Life Cycle of Plants
(Lesson 4. Weed Control in Pastures continued)
It is important to determine the life cycle of weeds to help determine when the plants will be most susceptible to control with chemicals. These life cycles include:
Annuals: Entire life cycle from seed germination to seed production occurs in one growing season and then the plant dies. Annuals can be controlled throughout the season but are usually most susceptible during seedling stage and seed head development. It is important to remember that the key to annual weed control is to eliminate seed production.
Biennials: Plants start from seeds, produce vegetative structures and food storage organs the first season. During the first winter a hardy evergreen rosette of basal leaves persists. During the second season, flowers, fruit and seeds develop to complete the life cycle. Then the plant dies. Herbicides should be applied as late as possible in the fall prior to a killing frost for best control of biennials. This allows for maximum seedling emergence and rosettes. Seedlings that emerge after spraying will remain vegetative until the following spring, and can be treated then. Long-term eradication of biennials is very difficult because of the large number of seeds each plant produces and the ease of seed transport by wind due to pappus (fuzzy material) attached to most biennial species seeds.
Perennials: Live for many years, and after reaching maturity produce flowers and seeds each year. Perennials are classified in many ways:
- Herbaceous: top dries back to the ground each winter and new stems grow from the root each spring.
- Woody: the top persists, as in shrubs or trees.
- Deciduous: will shed leaves during a portion of the year.
- Evergreen: leaves persist throughout the year.
Once you have the weeds identified and decide to use chemical control, you then need to select a herbicide to kill the weeds. Consider price, spot spraying vs. broadcast, and remember that many can and do kill desirable legumes. See Table 2. Chemical Weed Control in Grass Pastures.
Carefully read the label before purchasing. It is mandatory to follow the label instructions when using all pesticides including herbicides. The label is the law!