Bracken

Introduction

Pteridium aquilinum, (L.) Kuhn.

Bracken is a plant that has been around for hundreds of thousands of years.

Initially a lowland plant of woodlands the clearances offered it an opportunity to move out of this niche and it has subsequently expanded into a broad range of lowland situations right up to 600m where the limiting factor is frost and wind. A prolific plant, it is tolerant of a wide range of climatic conditions. It is highly disease resistant and is able to reduce competition from other plants by vigorously out-competing them and even exuding compounds, through the rhizomes (underground stems that are capable of producing the stem and root system of another plant), that inhibits the growth of other plants.

Bracken is generally a small component within natural woodland however it can become a problem if trees are cleared. It prefers well-drained sites as the young rhizomes cannot stand waterlogged soils. Within the Countryside Survey (1990) it was estimated to occupy 17,000km2 across the UK. It also forms a habitat favourable to ticks which can transmit Lyme disease.

Identification

The Bracken crosiers appear in May using energy that has been stored underground in rhizomes. Where Bracken grows it is generally best thought of as a single plant that is connected by a dense mass of black underground rhizomes that connect the plants together.

Plants require an established root system before fertile fronds are produced, typically requiring 3-4 years. Spore production can be staggeringly high with a single frond producing up to 30,000,000 spores. However, spores are probably only important in the colonization of new sites and most growth in the population can be attributed to its successful means of spreading vegetatively through its rhizomes.

An entire hillside can therefore be dominated by a one plant, this connectivity led directly to the effectiveness of the herbicide Asulox.

Cultural Methods Of Control

Cutting bracken fronds once or twice per year for a minimum of five years is thought to reduce the amount of bracken by up to 60% and to increase species diversity. The optimal timing for cutting bracken fronds is in the autumn before nutrient reserves are transferred from the fronds to the rhizomes below ground.

Ploughing should be carried out before late autumn to give good control. Ploughing should be repeated for a number of years.

Establishing ground cover that can compete with Bracken will help prevent the Bracken from becoming further established. The selection of appropriate species to compete with the Bracken will vary from site to site though species such as Creeping Soft-grass, Holcus mollis, and Cock"s-foot, Dactylis glomerata, are known to be effective competitors.

Chemical Methods of Control

Asulam, the Active Ingredient in "Asulox" is the most effective chemical treatment for Bracken and is currently available under “Emergency approval” which is reviewed on an annual basis. Most tree species are unaffected by Asulox and although some herbs and grasses may be sensitive they are generally protected by the dense canopy provided by the bracken itself.

Another alternative is to apply glyphosate through a microwipe weed wipe. Glyphosate is a non-selective herbicide (otherwise known as a total herbicide) that will kill nearly all green vascular plants that it comes into contact with. Therefore, care should be taken that the weed wipe is set at an appropriate height to come into contact with only the Bracken.

Control With Roundup ProVantage and Roundup ProActive

In accessible areas for ground application and/or where watercourses are nearby and/or where cost is an over-riding factor Roundup can be very successfully used as part of Bracken management strategies.

Timing of control is critical. Successful control using Roundup is dependent on the timing of the treatment in relation to the movement of nutrients and dry matter between the underground storage rhizomes and the fronds. As the fronds develop in spring the reserves in the storage rhizomes diminish. Treatment with Roundup during frond expansion in April, May or June will result in frond death but with little long-term effect on the rhizomes as the glyphosate is carried upwards with the nutrient flow. Once the fronds are fully expanded, the products of photosynthesis will start to be translocated down to replenish the underground reserves. Treatment of the fronds as they approach full size in July-August will give maximum translocation and long-term control of the stand.

Overall spraying is appropriate for large areas and thick stands. In many instances little or no other plants will be growing beneath the bracken canopy, and, in any case, the bracken fronds will intercept almost all of the herbicide spray.

Treated fronds will die back within four weeks of treatment, the Roundup being translocated down into the rhizome network killing both frond forming and storage rhizomes.

Large areas, especially scattered populations or patches in grassland, moorland or heath land, may be effectively controlled using tractor/quad bike-trailed weed wiper. Use of such applicators will ensure superior, cost-effective control of the bracken whilst leaving grass, heather and other plants unharmed.

Weed wipers, such as the microwipe weed wipe make efficient selective application of Roundup, possible.

The bracken should be "wiped" at full frond expansion but before they start to turn brown and die back. Optimum control is achieved during July/August. Later timing up to mid-Sept can still give satisfactory results but must be pre-senescence of the foliage. Do not treat when the fronds are wet or rain is imminent. Always ensure a height differential of 10cm between the bracken and the grass to maintain selectivity.

With large plants in dense stands, shading can result in incomplete coverage whether using an overall spray or a weed wiper, leading to some re-growth in the following year. However, in many situations using an efficient application technique, high levels of control are possible after just one year. Monitoring and follow-up treatment should be carried out as part of a long-term management programme.

If the Bracken is being controlled in an area accessible to livestock the animals should be kept away from the treated area whilst spraying and for 7 days where spraying is overall, and until the spray has dried on the leaf where spot treatment or weed wiping is carried out. However, it must be noted that treated bracken may become palatable and is of course poisonous. So, it may be prudent to exclude stock until the foliage has completely died down if the bracken takes up a large proportion of the available grazing area. This is also important if other poisonous weeds like Ragwort, Cowbane, Hemlock or Hemlock Water Dropwort are present in the treated area.