Investigation of different planting times of different rice cultivars to control the striped stem borer (Chilo suppressalis Walker)

Stem borer is the most important rice pest in the North of Iran. Using agronomical practices including adjustment of planting time had been suggested to escape the plant from heavily pest infestation. to study the effect of planting time on the stem borer infestation with six rice cultivars, a field trial was arranged in a split plot design with three replication during 2011-2012.Rice Cultivar is the main plot and Planting time is the subplot. The rice cultivars tested were Tarom and Kohsar (early maturity cultivars), Shirodi and Fajr (medium maturity cultivars), Nemat and Neda(late maturity cultivars). The three planting times were: the early Planting time ( 15 days before farmer's Planting time), the common Planting time ( simultaneously with farmer's Planting time) and the late Planting time (15 days after farmer's Planting time). Rice seedlings were planted at 25 cm x 25 cm planting distance in a 3 m x 9 m plot size. To estimate the pest damage, Dead hearts and white heads were measured on 10 sample hills on each plot after the end of growth germination , and before harvesting respectively. Also rice yields was measured on 80 sample hills(5 m2) on each plot. Data was compared by one-way Analysis Of Variance (ANOVA) followed by Duncan test. Parameters were analyzed using the SAS software.According to the results, the most degree of Dead hearts(11.9%) and white heads (31.23%) infestation was belonged to Tarom cultivar in the first planting time and Fajr cultivar in third planting time respectively and the least degree of Dead hearts (0.6%) and white heads (4.56%) infestation was observed on Neda in the first planting time. Also, 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.