Managing weeds with insects and pathogens - Ecological Management of Agricultural Weeds - page 402

Finally,improved understanding is needed of the basic biology and ecology
of herbivore-weed and pathogen-weed interactions. To avoid potentially
irreversible damage to non-target organisms, more research needs to focus on
factors determining host specificity, host recognition, and colonization, infec-
tion, and dispersal processes. How do weed genotypes differ in their suscepti-
bility to different types of herbivory and disease? To identify particularly
useful genotypes of control agents and to deploy them most effectively
against target weeds that vary genetically, temporally, and spatially requires
research focused on the population genetics and evolution of both the agents
and their targets.
Suppression of a dominant weed species by biocontrol agents may increase
the production of desirable plant species, but it might also result in increased
growth of other weed species that had been only minor components of the
community (Figure 8.3). Sequences of invasions by new plant species are also
possible. Randall (1996) described the history of a county in Oregon in which
Hypericum perforatum was suppressed by biocontrol agents, only to be replaced
by Senecio jacobaea , which was in turn suppressed by biocontrol agents, but
replaced by Carduus pycnocephalus. To prevent the substitution of one weed
problem for another, more needs to be learned about how selective herbivores
and pathogens and vegetation management practices affect the dynamics of
multispecies plant communities.
Research should also focus on interactions between weed biocontrol agents
and other organisms that can affect their performance through competition,
chemical interference, predation, parasitism, and disease.To improve the effi-
cacy of microbial weed biocontrol agents,we need to know how to predict and
manipulate their relationships with other microorganisms inhabiting plant
surfaces and soil. Tillage and crop residue management are particularly
important for regulating microbial interactions (Derksen, Blackshaw &
Boyetchko, 1996), and more interdisciplinary research is needed to determine
how microbial communities can be manipulated to better reduce weed seed
survival, seedling establishment, competitive ability, and reproduction.
Similarly, there is an important need to identify importation strategies and
habitat manipulations that minimize the effects of competitors, predators,
parasites, and pathogens on insect herbivores used as weed biocontrol agents.
Research addressing these and other issues presents excellent opportu-
nities for collaboration between plant, animal, and microbial ecologists, and
between basic and applied biologists. The results of such collaborations
should have real practical value in the development of the next generation of
weed biocontrol strategies.