The Enemy: Policeman’s helmet (Impatiens glandulifera)
Strategy: This state-listed noxious weed is an annual plant that can grow 6 to 10 feet tall and is home to India. It has hollow stems with a purple to reddish tinge. The flowers are white, pink or purple resembling an old-fashioned English policeman’s helmet. Its pod-like seed has the ability to explode when touched. The leaves are oblong and very serrated along the outer edge. This plant prefers moist areas such as landscapes, streams, rivers, canals and ponds. Landscape gardeners have purchased it and spread it among friends and find out it is extremely aggressive.
Attack: As a beautiful ornamental, this plant has the capability of spreading very rapidly as well as causing great damage to existing waterways by halting the movement of the water. The stalks look like green bamboo and reach 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 2,500 seeds each, all being launched close to 20 feet from the mother plant which is much more aggressive than native species.
Defense: As this plant is an annual, mechanical is the first chain of defense. Although this plant is an annual, it has a fibrous root system. Thus it is fairly easy to dig up with a shovel. Using a pre-emergent herbicide will be the best choice to keep the plant from germinating. Garlon, Vaslan or similar herbicides would be best along waterways. I can only encourage one 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.