Late summer is a best time to tackle Japanese knotweed, once it has flowered – usually late August, September and into October. This plant is very hard to get rid of and time of spraying, as well as amount of chemical applied are key factors in successful eradication. The most common mistake is related to amount of chemical applied. It is very important to read the dosage information from the label on your herbicide container and follow the instructions. Roundup is a systemic herbicide and its Bi-active or Gold are the only permitted chemical allowed near watercourses. The main advantage of this substance over the other less conventional herbicides is that it is transported deep down underground to the rhizomes. This effect however can only be achieved with small amount of chemical being applied. It is therefore not a good idea to go over recommended dose which only results in burning above biomass and instant “shut down” of a circulation in rhizome vascular system and subsequently survival of the plant. Timing of treatment is also critical in successful eradication. Trials show that when Knotweed is sprayed early in the summer it still has enough of vigour to resist chemical and survive. Spraying is most effective in September when flowers are in bloom and plant is just before its winter dieback. At this time all the nutrients from the foliage along with the chemical are transported into the rhizomes. Spraying must be followed up each year until no regrowth occurs.
Any advice please ring the LIFE project on 029 60633