Phytotoxicity Screening of Camelina sativa and Brassica carinata Oil-Based Formulations for Dendrolimus pini Management in Scots Pine

Botanical insecticides proposed for forest pest management must combine efficacy against target insects with acceptable effects on host trees. Following the demonstrated insecticidal activity of 2% Camelina sativa (CS) and Brassica carinata (BC) oil-based formulations against Dendrolimus pini, we screened their phytotoxicity toward Scots pine (Pinus sylvestris), the host tree, and toward barley and pea as taxonomically contrasting reference species. The formulations were incorporated into agar-solidified MS medium at 0.25%–2.0% or applied foliarly at 2%. Responses depended on species, formulation, concentration, and endpoint, with the strongest growth inhibition generally observed at 2%. Scots pine was particularly sensitive during seedling establishment: no normal seedlings developed after CS exposure at 0.50, 0.75, or 2.0%. At 2%, both formulations inhibited barley shoot growth; CS additionally inhibited barley root growth, and BC inhibited pea shoot elongation. Foliar application did not significantly alter the dry matter percentage of Scots pine, and contact angle did not explain the observed foliar responses. Because the 2% concentration corresponds to the rate previously shown to be insecticidal against D. pini, the results identify a potential host-plant safety constraint and demonstrate that formulation and dose optimization should precede semi-field testing.