Ability to Respond Total:14 / 25Ability to Respond = ( Ease of Response + Tools in Place )
Confidence:High
Confidence Notes:Performed species mapping and removal on Catalina Island in 2016.
Impact
Spread
Notes
Score
Spread Rate
Each plant generates 2,325 to 13,200 seeds/year dispersed by animals, wool, and water, leading to rapid spread. It forms dense populations that can expand within a year and potentially reproduce within a year. It's a prolific seed producer with high germination rates and long seed bank viability. The seeds easily travel in international trade.
5
Spread Amount
This herb grows on coastal dunes, prairie, grassland, and agricultural land. It forms dense clusters, as it's unpalatable to livestock and native herbivores. USDA reports that 24% of the US area is climatically suitable for it, including most of California according to the suitability map.
4
Damage
Notes
Score
Ecological
Onionweed can lower soil nitrogen, making makes it difficult for other plants to grow and compete. It also impact native birds or insects that rely on native grasses for food or habitat. Can form dense populations, out-competing native or desirable species.
3
Agricultural
This taxon grows on pasture and alters soil nitrogen, outcompeting desirable forage. Livestock avoid it. In other countries, it can reduce rangeland carrying capacity by up to 75% (Grice, 2002; Parsons and Cuthbertson, 2001).
3
Infrastructure
0
Cultural
0
Health
0
Benefit
Notes
Score
Ecological
Flowers are insect pollinated, so may be a source of nectar for native pollinators, There is no literature on this topic, however.
0
Agricultural
0
Infrastructure
0
Cultural
May have aesthetic value to some.
1
Health
0
Total
14
Ability to Respond
Ease of Response
Notes
Score
Detection
Onionweed is easy to identify. Although it may look similar to cultivated onion or garlic, it lacks the smell. It spreads through known methods.
5
Control
Grazing is ineffective. Mechanical removal may work for individuals but not for large populations and may cause seed germination. Chlorsulfuron is the most effective chemical treatment, followed by glyphosate, while other herbicides are less effective.
4
Tools in Place
Notes
Score
Entry
Listed on CCR 4500 Noxious Weed list and a federally listed noxious weed.
2
Control
Some jurisdictions in CA are trying to control Asphodelus fistulosus, including the Catalina Island Conservancy.
1
Outreach
Information on identification and treatment are available online. See references below.
