Published on 30th October 2023
Four insights into crop agronomy this November
Emily Harrod reviews crop progress and provides some insights for East Anglian growers this November
Growers have made good progress with drilling and we’re mostly there – thankfully given the weather from Storm Babet. Most of that left to be drilled is either following sugar beet or potatoes, but it could be touch and go now whether we get a dry enough spell for more drilling or whether it is switched into spring crops.
There are some good crops of oilseed rape around the region, but it’s probably split about 50:50 between the good and the failed or poor where a decision is still being made over the crop’s future this season.
Emily’s agronomy tips for November
1. Weed control options for wheat in November
There are probably three different scenarios you might be facing in November with weed control. There will be October drilled crops that have received a pre-emergence residual herbicide, those that haven’t and then, weather and land permitting, November drilled crops.
Starting with November drilled crops, if there are issues with particular grassweeds, Liberator (flufenacet + diflufenican) + Proclus (aclonifen) is still a key option. But it does have to be pre-emergence for the aclonifen, so if you have any doubts about the crop coming through if sprays are delayed then don’t risk it, and choose a metribuzin-based option in Octavian Met or Alternator Met (flufenacet + diflufenican + metribuzin).
The label has been changed on these metribuzin products so they can be used up until GS25 at the full rate of 1.0 L/ha. I’d still mix with them other residuals to increase the number of modes of action you’re applying where appropriate.
Both products are also useful where you’re topping up a pre-emergence application in October drilled crops, or where one hasn’t been applied. Where no residual has been applied and grassweeds are coming up thick and fast then stick to the 1.0 L/ha rate; you may be able to reduce it depending on pressure if a residual has been sprayed.
Cinmethylin-based products could also be an option in either situation depending on how high the grassweed pressure is, ensuring it is used at a different timing to aclonifen.
The third option, most likely where no treatments have been sprayed or if grassweed pressure is high, is to take the decision to spray the crop off with Roundup (glyphosate). It always feels like a drastic and hard decision but you have to think ahead and whether it is worth spending money on less than desirable, non-viable crop using fertilisers and fungicides that will increase the grassweed seed return and giving yourself more time for stale seedbeds and options for the spring.
2. Is it worth applying an autumn fungicide to oilseed rape?
The value of an autumn fungicide is quite often questioned because there isn’t always a yield benefit. But there are quite a lot of smaller plants / backward crops currently which are the most vulnerable ones to Phoma because there is less distance between the lesions and the petioles, with the consequence of potentially a higher rate of stem canker in the spring.
That means those backward crops are actually the ones that likely need a little bit more protection than the forward ones. In these crops Proline (prothioconazole) is a decent option as it doesn’t have any growth regulatory effect and is one of the cheaper options to get some protection on.
I haven’t heard of any reports of light leaf spot yet as we reach the last week of October, but it’s also worth keeping a look out for. We’ve dismissed it in the past in the east but it’s definitely becoming more prevalent with the weather we get in the autumn.
Overall, it’s a case of keeping a close eye on what disease is present, remembering we don’t have any curative options, and deciding which crops are going to make it because it means starting to spend a bit more money on it.
If you do use a fungicide don’t be tempted to delay application by waiting for the Astrokerb (propyzamide + aminopyralid) timing to reduce the number of passes. They often need doing at different times and you’ll compromise one or other by doing at the same time.
3. When to terminate cover crops?
Normally you should aim for around four to six weeks ahead of drilling to spray off over wintered cover crops. Winter is also a period where there will be fewer optimum glyphosate application opportunities so spraying off sooner rather than leaving it until the last minute makes sense.
If you’re planning to graze with livestock, you will still need to consider whether to use glyphosate afterwards. Often you might think you’ve grazed it enough, but there can be regrowth, or the tops haven’t been eaten sufficiently and need finishing off.
Cover crops are generally looking quite well and their growth stage at application also needs watching. If species are into stem extension that can make a difference to what rate is required and how easy it will be spray off. It’s important to consider which species are present, things like oil radish can be difficult to desiccate if it has started to elongate and higher rates will be needed (minimum 1440g a.s/ha).
4. Review sugar beet fungicide programmes
Initial fungicide applications in sugar beet were made a bit later than usual this season because of how much later the crop was planted this year. However, in some cases that was the wrong decision.
A lot of growers used azoxystrobin + difenoconazole which has let rust and Cercospora through. Coupled with the late applications, this has put pressure on the second and third applications.
It did give Caligula (prothioconazole + fluopyram) a chance to show its usefulness as a second or third application against Cercospora, but it is a reminder to check crops regularly and act quickly once disease is seen so it doesn’t put too much pressure on applications at the end of the season.