Is biological control a solution for maize plants protection against maize leaf weevil (Tanymecus dilaticollis Gyll) attack in climatic conditions specific from South-East of the Romania?

Abstract

Maize leaf weevil (Tanymecus dilaticollis Gyll) is the most dangerous pest of the maize, in south and south-east of the Romania. The attack is dangerous when maize plants are in first vegetation stages (plants emergence-four leaf stage, BBCH 10-BBCH 14), in some cases maize crop can be total destroyed. Each year, in maximum favorable areas for this pest, there is attacked, with different intensity degrees, one million hectares cultivated with maize. Seeds chemical treatment with systemic insecticides represented the most efficacy method of maize crops protection against attack of this pest, in climatic conditions specific for south east of the Romania. As result of the EU directive 485/2013, starting from year 2014, the use of the neonicotiond insecticides (imidacloprid, clothianidin, thiametoxan active ingredients) for spring crops seeds treatment, was restricted. However, in perioad 2014-2018, Romania obtained derogations for use of these insecticides for seed treatment of maize and sunflower crops. As result of EU states vote, in 27 April, 2018, it has decided total ban of using of this three active ingredients from neonicotinoids class at all field crops, starting from 2019. As result, in Romania, at maize crop, no active ingredient will remain available for seed treatment against maize leaf weevil attack. In this paper there were presented results of a three-year study, effectuated at NARDI Fundulea, concerning the efficacy of the biological insecticides, used both at seed treatment and foliar spraying (spinosad active ingredient and neem oil) comparative with seed treatment with imidacloprid active ingredient (600 g/l). In the three study years, the lowest attack level of the Tanymecus dilaticollis at maize plants it has registered in case of the variant with seeds treated with imidacloprid. In climatic conditions specific from south-east of Romania, in period 2016-2018 there weren’t statistical differences (p<0.5) between control (untreated) variant and variants treated with biological products, both like seed treatment and foliar spraying.