Green methods on trial

As a two-year initiative on sustainable growing, funded by the Dutch government, draws to a close, Gavin McEwan asks what has been learnt.

Growing plants in one of Europe's most densely populated countries means having to work extra hard to keep the neighbours happy. And moves at national and EU level are increasingly forcing Dutch growers to consider growing techniques that will have less impact on their surroundings.

This has given rise to the Telen met Toekomst (Growing with a Future) initiative, whose two-year run ends this year. Paid for by the Dutch government and the Product Board for Horticulture, it has been led in the nursery sector by the Dutch Tree Nursery Association. Thirteen fruit tree companies have been involved since the start, along with other branches of Dutch horticulture.

Lessons learnt will be disseminated across the Dutch grower sector. Donker tree nursery owner Albert Donker explains the benefits of co-operation. "The project offers the possibility to gain more knowledge and to learn from colleagues or research without spending too much time on it," he told journalists during a Plant Publicity Holland-organised tour.

Practical Research on Plant & Environment (PPO), part of the Wageningen UR, Europe's largest horticultural research body, is providing much of the technical input, with consultancy DLV Plant acting as an adviser. Kit constructors have also been brought on board to design tailor-made equipment.

PPO researcher Bart van der Sluis says: "We aim to promote sustainability and reduce environmental pressure, but in ways that are economically profitable."

However, results so far suggest there are no magic bullets. The withdrawal of herbicides such as Actor and Gramaxone, with Reglone to follow, have put fruit tree growers under pressure to find alternative means of weed control. But growers and researchers are talking in terms of reducing chemical use rather than abandoning it altogether.

Van Rijn-de Bruyn is a fruit tree nursery in Uden, in the south of the Netherlands, producing 800,000 young fruit trees and 1.2 million rootstocks per year. Director Pieter van Rijn says chemical use is becoming a major issue for Dutch growers.

"Fifty per cent of our production is in the Netherlands now, but it will be less in future," he says. "We are expanding production in Poland, Ukraine and Moldova. Eastern Europe is also a growing sales market for us."

Part of the appeal of growing in non-EU countries is that it allows the company to sidestep Brussels' mounting restrictions on pesticide use, he adds. "But we are very happy to have this project - we don't want to stop production in the Netherlands."

The nearby Fleuren nursery has also been involved in trialling. The fruit tree grower cultivates 100ha of the sandy south Netherlands soil, and ships over 100 lorryloads of young trees around Europe each year.

It has already given over 6ha of its apple whip fields to trialling organic production. This gives the company a financial buffer, says owner Han Fleuren. "If it goes wrong on the organic side it can very expensive to correct your mistakes."

However, organic production has its benefits too, he says. "In terms of the crop, you can't see the difference between a normal field and an organic one. And we can learn things from this small block and put them into practice elsewhere."

Mechanical weeding

A range of machines have been trialled at different sites. At Fleuren nursery, a specially commissioned machine, driven with tight margins between rows of whips, is capable of both spraying and mechanical weeding. Part of the design brief was for a machine that allowed the driver to view the weeding directly and that could be adjusted in situ to suit a differing number of tree rows.

Fleuren found his nursery had to use synthetic canes as they have to be stand up to being hit by the machine's blades.

Van Rijn-de Bruyn has also been incorporating mechanical weeding into its management regime. "We try to find a solution that will be a combination of mechanical and chemical weed control," says Van Rijn. "We can reduce chemical use by 60 per cent." Pieter's brother and fellow director Bart adds: "It's not possible to eliminate the weeds 100 per cent by mechanical means. It works for 90 per cent - for the last 10 per cent, herbicides must be used."

Controlled spraying

Fleuren nursery's organic regime still permits spraying with controlled doses of sulphur and neem (Azadirachta indica). The firm's combined weeder and sprayer allows side-on and upward spraying. "It's useful as the mites are on the underside of the leaves," says Fleuren. He adds: "Because we are a small industry, we have to develop equipment such as this ourselves."

Variety selection could reduce the need for spraying further, he says. "There are Dutch-bred varieties, such as Santana, that are well suited to organic growing. But growers want an organic Elstar, even though it's not resistant to scab or mildew without spraying." Fleuren nursery also uses the Santana apple variety as an inter-stem grafted onto standard M9/337 rootstock when growing other varieties, as Santana is Phytophthora-resistant. Alternative herbicides are also being trialled in the programme.

Complementary planting

Fleuren nursery has also trialled interplanting rows of young fruit trees with wild flowers, which provide a habitat to insects that keep down pests in the trees.

Fleuren is cool on the idea. "The researchers are enthusiastic about it, but we don't really like it because it creates a lot of seed that ends up on the rest of the field," he says. "We might put the beds on the side of the field instead though."

Next to this are rows underplanted with white clover (Trifolium repens). Dutch fruit tree growers are restricted to 90kg of nitrogen per hectare per year in their fertiliser. Clover nitrogenates the soil as well as forming a weed-suppressing blanket. "There are definitely fewer weeds," says Fleuren. "But the clover gets quite high, so the trees stay wet and you have to mow it. Or we could use a lower-growing variety."

Powdery mildew warning system

According to Van der Sluis: "Computer systems are being trialled that analyse the weather to predict the optimal moment for spraying."

A computer program analyses temperature, humidity and likely moisture levels on leaves then sends a fax to growers shortly before its recommended spraying time. This has already been followed by Donker tree nursery. Predictive rather than reactive spraying might sound like a recipe for greater fungicide use. But according to Donker: "Once powdery mildew is in the terminal buds of the plants, our customers will start off with powdery mildew in their plants. But if they receive clean plants, they need to apply less fungicides themselves. So in the end less fungicides are used."

HAIL HEADACHE

A freak weather event in the central Netherlands this summer has prompted researchers to consider radical solutions to the problem of hail damage to fruit trees.

In June, a 70km-long strip of the central Netherlands was bombarded by hail the size of ping pong balls. Right in the storm's path was Waginingen UR's fruit research station at Randwijk. Now in autumn, virtually every fruit on every tree at the station bears the signs of damage, along with many branches.

According to researcher at the station Marc Ravesloot: "We've never had anything like it before. It means we have to consider putting in hail nets."

Another alternative, he adds, was "hail cannons", which fire explosive charges into storm clouds to disperse large ice crystals before they fall.


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