The efficacy of dry medicinal plant powders against rice diseases

Ten out of twenty plant powders showed potent activity in inhibiting the radial growth of rice pathogens at 50 g L −1 and were selected for determination of their antifungal activity against rice sheath blight disease and dirty panicle disease under greenhouse conditions and in field trials at 10 and 25 g L −1 . It was found that the Zingiber cassumunar Roxb. and Curcuma longa L. powders suppressed sheath blight disease severity by 93 and 92%, respectively, on treated rice leaves at 10 g L −1 . The activity of the selected five plant powders that showed potent fungicidal activity in controlling dirty panicle disease under greenhouse conditions were evaluated in field trials at 25 g L −1 . The number of applications was shown to be a significant factor in controlling the disease. Three applications resulted in better disease control activity than either two or one application. The results in two consecutive years, 2018 and 2019, showed that the powders of Z. cassumunar Roxb., Coscinium fenestratum (Goetgh.) Colebr. and C. longa L. resulted in the greatest reductions of disease incidence: 57.87, 54.48 and 52.47%, respectively, whereas the powders of Piper spp. significantly reduced disease incidence by 40.79–41.95%, when applied three times in 2018. Moreover, all plant treatments also significantly increased rice yields over the control treatment (water) when applied two and three times. However, application of a combination of the fungicides, difenoconazole 15% + propiconazole 15%EC showed the best fungicidal effect against dirty panicle disease and improvement of rice yield. Results indicated that applying dry medicinal plant powders resulted in potent rice disease control efficacy and was a convenient method for farmers to use. However, it should be noted that the medicinal plant powders may stain rice leaves yellow when applied at rates of more than 25 g L −1 .