Biological weed control

Question 1

Definition of Biological Weed Control

Answer 1

Use of natural enemies to reduce a weed population with the aim of pushing it below the ecological and/or economic damage threshold

Question 2

What isn’t included in biological weed control?

Answer 2

indirect measures such as crop rotation, mixed crops

Other, non-chemical direct measures

microbial toxins

allelopathic effects

herbicide-resistant crops

Question 3

What are ecological mechanisms underlying biological control?

Answer 3

natural antagonists can limit plant populations

The majority of these antagonists have a restricted host circle

Question 4

Inoculative or ‘classical’ method

Answer 4

Release of non-resident control organisms

release a limited number of individuals on a small part of the target area

Target species have mostly immigrated, so the antagonists mostly come from the area of origin of the weeds

Main areas of application: Australia, North America, New Zealand, Hawaii, South Africa, tropical countries in Africa and Asia

Question 5

What are areas of applications of inoculative / classical method?

Answer 5

especially phytophagous insects

• no complete control of weeds possible
• Success comes relatively slowly
• Control organisms become part of the ecosystem
• Areas of application: extensive agro-ecosystems (e.g. pastures, forests, wetlands, ruderal sites, nature conservation and recreation areas, along traffic routes

Question 6

Procedure of classical method

Answer 6

Selection of target weed species and taxonomic, ecological and population biological investigations in the damaged area.

Search for potential control organisms in the region of origin of the target plant and investigations into their biology, efficacy and host specificity.

Import, release and settlement of selected control organisms and observation of control success.

Question 7

Inundative method or bioherbicides

Answer 7

Release of native organisms

large number of individuals over the entire area to be treated

almost exclusively use of fungi (mycoherbicides) possibly together with insects, but also bacteria or viruses

Question 8

Example of local antagonists

Answer 8

Rust fungus on field thistles

Question 9

System management approach

Answer 9

Shift the balance between host and pathogen population in favor of the pathogen, e.g. by strip cultivation, division of fields, …

no import of exotic control organisms or mass release

Question 10

Control with polyphagous herbivores

Answer 10

Pastures, e.g. in orchards or infrastructure

Use of fish against water weeds

lack of host specifity, therefore there is a risk that native herbivores will be displaced

Question 11

Microbial toxins
(not biological weed control)

Answer 11

Isolation of phytotoxins from non-phytotoxic organisms

Example: Bialaphos (Produced by Streptomyces viridochromogenes und S. hygroscopicus, first metabolite is phosphinothricin = gluphonate)

so far the only herbicide produced by fermentation

Question 12

Natural essences

Answer 12

Many natural substances have herbicidal effects

examples:
vinegar
salt
citronella oil (barrier H)
pine oil (produced during cellulose production from oine trees), approved in organic farming in NZ and AUS
pelargonic acid (Finalsan)

Natural essences might be the only herbicides registered for specific crops/indications
e.g. vegetable crops, oilseed rape
application eith hood sprayers in row crops