عنوان مقاله [English]
Introduction: Rice (Oryza sativa L.) is one of the world’s most important staple food crops. In Asia, it is the main item of the diet of 3.5 billion people. Rice stem borers are common insect pests in many rice growing countries. Striped stem borer (Chilo suppressalis Walker), belonging to Lepidoptera and family of Pyralidae is the most important rice pest in the Northern Iran. Stem borer larva damages rice stem and disturbs nutrient translocation from root to leaf. As the result, tillers in vegetative stage died, which is called dead heart. When larva infests generative stage, it causes empty panicle, which is called white head. Integrated pest management (IPM) practices for controlling the stem borers in Iran have not been fully implemented because of limited control technologies which are available. Farmers often rely on heavily insecticide application, although many insecticide applications are not effective. Therefore, many physical and cultural practices have been suggested, including adjustment of planting time to escape the plant from heavy pest.
Materials and Methods: The study was conducted in deputy of rice research institute in Amol, Mazandaran, Iran, during 2011-2012. The experiment was arranged in split plot design with planting time as main plot and cultivar as subplot and was replicated three times. Three planting times tested were the first planting time i.e. 15 days before farmers’ planting time, the second planting time (simultaneously with farmers’ planting time), and the third planting time (15days after farmers’ planting time). Six rice cultivars tested, representing three types of rice cultivar, Tarom and Kohsar (early maturity cultivars), Shirodi and Fajr (medium maturity cultivars), Neda and Nemat (late maturity cultivar). Rice seedlings were transplanted at 25 cm planting distance in a 3 m x 9 m plot size. Weeding and fertilization were done as recommended. No insecticide was applied. Dead hearts and white heads were measured on 10 sample hills on each plot after the end of growth germination and before harvesting respectively. Rice yields were measured on 80 sample hills (5 m2) on each plot. Sample hills were chosen diagonally. Effect of planting times and rice cultivars on striped stem borer infestation were determined by analyzing of variance using by two-way Analysis Of Variance (ANOVA) and the mean difference were tested using Tukey test. Parameters were analyzed using the SAS software.
Results and Discussion: Analyses of variance showed that there was significant difference between stem borer infestation at three planting time, cultivars and their interaction. Stem borer infestation in the third planting time was significantly higher than the other two planting times. The most degree of dead hearts (11.9%) and white heads (31.23%) infestation were belonged to Tarom cultivar in the first planting time and Fajr cultivar in third planting time, respectively. The least degree of dead hearts (0.6%) and white heads (4.56%) infestation was observed on Neda in the first planting time. Also, grain yield of all rice cultivars grown at the first and second planting was higher than that of the third planting time. As earlier discussed, rice crop of the first planting time was heavily infested with stem borer during early vegetative stage. Although affected rice plants had been replaced and recovery of replanted tillers was good, they grew slower. Yield potential of all six cultivars was significantly different. Yield of a cultivar depends upon its yield potential. However, biotic and abiotic threats could reduce its yield potential. The present study showed that stem borers are potential threat when their population is higher as shown in the third planting time. The least mean rice yield (3.875 t/h) occurred in the third planting time compared to those found at the first and second planting time, i.e. 5.356t/h and 5.321 t/h respectively.
Conclusion: It is concluded that adjustment of planting time is feasible effort to reduce stem borer infestation because rice plant be able to escape damage under heavily population of striped stem borer but it depended cultivar and climate condition.