Alhagi, commonly known as camelthorn, is a perennial shrub that has become a significant concern in various regions globally. Native to Eurasia, including parts of the Mediterranean, Middle East, and Central Asia, it has spread to many other areas, including the western United States, Australia, and southern Africa. Its presence poses challenges to both agricultural and natural landscapes.
Identifying Alhagi
Alhagi maurorum typically grows as an herbaceous perennial or shrub, reaching a height of up to 4 feet (1.2 meters) above ground. Its stems are intricately branched and grey-green, featuring numerous sharp, yellow-tipped spines that can be 1 to 2 inches (2.5 to 5 cm) long. The deciduous leaves are small, oval to lance-shaped, measuring up to 1/2 inch (1 cm) long, and are alternately arranged along the thorny branches.
Small, pea-like flowers, ranging from bright pink to maroon, emerge from the leaf nodes or spine tips, typically blooming from May to August. Following flowering, the plant produces reddish-brown, segmented seed pods, about 1 inch (2.5 cm) long, which are constricted between the seeds, giving them a bead-like appearance.
Understanding Alhagi’s Invasive Nature
A distinctive characteristic of Alhagi is its extensive root system, which can extend over 6 feet (1.8 meters) deep and spread laterally for more than 26 feet (8 meters), allowing new shoots to emerge far from the parent plant. A single plant can develop a main root that penetrates more than 49 feet (15 meters) into the ground, enabling it to access deep water sources and thrive in arid conditions where other plants cannot. This extensive root network, which includes both vertical taproots and spreading rhizomes, allows it to rapidly colonize large areas.
The plant’s aggressive growth pattern and ability to spread through both its root system and seeds lead to significant ecological and agricultural impacts. It out-competes native vegetation and cultivated crops for essential water and nutrients, leading to reduced biodiversity and diminished crop yields. The dense, spiny thickets formed by Alhagi can also impede animal mobility and interfere with agricultural practices and infrastructure.
Strategies for Alhagi Control
Controlling Alhagi requires persistent effort due to its robust root system and ability to resprout. Mechanical methods, such as repeated cutting or tillage, can be attempted, but these are often ineffective unless all root fragments are removed, as the plant readily resprouts from residual root pieces. Deep plowing before fruit ripening and early harvest in agricultural fields can help suppress its spread. Hand weeding can be effective for very small, isolated infestations, provided the entire root system is removed.
Chemical control often provides more effective management for established populations. Herbicides such as picloram, glyphosate, 2,4-D, dicamba, imazapyr, and metsulfuron have shown varying degrees of success. Picloram is considered one of the more effective options, offering long soil residual activity that can also control germinating seeds, though it is a restricted-use herbicide. Glyphosate is also used, particularly on actively growing plants in spring or fall, and may require repeated applications.
A tank mix of 2,4-D and dicamba has been reported to achieve high control rates. Imazapyr and metsulfuron are also options, with specific application considerations regarding timing and potential impact on desirable vegetation. Multiple herbicide applications over several years are necessary to exhaust the plant’s energy reserves and achieve lasting control.
Prevention and Ongoing Management
Preventing Alhagi establishment is the most effective approach to avoid future infestations, as eradication of established populations is challenging. Regular monitoring and early detection of new plants are important steps to address any emerging growth promptly. Inspecting areas, especially those near water sources or disturbed ground, helps identify new plants before they can establish an extensive root system.
Using certified, weed-free seeds for planting in agricultural areas helps prevent accidental introduction of Alhagi seeds. Maintaining healthy, competitive plant communities can also deter Alhagi by limiting available resources and space for it to establish. Sustained efforts and vigilance are important for long-term control and to prevent re-establishment of this invasive plant.