Researches Concerning the Effectiveness of the Maize Foliar Treatment Compared With Seeds Treatment for Chemical Control of the Maize Leaf Weevil (Tanymecus Dilaticollis Gyll) in the South-East of Romania

Abstract

Maize leaf weevil [(Tanymecus dilaticollis (Gyllenhal, 1834)] represents one of the most dangerous pests of the maize crops in Romania. Each year, around one million hectares cultivated with maize are attacked by this pest with different levels of attack intensities. In the case of the high weevils invasion, the maize seedlings could not survive, and the farmers have to sow their fields again, causing unexpected costs. Spring drought and higher temperatures that usually occur in Romania's south-east is even more favorable circumstances for the weevils attack. Also, maize monoculture has an increasing effect on pest density associate with a higher impact on the attack. The maize seeds' chemical treatment with systemic insecticides was the most effective method to reduce the loss. However, the use of neonicotinoid insecticides for seed treatment was banned in the European Union in 2019. As a result, no effective insecticides are available for maize seed treatment against T. dilaticollis in Romania. This study aimed to evaluate possible alternatives at seed treatment to control the maize leaf weevil. The experiences were carried out at the National Agricultural Research and Development Institute Fundulea, both under the field and greenhouse conditions, with artificial infestation, between 2015 and 2018. Maize foliar treatment with deltamethrin (100 g/l), thiacloprid (480 g/l), and maize seeds treatment with imidacloprid (600 g/l) active ingredients were assessed. In all years from this trial, in the field conditions studied foliar treatments haven't assign effective protection of the maize plants in early vegetation stages against maize weevil attack. In case of high pest attack in the absence of the seeds treatment, more than 90 % of the plants can be destroyed by the weevils. Until now, no alternatives are available to replace maize seed treatments with systemic insecticides.