Oilseed rape drilling thoughts and other jobs in August for East Anglian growers

Crop Progress

Winter barley harvest got underway in July for growers, although rain has slowed down progress as this is written. Specific weights on some early harvested barleys have been on the low side, with some small grains. Most oilseed rape had been desiccated by the middle of July, although no one had started at that point, while some of the early drilled, faster maturing varieties of wheat were also beginning to ripen. 

Rachel’s agronomy tips for August

1)      Look for moisture for oilseed rape establishment

Last year’s oilseed rape crop struggled because of a lack of moisture at establishment, and that’s definitely putting some growers off from including it in rotations for the coming season in East Anglia.

But while it’s difficult to predict the weather, at least as I write this in mid-July, there looks likely to be more seedbed moisture for oilseed rape establishment this August. That could provide a better opportunity to be successful.

Drilling early into moisture should help get the crop established and forward enough to cope with adult cabbage stem flea beetle damage, but it might mean the canopy is overdeveloped going into winter, which would need managing carefully. It will also be potentially more likely to be carrying a greater larval load over winter and into spring.

With early drilled crops, varieties ideally need to be fast at establishing but slower developing through the autumn to try and avoid those over developed canopies heading into winter. DK Exstar is a good example of that type of variety, and together with all the Dekalb varieties has the DK Establishment Scheme guarantee behind it.  

The alternative strategy is to drill later after peak flea beetle migration, but then you will need to choose a variety with a vigorous growth habit in the autumn to get it up and away, even with some beetles still around.

Other considerations when choosing drilling date include likely grassweed threat. Early establishment won’t leave much or any time for a chit of grassweeds before establishment. With grassweed control a struggle for some this season, there’s likely to be a higher seed return, and it will be important to take any opportunity for control between crops, even if that’s always a short window ahead of oilseed rape.

2)      Consider grassweed management tactics

Grassweed control in East Anglia has been less successful in place than many would have liked, after a dry autumn and then a wet spring hampered both residual and post-emergence contact herbicide activity and timing.

That means post-harvest management will need be carefully thought out to help start to get back in control. For example, is it the year to return to ploughing? If you’re using it rotationally and you’re at a point in a field where it has five or six years since you’ve last used it, ploughing does provide an opportunity, done well, to bury seeds and reduce their viability.

Think about following crops in the rotation – will one of them require deeper cultivations to establish because that may impact on the success of ploughing for grassweed management down the line, if you end up bringing viable grassweed seeds back up to the surface.  

Where ploughing isn’t an option, managing post-harvest stubbles to maximise grassweed germination outside of the crop will be key. Moisture and weed species are important factors. If it is dry wait to cultivate until there is moisture as very little will germinate without it, and it’s better to let seeds be eaten or degrade while you wait.

So far, it looks like there should be enough moisture to get seeds to germinate, so a tickle with a shallow cultivator to encourage seed to soil contact will likely be appropriate for most grassweed species, including black-grass, Italian ryegrass and sterile brome. The exception are the Bromus brome species – meadow, rye and soft. These usually require a period of around a month on the surface to mature, before a cultivation to encourage a chit.

3)      Multiple reasons to consider cover crops

With cover crops a key part of some Countryside Stewardship or new Sustainable Farming Incentive agreements, many will be committed to growing them already.

As well as the monetary value, cover crops can help with various challenges, such as reducing soil erosion of lighter soils, mopping up excess nutrients, improving soil structure and health, and helping weed management.

The latter has always been a balance between potentially suppressing weed germination, or having an open enough canopy to still let weeds germinate to spray off when you destruct the cover later. Which you choose will impact on seed rates.

Most cover crops will be established to overwinter ahead of a spring crop, although potentially there is time to plant a catch crop ahead of an autumn drilled cereals or winter beans.

The key for both types is to establish in August, if at all possible, as this will maximise growth before winter shutdown, and just as for oilseed rape, moisture preservation and seed to soil contact are crucial especially for the small size seed cover crop species. 

Remember when choosing species mix to consider following crops in the rotation as some choices may have an adverse impact on pests and disease carry over.

4)      Blight pressure will increase

Blight pressure has been relatively low through the early part of the potato crop, but warm and wet weather in July will have been more conducive to blight, while crops are at the stable canopy phase of development will also increase humidity within the crop canopy.

At this stage, both foliar and tuber blight become concerns – zoospores can wash down into the soils to potentially infect tubers with blight, so it is important to use products that will help reduce this risk.

While there are many actives available for foliar blight, the number of options for tuber blight is more limited. Fluazinam used to be the mainstay, but since resistance developed against that active, it is now the quinone-inside-inhibitors (QiL), such as Ranman Top (cyazofamid) and pyridinylmethyl-benzamide group containing fluopicolide, which is in Infinito, along with propamocarb.

These groups need to be used alternately, as QiL-containing products, shouldn’t be used consecutively, and there are also limits to the number of applications allowed meaning programmes do need to be carefully thought through.