Natalia Kwiecień

Legumes play an important role in agriculture by enriching soil with nitrogen, drawing water and nutrients from deeper soil layers, and supplying organic matter. They are also a valuable source of food for humans and animals. Protecting these plants from pests usually involves the use of synthetic products, whilst non-chemical methods remain poorly understood. The use of plant-based extracts is one possible approach. There is limited data in the available literature on the use of aqueous extracts (which is an easy and potentially low-cost solution) to protect legumes from pests. In particular, there is a lack of long-term studies conducted under field conditions. Accordingly, the aim of the three-year field studies was to determine the effect of aqueous tarragon extracts, prepared from dried and fresh plant material at concentrations conventionally defined as 2% (D2), 5% (D5) and 10% (D10) for the dried material, and 10% (F10), 20% (F20) and 30% (F30) for fresh material, on the control of two serious legume pests: Sitona spp. weevils and the broad bean weevil (Bruchus rufimanus Boh.). Aqueous extracts of tarragon reduced the area of losses and the percentage of leaf blade losses caused by adult Sitona spp. There were no significant differences between extracts using dry or fresh material as well as between different concentrations of the extracts. The effect of extracts was visible particularly during the early stages of plant growth in two out of three study seasons; this is especially significant given that these insects cause the worst damage during this period. No significant effect of the most studied extracts on the feeding of Sitona spp. larvae was observed. In D10 and F10 there was a significantly lower proportion of damaged nodules than in the control; however, this effect was markedly weaker than when Ch was used. All extracts from the dried plant material and F30 proved to be effective in reducing seed damage caused by B. rufimanus. However, the percentage of damaged seeds remained high, indicating that weekly application of tarragon extracts is not sufficient to protect broad beans against this pest. Taking into account the effect on the plants’ morphological parameters, the aqueous extract prepared from dried material at a concentration of 10% (D10) should be considered the most effective in practice. The damage caused by adult Sitona spp. and B. rufimanus differed significantly between years of the study.

Use of plant-based aqueous extracts offers a potentially simple and low-cost approach to pest control. However, their effectiveness under field conditions remains poorly recognised. The aim of the study was to evaluate the effectiveness of aqueous extracts prepared from dried and fresh Artemisia dracunculus L. plant material (D-Es and F-Es, respectively) in controlling Aphis fabae Scop. in field conditions. D-Es were applied in concentrations of 2% (D2), 5% (D5) and 10% (D10) and F-Es in concentrations of 10% (F10), 20% (F20) and 30% (F30). A reduction in the A. fabae population was observed with the use of both D-Es and F-Es (although not as strong as with chemical control (Ch)), with the greatest effect observed after using D-E at a concentration of 10% (D10-E). In the case of D-Es, the aphid-suppressing effect increased as the extract concentration rose. No similar result was observed for F-Es. Regardless of the concentration used, the individual F-Es did not differ significantly from one another. The strength of the limiting effect on A. fabae was arranged in the following order of treatments: Ch > D10 > F10 > D5 > F20 > D2 > F30. Analysis of the volatile compounds contained in D10-E revealed that the main constituents were methyleugenol (27.7%), elemicine (15.6%), (E)-isoelemicine (12.5%), terpinen-4-ol (9.3%) and linalool (4.3%). The extract exhibited the highest antioxidant activity and the highest concentration of polyphenolic compounds. Reduced numbers of the main aphid predators (syrphids and ladybirds) in the treatments with extracts went along with lower prey availability; however, the predator–prey ratio in these treatments was more favourable than in the control. This suggests that the use of F-Es and D-Es does not adversely affect predator abundance. The ease of preparation and availability of the material make D10-E suitable for use on organic farms or as part of integrated pest management.