General classification of weeds
Most farmers use a different method of classifying weeds since it is easier to understand and separate each weed from another in order to control them.
Classification according to growth season length
- Annuals: These weeds complete their life-cycle in one year. Due to the abundance of dormant seed and fast growth of annuals, they are very persistent and cost more to control than most other weeds. The most common type of weeds are annuals. There are two types of annuals (1) summer annuals and (2) winter annuals.
- Summer annuals: Most of these weeds germinate in spring, mature during summer and die in the fall. Summer weeds include cockleburs, morning glories, pigweeds, crab grasses etc.
- Winter annuals: These weeds germinate in the fall and winter and mature in the spring or early summer before the plants die. Common winter annuals are chickweed, cornflower, corn cockle, hairy chess etc.
- Biennials: These weeds have a vegetative growth cycle in the first year and a reproductive growth cycle in the second year. Common biennials are wild carrot, bull thistle and burdock.
- Perennial: Depending on the climatic conditions they will grow either vegetatively or reproductively. They may grow for longer than two years. Perennials are grouped into simple perennials and creeping perennials. Simple perennials reproduce through seed. Creeping perennials reproduce by creeping root systems and may reproduce through seed. Once a field is infested with a creeping perennial, it is the most difficult to eradicate. It usually takes at least 2 years to rid a field of creeping perennials.
Classification according to habitat
- Pioneer weeds: They are only found on soils which have been disturbed and where other plants will not grow due to the harsh environmental conditions.
- Facultative or optional weeds: These are weeds that are found in nature and between commercial crops where the soil is disturbed.
Classification according to leaf morphology
- Small leaf weeds: These are all grasses
- Broad leaf weeds: These are plants which have broad leaves in comparison with grasses
Classification according to season of appearance
- Winter weeds: These are weeds that germinate after the first winter rains have fallen. These are more applicable in the winter rainfall areas
- Summer weeds: These are weeds that germinate in spring or when the climate and moisture content of the soil permits germination.
Classification according to method of reproduction
- Simple weeds: These weeds can only reproduce through seed
- Creeping weeds: These weeds reproduce not only through seed but also vegetatively, through rhizomes and creeping root parts.
Scientific classification of weeds
The scientific classification of weeds is important when involved with research. Weeds are referred to in literature by their scientific names which follow the binomial system which is internationally accepted. Using a weeds common name can lead to misunderstanding in the scientific community since there are some weeds which have at least 30 different common names but only one scientific name.