Agriculture Reference
In-Depth Information
8
Managing weeds with insects and
pathogens
Introduction
Weeds and other plant species are susceptible to attack by a diversity
of invertebrate herbivores and pathogens. Virtually every plant organ pro-
vides a niche for some type of insect, mite, nematode, fungus, bacterium, or
virus (Harper, 1977, p. 484). Protection of crop plants from these organisms is
a major issue in crop production. Conversely, the promotion of herbivory and
disease to suppress weed recruitment, growth, and reproduction is a major
objective of biological control programs.
Biological control of weeds requires that sufficiently high densities of her-
bivores and pathogens are present when weeds are at susceptible developmen-
tal stages. For this to happen, herbivores and pathogens used as biological
control agents must be well adapted to abiotic components of the environ-
ment, such as temperature and precipitation regimes (Crawley, 1986; Cullen,
1995).To control weeds effectively, they must also largely escape the effects of
predation, parasitism, disease, competition, and chemical interference
(Newman,Thompson & Richman, 1998).
Three approaches are used in efforts to regulate weed populations with
herbivores and pathogens (Andow, Ragsdale & Nyvall, 1997).
Conservation
methods involve modifying the environment to retain or increase populations
of resident control agents and intensify the damage they inflict on weeds.
Inoculation
methods involve introducing relatively small numbers of biologi-
cal control agents that will suppress a target weed species as their populations
establish, increase, and disperse.In many cases, organisms used as inoculative
control agents are not native to the regions into which they are released and
are collected from the original territory of their introduced host weed.
Inundation
methods involve introducing either native or exotic control agents
in large numbers to suppress the target weed quickly. Organisms used as
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