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Prevalence of weeds along Pennsylvania roadways: Results from a ten-county survey. 2002. B. J. Clark, W. S. Curran and M. W. Myers. Proc. NEWSS 56:99.

Roadways in the state of Pennsylvania continue to be a vector for the transmission of weeds along their corridors to either natural settings or agricultural land. As the concern increases to stop the potential spread of invasive and troublesome weeds, roadsides are continually becoming more and more of a focus as a method by which weeds expand their distribution. This survey was conducted to assess the frequency and severity of weeds along secondary roadways in Pennsylvania.

Ten counties were chosen in the state based on high agricultural productivity. The ten counties surveyed included Bedford, Berks, Bradford, Butler, Centre, Franklin, Lancaster, Somerset, Washington, and Westmoreland. A minimum thirty-mile transect through each county along secondary roadways included ten pre-determined locations that were identified prior to data collection and ten random sample sites. A total of 200 sites were evaluated within the ten counties. Each data collection site included a 10 by 50 m area directly adjacent to the secondary road. All visible plant species were recorded by name and each species was assigned a numerical value to indicate severity. Plants were ranked on a 20 to 100 scale, where 20 equals <1 plant/100m2 and 100 equals >10 plants/m2. Rankings of 40 through 80 ranged from 1 plant/100m2 up to 2 to 9 plants/m2.

A total of 95 different plant species were identified in the survey. Of the total, 5 plant species occurred at more than 100 of the 200 collection locations. These five species were tall fescue (Festuca arundinacea Schreb.) identified at 174 locations, common ragweed (Ambrosia artemisiifolia L.) at 165 locations, wild carrot (Daucus carota L.) at 127 locations, dandelion (Taraxacum officinale Weber in Wiggers) at 106 locations, and crownvetch (Coronilla varia L.) identified at 100 of 200 locations. Although all five of the plants occurred frequently, only tall fescue had a severity rating greater than 80 (95). In contrast, shattercane (Sorghum bicolor (L.) Moench) was only identified at one site, but it was also present in high density (>10 plants/m2). Other weeds with a severity rating equal to or greater than 80, included horseweed (Conyza Canadensis (L.) Cronq.), hairy galinsoga (Galinsoga ciliata (Raf.) Blake), smooth bedstraw (Galium mollugo L.), fall panicum (Panicum dichotomiflorum Michx.), and several members of the mint (Lamiaceae) family. However, all five of these species or complexes were present at four or fewer sample locations.

Some plants of concern did occur in approximately 25 to 50% of the locations with severity ratings between 40 and 60. These weeds were common milkweed (Asclepias syriaca L.) (76 of 200 locations and a severity rating of 40), Canada thistle (Cirsium arvense (L.) Scop.) (80 locations; 45 severity rating), and bull thistle (Cirsium vulgare (Savi) Tenore) (25 locations; 42 severity rating). Of the 95 identified plants, a total of 42 are considered agricultural weeds, three of which are Pa noxious weeds. Few weeds of natural or undisturbed sites were identified in this survey.

In conclusion, secondary roadways of Pennsylvania are potential vectors of both agricultural and nonagricultural weeds. Roadsides must be monitored and carefully managed to ensure that harmful weeds do not increase in prevalence as a result of our transportation network.