Understanding weed groups . Weeds that infest Christmas tree plantations have one of four life cycles. Become familiar with the life cycle to know at what time of year the most susceptible growth stage is occurring. Summer annuals emerge in the spring, generally flower in the summer, and set seed before the first frost in the fall. Winter annuals germinate at the end of summer and overwinter as small, dormant seedlings.
Biennials are similar to winter annuals, but they genninate earlier in the summer.
As days lengthen and temperatures rise in the spring, both winter annuals and biennials are stimulated to flower, set seed, and die before the end of the summer. Perennials , as the name suggests, survive more than two growing seasons, and generally reproduce by seed or vegetative means. This is useful in determining herbicide selectivity. Sometimes, identifying a weed to one of these broad groups is sufficient. Other times, it is important to positively identify the plant to the actual species.