The Elmleaf Blackberry, Rubus ulmifolius, is an aggressive, non-native species introduced from Europe, North Africa, and Western Asia. This plant quickly establishes itself, forming dense, impenetrable thickets. Effective management requires specific knowledge of its physical characteristics and a commitment to long-term, multi-pronged eradication strategies.
Distinctive Features of Elmleaf Blackberry
The stems, or canes, are typically arching and can be armed with stout, broad-based prickles that curve backward, though some cultivated forms are thornless. The biennial canes often develop a white, waxy coating, known as a pruinose bloom, as they age.
The leaves are palmately compound, usually with three or five leaflets. The upper side is dark green, while the underside is covered in dense, woolly hairs, giving it a distinctive white or gray felt-like appearance. This semi-evergreen habit allows the plant to photosynthesize longer than many deciduous native plants. The flowers, which appear later than many other Rubus species, are generally pink, sometimes white, and are clustered in dense, conical plumes at the cane tips.
Understanding Its Invasive Nature
The Elmleaf Blackberry spreads aggressively both by seed and through vegetative means. The arching canes readily engage in tip-layering, rooting when the tip touches the soil and forming a new, independent plant. The extensive root system also facilitates spread through root suckering, especially when the main root crown is disturbed. This vigorous growth allows the plant to form massive, thorny thickets that completely exclude native flora, reducing biodiversity and displacing native vegetation. The dense, tangled mass of dead and living canes can also accumulate, creating a fire hazard in drier regions.
Long-Term Management and Eradication Strategies
Eradicating Rubus ulmifolius requires a comprehensive, multi-year plan because the plant easily regenerates from its crown and root fragments. A successful strategy integrates mechanical removal, cultural methods, and precise chemical treatments.
Mechanical Control
For small, young infestations, hand-pulling or grubbing is effective, provided the entire root crown is removed. This is easiest when the soil is moist, such as in the late fall or early spring. Pulling in dry soil can break the stems, leaving roots that will immediately resprout.
For larger patches, mowing or cutting the canes down to the ground is a necessary first step, but it is not a solution alone. Cutting encourages vigorous regrowth and must be followed up with herbicide application or repeated cultivation. Complete mechanical removal of large, mature plants often requires heavy equipment to dig out the root crown and surface soil. While this is highly effective, the soil disturbance can create an ideal seedbed for new blackberry seedlings, making follow-up monitoring necessary.
Cultural Management
Cultural controls focus on weakening the plant and encouraging competition from desirable vegetation. In large, rural areas, controlled grazing by livestock, particularly goats, can be an effective method. Goats will browse the foliage, repeatedly starving the root system by removing the plant’s food supply.
For smaller, cleared areas, soil solarization can be used as a non-chemical control method. This involves covering the moist, cleared ground with clear plastic sheeting during the hottest months to heat the soil. The resulting high temperatures can kill the remaining root crowns and reduce the viability of seeds stored in the soil. Replanting the area with competitive native grasses or perennial plants after control is achieved is necessary to shade out and crowd any potential regrowth.
Chemical Control Options
Herbicides are often incorporated into the strategy to ensure root kill, especially after mechanical cutting has removed the thorny canes. The most effective chemical control relies on proper timing, typically in the late summer or early fall, before the first hard frost. During this period, the plant is actively translocating nutrients down to its root system to store energy for winter, allowing the herbicide to be carried directly to the roots for maximum effect.
Glyphosate and triclopyr are the two most commonly recommended active ingredients for Elmleaf Blackberry control. Glyphosate is generally applied as a foliar spray to the leaves of actively growing canes. Triclopyr, which is often more consistently effective on woody species, can be used for foliar or cut-stump applications. The cut-stump method is highly selective and involves cutting the cane close to the ground, then immediately applying a concentrated herbicide solution to the cut surface. For water-soluble herbicides like glyphosate, application must be done within a few minutes to the cambium layer to ensure translocation to the roots.
Follow-Up and Monitoring
Regardless of the method chosen, the long-term success of Elmleaf Blackberry eradication depends on persistent monitoring and follow-up treatment. Blackberry plants can regenerate from root fragments and the dormant seed bank can produce new seedlings for years after the initial treatment. Sites should be inspected annually, and any re-sprouts or new seedlings must be treated immediately to prevent the infestation from regaining its strength. Eradication is often a multi-year commitment, but consistent attention will eventually lead to successful control.