RICE RATOONING - IRRI books - International Rice Research Institute

214 RICE RATOONINGAlthough the intensity was not high enough to kill the ratoon tillers, grain yield wasreduced. The data also provide evidence that inoculum of the bacterial pathogenmay be generated from ratoon tillers and stubble to infect a subsequent crop.MAIN CROP DISEASE CONTROL AND RATOONINGInitial field observation has shown that diseases in the main rice crop usually affectratooning and the kinds of diseases that occur on the ratoon crop. The effects ofdiseases caused by Rhizoctonia solani and Sclerotium oryzae were not always clear.In the 1980 wet season, the effect of main crop disease management onratooning of IR32 was studied. This cultivar is known to be resistant to some of themajor rice diseases of the Philippines: blast, tungro, grassy stunt, ragged stunt, andbacterial blight. A fungicide mixture of benomyl-thiram was applied at differentstages of rice growth (Table 4, 5). At harvest, rice stubble was cut about 15 cm high.Ratoon rating was at 35 d after ratooning.Table 4. Chemical control of main crop and ratoon rice disease development onratoon crop of IR32, IRRI, 1980.Disease incidence b (%)Time of fungicide application a Main crop Ratoon cropSH SR YD SH SR YDSeedlingMaximum tilleringFillingSeedling + maximum tilleringSeedling + fillingMaximum tiliering + fillingAll three stagesCheck11.735.018.326.726.78.38.312.384868380596160850000000044.152.138.338.543.517.619.743.1747671727372667422.619.421.217.013.020.818.024.4a Benomyl-thiram (20% ai.i.) at 1 g/liter H 2 O. b SH = sheath blight, SR = stem rot,YD = yellow dwarf.Table 5. Effect of fungicide application on stem rot infection of main rice crop and ratoon cropdevelopment.Main cropRatoon cropTime of fungicide application a Stem rot Yield Tillers/hill (no.) Ratoon b Yield(%) (t/ha) rating (t/ha)Basal Nodal TotalSeedlingMaximum tilieringFillingSeedling + maximum tilleringSeedling + fillingMaximum tillering + fillingAll three stragesCheck84868380596160858.1 a7.8 a7.7 a6.7 a7.4 a7.5 a8.3 b7.3 a10.1 a12.0 a10.5 a11.5 a12.2 a12.0 a11.4 a10.2 e8.1 abc6.4 bc6.2 bc5.6 c8.8 ab8.5 abc10.0 a7.0 bc18.218.416.717.121.020.521.417.20.80 bc0.77 c0.74 c0.77 c0.85 bc1.00 ab1.07 a0.72 c1.3 ab1.4 ab1.3 ab1.5 ab1.6 ab1.6 ab1.8 a1.2 ba Benomyl-thiram. b MH TRatoon rating = 1 – × tT × (1 – 0.1 × V), where 16 = av no. of tillersh 16/hill, MH = missing hills, T h = total no. of hills, T t = total number of tillers (nodal + basal), V =vigor rating: 1 = extra vigorous, 5 = intermediate, 9 = weak.