Addressing the challenges of brass growing in a changing climate – The Vegetable Farmer

Even if weather dries up in the second half of March, brassica and onion growers will still have a challenging time, says Andy Richardson of the Allium and Brassica Centre Group. After 60mm of rain in January, followed by another 100mm in the first half of February, soils are saturated at the time of writing.

Andy says: “Making decent seed beds will be challenging, particularly on medium and heavy soils, and planting into wet, compacted soil affects yield and quality. “Even if it stops raining now, and soils dry up, the medium and heavy fields are likely to become hard and cloddy.”

He adds that that the wet autumn weather left many unable to plough until the New Year, making things even worse for many growers. “So far in 2024, we’ve managed to plant set onions on sandy soils in a dry weather window at the end of January into early February. We’ve also managed to get maturing set varieties, such as Griffon, planted on medium soils but progress is somewhat stop/start.

We currently have 400ha of overwinter onions in the ground – of which 95 percent are sets, and these are mostly the variety Shakespeare.
Nevertheless, in general, overwinter fields look reasonable especially after late planting and the incredibly wet winter.”

Andy goes on to highlight that soil structure is particularly important for shallow-rooting crops, such as onions, leeks, cauliflower and broccoli. “Ploughing/cultivating whenever the soil is too wet can cause a hard pan to develop which inhibits rooting reducing the ability of the roots to grow down and scavenge for water and nutrients. “If onions grow roots down to 30cm they are doing well, which makes them particularly vulnerable to poor soil structure.”

Longer season brassica crops such as Brussels sprouts, Kale and storage cabbages develop a stronger root network and so are better able to cope with less than perfect conditions, so this should be considered when deciding which fields to plant the different crops in this spring.

Part of the planning should therefore include remedial action for soil compaction.

“Over the past year soils have been waterlogged, with hardly a chance to dry before becoming waterlogged again, so any remedial work will take more than 12 months to have any effect.”

Local weather and in-crop soil moisture stations are widely used to monitor the onion and leek crops to maximise yields through accurate irrigation timing. “By using such simple systems growers have more time to assess risks and take timely action to protect their crops. All crops will require as much attention to detail as possible, with nutrition and irrigation planning being of paramount importance.”

“More than ever, this year will be all about attention to detail and tailoring husbandry according 10 the needs of each particular field. It’s a good idea to routinely undertake soil nutrition analyses before planting to give the crops the best start.

This year, many growers may again have to contend with sulphur, manganese and magnesium deficiencies as well as acid soils. he observes. “These deficiencies are usually more pronounced in a struggling poorly rooting crop.”

Moving on to talk about weed control, he noted that it is always particularly challenging for horticultural crops such as alliums and brassicas, and finding new actives with good efficacy which do not damage the crops is challenging.

As a result, many onion growers are adapting, for example band/spot spraying for more targeted herbicide applications, because of the reduction in crop damage.

“We need to reduce contact herbicide use, so moving towards targeted applications will also make a big difference,” says Andy, adding that robots are increasingly popular with organic growers.

Brassicas are still dependent on the application of a residual herbicide before planting, followed up with mechanical control.

Whilst Ringspot has been a consistent challenge for growers in the Midlands and further south, Light Leaf Spot (LLS). normally a problem of northern England/Scotland has caused issues as far south as Cornwall this autumn, reports Andy.

As a result, predicting and assessing risks of disease has become increasingly important to brassica growers, not only to protect yield and quality but also to not waste valuable fungicide sprays when they are not necessary, he notes.

Brassica growers in Lincolnshire have had free access to the disease/pest forecasting system run by the Allium & Brassica Centre and sponsored by Syngenta Crop Protection, for more than ten years.

Because of its flat topography, weather stations and pest forecasting systems are relatively easy to set up in Lincolnshire, as relatively few can cover a large production area.

“One of the biggest disease challenges brassica growers have had this autumn/winter is light leaf spot. Unlike other leaf spot diseases which attack older leaves first LLS attacks marketable parts of the plant, it also has a long latent period so disease monitoring and disease forecasts are essential for effective control.” (http://www3.syngenta.com,country/uk/en/AgronomyTools/Pages/BrassicaAlert.aspx)

The situation at the beginning of 2023 was very different. he reflects, remarking that by the end of February, much of the polythened brassica crop had already gone into the ground in very good conditions.

“At the end of 2022 there had been a frosty period in December and January, with temperatures regularly going down to -5 deg C or below, and although this hit early winter cauliflower, this really set up some nice seedbed conditions.”

The set onion crop also looked promising; planting started in late January, and 90 percent had gone in by March 5, as spring appeared to have arrived early. Drilling started the first week in February and 60 percent were in the ground by March 5.

But on that date, the rain started, and by the end of the month, 120mm had fallen in the Peterborough region.

“This left us unable to turn a wheel until after Easter, so no drilling or planting took place until Easter weekend, more than a month later. As onions are daylength driven, drilling/planting after the end of March inevitably results in reduced yields. This coupled with cold, wet seedbeds hindered quick establishment and poor plant populations produced large, coarse, soft bulbs which don’t store well.

“In addition, the heavy rain on the fine seed beds also caused problems for the onions that had already gone in because the soil lost structure and slumped, washing down herbicides into the crop, so by April many early drilled fields were also starting to struggle.”

The cool, wet July and August did wonders for spring sets which averaged over 50t/ha but did little for drilled crops which were desperate for warm, dry conditions to enable them to mature. “Overall, 2023 was not a vintage year for onions, set yields were good. but drilled yields were down to 42-43t/ha, giving overall average yields of 45t/ha.”

At just under 8,000 ha the UK onion area was the lowest for nearly 30 years (1994) and with total production of only 360,000 tonnes, production was similar to 2022. Ten year UK production average is around 430,00 tonnes and in both 2022 and 2023 we were some 70,000 tonnes short.

“For only the third time in the past 20 years we will import more onions than we grew ourselves in 2023, but the tight stocks mean that prices are reasonable, with red onions currently commanding some of the highest prices seen in recent years.”

Early-planted brassicas grown under polythene went in as normal, but rather than the usual week’s difference with the first outdoor plantings, there was a month gap because of heavy rainfall in March. As a result, in June/July, the continuity of supply was disrupted.

However, brassicas that went in later grew well in the cool, damp months of July and August. Generally speaking, pest pressure was not too high either, reports Andy, adding that aphids came into the crops in June but never really got going in cool, damp summer conditions.

The very warm. wet autumn and winter. nonetheless. brought further challenges because getting crops to hold was difficult. Crops such as Brussels sprouts and cabbage were going over the top quickly with subsequent quality issues.

He remarks that modern allium and brassica production is a highly technical business, and growers have to make significant investments to produce high quality consistent produce and ensure it is on available throughout the year.

”The challenge is that we have increasingly erratic weather, so we need to be able to react to changes quickly and efficiently. Nevertheless, good husbandry and attention to detail will help produce crops that meet customer specifications and offer profitable returns for your business.”