Life History
Learn the growth pattern of the target invasive species, because it will determine the main options for the timing of control and removal. No matter what the growth cycle of a plant is, the key is preventing the plant from reproducing by seed or by vegetative cloning.
Annual
Annual plants live fast and die young. They complete their life cycles in one year, from germination from seed, through flowering and seed set. After the seeds mature, the plants die. Everything from seedling to seed production happens only once. The trick to managing these plants is removing them before they produce and distribute seed. Subsequent treatments are used to deplete the seedbank. Knowing what the seedlings of annuals look like is helpful for surveys and follow-up treatments.
The plants you see in the spring will certainly be gone by the fall; however, they will produce seed before they go. By applying herbicide during the growing season, annuals can be killed before they go to seed, reducing the odds of their survival in the next season. An alternative to using herbicide is to mow the plants when they are beginning to flower. Small infestations can be hand-pulled, but the resulting soil disturbance could promote germination of weed seeds.
Japanese stiltgrass is an annual weed that will flower in late summer, set seed in the late summer, then die off by autumn.
Biennial (& Associates)
Biennial plants complete their life cycle in 2 years. During the first growing season, the plant germinates from seed and persists through the growing season and winter, commonly as a rosette of basal leaves. In the second growing season, the plant sends up a flowering stalk, sets seed, and dies. Some plants may persist for more than one growing season before flowering.
Being able to identify the plant at all life stages is key. Initiating control during the first year stage can prevent the second growth stage from appearing, or drastically weaken the occurrence of the second stage by reducing the number of seed-producing plants. If the first year plants are not detected and removed, there is still a chance for effective control if the plants are removed just before flowering.
Some species live for two or more years before producing fruit, but after fruiting, the individual plants die. These are called “monocarpic perennials.” Teasels and giant hogweed fall into this category.
Perennial
Perennials have life cycles of two years or longer. They do not die after producing fruit. If not controlled, these plants will grow all season, set seed, then continue to grow into the next season. Some herbaceous perennials will die back to the ground then sprout again in the spring.
Reproduction can be by seed, or by cloning of plant tissue. Many important invasive perennials have multiple means of reproduction. Partial control may be achieved by mechanical means of preventing flowering; full control requires killing the root systems.
Further Reading
Photo Credits
- James H. Miller & Ted Bodner, Southern Weed Science Society, Bugwood.org
- Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
- Steve Hurst, USDA NRCS PLANTS Database, Bugwood.org
- Chris Evans, Illinois Wildlife Action Plan, Bugwood.org
- Cleveland Metroparks
- Cleveland Metroparks
- Cleveland Metroparks
- Cleveland Metroparks
- Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
- Cleveland Metroparks
