Revista Brasileira De Herbicidas 2013; 12(3): 220-231
Chemical control and leaf surface characterization of Conyza bonariensis and C. canadensis (Asteraceae)
The genus Conyza includes approximately 60 species which are widely distributed across the globe. The species Conyza canadensis and Conyza bonariensis are noted for their ability to invade abandoned areas, pastures, perennial crops and annual crops. The objectives of the present study were to: (1) characterize the leaf surface of C. bonariensis and C. canadensis by scanning electron microscopy, (2) evaluate the control of these plants with glyphosate mixed with herbicides distinct mechanisms of action. To analyze the leaf surface by scanning electron microscopy two segments of approximately 50 mm2 were taken from the median region of young (but fully expanded) leaves of C. bonariensis and C. Canadensis. The herbicide control study was conducted in completely randomized design with four replicates. Herbicides were applied post-emergence when plants showed three to four pairs of true leaves. The herbicide treatments were: glyphosate (0.42 kg ha-1), mixed with glufosinate-ammonium (0.5 kg ha- 1), 2,4-D (1.0 kg ha-1), bentazon (0.72 kg ha-1), chlorimuron-ethyl (0.15 kg ha-1), carfentrazone-ethyl (0.03 kg ha-1), metribuzin (0.48 kg ha-1) and sulfentrazone (0.6 kg ha-1), as well as the same herbicides applied in isolation and a control treatment without herbicide. Both species are amphistomatic (with stomata on the adaxial and abaxial surface), and both possess unicellular and multicellular non-gladular trichomes. C. bonariensis had a visually larger number of trichomes on the adaxial leaf surface. For C. bonariensis the following treatments were more effective than the control: glufosinate-ammonium and glyphosate mixed with glufosinate-ammonium, bentazon, chlorimuron-ethyl and metribuzin. For C. canadensis the treatments more effective than the control were: glyphosate + glufosinate-ammonium, glyphosate + bentazon, and glyphosate + metribuzin.
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