RICE RATOONING - IRRI books - International Rice Research Institute

AGRONOMIC PRINCIPLES AND PRACTICES OF RATOONING 173Table 11. Disease infections in the ratoon crop of IR32 (41).TreatmentPuddledStanding waterMidseason drainageUnpuddledStanding waterMidseason drainageStem rot(%)8.25.78.15.5Sheath blightrating a0.40.40.10.2a Scale: 1 = lesions limited to lower 1/4 of leaf sheaths; 5 = lesions present onmore than 1/2 of leaf sheaths, slight infection on lower (3d or 4th leaves); 9 =lesions reaching top of tiller, severe infection on all leaves.4. Shift in weed composition from the main crop to the ratoon crop (22). DT = days after transplanting,DAH = days after harvest.Rice ratoons are also prone to infection with certain diseases. Grassy stuntvirus, stem rot, and sheath blight have been observed infecting the crop (4, 41). Baharand De Datta (4) reported that all the rices used in their study were infected withvarying degrees of grassy stunt virus, which may partly explain why ratooning is notwidely accepted in the tropics. Samson (41) noted stem rot and sheath blight onratoon crops (Table 11). Stem rot appeared to be influenced by water regime andcutting height. Plots with standing water had a higher incidence of stem rot thanplots with midseason drainage. Longer stubbles (25 cm) also had higher stem rotinfection, producing less vigorous ratoons than shorter stubble (15 or 3 cm).Insect and disease problems could be minimized by breeding resistant ricesand applying appropriate pesticides.WeedsA change in either the cropping system or weeding treatment can cause a significantchange in the weed flora of the subsequent seasons (9). In reduced tillage, weeds