayed, whether through poor weather or other factors, check what’s changed by walking fields. Don’t assume that two or three weeks after a recommendation was made, that the black-grass or Italian ryegrass plants are still at two to three leaf stage, for example. If they’ve started tillering, you will need a higher dose.

Also check whether small grassweeds are being shaded by bigger plants, especially in cover crops. This could need an adjustment in plans to perhaps mow or grazing, ahead of spraying off, for example.

Monitor fields after spraying carefully – if there are surviving weeds, especially Italian ryegrass as the highest risk – don’t just spray again with glyphosate as that will increase the risk of resistance development. Use an alternative method of control, such as cultivation, to destroy those survivors to make sure they don’t come to seed.

Be careful of using Roundup® around stem extension of weeds. At this point all the plant’s energy is going upwards towards the flowering parts, so that’s where the glyphosate will go to, and it will kill the top of the plant but not the base. Using a higher dose won’t fix this, and you need to wait before applying glyphosate until the plant is through stem extension.

When applying Roundup®, as with every other spray, application technique is crucial. Whether it is just because of how effective glyphosate is, or it’s such a busy time of year, it can be easy to rush this particular job. Don’t! Appropriate forward speeds, boom heights, nozzle choice and water volumes are just as important to maximising efficacy and minimising resistance.

And if it is the first application of the spring with the sprayer, make sure the sprayer is working correctly – no leakages, correctly calibrated, etc.

Finally, if you suspect resistance, although in most cases it will be due to other factors, talk to your agronomist to arrange testing or other methods to investigate.

2) Assess weed growth stages for residual or contact herbicide decision

Generally, most wheat crops received a pre-emergence herbicide in the autumn, although there will always be some exceptions, and feedback, so far, is that they worked well.

Depending on what stage any weeds coming through will determine whether you can go down the residual top up route or need to apply a contact herbicide.

Late drilled wheats are most likely to benefit from a residual top up, where weeds have not yet emerged or only just beginning to. Our metribuzin-containing products, such as Alternator® Met, Octavian® Met and Cadou® Met can all be applied up to GS25, making them good options for this scenario. Metribuzin provides some contact activity including against broadleaf weeds. That will be useful in parts of East Anglia, such as Norfolk where groundswell, for example, can be a concern – metribuzin provides partial control up to four true leaves.

Where grassweeds are beyond one-leaf stage then contact herbicides, such as mesosulfuron-containing products, will start to become the better choice. In March, it’s possible to use our range at the full rate.

That includes Pacifica® Plus at 0.5 kg/ha where bromes are present in the field and Atlantis® Star at 0.333 kg/ha. Both deliver 15g/ha of mesosulfuron at those rates which will go a good way to controlling grassweeds, especially when applying to small plants.

3) Don’t forget last year’s brown rust experience for T0s in wheat

It was in March last year when we started to get reports of brown rust in wheat crops, and while the winter weather has not been quite as mild as last year, we’ve already had at least three reports of brown rust in Crusoe in the southeast.

Given those reports, how much inoculum there was last year, and most varieties on the Recommended List not having particularly good resistance, there is a potential risk to keep an eye on through the month leading up to T0 sprays.

Once brown rust gets into crops, it intrinsically roots deeper into the plant tissue making it harder to control, so if there is a risk you’ll want to make sure your T0 spray has brown rust activity, as well as yellow rust, which is the more usual target at the timing. Mildew is the other disease to watch out for, with a specific mildewicide required if infections warrant it.

For rusts, Firefly® and similar strob based products could be an option or a mix of tebuconazole and a strobilurin.

4) T1 is the crucial spray in winter barley

With the new chemistry available in winter barley this season, there’s been some talk around cutting back at T1 to save money to be able to use a much more expensive product at T2, where historically spend might be the other way.

I don’t believe that is a particularly effective strategy. Unlike in wheat where the flag leaf spray gives the most return on investment in most years, in winter barley the crucial timing is GS30/31. Yield in winter barley is set at this timing through maintaining as many viable tillers as possible.

Any disease infections around this stage can cause plants to abort tillers, and yield potential will be lost. The risk of cutting back at T1 either through product choice or rate to use Miravis® Plus at T2 for Ramularia control is you could be getting very good disease control on a reduced number of tillers.

That’s why it is worth applying strong chemistry at T1, which for a Bayer programme would be Ascra® Xpro® at 0.9 L/ha or Siltra® Xpro® at 0.6 L/ha. Both products give broad spectrum control of key diseases at T1 such as net blotch, Rhynchosporium and brown rust.

They also give some additional physiological benefits. We have some data showing how Ascra® improves tiller retention in barley compared with treatments without bixafen.

5) Monitor for light leaf spot in oilseed rape

Light leaf spot was bubbling away during the autumn in oilseed rape, and while pigeons may have been the greater concern over winter and perhaps will impact on investment levels in the crop, it could be worth treating in March – especially if no disease control spray has been applied so far.

Monitor levels by taking some leaves, if visual symptoms are not readily apparent in the field, placing in a plastic bag and leaving somewhere warm. Any infection should show in two to three days.

Applications of Proline® or Aviator® will help dampen down infections and keep them from moving up the plant and into the pods later in the season, reducing yields.

6) Earlier sugar beet drilling advice

I’m expecting earlier sugar beet drilling this season, weather permitting, because the non-approval of the neonicotinoid seed dressing won’t delay seed deliveries onto farm.

Those drilling conventional beet varieties could use a pre-emergence spray to start weed control programmes. For early drilled crops, a spray of Betanal® Tandem® paired with a residual from cotyledons fully emerged will make a good first spray or follow up to a pre-ememrgence. Remember the first spray is applied at a lower dose of 1.0 L/ha.

If you’re using the Conviso® system, there are some stewardship principles to follow. Organisation is key. Know which fields are or will be drilled with Conviso® varieties – either physically mark them in the field or on farm software so all the team knows where they are.

Don’t mix seed – if you’re drilling both conventional and Conviso® varieties, try to drill all the conventional first followed by the Conviso® or vice versa. Conviso® varieties are purple in colour so are easily identifiable compared with conventionals.

Also make sure any sugar beet dumps or remnants of Maus heaps from last year’s Conviso® varieties are sprayed off to make sure there are no volunteers, and the same with the fields to avoid any weed beet developing.

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Alternator® Met, Cadou®Met and Octavian® Met contain diflufenican, flufenacet and metribuzin. Ascra® Xpro® contains bixafen, fluopyram and prothioconazole. Atlantis® Star contains iodosulfuron-methyl-sodium, mesosulfuron-methyl and thiencarbazone-methyl. Aviator® contains bixafen and prothioconazole. Betanal® Tandem® contains ethofumesate and phenmedipham. Firefly® contains fluoxastrobin and prothioconazole. Miravis® Plus contains pydiflumetofen. Pacifica® Plus contains amidosulfuron, iodosulfuron-methyl-sodium and mesosulfuron-methyl. Proline® contains prothioconazole. Siltra® Xpro® contains bixafen and prothioconazole. Roundup® contains glyphosate.

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