nanomaterials Article Foliar Application of Low Concentrations of Titanium Dioxide and Zinc Oxide Nanoparticles to the Common Sunflower under Field Conditions Marek Kolencˇík 1,2,*, Dávid Ernst 3 , Martin Urík 4, L'uba Dˇ urišová 5 , Marek Bujdoš 4, Martin Šebesta 4 , Edmud ...