Biology of Weeds - Life Cycle, Types, Dispersal

Weeds can be defined as any unwanted plants growing in a particular population or plants growing out of place. Proper identification and some understanding of how and why weeds are present are important when selecting the best control strategy. Knowing whether that the weeds were previously present in a particular area or not, also helps to prepare control measures in the future.

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I’m Tapsendra Patel and in this article we will focus on the biology of weeds : types of weeds, their life cycles, and how weeds are dispersed.

Healthy plants gives high quality output to the farmers. How serious a weeds problem can? Is actually depends on type of crop grown in that particular area, and individual need's values of farmer.

Crops plants and weeds have the same common basic requirements :-
• Soil nutrients 
• Water
• Space 
• Light.
These factors are limited in nature, so desirable plants and weeds are in competition for them.

The 3 main types of weeds are :- 

 • Grassy 
 • Broadleaf
• Sedge and rushes.

Grassy

• Grassy weeds have blades that are much longer as compared to there wide.
• The blades have parallel veins. The stems are hollow and round with nodes and internodes.
• The nodes are close and hard.
• The leaf blades emerges in alternate pattern on each side of the stem.
• Examples include crabgrass, annual blue grass, and torpedo grass.

Broadleaf

• Broadleaf weeds usually have net-like veins in their leaves.
• These veins are connected to a main vein.
• This vein usually divides the leaf in two half. We can easily distinguish these weeds from grassy weeds as their veins and leaf shapes are different.
• Stems of broadleaf weeds are round and solid.
• Examples include woodsorrel.

Sedges and Rushes

• Sedges have triangular-shaped, solid stems, while rush stems are round and solid.
• Both sedges and rushes favor a moist habitat.
• Important members include yellow and purple nut sedge.

Life Cycles 

Knowing the life cycles of different weeds is important because it will help us to manage weeds in our field.
For example, effective control methods for perennial and annual weeds are different from each other. Also for warm-season annuals that grow in the summer, these didn’t required the application of herbicides in late days of the season, as these weeds will die with the emergence of cold weather. Also we do not need to apply control measures to cool-season annual weeds in the winter because similarly they will also die with the arrival of warm weather.

Weeds can have one of 3 different life cycles :-

• Annual
• Biennial 
• Perennial. 

Annual

• Annual weeds germinate from seed.
• These weeds grow ➡️ flower ➡️ produce seeds and ➡️  die in a year or less. 
• Grasses, sedges and broadleaf weeds can all be annuals. These weeds are grouped by the season in which they germinate and grow.
• Warm-season, or summer, annuals germinate and emerge in the spring. They actively grow in the summer and fall early and they die in the late fall or early winter.
Examples includes spotted spurge, crabgrass.
• Cool-season, or winter, annuals germinate and emerge in the fall. They actively grow during the winter and early spring and die in the late spring or early summer. Examples include common chickweed, annual bluegrass, and henbit.

Biennial

• Biennial weeds have a 2-year life cycle. They germinate from seed in the summer or fall.
• During the first year these weeds develop large root systems and a compact cluster of leaves close to the ground, known as a rosette.
• In the 2nd year biennials undergoes flower and then produce seed and die.
• Examples include cudweed, old field toadflax, and Carolina false dandelion.

Perennial

• Weeds that live more than 2 years are perennials.
• Many reproduce from rhizomes, other underground plant parts. All of these are considered as vegetative reproductive structures of weeds because they do not involve seed production process.
• Many perennials also produce seed and can reproduce from these seeds.
• In the winter season some perennials are dormant. They lose their above ground leaves or stems.
• In the spring, dormant perennials initiate growth from reserves food material (carbohydrate) stored in their roots.
• Perennial weeds are the most difficult to control. This is because they reproduce by both seed and underground vegetative structures.
• The underground structures are difficult to control because they are much more resilient than seedlings.
• Examples include torpedo grass, purple, and vines such as the greenbrier.

Perennial weeds may also be grouped by type of root system and how they reproduce :- 

• One is Simple perennials reproduce by seeds. Root fragments also may spread by mechanical means such as plowing and produce new plants.
Examples include yellow nutsedge, wild onions,and wild garlic.
• Another one is Creeping perennials produce both seeds and rhizomes. The rhizomes store carbohydrate reserves and can initiate new shoot and root growth at nodes along a stem.
Examples include common Bermuda grass, torpedo grass.


We must properly identify weeds so that we can choose the most effective control measures that to be executed in the fields.

We can get help in identifying weeds by one of our most popular mobile application i.e WEED MANAGER app which is developed by ICAR-Directorate of Weed Research, Jabalpur (M.P) which is available in Google play store and can be downloaded in any android Mobile OS.

Soils contain tons of plant seeds that are ready to grow when given the proper conditions becomes available to them. Many of these are lie dormant but as soon as there is void and empty space present in soil and seeds may germinate.

How does the field and soil get weeds ? 

Possible reasons may be :- 

• We may have brought in with some soil or mulch that was contaminated with seeds of weeds.
• Weeds can be brought in from plants that are purchased may be contaminate.
• People and animals can also bring them in.
• The weeds can come in from the neighbors, visitors, labours too.
Dispersal capacity of there seeds are also very high, so they can cover long distance through wind, water, and insects.

In this article hopefully we learned more about the types of weeds, their life cycles, and how weeds are dispersed. 

  - TAPSENDRA PATEL