Technical
“Rhododendrons have been identified as major reservoirs for tree disease, including Sudden Oak Death. Since 2009, the spread of the fatal disease to Japanese Larch has been widely linked to the plant”
hododendron (Rhododendron ponticum), brought to the UK by the Victorian plant hunters, was widely planted throughout upland Britain in gardens, and in woodlands on sporting estates, to provide cover for game birds, particularly pheasants. From this beginning, the species has escaped into woodland, both natural and commercial, scrubby areas and into open country.
R
It is commonly seen on golf courses and in parks, where it can become a problem. High densities can greatly reduce biodiversity and the invasion is so great in some areas, especially in wet western Britain, the decision has been made to establish management programmes.
More recently, Rhododendron plants have been identified as major reservoir for tree diseases Phytophthora ramorum, and Phytophthora kernoviae (sometimes known by the US term of Sudden Oak Death). Since 2009, the spread of the fatal disease to Japanese Larch (Larix kaempferi) has been widely linked to Rhododendron. These diseases are notifiable pathogens and destruction of infected plants is a statutory requirement. Contact your local Fera plant health and seeds Inspector for more details.
Identifying the enemy
Rhododendron can be a problem for land managers, and has been implicated in the spread of sudden oak death
Other members of the large Rhododendron family include the Azaleas and all are grown for their spectacular flowers, usually borne in spring. Leaves are spirally arranged; leaf size can range from 1-2cm to over 50cm (20 in). They may be either evergreen or deciduous. In some species, the undersides of the leaves are covered with scales (lepidote) or hairs (indumentum). Some of the best known species are noted for their many clusters of large flowers.
Rhododendron Ponticum is included under the Wildlife and Countryside Act 1981 as
an invasive non-native species and it is an offence under Section 14(2) of this legislation to “plant or otherwise cause it to grow in the wild”.
The sheer physical size of the plant, up to 8m in places, together with its tough, waxy leaves make Rhododendron a difficult weed to control. In addition, it will quickly re-grow if it is not completely killed.
Going into battle
There are several methods of controlling Rhododendron using Roundup. Overall spraying is not suitable for larger plants or for thick stands, as it is difficult to spray and the older plants tend to be less susceptible. These taller bushes must first be cut back to ground level before treatment. They can either be hand cut using power tools, such as a brush saw or chainsaw, or by using a hydraulic flail, typically mounted on a crawler or other tractor reach arm. The cut stumps may be treated immediately using the cut stump method or the foliage left to re- grow for 2-3 years and then sprayed.
Fortunately there are many different options for using Roundup liquid products and Ecoplug to control Rhododendrons depending on the time of year.
Choose your weapons Foliar Sprays
An overall spray applied to the foliage will provide effective control of young bushes up to 1.3m high, or as regrowth 2-3 years after cutting back. The best time for application is from early May to late September but, in milder areas, applications earlier and later than this have proved successful. A high dose of Roundup Pro Biactive/Roundup ProBio (10l/ha) is required for this species and complete coverage of the plant is required. Addition of Mixture B, a non- ionic surfactant/spreader, at 2% of the
OCTOBER/NOVEMBER 2013 PC 131
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