Synergism of Neem and Karanja Oils against Colorado Potato Beetle Larvae in Field Conditions

The increasing scarcity of active substances approved for use in plant protection is reflected in the growing effort to find suitable plant protection alternatives. Products based on plant oils could provide a promising environmentally friendly solution. In previous research in laboratory conditions, the synergistic effect of neem and karanja oils on Leptinotarsa decemlineata (CPB) larvae was observed. The aim of this current study was to verify whether the synergistic effect would also be observed in field conditions. The active substances used included azadirachtin A (NeemAzal® T/S); in both a reduced dose of 10.6 g/ha and a normal dose of 26.5 g/ha (Neem1, Neem2), Pongamia pinnata oil (Rock Effect New–REN); in a reduced dose of 1987.6 g/ha, and a mixture of both reduced doses (MIX). The protective effect was expressed by a visual estimation of the damaged leaf area on the potato plant. The MIX variant was always among the least damaged variants throughout the experiments, while the control was always the most damaged variant. A synergistic effect was observed at site I in 2021 when the MIX variant was more than 10 times less damaged than the control; in other cases, it was around 3 times less damaged. Treatment with MIX provided a protective effect comparable to NeemAzal® T/S in the full dose. This mixture can therefore be used to expand the portfolio of suitable preparations against CPB larvae in potato production.