The number of natural predators around greenhouses significantly increases relative to standard verges with short-mown grass. The bushes, trees, and flower fields provide natural enemies with alternative prey, pollen, nectar, and hiding places, allowing populations of natural enemies to establish and develop. However, this also results in more pests, such as thrips, appearing next to the greenhouse, writes Margreet Schoenmakers on behalf of Knowledge in your Greenhouse.
In agriculture and horticulture, maintaining biodiversity is of great importance for the pollination of crops and the control of pests. However, the extent to which the immediate environment of greenhouses influences pest control within greenhouses is largely unknown. Therefore, flower fields, trees, and shrubs next to greenhouses in the Bommelerwaard and Oostland areas (the Netherlands) were monitored for 2 to 3 years.
The planted trees and shrubs proved to be particularly useful for the early attraction and facilitation of predators with specific aphid species that are not harmful to greenhouse crops. As such they can be an important addition to flowering herbs that mainly provide nectar and pollen for natural enemies.
However, the study also shows that the increasing diversity of flowering plants near greenhouses raises the total densities of thrips, including potential pest species such as Thrips tabaci and Thrips fuscipennis. The extent to which these populations migrate to greenhouses is unclear and needs to be further investigated.
The analysis of thrips and thrips predators per flowering plant species shows interesting differences. The flower samples reveal there is a large variation in attractiveness to thrips between the plant species. This offers opportunities to select plant species that are not very attractive to thrips while being good host plants for Orius.
Aside from contributing to the general recovery of biodiversity, the research shows that functional biodiversity has great potential as the increased numbers of natural enemies contribute to the control of pests in and around greenhouses. To what extent this can actually be achieved without running too many risks of increased pest pressure needs further research.
The research was conducted by WUR Greenhouse Horticulture and was funded by the Dutch Ministry of Agriculture, Nature and Food Quality through the Top Sector Horticulture & Starting Materials, the KIJK foundation, the municipalities of Pijnacker-Nootdorp, Westland, and Greenport West-Holland.
See also: Functional Biodiversity in and around the Greenhouse (in Dutch)