Aquatic Weed Control with Roundup Pro Biactive

Aquatic Weed Control with Roundup Pro Biactive

Aquatic use means spraying in or on land immediately adjacent to a body of water, where the land immediately adjacent to is defined as the bank of the body of water. The body of water can be enclosed (i.e. ponds or reservoirs which do not drain to a watercourse) or open (i.e. rivers and streams which drain to a watercourse).

All aquatic use of herbicides requires Environment Agency approval. Contact the local EA office before work begins.

Safety to the environment

Safety to the environment is an important consideration when treating weeds in and around water. Roundup Pro Biactive is particularly suitable for these areas. It gives effective weed control, and is quickly broken down in soil or sediment into harmless natural substances. It is non-residual, and does not harm animals, birds, fish, insects and other wildlife.

When Roundup Pro Biactive is used correctly, only a small proportion of the spray reaches the water. Any herbicide which enters the water is broken down by microbes. This was confirmed by monitoring sites after application. The amount of glyphosate found in slow-flowing water one hour after treatment, and in still water 12 hours after treatment, is barely detectable.

At these sites, the variety and number of microorganisms showed no significant change during the year after treatment.

Evidence suggests that Roundup Pro Biactive has less effect than mechanical weed control on wildlife.

Government Approval

The Department of Environment, Food and Rural Affairs imposes strict control on the use of herbicides in aquatic areas.

Glyphosate, the active ingredient in Roundup Pro Biactive, is one of only two active ingredients approved for such use.

Before granting approval, DEFRA considers extensive data on the herbicide’s characteristics, including it’s toxicology, degradation, persistence, and effects on invertebrates and fish.

Roundup Pro Biactive provides long-term control of aquatic weeds in ditches and drainage channels. It controls emergent and floating weeds including especially difficult to kill species such as reeds,

rushes, sedges and grasses. Roundup Pro Biactive has a favourable toxicological and environmental profile.


Emergent Weeds

Spray when the weeds are actively growing with a full emergence of green leaf at the flowering and up to die-back stage. For the control of watercress, the best results are from June applications. Bulrush from late July applications and for all the remaining species from mid-August to mid-September. Leaf symptoms on the weeds begin with a grey/ greening and then yellowing of the foliage usually appearing within 14-21 days of spraying in the early Autumn.

Complete foliage desiccation usually occurs 30-40 days after spraying. At this stage the weeds can be cut and removed. During cold conditions leaf symptoms may not appear before natural die-back but no growth will occur in the season following spraying.

Floating Weeds

Spray when there is a maximum emergence of floating leaves. For the control of Water Lilies, the best results  are obtained from applications made from mid-July to mid-August. From 7-21 days after spraying the foliage turns yellow, gradually disintegrates and sinks below the surface of the water. A few leaves may remain green until the end of the season but do not regrow in the following year.

Adjuvants must not normally be used with Roundup Pro Biactive in aquatic areas, but for floating weeds where wash-off can be a potential problem the addition of 475 ml TopFilm®, (a natural biosponge

called Biocar® made from maize) may improve control of species where herbicide wash-off is a problem, e.g. Hydrocotyle ranunculoides (Floating Pennywort), Myriophyllum aquaticum, (Parrot's Feather),
Potamogeton natans, (Broad leaved pondweed), reeds and rushes, Nymphoides peltata (Fringed water lily). TopFilm® is an approved adjuvant for use in water.

Rates of Use

Roundup Pro Biactive herbicide MAY BE USED for the control of aquatic weeds in the presence of fish if used in strict accordance with the recommendations in this section.

Emergent Weeds include: Bulrush, Common Reed, Creeping Bent, Reed Canary Grass, Reed Sweet Grass, Sedges, Soft Rush, Watercress, Whorlgrass
Floating Weeds include: White Water Lily, Yellow Water Lily

Target Weeds Roundup Pro Biactive Volume of water for hydraulic sprayers
Emergent Weeds 5.0 l/ha 200-400 (optimum 250)
Floating Weeds 6.0 l/ha 100-200


Any knapsack sprayer, tractor-mounted or boat mounted sprayer may be used provided it is capable of applying the appropriate spray volume accurately and at the correct pressure, to achieve a ‘medium’ or ‘coarse’ quality spray, (BCPC definition).

Avoid high water volumes which may lead to run-off and loss of chemical.

Applications made in flowing water should be sprayed against the direction of flow.

Roundup Pro Biactive must be applied as a directed spray to green, actively growing weeds and drift must be avoided.

Applications must be made before the leaves of the weeds have started to die back.

Hand-held weedwipers may be used to apply Roundup Pro Biactive directly to weeds, using a concentration of 1 part of Roundup Pro Biactive to 2 parts of clean water.

When operating in or near water, it can be difficult to get the spray nozzle over weeds growing at a distance from the bank. Consider using a telescopic hand-held lance which extends to give a spray range of up to 5 metres. These lances are also useful for spraying tall bankside weeds such as Giant Hogweed and Japanese Knotweed.

All spray equipment should be checked and cleaned thoroughly before and after use, and should be calibrated regularly.

With a boat-mounted sprayer, use the slowest forward speed to cause minimum disturbance to the leaves of the weeds. When disturbed by the wash, water lilies may require retreatment.

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