RICE RATOONING - IRRI books - International Rice Research Institute

INSECT PESTS IN RATOON RICE 197Field trialTransplanted and wet-seeded main crops of IR1917 (susceptible to insects butresistant to tungro) were grown side by side. To ensure the same maturity date, thewet-seeded crop was sown at 120 kg seed/ha 2 wk ahead of transplanting. Nopesticides were used. Nitrogen was applied at 100 kg N/ha in 3 equal splits: basal,maximum tillering, and panicle initiation. P 2 O 5 and K 2 O at 30 kg/ha were basallyapplied.The field was kept weed free and ponded 3-5 cm deep throughout the growingperiod. Prior to harvest, the field was divided into 24 bunded plots (9 × 12 m) for arandomized complete block design. Twelve plots were thoroughly plowed andpuddled and half wet-seeded, half transplanted for second crops. Mature plants wereratooned in the other 12 plots by cutting stalks at 15 cm. Canals gave independentirrigation to each plot. Water was supplied continuously (flooded 3 times a week) orintermittently (flooded once a week for 1 d).Fertilizer (60 kg N/ha) was broadcast in the ratoon 1 d after harvest of themain crop and basally applied in the transplanted and wet-seeded second crop.Main crops were sampled weekly for leafhoppers and planthoppers and theirnatural enemies with a FARMCOP suction machine (2). Sampling on the ratoonsand second crops was twice a week. FARMCOP samples of 1 m 2 were taken from 3sites selected at random in each plot in a stratified grid on each sampling date.A similar sampling area was used to determine RWM, LF, and SB numbers.Greenhouse trialRatoon and transplanted check plants were studied for their suitability as hosts toinsects that prefer to feed on rice at the vegetative stage (RWM, CW, greensemilooper [GS], and green hairy caterpillar [GHC]) and to insects that can attackrice from the vegetative to ripening stages (BPH, GLH, WBPH, YSB, and LF).To grow the ratoon, we transplanted IR1917 seedlings in earthen pots 30 cm indiameter and 25 cm high. When the plants matured, they were cut 15 cm above thesoil surface. The check was grown by transplanting 30-d-old seedlings in pots of thesame size filled with puddled soil. Both ratoon and transplanted rice were grownwith and without 60 kg N/ha.When ratoon and transplanted rice were 3 wk old, they were covered withcylindrical mylar film cages (10 × 75 cm) with nylon mesh windows on 1 side and ontop. These gave access to measure insect survivorship, development period, andweight, the criteria for assessing host suitability. Each treatment was replicated sixtimes in a randomized complete block design.Survivorship, weight, and developmental period were determined separatelyfor all species except whorl maggot. Ten first-instar larvae or nymphs wereintroduced into the cages over the potted plants, using an aspirator or a fine camelhair brush. Plants were hand-infested with greenhouse-collected mature RWM eggs(dark color) by inserting a leaf section containing the eggs into a slit made on anunfurled leaf or between the youngest leaf and leaf sheath (10 per plant).