Mode of application of seed protectants for sale storage of rice seeds

Abstract

Storage experiments were conducted in rice variety Mo 16 (Uma) during 2021 2022 to evaluate the efficacy of mode of application of seed protectants in management of storage pests in rice and to assess their impact on seed quality and longevity. The experiment was laid out following a completely randomized block design with 11 treatments and three replications. Three different seed protectants viz., Bifenthrin 10% EC, Deltamethrin 2.5 WP and Chlorfenapyr 10% SC were used in the study. Seeds dried to 12-13 per cent moisture content were filled in 1) Jute bags surface sprayed with the protectants @ 30 g a.i.m-2 [T1: Bifenthrin 10% EC sprayed jute bag (Bifen.10EC Sp.), T4: Deltamethrin 2.5 WP sprayed jute bag (Delta.2.5WP-Sp.) and T7: Chlorfenapyr 10% SC sprayed jute bag (Chlorfen.10SC-Sp.)], 2) Jute bags impregnated with the protectants @ 1000 ppm (T2: Bifenthrin 10% EC impregnated jute bag (Bifen.10EC-Im.), T5: Deltamethrin 2.5 WP impregnated jute bag (Delta.2.5WP-Im.) and T8: Chlorfenapyr 10% SC impregnated jute bag (Chlorfen.10SC-Im.). Seeds treated with protectants @ 0.5 ppm comprised the treatments T3: Bifenthrin 10% EC seed treatment (Bifen.10EC-St.), T6: Deltamethrin 2.5 WP seed treatment (Delta.2.5WP-St.) and T9: Chlorfenapyr 10% SC seed treatment (Chlorfen.10SC-St.), while seeds treated with diatomaceous earth (Diatom-St.) as well as untreated seeds (Control) packed in untreated jute bags, served as T10 and T11, respectively. The packed seeds were stored under ambient storage environment and the impact of mode of application of seed protectants on storage pests population (Experiment 1) and their impact on quality and longevity of stored seeds (Experiment 2), were assessed. Results of Experiment 1 pointed out that the incidence of beetles, the weight of damaged seeds, and the number of infested seeds were significantly low in treatments T8 (Chlorfen.10SC-Im.) followed by T7 (Chlorfen.10SC-Sp.), T9 (Chlorfen.10SC-St.), T5 (Delta.2.5WP-Im.) and T6 (Delta.2.5WP-St.), while the weight of undamaged seed was significantly high in these treatments. Pesticide residue analysis revealed that treating seeds with deltamethrin T6 (Delta.2.5WP-St.) resulted in a higher residue of 92.34 ppm. The residues of Chlorfenapyr did not vary between spraying (T7: Chlorfen.10SC-Sp.), impregnation (T8: Chlorfen.10SC-Im.), and seed treatment (T9: Chlorfen.10SC-St.), with the residues being 0.047 ppm, 0.048 ppm and 0.046 ppm, respectively. With bifenthrin, T3 (Bifen.10EC-St.) registered the highest level of residue (78.47 ppm) followed by 36.67 ppm in T1 (Bifen.10EC-Sp.) and 38.83 ppm in T2 (Bifen.10EC-Im.). However, in all the treatments, the residues were below detectable level after nine months of storage. Results of Experiment 2 revealed that seed quality and longevity during storage were significantly influenced by the mode of application of seed protectants. Longevity of seeds in T4: Delta.2.5WP-Sp., T5: Delta.2.5WP-Im., T6: Delta.2.5WP-St., T7: Chlorfen.10SC-Sp., T8: Chlorfen.10SC-Im. and T9: Chlorfen.10SC-St., was found to be high. These seeds retained viability (Germination > 80 %) for seven months of storage (7 MAS) compared to six months (6 MAS) in the case of other seeds stored in Bifenthrin 10SC impregnated jute bags (T2), seeds treated with diatomaceous earth (5g per kg of seed: T10) and untreated control. However, seeds stored in surface sprayed bags 9T1) lost viability at 6 MAS. Germination, shoot and root length, seedling vigour indices I and II and field establishment of seedlings, were found to be significantly high in T7: Chlorfen.10SC Sp., T8: Chlorfen.10SC-Im., T9: Chlorfen.10SC-St., T5: Delta.2.5WP-Im. and T6: Delta.2.5WP-St., at both 7 MAS and at the end of storage period (9 MAS). The seed moisture content and electrical conductivity of seed leachate were also found to be significantly low in these treatments. Significantly low germination and seeds quality parameters were observed in T1: Bifen.10EC-Sp., T2: Bifen.10EC-Im. and T3: Bifen.10EC-St., as well as the untreated control (T11). Application of Bifenthrin 10% EC, thus proved to adversely impact seed quality. The correlation between weekly storage temperatures recorded during the 40 weeks of storage period and germination per cent of Uma variety was analyzed. Temperature within the storage environment during 1st and 3rd week was found to exhibit a significant positive correlation with germination in Uma. Relative humidity in the storage environment registered a significant positive correlation with germination (%) during 1st, 2nd, 3rd and 4th weeks of storage. In addition to the above, the seeds where subjected to accelerated ageing for a period of 0-14 days. The quality parameters of samples drawn at an interval of two days from the accelerated aged lots indicated that treatments T8: Chlorfen.10SC-Im., followed by T9: Chlorfen.10SC-St., T7: Chlorfen.10SC-Sp. and T5: Delta.2.5WP-Im., were significantly high compared to other treatments. It was evident that application of seed protectant Chlorfenapyr.10SCeither as spray over the jute bags (T7) or using it for impregnating the seed bags (T8), or utilizing it directly for seed treatment (T9), was helpful in protecting the seeds from insect pest during storage. These modes of application of seed protectant Chlorfenapyr.10SC, were beneficial in maintaining higher seed quality parameters including seed health of rice variety Uma during storage. From the above, it is hence summarized that although the use of pesticide impregnated bags or seed treatment with the protectants were beneficial, spraying the seed protectant over the bags containing the seed would be a more viable, less cumbersome and environmentally safe mode of application of seed protectant.