Key March technical advice for growers in the southeast

Crop Progress

Crops haven’t moved much in February in the southeast, although they greened up in the middle of the month after a dry spell for around 10 days. Then we had another 25mm of rain and everything seems to have stopped again, as we approach the last week of the month.

But we’re in a better place than some other parts of the country. Most cereal crops were drilled, and most even received a herbicide at some point. Obviously there is a range of drilling dates with a small minority of wheats drilled at the end of January into early February, so time will tell how they turn out.

Generally, cereals are behind where you would expect, and haven’t tillered as much you’d hope meaning there is bare soil in places. Earlier drilled crops look quite reasonable though, and oilseed rape has fared better than in many recent seasons, despite the rainfall, probably due to the mild winter. They’re around the growth stage you would expect for this time of year. I hope this statement doesn’t come back to bite me in a month’s time, as the jury is still out on what cabbage stem flea beetle larvae might do.

One interesting observation I picked up on from Bartholomews was where they had dug plants from September drilled wheat over chalk and compared with October drilled on heavier ground, which had around 50% less root mass. Growers will be rightly wary of how well-rooted some of these cereal crops are, and ideally we need a gentle switch into spring.

Richard’s agronomy tips for March

1. Prioritise grassweed control

Other than getting fertiliser on where it hasn’t been applied, weed control in wheat is likely to be the top priority as we head into March, especially where a herbicide hasn’t been applied in the autumn.

Fortunately, where they were applied residual herbicides have worked pretty well, no surprise given the moisture, but a follow up with a contact herbicide is likely to be required in most cases.

Options where you have difficult grassweeds, include Atlantis Star (mesosulfuron + iodosulfuon + thiencarbazone), which during its launch year last season was well-received, working well again both black-grass and Italian ryegrass.

One word of caution whichever herbicide you use is to avoid applying to a stressed crop. A lot of crops have struggled through winter so just making sure they have greened up and looking healthy before applying a herbicide is important to not knock them back again.

Mesosulfuron-based products work best when applied to actively growing weeds, and there is also a benefit of applying on a clear, blue sky day when maximum photosynthesis is happening which will help uptake of the chemical and hopefully result in better efficacy.

I’ve been receiving lots of questions about whether to add a residual herbicide. Choice is limited to Liberator (flufenacet + diflufenican) with Atlantis Star, but there is more flexibility with other mesosulfuron products.

Whether you need one probably depends on what the field and grassweed looks like – those fields that look like it is still November with bare soil leaving the opportunity for another flush of weeds could benefit from a residual, but if you’re trying to control tillered grassweeds it’s not going to add much benefit.

Remember the latest time of application if you’re going to use a residual – for Liberator it’s the end of March, while for Octavian Met or Alternator Met (flufenacet + diflufenican + metribuzin) it is GS25 for example.

2. Assess light leaf spot pressure

Disease control programmes will begin in some crops in March, with oilseed rape likely to be the earliest priority. A number of crops didn’t receive a fungicide in the autumn due to the inclement weather, and with some crops looking like they will be worth decent investment, a spray for light leaf spot as soon as possible could be necessary.

Historically light leaf spot is encouraged by cooler weather, which for the large part we haven’t really had, and periods of leaf wetness, of which we’ve had plenty. Disease usually spikes from January through into March. If you’re not sure of incidence, you can check by sampling leaves and putting in a plastic bag and leaving somewhere warm for a few days to develop any symptoms.

Where spraying is justified, a robust rate of Proline (prothioconazole) or Prosaro (prothioconazole + tebuconazole) would be a good option. I’d suggest a rate of 0.44 L/ha of Proline if nothing has been applied previously or 0.32 L/ha where a fungicide has been applied in the autumn.

3. Will wheat require a T0 spray this season?

There will be plenty of growers who, understandably, won’t want to invest heavily in fungicides on wheat crops this season, especially where yield potential has been hit.

In the southeast where crops were drilled mostly in the usual windows and are generally in better health, my view is that T0s are still worth considering and have technical merit. Looking back to last year when Septoria pressure was at its highest at T1, the use of T0 fungicides where applied helped dampen down that pressure so they weren’t in the ground from October until the third week of April without receiving any fungicide.

And unfortunately, backward crops are not immune to disease, and once they pick up some nutrition there’s likely to be rapid growth making them more susceptible to diseases. Research has shown, for example, that later drilled crops are more at risk from yellow rust, although there should be lower risk from Septoria.

Where yellow rust is a risk an application of tebuconazole or a strobilurin would be your best bet. I’d also consider in the earlier drilled crops applying folpet or a lower dose of a Septoria-active azole such as prothioconazole where appropriate.

4. Where to use Ascra in winter barley fungicide programmes?

Building yield in winter barley is all about having high numbers of viable tillers, rather than the number of grain sites as it is in wheat. That means tiller retention is critical for maximising yield, and any disease early on can cause the plant to abort tillers – hence the GS30/31 timing is usually the most important for disease control in the crop.

As this is written it is still too early to know what disease issues will occur, although we are finding brown rust in hybrid barleys. Net blotch is one we are concerned about as there have been increasing problems with insensitivity to both azole and SDHI chemistry.

However, we have seen a benefit of the fluopyram in Ascra (bixafen + fluopyram + prothioconazole) against the net blotch mutations that affect sensitivity. It also helps against Ramularia.

You can only apply Ascra once in winter barley, so that leaves a conundrum about where best to use it, with Ramularia a T2 disease while generally the strongest responses to fungicides come from a T1 timing.

My view this season is to use it at T1 at 0.9 L/ha in most situations. As well as the benefits in disease control from the dual SDHI loading, the physiological benefits from using the product will be useful. I think crops will need a helping hand in terms of rooting and top growth biomass, which the SDHIs delivered in Ascra will help with, as well as improved nitrogen use efficiency.

If you do have major concerns about Ramularia later in the season then you could keep Ascra back for T2, and go with the tried and trusted Siltra at 0.6 L/ha. This delivers high loadings of prothioconazole and bixafen giving good control of all key barley diseases.

5. Plan potato herbicide programmes

Writing this in February after another lot of rain it’s hard to see much movement on potato land for a few weeks, but you never know when a dry spell will come, and once conditions improve potato growers will be keen to get ahead and start ridging up and planting potatoes.

Fortunately, potato cyst nematode isn’t a huge problem with potatoes in the southeast, with usually alternative fields available if PCN is detected.

Early weed control will, as ever, be vital for establishing good potato crops, with not many options available post-emergence. Our recent introduction Emerger (aclonifen) has become a backbone of many herbicide programmes in the region, performing effectively, and dependent on variety, can be used in conjunction with metribuzin. A choice of either Artist (flufenacet + metribuzin) or Sencorex Flo (metribuzin) is a very robust and c omprehensive herbicide programme.

Remember when using Emerger it should be applied within seven days of planting, or at least one week before crop emergence and when spraying maintain constant agitation. For other best practice application advice go to our website here: https://cropscience.bayer.co.uk/our-products/herbicides/emerger