FACULTY OF AGRICULTURE

Master Student

Department of Plant Protection

Definition of a Weed

The definition of weeds is predicated on human perception , desire and needs.

 A weed is a plant which interferes with human activity or welfare.

It is also defined as plant growing in a place where it is not desired at a particular point in time.

BIOLOGICAL WEED MANAGEMENT

Biological weed management refers to the use of living organisms such as insects, nematodes, bacteria, or fungi, to reduce weed populations.

It involves the control or suppression of weeds through the action of one or more organisms by natural means, or by manipulation of the weeds, organism or environment.

Action of Living organism on weeds

1. Action on root of the weeds. Some biological control agents attach to roots

and thereby stunt plant growth. Some bacteria live on root surfaces and release

toxins that stunt root growth. Many fungi infect roots and disrupt the transport

system, which reduces leaf growth. Beneficial insects and nematodes feed directly onthe weed roots causing injury which allows bacteriaand fungi to penetrate.

Deleterious rhizo bacteria (DRB) live on the surface ofweed roots release chemicals that reduce weed growth.(Photo provided by Bob Kremer, University ofMissouri)

The Knapweed Root Weevil-Cyphocleonus achate. Lays eggs at the base of knapweed plant , egg hatches to larvae which mine the central root and damaging weed’s vascular and tissue cause root gall formation

Cont,,,2. Action on the leaves of the weedsInsects that feed on leaves reduce the leaf surface available for energy capture. Fungi and bacteria that infect leaves reduce the ability of the leaf to make sugars. In either case, there is less energy available for weed growth.

The leafy spurge flea beetle is one of a number of agents introduced to control this rangeland pest.

Advantages of Biological weed control

Living organisms used in biological weed control are specific feed on the target weed plant, leaving non- targeted undisturbed.

Compared to other control methods, biological method require little human effort that the agents can sustain themselves and spread on their own.

Animals and plants as well as people in an area where biological control is being used are unaffected by this method of control.

Disadvantages of Biological weed control

Biological control agents usually only affect their target organism, but there is a chance that they may feed on a beneficial organism.

Biological control programs is expensive and cost time for scientists in researching biological control agents, how they work and how they will affect the environment.

Not all weeds can be controlled by biological agents, or weeds may be so similar to the beneficial plant that is risk of introducing the control agent.

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