SEED TREATMENT WITH PYROQUILON FOR THE CONTROL OF LEAF BLAST IN BRAZILIAN UPLAND RICE

The effect of seed treatment with pyroquilon fungicide on rice leaf bl ast caused by Pyricularia oryzae Cav. was studied in field and blast n ursery experiments. In the field, pyroquilon (4.0 g/kg seed) treatment kept leaf blast severities below 5% at 38 days after sowing (d.a.s.) in susceptible cultivars (cvs) IAC 47, IAC 25, IAC 164, and L-50. In t he blast nursery experiment, seed treatment with carbofuran insecticid e did not affect the efficiency of pyroquilon. Seed treatment with pyr oquilon (4.0 g/kg seed) or pyroquilon (4.0 g/kg seed) + carbofuran (4. 8 g/kg seed) significantly reduced leaf blast at 38 d.a.s. in cvs IAC 25, IRAT 112 and IAC 47. Leaf blast and biomass production at 58 d.a.s . were negatively correlated (r = -0.91, P = 0.01). Under low disease pressure, pyroquilon seed treatment reduced leaf blast severity at rat es of application greater-than-or-equal-to 2.0 g/kg seed. At high dise ase pressure, higher rates of application (4.0 g/kg seed) were found n ecessary for maximum disease control in a susceptible cultivar. Seed t reatment had little or no effect in more resistant cultivars. The resu lts indicate that treating seed with pyroquilon provides adequate prot ection against rice leaf blast during the vegetative phase in suscepti ble cultivars.