Jointed Goatgrass

Jointed Goatgrass is native to southeastern Europe and western to central Asia, with its natural range spanning the Mediterranean basin through the Caucasus region into parts of Iran and Central Asia.

• Native range includes countries such as Greece, Turkey, Iran, and regions of the former Soviet Union in Central Asia
• Introduced to North America in the late 19th century, likely as a contaminant in wheat seed imports
• Now widely naturalized across the Great Plains and western United States and Canada
• Major infestations documented in Kansas, Nebraska, Oklahoma, Colorado, Montana, and parts of the Pacific Northwest
• Also reported as an introduced weed in parts of Australia and South America

As a member of the genus Aegilops, Jointed Goatgrass shares deep evolutionary ties with cultivated wheat:

• The genus Aegilops is one of the ancestral gene donors to modern bread wheat
• Bread wheat (Triticum aestivum) is an allohexaploid (2n=42, AABBDD) whose D genome was contributed by Aegilops tauschii, a close relative of A. cylindrica
• This close genetic relationship means that Aegilops species can hybridize with wheat under natural conditions, making them subjects of both agricultural concern and scientific interest for wheat breeding programs

Jointed Goatgrass is a winter annual grass that closely mimics the growth habit of winter wheat, an adaptation that has made it a particularly insidious weed.

General Habit:
• Annual, tufted grass growing 30–70 cm tall
• Erect to slightly decumbent stems (culms)
• Life cycle closely synchronized with that of winter wheat — germinates in autumn, overwinters as a rosette, resumes growth in spring, and sets seed in late spring to early summer

Leaves:
• Leaf blades flat, 3–8 mm wide, up to 15 cm long, with fine, short hairs on upper surfaces
• Ligule membranous, short (~1 mm), truncate
• Auricles present, small and clasping, sometimes nearly absent
• Leaf sheaths slightly hairy, especially on lower portions

Inflorescence:
• Spike-like, cylindrical, and distinctly jointed (hence the common name), 5–10 cm long
• Spikelets are sessile, arranged alternately along the rachis (central axis of the spike), each fitting into a cavity formed by the adjacent rachis segment
• Each spikelet typically contains 2–3 fertile florets
• Glumes (outer bracts) are rigid, with 3 prominent veins and awns of varying length

Seed (Caryopsis) and Spikelet Disarticulation:
• The defining morphological feature: the spike disarticulates (breaks apart) at maturity into individual segments ("joints"), each containing one or more spikelets
• These joints are cylindrical, ~5–8 mm long, and closely resemble small grains of wheat
• Seeds are ~8–10 mm long, reddish-brown caryopses
• A single robust plant can produce 100–300+ seeds
• Seeds can remain viable in the soil seed bank for 3–5 years or longer

Roots:
• Fibrous root system, typical of grasses
• Roots extend to moderate depths, allowing the plant to access soil moisture during dry periods

Jointed Goatgrass thrives in the same agroecological conditions as winter wheat, which is central to its success as a weed.

Habitat:
• Primarily a weed of winter wheat fields, fallow fields, roadsides, and disturbed grasslands
• Prefers loam to clay-loam soils
• Found at elevations from lowland plains to moderate elevations in the western United States

Climate & Seasonality:
• Winter annual: seeds germinate in autumn (September–November in the Northern Hemisphere)
• Plants overwinter in a vegetative rosette stage, tolerating freezing temperatures
• Rapid vegetative growth resumes in early spring (March–April)
• Flowering occurs in May–June; seeds mature and disperse in late June–July

Competitive Impact:
• Yield losses in heavily infested winter wheat fields can reach 25–50%
• At densities of 100 plants per square meter, wheat yield reductions of 20–30% have been documented
• Also serves as a host for several wheat pathogens, including:
- Wheat streak mosaic virus (WSMV)
- Eyespot (Pseudocercosporella herpotrichoides)
- Take-all disease (Gaeumannomyces graminis)

Seed Dispersal & Persistence:
• Primary dispersal: mechanical — joints contaminate wheat grain during harvest
• Secondary dispersal: wind, water, animal movement, and human activity (farm equipment)
• Seeds exhibit some dormancy, allowing staggered germination over multiple years
• Soil seed bank persistence of 3–5+ years makes eradication extremely difficult

Jointed Goatgrass is not intentionally planted; it is regarded as a noxious weed in many jurisdictions. However, understanding its biology is essential for effective management.

Management & Control:

Cultural Practices:
• Crop rotation with spring-planted crops (e.g., corn, sorghum, sunflower) disrupts its winter annual life cycle
• Delayed autumn planting of wheat allows pre-plant tillage or herbicide application to eliminate emerged seedlings
• Certified, weed-free wheat seed should be used to prevent introduction
• Thorough cleaning of combine harvesters between fields prevents mechanical seed spread

Chemical Control:
• Its close genetic relationship to wheat makes selective herbicide control extremely challenging
• In the United States, the introduction of imidazolinone-resistant (IR) wheat varieties (e.g., Clearfield® wheat) enabled the use of imazamox herbicide for selective control
• Glyphosate can be used in fallow periods or pre-plant burndown
• Always follow local herbicide label recommendations and resistance management guidelines

Mechanical Control:
• Shallow tillage in autumn can destroy seedlings before wheat planting
• Hand-roding (removing seed heads before maturity) is practical only for small infestations

Prevention:
• Inspect fields regularly in autumn and early spring
• Clean equipment thoroughly when moving between fields
• Monitor field margins, roadsides, and fence lines where infestations often begin