Development of the Alaska agricultural weed flora 1981-2004: a case for prevention

Authors: Conn, Jeffery; Werdin Pfisterer, Nancy; BEATTIE, KATHERINE - ABR, INC.

Submitted to: Weed Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2010
Publication Date: 2/20/2011
Citation: Conn, J.S., Werdin Pfisterer, N.R., Beattie, K.A. 2011. Development of the Alaska agricultural weed flora 1981-2004: a case for prevention. Weed Research. 51(1):63-70.

Interpretive Summary: Eighty agricultural fields within Alaska were quantitatively surveyed in 2004, 23 years after a similar study in 1981. The purpose of the study was to determine if new weed species had established and whether shifts in weed species may have occurred due to changes in tillage practices and herbicide use. Percent ground cover was determined for each weed species in each of ten 1 m2 quadrats in each field. Also determined was the crop grown, amount of shade produced by the crop canopy, age of the field, weed control method, surrounding vegetation type, altitude, latitude and longitude. Multivariate statistical procedures were used to group fields based on their weed composition and to determine which environmental and management variable best explained the weed makeup of the fields. Six weed species were found that were not present in 1981: large mouse ear chickweed, horseweed, charlock mustard, bladder champion, perennial sow thistle, narrow-leaf hawksbeard, and orange hawkweed. Canopy shading, elevation, latitude and longitude were important factors influencing the weeds that were found. Crop influenced the weed composition and two distinct crop-related groups of fields were found based on weed flora: potatoes/vegetables and hay/grass seed. Exotic weed species had colonized fields that were cleared in 1978-1980 and that largely weed-free in 1981. The failure to use weed prevention resulted in 40000 ha of new agricultural land that must be managed for alien weeds with associated economic and environmental costs.

Technical Abstract: Agricultural fields in Alaska were surveyed in 2004, 23 years after a similar 1981 study, to determine if new weed species had been introduced and whether different environmental and management variables were correlated field weed species composition. Percent cover of each weed species was determined in each of ten 1-m2 quadrats. Environmental/management information collected for each field included: field age (time since clearing), weed control methods, crop, elevation, latitude, longitude, surrounding vegetation type, and canopy shading. Detrended Correspondence Analysis (DCA) was used to ordinate fields based on weed vegetation. Spearman correlation analysis was used to determine whether ordinal variables (field age, latitude, longitude, elevation and canopy shading) were correlated with field ordinations. The relationship of categorical variables (crop, weed control method, surrounding vegetation type) were evaluated by overlays of these variables on DECORANA ordinations of fields. Six new weed species were found: large mouse ear chickweed, horseweed, charlock mustard, bladder champion, perennial sow thistle, narrow-leaf hawksbeard, and orange hawkweed. Canopy shade, elevation, latitude and longitude were important weed flora determinants. The crop grown also influenced the field weed floras. Two distinct crop-related groups of fields were found based on weed flora: potatoes/vegetables and hay/grass seed. Exotic weed species had colonized fields that were cleared in 1978-1980 and that largely weed-free in 1981. The failure to use weed prevention resulted in 40000 ha of new agricultural land that must be managed for alien weeds with associated economic and environmental costs.