Effectiveness and safety of botanical pesticides applied in black pepper (Piper nigrum) plantations

Summary

Black pepper (Piper nigrum L) is an important commodity of Indonesia, which has been cultivated since the 6th century. The plant plays an important role in local economies since 95% of the plantations are cultivated by smallholder farmers. Because of this important economic value, proper plant production is highly valued. One of the central factors to maintain plant production is how to control key pests of the plant such as the root-knot nematode, Meloidogyne incognita, the stem borer, Lophobaris piperis, the tinged bug, Dasynus piperis, and the bug, Diconocoris hewetti (Chapter 1). Currently, farmers habitually use synthetic pesticides to control these pests. However, this habit poses not only a serious health risk to local workers and the people living near the treated areas, but also threatens non-target species (Chapter 2). Therefore, it has become an important issue to find relatively easy alternative control strategies, which are comparable effective as the synthetic pesticides, but safer to the farmers, consumers, and the environment and available at low price. One of the possible alternatives would be the use of botanical pesticides. Indonesia seems to be in a good position to develop and utilize this pesticide since the country has a rich biodiversity of plant species. Nowadays, the increased consumer request in developed countries for organic products stimulates the interest in the use of botanical pesticides.
Chapter 3 describes the nematicidal activity of 17 plant extracts against the root-knot nematode, M. incognita. Results demonstrate that shapes of the dead nematodes in laboratory experiments can clearly be distinguished differed in a characteristic way, and groups of pesticides and plant extracts. This phenomenon may be an indicator for the modes of action of the tested pesticides. The green house experiment indicates that raw material of clove bud is comparable effective as the recommended synthetic pesticide. Chapter 4 describes contact toxicity, oral toxicity and repellency of 17 plant extracts against the model insect species Tribolium castaneum. This study shows that the most promising candidates for consideration as botanical pesticides are extracts of pyrethrum, sweet flag, tobacco, clove, lemongrass, neem, vetiver, graviola, citrosa and black pepper.
Formulation of three of 10 most potent extracts was developed and tested in the laboratory followed by field experiments. Laboratory experiments indicate that extracts from pyrethrum, sweet flag and clove show the highest toxicity and/or repellent effect toward L. piperis. Field experiments reveal that the formulation is able to control most pest species of the pepper plants in the meantime being less toxic towards the 11 monitored species of natural enemies for known pest organisms such as caterpillars, aphids, moths, beetles than that of the recommended synthetic pesticide, deltamethrin. Furthermore, the field experiments reveal that within 9 hours after application the treated plants are recolonized again by ants and spiders, indicating a short degradation period of the formulation.
Altogether it is concluded that the newly defined botanical formulation provides an effective and environmentally friendly alternative for controlling several pests of black pepper (Chapter 5).
The safety of five botanical pesticides i.e. pyrethrum, clove, sweet flag, and derris is evaluated for human oral exposure via consumption of treated products. Based on literature data from human and animal studies safe levels for daily oral exposure to the various botanical preparations and/or their active ingredients were derived and these outcomes were compared to the estimated maximal daily intake of residues of the botanical pesticides expected to be present on pepper berries treated with these preparations as pesticides. Results indicate that use of extracts of sweet flag containing beta-asarone would result in a MoE that would not indicate a high priority for risk management. However, because for beta-asarone restrictions in applications as food additive are indicated and since use as a pesticide implies an avoidable risk, it is concluded that the application of this botanical pesticide should not be encouraged. The use and use levels of the other three botanical pesticides evaluated are not of safety concern (Chapter 6). Finally, in chapter 7, the implications of the presented work are discussed, with emphasis on the potency, suitability and the safety of the botanical pesticides when used against pests associated with pepper plants. Overall, the results obtained confirm the hypothesis that botanical pesticides have the potency to be used to control pests of black pepper, providing a promising alternative for synthetic pesticide use, especially because they pose lower risks for the local environment.