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United States Department of Agriculture

Agricultural Research Service

Title: Relationship among growth attributes of spotted knapweed (Centaurrea maculosa) in western Montana

Authors
item Story, J. - AG EXP ST, CORVALIS, MTM
item Smith, Lincoln
item Good, W. - AG EXP ST, CORVALIS, MT
item White, L. - AG EXP ST, CORVALIS, MT

Submitted to: Weed Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 20, 2001
Publication Date: September 1, 2001
Citation: Story, J.M., Smith, L., Good, W.R., White, L.J. 2001. Relationship among growth attributes of spotted knapweed (Centaurrea maculosa) in western Montana. Weed Technology. 15:750-761.

Interpretive Summary: Spotted knapweed is an alien weed that has invaded over 4.5 million acres in Montana alone, causing an estimated annual loss of $14 million dollars. Introduced insect biological control agents do not directly kill the plant and the impact of root-feeding insects is difficult to document. Measuring such impact on the plant requires collecting detailed measurements of plant morphology, which is extremely time-consuming for field studies. We studied the relationships among different measurements of plant morphology, with respect to plant age to 1) describe how the plant grows and changes over its multi-year life span, and 2) determine a minimum set of observations that would be suitable for describing overall plant size or vigor. We found that most knapweed plants did not bolt (to produce flowers) until the third or fourth year, indicating that there is a long immature stage, which should be targeted for attack by new biological control agents. Root diameter can be used as a non-destructive measure of approximate plant age, especially for the first 5 years. Root diameter was also highly correlated to many morphological measurements, including number of flower heads per plant and above ground biomass, which are most relevant to measuring overall plant vigor. Measurements of root diameter, plant height and number of stems are easy to perform and should provide a good representation of plant fitness.

Technical Abstract: The objective of this study was to identify a minimum set of measurable plant characteristics that are representative of spotted knapweed, Centaurea maculosa, vigor. We measured plant age, root diameter, plant height, number of stems per plant, above ground biomass, number of flowerheads per plant, and mean number of flowerheads per stem. Knapweed age was positively correlated with root diameter, number of stems, above ground biomass, and the proportion of plants that bolted (produced flowering stems). Most knapweed plants did not bolt until the third or fourth year. Root diameter can be used as a non-destructive measure of approximate plant age, especially for the first 5 years. Root diameter was also highly correlated to number of capitula per plant and above ground biomass, which are most relevant to measuring overall plant vigor. Plant height was positively correlated with above ground biomass, number of flowerheads per plant, and mean number of flowerheads per stem. Number of stems per plant was positively correlated with plant height, above ground biomass and number of capitula per plant. Above ground biomass was positively correlated to the number of flowerheads per plant and to the mean number of flowerheads per stem. Measurements of root diameter, plant height and number of stems are easy to perform and should provide a good representation of plant vigor.

Last Modified: 12/21/2014
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