2.4 Weed Classification – Life Cycles

Now let’s look at some of the ways that weeds can be classified. One way is by their life cycle, how many growing seasons they are viable. Plants that are classified as annuals grow for just one season; the same plant will not come back the next year. Annuals tend to reproduce by seeds, putting all their energy into seed production. Annuals can be classified either as a summer annual or a winter annual.

• Summer annuals grow during the normal growing season of our crops, germinating in the spring and then producing seed and die off in the fall. An example of that is yellow foxtail.
• Winter annuals germinate in the fall and then go dormant during the winter. Then in the spring, at the start of the next crop production season, they will finish growing and produce seeds early on in the season. There are two different types of winter annuals: obligate winter annual or a facultative type. An obligate type will always germinate in the late summer/early fall, go dormant in the winter, and then early in the spring finish growing until it reproduces (ie Purple deadnettle). In contrast, facultative types can germinate in either the spring or late summer/early fall (ie shepherd’s-purse).

In the following video clip, Dr. Namuth-Covert describes an example of how farming practices can create a niche for new weeds to thrive, in this case, a winter annual in no-till field systems.