Kochia, scientifically known as Bassia scoparia, is a rapidly growing, summer annual plant in North America. Originating in Eurasia, it was introduced to the continent in the mid-to-late 1800s, often as an ornamental plant. It quickly escaped cultivation and established itself across most of the continent, particularly thriving in the semi-arid and arid environments of the Great Plains and the West due to its aggressive growth cycle and tolerance for harsh conditions.
Identification and Growth Characteristics
The Kochia plant is an erect, highly branched herb that can reach heights of up to six feet under favorable conditions. When mature, it often takes on a dense, bushy, pyramidal, or “Christmas tree” shape. The stems and branches are typically covered in soft hairs, and the plant’s color ranges from blue-green to gray-green, often developing a reddish or purplish tinge in the fall.
The leaves are simple, alternate, and narrowly linear or lance-shaped. Young plants have more ovate leaves that become narrow as they mature, and they are covered in fine hairs, particularly on the undersides. Kochia has a broad window of emergence, able to germinate at low temperatures as early as January and continue to emerge throughout the summer.
Kochia is resilient due to its tolerance for drought and high-salinity soils, allowing it to colonize areas where many other plants struggle. In the fall, once the plant is dry and has set seed, the entire structure detaches from the root near the soil surface. This process transforms the plant into a wind-driven tumbleweed, efficiently scattering seeds across long distances as it rolls.
Environmental and Agricultural Impact
Kochia’s aggressive growth and high seed production make it a significant threat in agricultural landscapes. The plant is a fierce competitor with cultivated crops, rapidly consuming available soil moisture and nutrients. This competition leads to substantial reductions in crop yield, especially when it establishes early in the season.
Kochia poses a health risk to livestock, particularly cattle and sheep, when consumed in large quantities. The plant can accumulate high levels of compounds, including nitrates and oxalates, which become especially concentrated under drought stress or when the plant is mature. Nitrate toxicity can occur rapidly, while oxalates can bind with calcium in the bloodstream, leading to kidney failure.
The plant also affects human health by contributing to late-season allergies. Kochia produces copious amounts of pollen that is shed near the end of summer and through the beginning of fall, with peak season typically occurring in August and September. This pollen is a common cause of hay fever symptoms, including congestion, sneezing, and itchy eyes. The weed’s sheer abundance ensures that its pollen is widespread during this period.
Control and Management Strategies
Controlling Kochia presents a considerable challenge due to its ability to germinate early and its widespread development of herbicide resistance. Preventing the plant from setting seed is a primary goal, as Kochia seeds are generally short-lived in the soil, often viable for only two or three years. Non-chemical methods are most effective when the plants are small; hand-pulling or hoeing is practical for small infestations.
Mowing can be used to prevent seed production, but it must be done before mid-August when the seeds typically become viable. Mowing may not fully eliminate the problem because the plant can regrow and set seed closer to the ground. Cultural practices, such as strong crop rotation and increasing crop seeding density, help cultivated crops outcompete the weed for resources.
Chemical control is complicated by the fact that many Kochia populations have developed resistance to multiple groups of herbicides. Widespread resistance to Group 2 (ALS inhibitors) is common, and resistance to glyphosate (Group 9) has also spread rapidly across agricultural regions. Effective chemical management requires a strategy of rotating and combining herbicides with multiple effective modes of action for pre-seed and post-emergent applications. This integrated approach is necessary to manage Kochia populations.