Challenging times for leafy salads and brassica – The Vegetable Farmer

Phoebe Sutton, of LED lighting specialists Vertically Urban, spoke on plant light responses in controlled environment agriculture, and focused on the key advantages of the technology for boosting and manipulating crop growth and production.

“With the advantages of small unit sizes, good energy efficiency, long operating life, cool emitting surfaces and targeted wavelengths, LED lighting systems offer protected crop growers significant advantages over conventional lighting,” she suggested. “The ability to manipulate intensity, duration and spectra means lighting can be tailored to help ensure crops meet growth targets and meet specification.

“Blue light shortens plants and enhances colour, while green light penetrates the canopy to help increase yield. Red light is essential for photosynthesis and yield, while far-red light can be used to elongate plants. All these can be incorporated into lighting design to manipulate plant growth.”

‘Don’t be a more-on’ urged Ben Taylor-Davies, Herefordshire farmer and regenerative agriculture adviser known as RegenBen, in his presentation ‘The Healthy Food Dichotomy’. “The traffic, treatment and compaction they are subjected to means Grade 1 vegetable soils are often given Grade 5 treatment,” he suggested.

“To get the maximum from these damaged soils, growers often then raise fertiliser inputs to try to compensate for their lifelessness and poor structure, ultimately spending more to try and achieve the same results. Consequently, the profitability of farm input suppliers and farmers is going in different directions.”
Much of his own approach to the problem as a potato grower has been to minimise soil movement at establishment and use cover and companion crops to retain living roots in the soil as much as possible, and crowd the soil surface so that no (weed) species becomes dominant.

“Beyond aiding soil retention and structure – particularly important in vegetable production where a lot of soil is exposed – this helps harvest solar energy to feed soil life, and boosts control over what ends up leaving fields via drains and ditches,” suggested Mr Taylor-Davies.

“Potato and vegetable production is challenging from a soil preservation stand point, but we’ve managed to reduce our pre-planting operations to a single powered pass and no ploughing prior to it, aiding soil structure with the addition of compost and companion cropping at planting. We have eliminated nematicide use, chiefly through variety selection, and reduced our pesticide usage by 92%, primarily by encouraging soil biology.

“As a result, we have one field where I was sufficiently confident to grow potatoes twice in seven years, and we’ve cut blight sprays to two per crop, late on close to senescence. Root and vegetable growers are showing increasing interest in these techniques – now the industry has to find a way to encourage buyers to recognise them and reward the result.”

With the dissolution of AHDB’s horticulture and potato divisions, the British Growers’ Association’s Jack Ward addressed the future for crop protection and EAMUs. “It soon became evident the next step in grower collaboration following the dissolution of AHDB Horticulture needed to be based around crop protection – i.e. handling the EAMU system-on a voluntarily-supported basis,” he recalled of the past two years’ events.

“As the British Growers Association handles the administration for most of the produce associations, it was deemed the natural administrator for this, and since June we’ve been working on a system that will handle EAMUs once the AHDB’s remit comes to an end. This will be operational on April 1, 2023, with resourcing and staffing now being finalised, along with the transfer of any residual funding from AHDB Horticulture’s dissolution.

“Each crop association will decide on the EAMUs its membership requires. The big unknown is the level of support that will come from growers. Fairness of contribution will be difficult to police, and peer pressure will be vital to contributions to ensure success. Of the 1,150 growers recognised by AHDB Horticulture, only about 850 voted in the ballot, so apathy is the real danger.”

Warwick University’s Rosemary Collier updated delegates on emerging pest threats, including sweet midge and cabbage stem flea beetle, noting that brassica growers only started to raise concerns about the former as recently as 2019. “The pest is actually European native, and has always been around,” explained Prof Collier.

“The main impact is blindness/distortion of the growing point. In 2020 and 2021 AHDB set up a collaborative monitoring project across the UK and Ireland to increase understanding of the problem, using pheromone traps.

“Identification is impossible without microscopes, and even then misidentification is possible. Numbers were most significant from June onwards, peaking in July-August. Most fields had a very low ‘background’ population, but some had larger infestations of over 50 midges/trap/week, potentially linked with rotation/lack of spatial separation, and possibly also reduced pesticide use or organic production.

“North American IPM for swede midge combines use of clean transplants, a two-to three-year rotation gap of non-brassica crops, detection/monitoring, insecticide applications as required, post-harvest waste destruction and control of host weeds such as shepherd’s purse. Brassicaceous cover crops and oilseed rape require the same treatment.

“Most of the insecticides applied to brassicas probably have some impact on swede midge. This, plus rotational impacts, may be why the ‘background’ population in most crops is low. Most British sites monitored in 2020/21 had populations below the North American treatment threshold.”

Meanwhile, vegetable growers should benefit from AHDB-funded ongoing work into cabbage stem flea beetle, a major pest of oilseed rape, noted Prof Collier.” Susceptible horticultural crops include spring greens/pak choi, and there are few insecticides approved, while CSFB is resistant to pyrethroids in many areas. A broad IPM approach remains best to minimise effects.”