Scotch broom (Cystisus scoparius) is an upright perennial shrub in the pea family (Fabaceae) growing 3-12 feet in height. It is originally a native to the British Isles and central and southern Europe. Since it’s introduction into the United States it has become a highly aggressive invasive species.
This weed is commonly found in open forests, roadsides, grasslands, pastures, cultivated fields, dry scrubland, wasteland, dry meadows, dry riverbeds and other waterways. It can tolerate a wide range of soil conditions but thrives best in full sun on dry, sandy soils (pH 4.5-7.5).
Scotch broom is a significant invader of rangelands and forests in the Pacific Northwest but also poses issues in some eastern states.
It displays rapid growth with the ability to grow 3 feet in the first year. It forms dense impenetrable stands that degrade rangeland, prevent forest regeneration, and create fire hazards. It invades rapidly following logging, land clearing, and burning. It can form pure dense stands for miles along highways and roads, crowding out native species and destroying wildlife habitat.
Mild poisoning can occur from Scotch broom. Large quantities are required to cause symptoms in animals such as horses. Alkaloids have been identified as the toxin. Cytisin, sparteine, and isosparteine are found in the twigs, leaves, and seeds in small amounts.
Control and Management:
• Manual – Hand pull, hand hoe or dig out small plants; brush cutters, power saws, axes, machetes, loppers, clippers, and mowers can be used to cut shrubs; where appropriate, burning is effective to deplete the seedbank but must be repeated in two to four years.
• Chemical – It can be effectively controlled using any of several readily available general use herbicides such as glyphosate, 2,4-Dor triclophyr when used just after plants have flowered. Follow label and state requirements.
• Biological Competition – Sow native plant species that have the potential to out-compete this shrub.
• Biocontrol – Three biocontrol agents are currently used: the Scotch broom seed weevil (Apion fuscirostre), twig miner (Leucoptera spartifoliella), and the Gorse or broom tip moth (Agonopterix nervosa).