Funny weather upsets our invasive plants & stem injecting knotweed

We had some late frosts this year and an almost unheard of very prolonged and hot summer. This meant that our dominant invasive friend, Himalayan balsam, came out to play later than usual and really struggled in the heat, wilting pathetically in July. Sadly, the inevitable rains came down and the balsam went up. Furthermore, the long mildish late Autumn with good spells of sunshine and rain has brought up an abundance of small Himalayan balsam. Speaking to a colleague in Cardiff this was also happening in Cardiff in late August. After a walkabout on our Nature Reserve late on this evening I was amazed to see more little balsam plants out in flower on the second of October. The common mantra is don't pull or cut late in the season (very late August or early September) here I was pulling it up happy in the knowledge that there were no ready seed pods. Even some left over bigger plants had seed pods yielding with much effort white, unripe seeds. So I imagine those people who have given up for the year are advised to take one last look especially along or near waterways and pull them up.

7 inch high Himalayan balsam in flower Oct 2nd.

We have 1 Japanese knotweed stand as well which has been treated by Torfaen Council Ranger Jon Howells and volunteers for the past 3 years. It is now a small stand of only 15 or so stems. The summer heat and dry soil has almost killed the plant with leaves for much of the year being yellowish rather than a vibrant green. However, the sudden wetness with sunshine has brought parts of the plant back to life with little green leaves emerging in October. On a few stems the plant has just come into flower almost a month after most over plants found abundantly throughout Torfaen.

OUR SICKLY LOOKING KNOTWEED STAND (UNTREATED APART FROM A GOOD DROUGHT)

Some small green leaves coming through with small flower bracts

One stem with no leaves and flowers emerging

The plan on Friday morning is to treat the Japanese knotweed with herbicide (glyphosate) with a technique called stem injection. Japanese knotweed stems resemble bamboo with hollow stems. The stem injector has a needle with the hole not at the end like a drug needle, but part the way along.

The hole of the needle is on the side to help prevent blockages and safe infusion into the hollow stem

This means when you put it into the stem it doesn't get blocked and when you depress the syringe trigger it empties into the stem. For Japanese knotweed the best way of doing this is just below the 3rd node above ground level. The plant then takes the glyphosate down into the rhizomes where it starts to kill the plant. The best time of the year to do this is when the plants are at terminal height and when the plant is in flower. Like we discussed earlier, you have to go off the plant not a set date in the calendar and this year for this clump it is very late. This stand was much bigger in previous years and it has been sprayed in the past. This is the usual method for large stands, but you need to be much more careful with weather conditions i.e. not very windy and dry. You are also much more likely to get some drift onto nearby plants which may kill them too. This isn't always a terrible thing as you need to get close to the plants to be able to treat them. With Stem injections the weather is less of an influence, it just takes a lot longer as each stem is injected. Furthermore, you normally spray with a 3-4% glyphosate solution, stem injections are normally 1 ml of neat or 2ml of 50% strength glyphosate so is a much less efficient way of introducing glyphosate into the plant.

Stem injecting a small knotweed stem, Fri 4th Oct 2013

Importantly, when using herbicides you still need the right training, or to be working with someone who is properly trained if you are working on public or someone else's land (PA1, PA6 and if near water PA6W). As the LNR is publicly owned, permission was granted from Torfaen County Borough Council (TCBC) to do this. We are using a little of TCBC's glyphosate for the treatment and one of Keep Wales Tidy's stem injector kits; a nice example of partnership working. There are many volunteer groups across Wales who are now supporting local authorities to tackle invasive species which has to be a better way of tackling these especially in these difficult economic times and we are proud to be doing our part in this.