The Enemy: Policeman’s helmet (Impatiens glandulifera) is a annual plant that can grow 6 to 10 feet tall that is home in India. It has hollow stems with a purple to reddish tinge. This plant has been recently put onto the states Noxious Weed List as an Early Detection – Rapid Response Weed. The flowers are white, pink or purple resembling an old-fashioned English policeman’s helmet. Its pod-like seed has the ability of exploding when touched. The leaves are oblonged and very serrated along the outer edge. This plant prefers moist areas such as streams, rivers, canals, and ponds. It is extremely aggressive and was recently found in 7 or 8 locations as one gardener spread it to another.
The Strategy: As a beautiful ornamental this plant has the capability of spreading very rapid as well as causing great damage to existing waterways by halting movement of the water. With stalks that look like green bamboo and reaching a growth of 10 feet, whether in the shade or sun, the plants grow so dense that animals cannot even travel through them. With this growth habit it replaces all grasses and forbs. Furthermore, each plant can produce from 800 to 2500 seeds each, all being launched close to 20 feet from the mother plant which is much more aggressive than native species.
The Defense: As this plant is an annual, mechanical is the first chain of defense. Although this plant is an annual it as a fiberous root system thus fairly easy to dig up with a shovel. Little research has been done on what herbicides can be used to control this plant nor is there an insect that uses this plant other than for pollination. Using a pre-emergent herbicide will be the best herbicide to keep the plant from germintating. We encourage the public not to buy plants over the internet or at least consult with a local nursery to ensure that your desired plant is not on a HIT list.
PLEASE NOTE – The proper use and application of herbicides can be an effective way to control and eradicate noxious and invasive plants. Before using herbicides, always carefully follow the label and safety instructions on the label. While we recommend the use of herbicides as one of the effective tools for integrated pest management, the Idaho Weed Awareness Campaign assumes no liability for herbicide applications.