Targeted spray application for vegetable crops

Vegetable crops create some of the most diverse and challenging targets for sprayer operators through the season. The Vegetable Farmermet up with Syngenta specialists to get some in field guidance and hear about the latest research trials.

From bare soils with pre-emergence herbicides, to upright onions, dense cabbage heads and the huge biomass of Brussels sprouts, each application requires a different approach to balance efficacy, with timeliness and all-important environmental protection, according to Syngenta application specialist, James Thomas.

“Trials results have consistently shown that fine tuning application technique for optimum coverage can make at least 10% to 30% difference in product efficacy. But in an on-farm situation, that has to be set against the practicality of physically covering the required area and the limitations of weather conditions,” he said.

“Furthermore, operators have to be extremely conscious of potential for environmental losses during spraying, which is coming under increasing regulatory scrutiny.”

With all these elements in play, Mr Thomas highlighted that fine-tuning sprayer set-up and operation for the key factors of nozzle selection, water volume, pressure and speed could give significant gains. “In vegetable crops it is especially challenging, as the targets may be very different through the day, where operators need to adapt and change for each application.”

Bare soil challenge

Starting the season with pre-emergence herbicides, for example, Syngenta has been investigating techniques to achieve more consistent coverage of the soil surface and optimise results for an extremely difficult target. The lessons learned for black-grass control in arable crops could be equally applied for vegetable seedbeds, said Mr Thomas.

“Unlike a growing crop, bare soil offers nothing to trap and hold the spray – especially fine droplets. In some conditions there is risk that a significant proportion of the finest droplets never have the momentum to reach the target soil surface, particularly if it’s windy or there is thermal inversion, with rising warm air from the soil on a cool morning, for example.”

Where conditions are compromised, the Syngenta research has shown that new designs of 90% Drift Reduction Technology (DRT) nozzles, such as the Teejet TTI110-05, can perform better than conventional finer droplet nozzles and with a significant reduction in drift risk.

“There’s two elements to drift to consider,” pointed out Mr Thomas. “The physical loss of product from the field, and the sideways movement of the spray pattern caused by gusts of wind during application – leading to inconsistent coverage on the surface that would result in less effective results.”

Low Slow Covered

In all instances, he urged that the company’s pre-emergence application mantra of ‘Go Low; Go Slow; Get Covered’ will give positive results.

Boom height has one of the biggest influences over spray drift. A sprayer operating at one metre boom height would have 10 times the drift, compared to operation at the recommended 50 cm boom height – with trials showing a physical 17% better weed control at the lower height, he claimed.

Allied to height, faster forward speed immediately creates more turbulence behind the sprayer that increases risk of drift, and at faster speeds operators tend to work with higher booms to avoid problems with greater instability. “Going slower, typically at 10 – 12 km/hr, has consistently improved results with weed control in the field,” he reported.

New trials have also shown clear advances with new 90% DRT nozzles operated at water volumes of 200 l/ha, with up to 20% better results from residual pre-emergence grass weed herbicide applications, compared to conventional treatment at 80 or 100 l/ha.

“The trials have shown no real advantage in further increasing water volume, to 400 l/ha for example, so 200 l/ha demonstrates a reasonable compromise between work rate and product efficacy.”

Mr Thomas highlighted Syngenta is investing in new pre-emergence application trials in vegetable and potato crops for the coming season, to validate the previous trials and test new 90% DRT nozzle designs that the company has been developing.

For post-emergence residual herbicides, however, Mr Thomas pointed out that a narrower angle fan can prove effective at reducing the amount of spray intercepted by leaves and ensure more reaches the target soil surface. For these applications, he recommended the Syngenta Vegetable Nozzle, with its 65 degree fan, applying water volume of 200 to 400 l/ha using an 06 or 08 size.

Onion applications

Results of 2018 eastern counties application trials for mid-season onion treatments, highlighted that whilst conventional flat fan nozzles appeared to give good effects, in terms of coverage and deposition, detailed analysis showed a large variation between individual plants.

Syngenta vegetable specialist, Simon Jackson, reported findings that the angled Syngenta 3D Nozzle gave more consistent results, with comparable performance for both fungicide deposition and overall leaf coverage.

“That would be the nozzle of choice in ideal spraying conditions,” he advised. “However, for greater flexibility, the Lechler IDTA and Teejet TTi would be the next best option for fungicide application. Particularly with the trials showing the addition of an adjuvant significantly increases deposition and coverage.”

For applications targeting thrips, Mr Jackson said the IDTA and TTi nozzles were particularly effective for coverage of onion stems, when an adjuvant was included in the tank mix.

In terms of water volume, there was a general trend of increasing rates giving greater deposition and coverage, however more work is planned to refine recommendations for specific nozzle combinations and adjuvant use, he added.

Hitting Brussels buttons

Waxy leaves make Brussels sprouts a particular challenge for both fungicide and insecticide applications. Syngenta trials in Holland and the UK has sought ways to improve spray retention and targeting throughout the crop.

“Having so much leaf at the top can lead to interception of the spray and excessive run off, whilst the button target is hidden below the leaf,” according to Simon Jackson.

“The work has consistently shown the advantage of adding an adjuvant to the spray mix, leading to better deposition and leaf coverage,” he advised.

“Angled nozzles were good for coverage and deposition at the top of the canopy but delivered a poorer performance further down, with lower deposition and coverage on the buttons and lower leaves.

“The Lechler ID3 gave improved deposition and coverage further down in the canopy and on the buttons, and so would be the choice for disease and insect control when buttons are present,” concluded Mr Jackson.

Insect target

Achieving high levels of pest control with insecticide treatments is an essential factor for resistance management, added Syngenta vegetable specialist, Simon Jackson. But that can be difficult in dense vegetable crops, where pests can be sheltered under leaves or deep in the heart of the crop – particularly with contact action products reliant on hitting the target.

With autumn Whitefly, where pest pressure was extremely high and sustained last season, some growers had reportedly resorted to making one pass with a sprayer applying just water to simply disturb insects and get them flying, and then a following immediate pass with a second sprayer to hit insects on the wing.

However, there is a new option in many vegetable crops for this season, with the systemic activity of Minecto One. Applied primarily for caterpillars and chewing pests, it has been shown to give control of sucking pests, including Whitefly, thrips and leaf miners.

Mr Jackson advocated sprays should be applied in sufficient water volume to achieve good penetration of the crop canopy, to target pests and gain maximum effect from the systemic movement within the plant.

“The xylem mobile systemic activity makes it especially effective in targeting chewing pests to prevent leaf and plant damage,” he advised. “For sucking pests, trials have shown results can be enhanced in brassicas with the addition of Phase II (methylated rapeseed oil) adjuvant in the tank mix; that mix has also shown to give a good reduction in aphid numbers.”

Carrot cover

Carrot crops typically require multiple applications over the course of the season, with each treatment presenting a more challenging target. Young carrots are relatively good at capturing and retaining spray, especially when applied with an angled nozzle, advised Simon Jackson. His best option in small crops would be a 3D Nozzle, alternated to face forwards and backwards along the spray boom. However, if spraying conditions are sub-optimal, using an Amistar Nozzle would be beneficial as a reduced drift selection.

“As the crop gets larger and the canopy denser, getting the spray through to the target is a priority, especially with crown target fungicides,” he added. “At that point I would advocate switching to a narrow angle Vegetable Nozzle and increasing the water volume up to 300 or 400 l/ha to help get the spray through.”