The investigation of allelopathic effect of some weed species against Phelipanche aegyptiaca (Pers.) pomel and Orobanche cumana Wallr.

The production of some important cultivated plants in Turkey, such as tomatoes, lentils, faba beans, sunflowers, potatoes, and tobacco, is under threat from parasitic weeds. Studies have shown that a single method is not sufficiently effective in controlling these weeds. Therefore, allelopathy studies, which have the potential to be used both as environmentally friendly solutions and as bioherbicides, have gained importance as an alternative approach. In this context, the effects of extracts obtained by two different methods from Tree of Heaven (Ailanthus altissima (Mill.) Swingle), Field Bindweed (Convolvulus arvensis L.), Sticky Fleabane (Inula viscosa (L.) Aiton), Three-lobed Morning Glory (Ipomoea triloba L.), and Ribwort Plantain (Plantago lanceolata L.) were tested against parasitic weeds (Phelipanche aegyptiaca (Pers.) Pomel and Orobanche cumana Wallr.), which cause significant damage to tomatoes and sunflowers. For this purpose, the effects of water and methanol extracts obtained from these plant species on the germination of both parasitic and cultivated plant seeds were examined under laboratory conditions. Then, pot experiments were conducted to determine the highest extract concentration that does not cause phytotoxicity in cultivated plants. In the final stage, the effects of the extracts on the growth of both the parasitic weeds and the cultivated plants were investigated in pots infested with the weeds. When the effects of extraction methods on the germination of parasitic weeds were compared, water extracts showed the highest inhibition at a 100% doses in Phelipanche aegyptiaca. The water extract of A. altissima inhibited germination by 76.5%, C. arvensis by 82.9%, I. viscosa by 91.6%, I. triloba by 97.6%, and P. lanceolata by 91.2%. In O. cumana, water extracts were also more effective. The water extract of A. altissima inhibited germination by 95.4%, while C. arvensis exhibited 97.9% and 99.5% inhibition at 50% and 100% concentrations, respectively. The water extract of I. viscosa inhibited germination by 90.5%, I. triloba by 95.8%, and P. lanceolata by 98.7%. None of the extracts, at any dose, negatively affected the germination of tomatoes or sunflowers; however, variations in radicle length were observed. In the dose determination experiments, only the 100% dose of A. altissima and I. viscosa exhibited phytotoxic effects on tomatoes; so their 50% dose were applied in pot trials. In sunflowers, no phytotoxic effects were observed at the 100% dose of any extract.In the pot experiments examining the effects of the extracts on parasitic weeds, A. altissima extract reduced the shoot number of P. aegyptiaca by 17% and its dry weight by 44%. For O. cumana, the extracts of P. lanceolata, A. altissima, and I. viscosa reduced the shoot numbers by 42%, 48% and 60% respectively, while decreasing fresh and dry weights by 57–65%. Regarding the effects of the extracts on cultivated plants, in tomatoes, compared to the positive control, plant height increased with C. arvensis, remained unchanged with I. viscosa and I. triloba, and decreased with A. altissima and P. lanceolata. Root fresh and dry weights increased with I. triloba and P. lanceolata but remained unchanged in the other treatments. Stem fresh weight increased with C. arvensis, while no significant differences were observed in stem dry weight among the treatments. In sunflowers, the extracts increased plant height and showed no phytotoxic effects. It was determined that A. altissima exhibited high allelopathic potential against P. aegyptiaca in tomatoes, while I. viscosa and A. altissima had high allelopathic potential against O. cumana in sunflowers. These findings suggest that future studies could focus on the bioherbicidal effects of these two species.