When planning new woodland, hedging or tree planting, it is vital to remove pernicious and invasive weeds before planting to give the trees the best possible start. Weeds can compete with the young tree for soil nutrients, light and water, thus delaying establishment and growth.
Choosing the right product is essential however, to avoid damage to the tree or unintended environmental effects. Glyphosate products, such as Roundup ProBio and the new Roundup ProVantage, can play an important role prior to planting as there is no residual effect in the soil, so the treatment will not affect the trees through their roots and planting can start seven days after spraying. Trials show spraying pre-planting improves both tree survival and subsequent growth.
Once planted, further targeted sprays will be necessary to maintain a weed free area around the trees. A circle of 1.5m in diameter is optimum to remove competition for moisture, light and nutrients and should be carried out as necessary - usually between April and September. Apply the higher perennial dose rate for a mixture of perennial and annual weeds (see table below).
Couch, perennial grasses, perennial broad-leaves and annuals can all be controlled using Roundup.
Suckers and basal shoots
Species such as Prunus have a tendency to produce suckers. Roundup can control suckers arising from Apples, Pears, Plums, Cherries and Damsons by spraying in the late spring whilst sap is rising strongly. This should only be done on trees established for more than two years. Spraying glyphosate in summer and autumn, when the sap flow is towards the mother plant, allows uptake through side shoots and suckers to move back to the mother tree and can result in damage. Spraying suckers at this time of year should be avoided, or they should be cut down a week before spraying commences.
Lime trees produce a fringe of basal shoots from the base of the bowl. These basal shoots should be avoided with direct applications in the same way as suckers, especially during summer and autumn, as some uptake to the mother tree can occur. There is no label recommendation to control such shoots, but the risk of damage is similar to suckers and is dependent on the season. Any damage to mature trees is usually outgrown within the year.
Operators who carry a pair of secateurs in their pocket can soon snip off any branches or suckers which are inadvertently sprayed!
There is no danger to trees from Roundup via the soil, as it is not residual and has virtually no leaching potential, being tightly bound to the soil particles and quickly broken down to harmless components.
Mature trees, which have brown bark, will not absorb glyphosate, but sprayer operators should avoid any wounded areas on trunks as entry direct to the cambium can result in damage. Immature green bark may also allow some glyphosate uptake, making whips especially susceptible to damage.
Any green area can absorb the product and potentially cause damage, so care should be taken around low hanging branches that leaves are not sprayed. Avoid buds over winter as droplets can lodge in the axils and be absorbed into the plant. Using a guard or hood over the nozzle of the sprayer should minimise accidental damage.
An alternative method is to use a hand-held weedwiper, taking care not to let the rope wick touch any part of the tree.
As droplet size is important in minimising drift into the foliage, care should be taken that the correct nozzles are chosen to produce nothing finer than a medium spray (BCPC definition) or CDA drops of 200-300 microns, and that the correct pressure for the application equipment is adhered to. Low pressure or low drift nozzles are recommended.
Tree shelters fitted around young trees help provide protection against vermin and adverse weather conditions. Where trees are fitted with solid shelters, there is no need to use a spray guard or direct the spray away from the tree, but spiral shelters or those with holes do not provide sufficient protection and should be treated as if there was no shelter.
Early spring application: Perennial weeds grow from root reserves, with sugars rising in spring. Glyphosate uptake is therefore not as efficient as late summer or autumn treatments when the sugars are flowing down to the roots for winter storage.
When planning weed control programmes, this factor needs to be taken into consideration. Where early spring treatments are carried out, then a second application for complete control of perennial weeds may be necessary in the summer.
Winter application: Weather conditions have minimal effect on glyphosate applications. Cold weather, leading to leaves moist with dew in mornings and light frosts, plus slower growth, do not present a problem.
As Roundup ProBio and Roundup ProVantage are rainfast in just one hour on annual grasses and couch, and in 4-6 hours on other weeds, a catchy day when only the morning is likely to be dry, can be considered a spraying day.
It is possible to spray on frost in the morning as long as leaves will dry later - frost is only a problem if it continues for days and causes the weeds to stop growing and become flaccid.
Spraying can also be carried out on the dew/mist in the morning as long as the day will stay dry; although operators should avoid spraying in the evening as increasing dew leads to run-off. Use a medium-coarse spray to avoid driftable fines.
Plants can often take months to develop full symptoms in cold conditions, but will be controlled if winter spraying guidelines are followed.
Weed growth stages
The best time to kill perennial broad-leaved weeds is around flowering. Perennial grasses, like couch, should have 4-5 actively growing leaves, each with 10-15cm of new g
rowth. Annual grasses and broad-leaved weeds need to have at least 5cm of leaf growth or two expanded true leaves before they will take up the herbicide. Poorer uptake also occurs during the rapid stem extension phase, as the flowering stem is extending, and should also be avoided, if possible.
Amey undertakes large scale planting schemes as part of road construction and sports facility contracts, and Clive Parker, Senior Consultant (Horticulture & Arboriculture) for the Consulting and Strategic Infrastructure division, says that protecting young trees is vital.
"How we do it depends on the nature of the scheme - some ornamental plantings will be mulched with bark or woodchip, but glyphosate is an essential part of the armoury."
Mr Parker points out that adhering to recommended rates is important to prevent damage to trees, and adds that using residuals is necessary in some planting situations, again in a carefully planned tank mix with glyphosate.
"We like to take a holistic approach, but recognise that alternative controls such as mowing close to trees can be harmful. Amey uses a team of environmentalists and one of the priorities is to ensure that products work and are safe. We always have to consider other methods of weed control, however, as restrictions on chemical products become tighter."
Where Amey hands over the ongoing maintenance of the site to the groundsman or another contractor, training is provided to ensure that appropriate weed control measures can be used. "Where the site is a school, there is also the opportunity to educate pupils about tree care," says Mr Parker.
He comments that the first two to three years after planting are crucial, after which the young trees become virtually self-managing.
Tree plantations are increasingly in demand for their ability to screen sensitive sites, and contractor Amenity Land Solutions has recently completed a project at a solar farm in Shropshire.
Contracts manager Dave Harvey explains: "Using the tree shelters to protect the trees themselves, we spray with glyphosate post-planting for up to twelve months. There are very few other products that can be used on young trees and, whilst Kerb will tackle grass, it won't control other weeds."
With trees planted in triple rows 300mm apart, a standard knapsack with a 60 or 80deg nozzle can safely work around the trees.
"There's insufficient space to use guards, which also run the risk of dripping when the sprayer is switched off."
The contract, for a Belgian specifier, lasts for twelve months before the local authority takes it on, and includes planting white clover between the panels to minimise maintenance requirements.