Weeds usually can be divided into two groups: broadleaved weeds and grassy weeds. These names are descriptive of their appearance. This grouping is not specific enough, however, if you anticipate selecting chemical herbicides for weed control. A number of reliable sources of information can assist you in properly identifying weed species. Many of the larger book stores and garden supply dealers have a garden book section containing publications on weed identification.
In addition to knowing what weed(s) you are attempting to control, you should also try to learn something about the specific weed(s) involved. By understanding the growth cycle of the weed, you will be able to plan a more effective control program against its most susceptible phase of growth. The type of control program used on annual plants, for example, will differ from that selected for biennial or perennial plants.
Annual plants are those that complete their entire life cycle in less than a full year. These plants grow from seed, develop into a mature plant, set flowers and seeds, and finally die after the seeds are shed. There are two types of annual plants: summer and winter annuals. Summer annuals germinate from seeds in the spring, live through the summer, and set seeds in the fall. Winter annuals germinate from seeds in the fall, live over the winter months, and set seeds the following spring. Annuals, therefore, maintain their populations through the production of seeds with each generation. Any program to control annual weeds should be designed to either eliminate the young seedlings or at least prevent the development of seeds.
Biennial plants require two growing seasons to complete their life cycle. These plants enter a nonflowering stage during the first season after germination of the seed. The root system on the young plant stores food and overwinters. During the second season, a new plant grows from the root and develops flowers that set seed to reproduce the plant. These types of weeds are best controlled in the young growing stages of the first-year plant.
Perennial plants are able to live for two years or more. Each year they are able to flower and set seed. In addition to producing seeds, some perennial plants reproduce and persist by vegetative structures such as bulbs, tubers, budding roots, rhizomes, and stolons. These multiple reproductive mechanisms make perennial plants especially difficult to control. In addition to destroying the top growth, which will prevent seed development, you must also eliminate the underground vegetative portions to assure any degree of success in reducing their population.