When the pretty flowers take over
Ditches, many hay fields and untended fields are bright with oxeye daisies and bright orange and yellow hawkweed flowers.
Indeed, it is a pretty sight but there is more to it. Both of these are extremely invasive and they will soon be joined by lovely lavender spotted knapweed. All of these European imports displace native plants needed by our native species. Orange Hawkweed, introduced in 1828 as an herbal remedy ad ornamental, has spread across the country in areas of gritty, well-drained and infertile soils, but can also invade moist meadows, hay fields, pastures, tree plantations, forested areas and urban areas.
This plant spreads in many ways, and a single plant can form a 2- to 3-foot area in a single year. A seed that finds a hospitable spot can germinate immediately. A March seedling can produce flowers by mid-June and viable seeds by August. Those seeds can remain viable for up to seven years. There is also some evidence that the plant is phytotoxic, meaning that it produces chemicals that inhibit seed germination and plant regeneration by other species. Orange hawkweed and a non-native yellow-flowered hawkweed we are also seeing spreads by barbed seeds (each tall stem can produce five to 35 flower heads that each produce up to 12 to 30 seeds). They spread by wind, water or as hitchhikers. It spreads vegetatively by rhizomes, runners and by adventitious rootbuds. The low rosette that first forms after germination can be easily missed in lawns or other areas and that is the time for control.
Why and how have these aggressive non-native invaders spread so rapidly in our county? There are several. Much of our soil presents ideal growing sites -- well-drained, gritty and of low fertility. Ditches are frequently disturbed by utility work for cable installation or for power line clean-up. This leaves open soil, a welcoming invitation. Four-wheelers disturb the soil and transport seed on those big fat tires. Last, gravel spread on township roads, on road edges, or for slippery roads may have come from infested gravel pits.
Increasing and maintaining fertility in lawns or susceptible areas before this plant gets a foothold helps other plants and grasses grow more thickly so seeds won't readily germinate. Early detection is critical for success in controlling and arresting the spread of this invasive. Control after spread is extremely complicated and fraught with challenges.
Digging the plant at the first year rosette stage is easy but dig deeply enough to remove below-ground root structures; it becomes complicated when there are many plants. This plant very rapidly forms solid mats that are difficult to remove mechanically.
If you mow to keep seed from forming, the plant compensates with aggressive vegetative growth. Chemical control must be done in early spring when plants are in the rosette stage. Non-chemical control is difficult, if not impossible, given the extent of some infestations.
There is no substitute for good land stewardship. Without weed inspectors trained to recognize invasives early and to help landowners address them, invasives will become worse. If we don't deal with this plant early and colonized areas continue to develop, what will we do when it invades our forests and dominates our wild areas? Orange and the meadow hawkweed complex are only two of the invasives that have gained purchase in our county.
Information for this article came from the U.S. Department of Agriculture and the Montana Extension Service. Refer to the revamped and updated University Of Minnesota Extension Service website -- www.extension.umn.edu/garden/yard-garden/ -- for more information on horticultural topics.
In addition, local Master Gardeners will again answer your questions on home horticulture. Call (218) 444-7916, leave your name, number, and question and you will receive a return call.