Efficacy of four systemic insecticides against the green pit scale insect (Palmapsis phoenicis Ramachandra Rao) (Homoptera: Asterolecaniidae) infesting date palm in Northern Sudan

Abstract

A series of small scale field experiments were carried out in Elgaba scheme, and El Golid area during seasons, (2003/2004- 2004/2005) to evaluate the efficacy of four systemic insecticides; imidacloprid as Confidor 200SL, Rinfidor 20%SL and Comodor 20% SL and thiamethoxam as Actara 25WG, against the green pit scale insect (Palmapsis phoenicis Ramachandra Rao). Two methods of application, soil application and trunk injection were used. The insecticide thiamethoxam as Actara 25WG was tested at 9, 12, 15 and 18g /palm and 6, 8 and 10g/palm for soil application and trunk injection, respectively. While imidacloprid as Rinfidor 20% SL and Comodor 20% SL was tested at 20, 25 and 35 ml/palm and 10, 15 and 20 ml/palm for soil application and trunk injection, respectively. Confidor 200SL (imidacloprid) was used as standard (35ml/palm) for soil application and 10, 15 and 20 ml /palm for trunk injection The specific dose was diluted with eight liter of water in a container and drenched around the date palm tree (3m id) and then irrigation scheduled every 10 days . The Completely Randomized Design with six replicates (one palm = replicate) was used. The insects (all developing stages) were counted (cm2/leaflet). Eight leaflets from each palm were inspected at biweekly intervals. Dates yield and quality were determined at harvest. Residue analysis was carried out on dates, soil and intercropped plants twice (at rutab stage and harvesting). The economics of control using this method were studied .Varietal susceptibility and expected natural enemies were also investigated. Results indicated that the % mortality (adult and immature stages) were significantly higher in insecticides treatments than the untreated control by the two application methods. Results of residue analysis indicated that, no residues of both imidacloprid and thiamethoxam were detected in dates, soil and intercropped plants when treated with the high doses. The higher doses remained effective throughout the experimental period. Date palm treated with the higher doses of tested insecticides, developed normally and the dates reached maturity (ripening) and the yield was increased by more than 70% compared with the untreated control. All insecticides checked termites and many other pests, but did not affect mites. The two methods of application were found highly economical and safe for the users with minimal environmental impacts. Partial budget analysis indicated the profitability of the two packages as indicated by the marginal rate of returns of 364 % for imidacloprid. Survey of the natural enemies recorded two beetles associated with the pest. Among the four varieties tested Gondiella was the most susceptible variety while the least susceptible variety was Wad laggi.