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As you can see in the
photos below, insects attack roots and create pathways for aggressive
plant pathogenic root zone fungi which enter and extensively invade
roots. Insects can also carry fungi externally or possibly
internally, which assures an impact of highly pathogenic strains on weed
density.
This same dynamic is seen
pervasively in the native range of leafy spurge (where the weed is rare)
and applies to knapweeds and possibly most perennial weed species which
are problems in rangelands.
Research Strategy:
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Correlate presence of
disease at high-impact release sites
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Identify and characterize
associated plant pathogens for pathogenicity, virulence & host range
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Show effects of
insect/pathogen synergisms in controlled experiments
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Study mode of association
of plant pathogens with insects
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Test pathogens for field
performance alone and in association with insects at release site
Research leading to and
developing the theme of insect/pathogen impact on range weeds:
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Caesar, A. J., Rees, N.E., Spencer, N.R.,
and Quimby, P.C. 1993. Characterization of Rhizoctonia spp. causing
disease of leafy spurge in the Northern Plains Disease 77:681-684.
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Caesar, A.J. 1994. Comparative virulence
and host range of strains of Rhizoctonia solani AG-4 from leafy spurge.
Plant Disease 78:183-186.
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Caesar, A.J. 1994. Pathogenicity and host
range of Agrobacterium tumefaciens from Acroptilon repens and Euphorbia
esula. Plant Desease 78:796-800.
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Caesar, A.J. Potential of Plant Pathogens
for the Biological Control of Leafy Spurge. Pages 66-74 in R. A.
Andrascik, ed. Proceedings of a Symposium on strategies for the control
of leafy spurge in Theodore Roosevelt National Park. National Park
Service, Medora, ND. 1995.
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Caesar, A.J. 1996. Identification,
pathogencitiy and comparative virulence of Fusarium spp. associated with
stand declines.
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