Lw. Lass et al., DETECTION OF YELLOW STARTHISTLE (CENTAUREA-SOLSTITIALIS) AND COMMON ST-JOHNSWORT (HYPERICUM-PERFORATUM) WITH MULTISPECTRAL DIGITAL IMAGERY, Weed technology, 10(3), 1996, pp. 466-474
Ground-based surveys to regularly document the size, shape, and locati
on of weed populations usually are not economically feasible. Digital
images of vegetation in semiarid rangeland were obtained from four cha
rge-coupled devices with spectral filters mounted in an airplane. The
ability to distinguish yellow starthistle and common St. Johnswort fro
m other rangeland vegetation in images with 0.5, 1, 2, and 4 m spatial
resolution was assessed. Detection, positioning, and measurements of
size and density of yellow starthistle and common St. Johnswort coloni
es with densities as low as 30% ground cover were possible at all thos
e resolutions, Images indicated yellow starthistle occupied about one-
third of a 180-ha study area, Images taken in June indicated 2 to 10 h
a less yellow starthistle ranging from 30 to 100% cover than images ta
ken in July for all resolutions. Images indicated common St. Johnswort
occupied less than 4 ha of the 180-ha study area. This procedure prov
ides a method to establish baseline plant community composition and a
way to monitor species population changes and dispersal over time.