Crop Clinic

It prefers damp soils, so has rapidly colonised riparian areas (such as river banks and meadows). It establishes readily from seed, and from a single plant a dense stand can develop over a few years. Its rapid spring growth, reaching about 2m or more in height in suitable conditions, shades out most other grasses and herbs, so they cannot compete and die-out. When the Himalayan balsam dies back in the autumn, bare areas are left which, if on river banks, may be subject to increased erosion.

One of the best methods of suppressing the incursion of Himalayan balsam is by maintaining a dense grassy sward, which suppresses the germination of the seed. However, as the weed will readily colonise any gaps in the sward, a close watch should be maintained for any seedlings if there is to be Himalayan balsam in the area.

Otherwise, Himalayan balsam is not tolerant of grazing and trampling by stock, but this may not be possible in some riparian areas. However, stock do prevent spread into water meadows and similar areas.

It should be noted that the plant is an annual establishing solely from seed. The seed can stay alive in the soil for about 18 months. So a key strategy to prevent spread is to kill the plant before it sets seed in June- August, and if this is done for a couple of years then local seed bank should be depleted and eradication possible so long as there is no further incursion of seed from elsewhere, such as a population upstream.

It is easily pulled out of the ground by hand, so small infestations amongst other vegetation are best controlled in this way.

Larger areas of infestation can be cut by hand or strimmed by machine, but it must be cut beneath the lowest leaf node, near the soil level, or it can regrow. Clearly mechanical control will only be possible where there is adequate safe access.

Use of herbicides for control is limited by the fact that the weed is generally found next to or near water. In those cases only certain glyphosate and 2,4-D amine products can be used. Where it is found away from water, a wide range of cereal and grassland herbicides give good control. The plants should be treated before flowering, ensuring the foliage is well covered. An alternative is to use a wiper system that spreads glyphosate onto the foliage directly.

Where glyphosate is used most other vegetation will also be killed or at least seriously damaged. So an overall treatment is really only suitable for dense stands where no other important vegetation is present. Where other vegetation present needs to be retained, a wiper system can be used. In such situations it may also be possible to use 2,4-D amine. Although this will kill or damage many broad-leaved weed species, it does not kill grasses. This allows retention of a ground cover that reduces the potential for soil erosion. This may be the preferred option for grassy river banks.

Where these herbicides are to be used near water, inform your local environmental agency (eg SEPA, Environmental Agency), from whom you may need to get permission if there is extensive use, and any relevant water, river and fisheries authorities. This is particularly important if water is being extracted locally for crop irrigation.