By Kim Wilson, UC Master Gardener
Invasive Plants
Non-native weeds or plants that can survive, reproduce, and spread without human intervention.
They cause economic or environmental harm.
Can be introduced into the environment accidentally but more often intentionally for their ornamental, food, forage or medicinal value.
Naturalized Plants
Non-native plants that can survive and reproduce without human intervention.
They are only considered invasive if they spread beyond where they were introduced, causing economic or environmental harm.
Agricultural or Garden Weeds
Native or non-native plants that require human disturbance (tillage, fertilization, irrigation) to become established and persist.
They may have economic or environmental harm via health problems for livestock, agricultural expense.
Introduction accidental via people, animals , equipment, or seed contamination.
Environmental and Economic Impact of Invasive Plants
The primary reasons to avoid planting invasive species are that they can survive and spread without human interference and cause economic and environmental harm.
Invasive plants outcompete and displace native plants.
Loss of native plants > loss of insects that feed on the native plants> loss of animals that feed on the insects and loss of nesting, roosting and food source.
Increase risk of wildfires and floods, change soil fertility, promote soil erosion and clog waterways.
Impact livestock forage, animal and human health, decrease land value and recreation.
Invasive plants can serve as preferred host for invasive insects. Tree of heaven is an invasive tree that is the preferred host to adult spotted lanternfly (SLF). SLF is a new invasive pest from China that is now in eastern United States and currently is not in California. It is a significant pest of a wide variety of fruit crops and woody ornamentals.
Invasive Plants and Plant Nurseries
The California Invasive Plant Council Inventory states that 37% of the invasive plants were accidentally introduced while 63% were intentionally introduced.
80% of the intentionally introduced invasives were obtained from plant nurseries. While the number of invasives sold has decreased some stores continue to sell invasive species.
Big box stores and internet stores that sell plants throughout a large geographic area may have inventory with plants invasive in our county. Remember plants from another state or county may behave invasively in SLO County.
Prevention
Consult resources to determine which plants are invasive in our county and avoid planting them.
Avoid inadvertently transporting invasive plant seeds, fruit or root pieces. Clean shoes, camping material, vehicle and bike tires. Brush dogs after hiking or camping. Buy hay and straw from local sources to prevent seed contamination.
Early Detection and Removal
Monitor property to detect any invasive plants and weeds. Early detection with prompt removal of small population of invasive plants is the most effective tactic.
Remove plants before flowering. If plants have flowers or seed heads, be careful not to disperse these parts which would result in further spread of the plants.
If flowers or seed heads are present, cut them off, bag and place in trash. Then remove the remainder of the plant and place in the green bin.
If you cannot remove plants at minimum keep plants in vegetative stage (prune to prevent flowering). This will prevent formation of seed heads and spread of the plants.
The County of San Luis Obispo Department of Agriculture Weed Management Program conducts surveillance throughout the county to identify new invasive plants and look for signs of spread. They control the invasive plants through physical removal, herbicides and biological control using beneficial insects.
Consult the weed management area page for San Luis Obispo County on CAL IPC listed in resources for new invasive weeds.
References and Resources
Don’t Plant a Pest! Central Coast. CAL IPC. Don’t Plant a Pest! – California Invasive Plant Council (cal-ipc.org)
Invasive Plants. Pests in Gardens and Landscapes. UC IPM. Invasive Plants--UC IPM (ucanr.edu)
Plant Right. PlantRight – Promoting noninvasive plants for California
San Luis Obispo Weed Management Area. CAL IPC. San Luis Obispo County WMA – California Invasive Plant Council (cal-ipc.org)