Digging out plants
Advantages
- Digging is the most thorough method of eradicating rooted plants. Provided the job is done carefully, repeat treatment should not be necessary, except to control the spread from remaining stands, or to remove new stands before they become established.
- Digging can be selective provided workers recognise the species to be controlled.
- Digging, especially in the case of rhizomatous plants, lowers the bottom level by about 150mm (6″), giving an immediate increase in water depth.
- Digging is suited to voluntary group work, provided it is properly and safely organised.
Disadvantages
- Digging is slow and labour-intensive.
- Digging must be done thoroughly to be effective, since remaining roots or rhizomes will resprout and spread quickly to fill the cleared space. With some species, broken pieces of rhizome or stem may reroot and spread the problem more widely.
- Digging is difficult in water over about 600mm (2′) deep, and the deeper and more turbid the water, the less thorough the results. It helps if the water level can be lowered to about 300mm (1′), leaving sufficient water to float cuttings to the bank.
- By stirring up bottom ooze, digging may release stored nutrients and lead to rapid eutrophication or deoxygenation of shallow ponds. For this reason, digging should not be done in spring or summer.
Methods and organisation
Keep these points in mind:
- Never work alone in or close to water, and don’t work in deep or fast flowing water. Beware of slippery and unstable banks, and underwater hazards. Within the limits of the water depth, groups can work in line to ensure thorough clearance.
- Define and mark out the areas which need clearing, and concentrate the group’s effort on completing those in the time available. Leave other areas undisturbed, and return to them later as necessary.
- In shallow water, use a spade or garden fork to dig up plants. In deeper water, if wearing waders or working from a boat, use a muck rake. In very soft silt, plants can be pulled up by hand.
- Wear rubber gloves to protect your hands, particularly against cuts which could become infected with Leptospirosis (Weil’s disease). Cover any cuts with waterproof plaster, and avoid further contact with pond or river water.
- Most rooted aquatic plants grow from rhizomes which interconnect to form a dense, tough mat. First find or cut an edge along the mat. Then cut under the edge to free it from the bottom, cut or break it apart and pull it up for disposal. Don’t try to lift the rhizomes out before they have been cut free from the bottom. Once free of silt, rhizomes float making them easy to collect.
- Start at the inner edge and work outwards into deeper water, pulling the material behind you to be collected by workers on the bank or in shallow water.
- If you aim to leave a marginal fringe, minimise damage to this while working. Float the plant material or load it into a punt to carry it to another bank for disposal. If it must be pulled in through the fringes, work from a few locations to minimise trampling, and stand on a wide plank to avoid sinking into the mud.
- When using a punt, pole with a muck rake or paddle with a spade or shovel. Only two volunteers should work from it at once if using muck rakes or other sharp tools. One should be in the bow, one in the stern, working on opposite sides. A third volunteer may be needed in the middle to hold the punt steady in a breeze or current. To dig out plants, lean over the punt side, and get the muck rake tines under the rhizomes. Ease the tines upwards to break the suction, and then lift. Because of drift, it is hard to do a thorough job from a punt.
Cutting and hoeing
Advantages
- Cutting, but not hoeing, can be done in deep water to the limits of rooted plant growth.
- Cutting and hoeing are relatively quick and easy jobs for one to three people.
- In water which can be waded, non-rhizomatous plants can be uprooted as effectively by hoeing as by digging, while at the same time excess silt and mud can be pulled out. A draw hoe or similar shaped implement is suitable for small areas.
- Cutting and hoeing can be carried out without great difficulty in flowing water.
- Cutting, with or without hoeing, can help control the flow pattern in rivers where the need is to define and limit plant beds to prevent siltation or erosion (see below).
Disadvantages
- Cutting, without removing plant roots, encourages regrowth, and if done too early in the season will necessitate a repeat treatment later in the year. Normally submerged plants should be cut in summer, and emergents in autumn.
- Cuttings must be removed and disposed of promptly to prevent deoxygenation. In flowing water, a boom should be fitted at an angle across the river below the work area so that cuttings are deflected into the corner from where they can be removed.
- Hoeing large areas may cause turbidity and smother aquatic organisms in silt and mud. The effects of this can be greatly reduced by use of a geotextile mat, called Sedimat, which is made of jute, hessian and wood wool. This product has been developed specifically for the trapping of disturbed sediments during construction and management work in flowing water. One or more mats, each 1.2 x 3m (4×10′), are laid down on the bed of the stream immediately below the work area, and anchored by stones. These trap up to 80% of the disturbed sediments, and can then be lifted out, normally using a digger and bucket, and laid on the bank of the stream. They can then be staked down and seeded to provide bank stabilisation.
Cutting and hoeing shallow streams and rivers
If the channel can be waded, vegetation can be cut into a ‘side and bar ’ pattern. Patches of vegetation are left at the side to prevent lateral erosion, with occasional bars of vegetation across the channel below bends to distribute the current and provide food and shelter for fish. The pattern depends on local conditions, and a good knowledge of the river is needed to achieve best results. If you are unsure of the effects, it is best to ‘under cut’, but inspect frequently and enlarge the cleared areas as necessary. Change the pattern of cutting from year to year.
On sharp meanders where the channel is liable to change course, you should clear inner bends completely while leaving compensating growth on the outside to resist erosion.
Cutting in deep water
In rivers too deep to hoe, a chain scythe can be used.
Use the following method when scything streams or rivers:
- Open up the cutters to form a continuous line.
- Join a length of rope to the split ring at each end of the chain. The ropes must be long enough to allow the cutters to settle in the weed when held at or near the banks.
- Two people are required to work the scythe. Standing one either side of the channel, work the cutters back and forth with a sawing motion. The chains act as flexible weights to keep the cutters down in the water.
- Clearing upstream, all weed can be cut by slowly working the cutters along the bed. Working downstream allows controlled cutting, with some weed left to shelter aquatic life. The work rate depends on the weed’s density and on any obstacles encountered. If the cutters hit an object, both operators should pull on their ropes to bring the blades to the surface, clearing the obstruction.
In still water, operate the cutters from two boats or from a boat and the bank. It is best to anchor the boat, otherwise one person must hold it steady while another operates the cutters. Take advantage of any wind, so that cut weed is carried to one side or behind the cutters.
Mechanical cutters
Various types are available including boat-mounted cutters, and machines such as hydraulic excavators which work from the bank, using special weed-cutting buckets. For further details see RSPB, NRA and RSNC (1994).
Cutting emergent plants
Emergent vegetation is most effectively controlled by digging out the rhizomes, but in some cases it may be best to cut despite the regrowth which this allows. These cases include temporary clearance, or where a large area such as an interconnected system of drainage ditches must be cleared quickly, or where the water is too deep to dig out the plants easily. To make cutting as effective as possible, cut reed (Phragmites communis) in July for greatest effect. The replacement crop should be negligible, especially if the stubble is flooded to impede growth. The time of cutting is less important for other plants such as great pond sedge (Carex riparia), reed sweet-grass (Glyceria maxima) and narrow-leaved reedmace (Typha angustifolia).
Raking and dragging
Like cutting, raking and dragging tend to encourage regrowth of submerged plants. On floating algae, raking and dragging should only be used as a last resort where preventative treatment using barley straw has not been used. Raking and dragging can be used as a temporary measure to reduce other free-floating plants such as duckweed, but plants will rapidly spread to cover the cleared area during the growing season. Long-term measures to increase shading, and reduce nutrient inflow into the pond or watercourse are the only methods of establishing a more balanced ecosystem.
