Effects of Plant Extracts on Crop Diseases, Two-Spotted Spider Mites, and Weeds

This research was conducted to evaluate the controlling effects of various plant extracts obtained from 38 agricultural materials of traditional agriculture against rice blast (Pyricularia oryzae) in rice plants. We also evaluated the inhibition rates of other crop pathogens, two-spotted spider mites (Tetranychus urticae), and weeds by three selected plant extracts. Rice blast was completely suppressed by 3% ethanol extracts of Rheum palmatum roots, and suppressed by 97% and 77% in response to treatment with 10% ethanol extracts of onion (Allium cepa) bulbs and pine tree (Pinus densiflora) leaves, respectively, under in vitro conditions. Moreover, a seedling bioassay revealed that rice injuries of two cultivars (Ilmibyeo and Hopyeongbyeo) caused by rice blast were reduced by 40-71, 29-63, and 23-63% in response to treatment with 5% and 10% ethanol extracts of R. palmatum roots, A. cepa bulbs, and P. densiflora needles, respectively, compared with non-treated controls. The selected R. palmatum extract also controlled crop diseases caused by Phytophthora capsici, Bortytis cinerea, Rhizoctonia solani, and cucumber powdery mildew (Sphaerotheca fuliginea). R. palmatum extracts at 10% reduced two-spotted spider mites by 46% when compared with each control. A broad leaf weed, Quamoclit coccinea Moench and a grass weed, Echinochloa oryzicola were inhibited 46-55% by R. palmatum roots, A. cepa bulbs, and P. densiflora needles at 10%. Thus, the selected plant extracts may be used for control of crop diseases and weeds in organically cultivated crop fields.