Himalayan Balsam Wales

Control

General information

Before you go

If you want to access private land, you should always seek permission first.

When?

Control of Himalayan Balsam should ideally happen when the plants have grown to a good height, but have not yet flowered. This is usually around June.

However it may be easier to leave them until the end of June, start of July, when the plants have flowered, as they will be easier to spot.

Some websites suggest it is ok to leave it slightly later, but before they have formed seed pods.

Flowering may vary from season to season, and also with microclimate (there is suggestion, for example, that plants growing at lower altitude or closer to the sea may set seed earlier than plants grown higher up). The seeds aren’t formed until August/September.

If you clear the balsam in June/July, you are likely to find that new balsam plants germinate in the cleared areas and can grow and flower rapidly in the warmer summer soil. You are therefore likely to have to clear it a further two times or even 3 times before winter. Some balsam plants have been seen flowering in October in cleared areas, although it is uncertain whether these went on to produce seeds.

Which method?

A study in the Wye Valley in 2005-2008 suggested that mechanical control (strimming) was the most effective in terms of getting all plants, not affecting native plants too severely, and in terms of time effectiveness. Areas treated by chemical sprays were also effective, but tended to kill off native plant species too, leaving areas bare and vulnerable to erosion. Chemically treated areas also had the highest proportion of re-growth the following year, presumably because it is less clear to see if all plants have been treated (cut plants were obviously cut). Hand pulling is potentially the gentlest for native species, and most certain to kill the plant, but it is very time consuming, and in areas prone to erosion may not be the best choice, as the soil is destabilised in the process.

What do I do with the plants?

It is preferable to leave the cut/pulled/sprayed plants on site, but it is important to try to prevent them from re-growing or continuing to produce seed if they are in flower. It helps to leave them in an exposed place to dry out and die quickly. It is therefore preferable to leave the plants scattered rather than collecting them into piles for composting, because it is important that the roots of pulled plants dry out to kill the plant, and it is best not to risk spreading seed by moving plants about. There is a chance however that some will still manage to produce seed, but this will be fewer than if the plants had been left to grow, so is still worth doing.

However, if there is a very large volume of pulled plants, they can be left in piles to compost and, where possible, covered with a tarpaulin to prevent re-growth.

If the plants have already set seed, they could be burnt on site, if possible. If you intend to do this, (or burn any other material on site), you are likely to require a waste exemption from the Environment Agency. Information on how to apply for an exemption is available on their website.

If the choice is to transport them off site, it should be noted that they are treated as hazardous waste, and only very limited waste disposal stations will accept them, and at cost. They should under no circumstances be taken off site and disposed off in normal compost, or at a normal waste disposal station.

Hand pulling

The plants are easy to pull, and in areas that are sparsely populated, or on difficult terrain, this may be the best option. Also, if many people are involved in controlling the plants (e.g. groups of volunteers), this may be a viable option. Make sure you follow the general health and safety advice.

Strimming

Strimming is a good option where stands are dense, and where the ground is reasonably level. Care should be taken to strim the plant below the first node, as it will otherwise re-grow and flower later in the season.

Strimmed plants can be left on site to compost, but only if the seed pods have not yet formed.

Herbicide control

Herbicide control (chemical) should only be carried out by persons qualified to do so, and, if in proximity to a water course, should be done only after consultation with the Environment Agency.

There are two chemicals normally recommended;

  • Glyphosate: treat with a weed wipe in mixed stands, or by foliar spray in dense stands, before flowering. If all plants are controlled, then spraying should only be required for 2-3 years.
  • 2,4-D amine: This weed killer controls many broadleaved annual weeds, and will not kill grasses. So it may be preferable if grasses are to be retained for stabilising purposes. Treat during early stage at the rosette stage for effective control.

The Wye Valley study tested various concentrations of Glyphosate and found that a low concentration of 2 litres/ hectare worked as well as double the dose. The manufacturer recommends 5 litres/ hectare.

Grazing

Grazing will also keep the plants under control, and in grazed fields you will tend to only find balsam in hedges or behind fences where stock can’t get at it. Cattle especially seem to like balsam, and they have been actively used as control in at least one instance (see http://www.wildlifetrusts.org/reserves/wilden-marsh for more info). You will still need to hand pull or strim areas where stock can’t get to, but it will be a big help.
Please only consider using stock if it is safe to do so (all necessary fencing etc in place), and if it is suitable for the land.