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Crop Advice & Expertise

How to start the new growing season successfully in the South

Matt Siggs has six agronomy pointers for August as preparations start for a new season in the south

Matt’s agronomy tips for August

1. Consider cover or catch crops after harvest

One way to make the most of the window between harvest and sowing the next crop in the southwest is to consider growing a cover crop. We potentially have as much as 10 weeks between harvest and a middle of October sown cereal crop, where a catch crop could be improving soil structure, organic matter and other soil health benefits.

Combinations of options including buckwheat, black oats and phacelia could all be considered. Mustard is another possibility but with all these think about the impact on the rest of your rotation, as it could create other problems, such as club root or other pest and disease issues.


2. Plan post-harvest cultivations

If you’re not establishing cover crops, then plan post-harvest cultivations. Brome is one of the bigger weed issues in the southwest with a bit more no-till being practiced.

Identifying which species of brome is critical – just before harvest is a good opportunity as the seed heads are different – as what you do with post-harvest cultivations changes depending on species.

Anisantha species: Cultivate and bury sterile and great brome seeds as soon as possible after harvest, unless chopped straw provides good seed cover.  Allow the weed to chit and produce 1-2 leaves and then apply Roundup (glyphosate) to reduce the population burden as much as possible.

Bromus species: Leave meadow brome, soft brome and rye brome on the soil surface for one month to ripen before cultivating. Then shallow cultivate to place seeds in moisture and spray off emerged weeds with Roundup at the 1-2 leaf stage for best control.

If you have a mixed population, it can be difficult to know what to do, but my advice would be assess the field population levels and whichever species is in the majority use that to decide your cultivation choice.  The Bromus species can be the trickiest to deal with using chemistry alone so it may be better to leave the field for a month to encourage the more difficult to control in-crop bromes – rye, soft or meadow brome – to germinate. With the Anisantha species you can achieve a decent level of control with pre- and post-emergence  herbicides in the autumn while the weed is still small actively growing which improves the efficacy of herbicides so targeting the Bromus Species could be the right strategy. .

For those with black-grass or rye-grass, similarly to sterile brome, then cultivations straight after harvest are best for creating a stale seedbed, but minimising soil movement is important to avoid bringing up buried seed. Even a Cambridge roller across the stubbles can be enough to create some seed to soil contact and help conserve soil moisture for the following crop.

Once there’s been a decent population growth and majority of the targets are 1-2 leaves, spray off with around 720g/ha of Roundup (glyphosate). The optimum number of applications pre-drilling is two – more than that and you start to increase the risk of reduced sensitivity developing.


3. Moisture is crucial for oilseed rape establishment

Earlier establishment of oilseed rape to avoid cabbage stem flea beetle adult attacks has been a successful trend in the past couple of seasons, and is likely to continue. It’s all about moisture and getting good seedbeds, so the minimum amount of soil movement you can get away with while still getting good seed to soil contact to encourage crops to get away quickly is important.

Think about seed rates carefully when drilling early – ideally you want to end up a similar target population as later drillings. If you overcook seed rates and get a higher plant population, you could just be storing up problems with CSFB larvae later on, and other pest issues, such as cabbage root fly.

Varieties for early drilling also need to be considered – it’s a balance between a variety that will get out of the ground quickly but won’t then bolt before Christmas. The second half of August is still the optimum time to drill oilseed rape, but watch the forecast and likely soil moisture levels closely.

All the Dekalb varieties have excellent agronomic characteristics from pod shatter resistance, in-built disease resistance and turnip yellow virus resistance, so there will be one to suit your situation. 

In addition, if you grow one of four popular varieties, DK Exstar, DK Excited, DK Extremus or DK Imprint CL, there is the added bonus of the Dekalb 2021 Establishment scheme, where if establishment fails on blocks of 6ha or more you can get a credit back of £100/bag of seed.


4. Consider using pre-harvest Roundup where required for spring barley

Spring barley is a key crop for many in the south west. A pre-harvest Roundup can be useful in evening up crop ripening, particularly in spring barley which can start to side-tiller at the wrong time in the season affecting grain moisture across the whole field. It can also help speed up harvest if we end up with a catchy harvest.

If you have more difficult perennial weeds, such as thistles or docks, you will need to adjust rates accordingly. For easier annual weeds a rate of 720g/ha should suffice, while for perennials the dose can be up to 1440g/ha.

Timing is when the crop is below 30% moisture content, and make sure you adhere to harvest intervals.  


5. Finish off potato blight programmes

Some main crop crisping potato varieties have started to be lifted. So far, blight has been kept out by decent programmes, but for crops still in the ground, finish off the programme with particular regard to tuber blight.

Infinito (fluopicolide + propamocarb) is a good alternative mode of action to Ranman Top (cyazofamid) for tuber blight. There are limited options for controlling tuber blight after the resistance issues with fluazinam, so it is important to make use of what we have got.


6. Start pest control programmes in autumn cauliflowers

Autumn cauliflower transplants were going in July. Most will have around 4-6 weeks mealy cabbage aphid control from Verimark (cyantraniliprole) before crops will need to be monitored for follow ups.

With limited options, Movento (spirotetramat) is a useful part of the armoury. It provides excellent long-term population control, but lacks the knockdown effect growers were used to with thiacloprid, so timing is important before populations build up too much. A follow-up application if required can be applied after four weeks.

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