The life history of weeds

Weeds progress through a series of stages in the life cycle: germination, establishment, growth, reproduction, dispersal, and dormancy. Management tactics generally apply to a particular stage. Moreover, differences in the behavior of species in each stage lead to differences in susceptibility to control by a particular approach. Thus, life history is an organizing principle for the integration of weed management tactics.

Although agricultural weeds commonly share many ecological attributes, they are by no means a homogeneous group of species. In particular, four broad categories of life history can be distinguished (Table 2.2). Annual weeds grow from germination to reproduction within a single growing season. With few exceptions, their seeds persist in the soil for at least a few years and in many cases for decades.

Stationary perennials live from two to several growing seasons (biennials are included in this group). Because they generally do not rejuvenate via vegetative reproduction, they eventually die. As with the annuals, their seeds usually persist in the soil for at least a few years, and often much longer. Under favorable conditions some of these species may set seed the year of

Table 2.2. Four types of weed life-history strategies

Character

Annuals

Stationary perennials

Wandering perennials

Woody perennials

Vegetative life span

< 1 year

2 to a few years

Long, indefinite

Long

Vegetative propagation

No

Accidental

Yes

Some species

Usual seed persistence

Years to decades

Years to decades

A few years

Months to years

Energy allocated to seed production

High

Medium high

Medium low

Low

Seed size"

Mostly small

Mostly small

Mostly small

Mostly large

Usual mode of establishment

Seeds

Seeds

Vegetative propagules

Seeds

Main dispersal modes

With soil, manure

With soil, wind, feces, crop

With soil

Birds, wind

Position in succession

Year 1 (2 in gaps)

Year 1 to 5 (10)

After year 1

Middle

Taxonomy

Monocot and dicot

Mostly dicot

Monocot & dicot

Mostly dicot

Crop types

Annual

Forage, annual

All

Orchard, pasture, swidden, no-till

Examples

Chenopodium album

Rumexcrispus

Imperata cylindrica

Lantana camara

Growing Soilless

Growing Soilless

This is an easy-to-follow, step-by-step guide to growing organic, healthy vegetable, herbs and house plants without soil. Clearly illustrated with black and white line drawings, the book covers every aspect of home hydroponic gardening.

Get My Free Ebook


Post a comment