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The efficacy of the pre-and post-planting application of neem seed oil (NSO) or/and diazinon and time of harvest for the control of sweetpotato weevil, Cylas puncticollis (Boh.) was evaluated during the 2009 and 2010 cropping seasons. Forty-eight plots of 3 x 4 m 2 each were demarcated and 240 sweetpotato (var. TIS2532.op.1.13) vine cuttings were dipped into 0, 30 and 50 mls NSO and 30 mls of diazinon (60 EC) mixed in 2 and 10 litre soapy water, respectively and kept for 30 mins before planting. Similar treatment was also basally applied post-planting at 1MAP. In 2009, results showed that treatments (NSO or diazinon or their combinations) did not significantly influence percentage plant stand at harvest in both years, but lower percentage plant stands were obtained at 6 MAP (47.72%) than at 5MAP (56.87%). Significantly higher mean total weights of 34.44 t/ha was obtained in 2009 and 8.99 t/ha in 2010 respectively. Similarly, yield ranged from as high as 53.69 t/ha at 5MAP in 2009 to as low as 5.51t/ha at 6MAP in 2010. Significantly lower attributes of C. puncticollis as a pest were obtained in 2009 than in 2010. Treatments significantly suppressed root damage from 68.59% (Pr0Pt0) to 44.38% (Pr3Pt3) at 5 to 6MAP. Time of application was significant as 50 mls of NSO applied pre-and post-planting gave highest (35.30%) control of the pest at harvest.

The performance of different maize varieties aginst Sitophilus zeamais infestation was evaluated in a laboratory. Seventeen maize varieties comprising fourteen hybrids (ACR.97 TZL COMP.1-W, ACR.8328 BNC7, TZL COMP.4C2, OBA SUPER 1 and 2, SINE 9449-SR, IWD SYN C3F2, TZL COMP.1SYN STR-Y, TZSR White and Yellow; 95TZEE-W, MASYN VAR-3 F2, ADV.NCRE-STR and BG 97 TZE COMP.3XL) and three local cultivars (Akparike, Bende and Ogbia muno) were screened to ascertain their level of susceptibility to S. zeamais in the study area. Number of adults that emerged from the 17 varieties differed significantly (P ≤ 0.05) and ranged from 2.00 for the improved variety ADV.NCRE-STR to 62.0 in the local cultivar Bende. Significantly higher weight losses were recorded on local cultivars. Heavier males emerged from the local cultivars Akparike and Bende and lighter (P ≤ 0.05) weights were recorded on Oba super 1, TZL Comp.4C2, TZSR White, ADV.NCRE-STR and MASYN VAR-3F2. Grain hardness test showed that the hybrid variety MASYN VAR-3F2 (275.12N) was the hardest followed by TZSR-Y (259.42N) and the softest were local varieties Akparike (116.62N) and Bende (91.65N). Seed coat thickness result indicated that the local variety Akparike (0.38mm) had the highest value of seed coat thickness followed by MASYN VAR-3F2 (0.22mm) and the least seed coat thickness was BG 97 TZE COMP.3XL (0.03mm). Results indicated that the local cultivars commonly cultivated in the Niger Delta (Bende, Akparike and Ogbia muno) supported higher S. zeamais adult progeny than the improved varieties which had harder seeds and thicker coats. The fact that Akparike which has thick testa was susceptible shows that physical factors alone are not responsible for the observed resistance.

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