Good field preparation will give a clean start. But how do you keep it clean? Cultural techniques can reduce and even eliminate herbicide use but care must be taken to ensure that they do not propagate perennial weeds and that repeated practices do not damage soil structure, accelerate the degradation of organic matter or leave soil prone to erosion. Labour costs can render cultural techniques impractical for some crops.
Living mulches, which can reduce soil erosion/run-off, increase organic matter and reduce temperature fluctuations as well as suppressing weeds, may be a solution in some circumstances. However, depending on the type, the mulch can compete with the crop, may attract pests and diseases and the vegetation is likely to need maintenance.
For many growers and nurserymen, herbicides remain the answer to weed control. But choice is becoming increasingly limited as products become unavailable and resistance to chemicals increases. The pressure is on to target the pesticide and to use lower doses.
An integrated approach, with mown living mulch and chemical control, is adapted by many fruit growers.
Assessed for LERAP (Local Environmental Risk Assessment for Pesticides) "low drift" status, Micron's Enviro range of shielded equipment has been awarded three-star accreditation - the highest rating currently available in the UK - by the Chemicals Regulation Directorate. The range includes the Varidome, Spraydome, Undavina and Spraymiser. The James Hutton Institute uses Varidome and Undavina spray atomisers.
Formed in April 2011, the James Hutton Institute is a leading, multi-site scientific organisation encompassing a distinctive range of integrated strengths in land, crop, water, environmental and socio-economic science. It strives to tackle today's major global issues such as preserving our natural resources, developing next-generation crops and delivering sustainable production systems.
Based in Dundee and Aberdeen, it has four main farms where most of the laboratory research is put into practice, including pioneering work on a whole range of soft and top fruit.
Hartwood Farm is a 350ha livestock farm in Lanarkshire that undertakes research on soil, land and the environment, with most of the area used for sheep and cows. Glensaugh Farm near Fettercairn has just over 1,000ha and is probably best described as a high-lying marginal farm on an upland estate. There is some woodland, around 30ha of arable land and more than 900ha of moorland hinterland supporting sheep, deer and cows.
The institute also runs the 100ha Mylnefield and 170ha Balruddery Farms near Dundee, both of which are managed by Euan Caldwell as one unit. These predominantly arable farms roll over the lower south-facing slopes of the Sidlaw Hills, with heights ranging from 8m above sea level at Mylnefield to 124m above sea level at Balruddery.
With almost 400 separate trials on the go, half the land area is dedicated to field experiments supporting the study of crops, plants and their interaction with land, soil and the environment. "The plant breeding programmes, which we are well renowned for, are raspberries, blackcurrants and potatoes. But we also work extensively on blueberries, strawberries, apples, pears and plums, among other crops," says Caldwell. "The remaining half of the land area is used to grow commercial crops and enables us to return any field that has been used for field trials back to a 'blank canvas'. It takes around two years (more in the case of perennial crops) of commercial cropping to remove the footprint of a previous trial before it can be used for experimental purposes again."
All of the fruit trials and some environmental projects are carried out at the Mylnefield site in Invergowrie, whereas Balruddery Farm is where most of the other crop-breeding programmes take place and also hosts a long-term experimental platform, the 40ha Centre for Sustainable Cropping, for research on the sustainability of arable ecosystems.
Caldwell's role is to manage the two farms and co-ordinate the on-site field trials and experiments to enable the researchers to put their science into practice. "We are a LEAF (Linking Environment & Farming) farm and are proud to have been the first LEAF innovation centre in the UK," he says. "Like most farms, part of our work involves undertaking a range of varied spraying activities on diverse crops, which include soft and top fruit, potatoes, cereals, beans and oilseed rape.
"Part of our LEAF strategy to minimise chemical input is to spray only when we need to and to target only the specific areas where we need control (for example, at the base of the fruit rows). Maintaining grass pathways between the rows with a mower and using a Micron sprayer to target the base of the plant is one of our solutions."
He continues: "To control weeds in raspberries and blackcurrants, we use a Micron 100-litre Spray System equipped with either two Spraydome 400s or two Undavina 600s, depending on what is required, mounted on the front linkage of a Fendt 209V vineyard tractor. This frees up the rear of the tractor to enable a further grass-cutting operation in the same pass."
The Undavina and Spraydome spray atomisers are fully shielded under a circular, freely rotating head to virtually eliminate drift. They also incorporate a spring-loaded arm that gently deflects around the base of the bushes, allowing spraying right up to the base.
"We first used this equipment in the summer of 2012 after it was recommended to us by AM Phillips, which has supplied the majority of our spraying equipment for around 20 years," says Caldwell. "With a number of trials underway, the sprayers get used regularly as we pass through each plantation roughly once a month during summer. We have used glyphosate at 4l/ha in 80l/ha water, glufosinate-ammonium and Diquat products at the same rates at various stages through the season, all with excellent results.
"Because of its shielded construction, the Spray System allows us to control the placement of the chemical and reduce drift, which is very important in ensuring that there is no damage to the experimental plots that are assessed for growth characteristics.
"Before we purchased the Micron equipment we used Dichlobenil granules to control weeds in the spring. Our need for accuracy is great so this was often followed up later in the season by teams of workers hoeing and strimming weeds and we were able to hand-lance weeds with Diquat if circumstances allowed. Using Micron CDA sprayers saves many man-hours per plot, the ratio being at least one spraying hour to 10 hoeing hours".
Caldwell estimates that the equipment will pay for itself within two years through reduced labour costs alone. As well as his raspberries and blackcurrants, he plans to use the sprayers on top fruit in the future.
Lack of products sees nurseries turn to topping for pots
With the loss of Ronstar Granules, the industry is in a dilemma. Work being carried out by AHDB Horticulture will lead to several alternative products but as yet none have arrived through the Managing Ornamentals Sustainably programme. For now, nurserymen must look to Flexidor 125 - the only product available for use under protection - and Dual Gold, which has a very good crop-tolerance spectrum but is limited to use only in May. There are one or two products with limited action, including Lenacil-based ones such as Venzar, that can be used in certain situations.
"The ornamentals industry is suffering quite badly from a dire lack of products for container plants," says nursery stock consultant John Adlam. "The diversity of ornamentals on the one hand is a major strength of our industry, but when it comes to controlling weeds it can be quite a nightmare. You can end up with a bed where you can spray that plant, not that one, but the one after you can. Our diversity is almost our biggest Achilles heel when it comes to weed control."
Adlam also points out that the industry still does not have really satisfactory products for controlling existing liverwort growth in crops. "We have a strong need for something to enable growers to control existing liverwort growth," he says. "The changes in Mogeton basically remove it for use in container-grown crops. There are products such as Lenacil that will prevent liverwort growing, but when you are trying to control bad liverwort growth we have a problem."
A new product from Fargro, Mosscade is effective on small liverwort growth and in preventing infestations but requires repeated applications on heavy liverwort growth.
As a result of the loss of herbicides for use in container-grown crops, more nurserymen are turning to bark topping to suppress weeds. Irrigation practices can also help. Adlam says: "With capillary beds and drip irrigation, where you've got a drier surface - and definitely if you can dry the pots off once every 24 hours - the growth of liverwort and weeds is considerably suppressed."