White Sweet Clover
Melilotus alba
Identification
The distinguishing features of White sweetclover are the tiny white flowers and its light green, erect, branched stem that can grow up to 8 feet tall. The flowers are also fragrant and bloom in early and late summer of its second year and then die.
The seeds contained within the dark grey or black pods are easily spread through water, enabling their colonization of glacial river floodplains and riparian areas. You can also find White sweetclover thriving in disturbed areas such as roadsides, gravel fields, and lands affected by wildfires. Chances are high that you have seen White sweetclover driving down the Parks and Elliott Highways. It is especially prevalent along the Dalton Highway, where grading and mowing equipment have spread the seeds along the roadsides.
Invasiveness
Its agricultural value as a nitrogen-fixing cover crop and as a forage plant for livestock is what led to the introduction of White sweetclover to Alaska. The plant’s abundant nectar is also coveted by honeybees and other pollinators. However, once White sweetclover pervades a natural area, its smothering, dense thickets become extremely difficult to remove, it overtops and shades native plants, and it can alter the soil conditions.
The cold-adapted White sweetclover also produces a massive amount of seeds that remain in the soil for decades. It spreads from cultivated areas to roadsides and riverbanks, and is particularly harmful to riparian communities in Alaska.
Eradication
White sweetclover can be managed by pulling and cutting, but several treatments will be needed each year to exhaust the seed bank. The decades-long viability of the seeds requires areas where control practices have taken place to be monitored for many years. Burning has proven to be an ineffective tactic in Alaska. Biological methods such as insects or grazers have not been identified due to White sweetclover’s use as a forage plant. Several herbicides have been identified as effective and timing their application is critical because the chemical used may only be effective at certain life stages of the plant.
Fairbanks Soil and Water Conservation District is actively engaged in early detection and removal efforts for White sweetclover at Creamer’s Field Wildlife Refuge. This includes conducting surveys to identify its spread, as well as holding educational events where the community is engaged in identifying and removing the invasive plant.