3 last agronomy tasks to complete before winter in the south

Crop Progress

Winter wheat drilling in the south started about seven days earlier than it would do in a typical year. While technically it would be better to delay the start of drilling into mid-October, it understandable and, perhaps this year given the rain in October, fortunate that many did start earlier. In the South East as much as 80% of the planned wheat area is drilled.

It has been a fantastic autumn to establish oilseed rape. Drilled into moisture and warm seedbeds in August there were quite a few crops above boot height before the end of October and even some above welly height. Most crops have grown away from adult cabbage stem flea beetle attacks, although time will tell what happens with larvae.

Richard's agronomy tips for November and the winter

1. Spray off or top up grassweed control in early drilled wheat crops?

The earlier drilling led to challenging conditions for good activity from pre-emergence residual herbicides when it was still dry in September. And then in October it became more difficult to apply pre-emergence herbicides post-drilling because of the windy and / or wet weather.

The change in weather also focused minds on drilling so for a combination of reasons there has been a lot of peri-emergence herbicide sprays for grassweeds rather than pre-emergence, which isn’t ideal from an efficacy point of view.

That leaves growers with a decision to make on whether to continue with top up herbicides this autumn or to consider spraying off the crop with Roundup (glyphosate) where grassweeds have got away.

The decision needs to be made on a case-by-case basis, and will depend on grassweed pressure historically on farm and the willingness to tolerate grassweed seed return for future years.

Where the decision is to continue with the crop, then top up options can be built around 0.3 L/ha of Liberator (flufenacet + diflufenican), usually in mix with other actives.

There has been some discussion about including contact herbicides at this timing, and whether applying Atlantis OD (mesosulfuron + iodosulfuron) might be the best strategy particularly in crops drilled in September. Bayer trials historically have shown that applying the contact in autumn to hit black-grass at 1-3 leaves gives the best control.

In October-drilled crops, growers might want to apply a residual top up in November, before coming back with the contact, if required, when the black-grass reaches that growth stage.

2. Watch out for light leaf spot in oilseed rape

With well-established oilseed rape crops, there is much more willingness to invest in protecting the crop than in recent seasons.

Thankfully there is little Phoma being found so far, which could be because of the good resistance to the disease in lots of varieties now, plus also the reduced area of crop reducing spread and risk.

But if the wet weather continues it will be worth monitoring for light leaf spot. The Bayer SpotCheck service, in conjunction with ADAS, allows you to check whether crops are harbouring any light leaf spot or other oilseed rape diseases.

It can be difficult to spot the disease – last year ADAS trials showed that in infected crops (confirmed by incubation) it might be up to eight weeks before symptoms are visible in the field. Curative treatment is less effective than preventative, so if an early diagnosis helps with control.

If light leaf spot needs treating then Proline (0.46 L/ha) will help protect crops from both Phoma and light leaf spot through winter, before applying a follow up if required in March. Bayer trials have shown a 0.4t/ha yield increase from two sprays where light leaf spot is a significant issue.

3. Decide on how and when to terminate cover crops

More farmers are growing overwinter cover crops to help mop up nutrients that would otherwise leach from soils and to improve overall soil health. This autumn, as with oilseed rape, has seen particularly good establishment of cover crops especially where drilled early into warm, moist soils.

For cover crops being grown ahead of spring crops there are a number of areas to watch out for when deciding how and when to terminate.

First, if they’re being grown as part of a Countryside Stewardship scheme or Ecological Focus Area (EFA) make sure you follow the rules carefully.

Destruction of the cover crop will depend on what species you’re growing. Obviously some species, especially buckwheat, but also phacelia and to a lesser extent mustard are non-winter hardy and will die back with a good hard frost.

Other species, such as vetches, cereals, radishes and other brassicas will need intervention. There are three main methods for destruction: mechanical, grazing and chemical.

Mechanical methods will usually be the quickest turnaround – typically by flailing and discing in, although some may consider ploughing or full inversion, even though this feels counterintuitive for soil health.

Grazing with sheep is another option. Mob grazing is preferred, if possible, as this help prevent or minimise damage to soil structure from the animals.

Finally, there is chemical destruction with Roundup. Again, it is important to consider what species you have in the cover crop mix, and then choose your rate of glyphosate based on the most stubborn species. Typically, that will be either brassicas, whose leaves after winter will be waxed up reducing chemical uptake, or legumes, which when applying in the cold won’t have much active growth and again take longer to take up the glyphosate.

Because of the slow growth and uptake, you need to allow at least six weeks for die back before you can drill the spring crop.

For the majority of cover crops mixes somewhere between 720-1080 g ai/ha of glyphosate in a branded Roundup formulation should be sufficient, although if you have particularly stubborn species you might need to use 1440g ai/ha to ensure kill.

Remember because it takes a while to work you only have one shot before you will want to drill the spring crop.