This season, the home gardening magazines seem to have added biological control to the multitude of benefits that flowers bring to the landscape. By providing nectar and pollen, flowers can attract and keep the natural enemies of many pests in the home landscape. Lists of flowers that are especially effective at bringing in predators and parasites seem to pop up everywhere. Whether or not planting a specific flower will actually help reduce the abundance of a problematic garden pest depends on how effectively the flower brings in the more effective natural enemies.
A Rutgers University study used two wasp parasitoids of Colorado potato beetle to explore how flower architecture and nectar scent affect parasitoid attraction and retention. Using artificial flowers, they found that the presence of flower nectar greatly increased the time the wasps stayed on the flower when compared with a sugar control. Parasitoids stayed on artificial flowers when the nectar source was easily reached.
The rate at which parasitoids left flowers was strongly correlated with the degree of nectar concealment. They classified flower types by degree of nectar concealment, and planted them in a garden. Using video cameras to follow foraging activity, they found nectar accessibility did indeed increase residence time on flowers. Interestingly, they found that on umbelliferous flower types, nectar accessibility was determined by both flower morphology and strength of the parasitoid. Pediobius foveolatus, the stronger of the two parasitoids in this study, was better able to spread petals and stamens than Edovum puttleri. As a consequence, it stayed much longer on flowers.
Thus it seems that both flower architecture and insect morphology are intrinsically linked to successful foraging. Still, the idea of prescribing flowers to manage pests has a long way to go. Other factors including location of flowers relative to sunlight and the pest, stability, volume, and composition of nectar need to be explored (MBCN Vol. IV, No. 5). For now, getting home gardeners in the habit of planting more flowers may make it easier to get them to plant the flowers that could help them with pest problems in the future.
Patt, J. M., G. C. Hamilton, and J. H. Lashomb. 1997. Foraging success of parasitoid wasps on flowers: interplay of insect morphology, floral architecture, and searching behavior. Entomol. Exper. Applic. 83:21-30.
Fungus Controls Damping-Off
Soilborne diseases are constant problems in the horticultural industry, requiring the use of chemical fungicides. For years people have observed that some soils tend to suppress soilborne diseases. Beneficial soil microorganisms are responsible for this disease suppression. Gliocladium virens is an antagonistic fungus that can control damping-off caused by the fungi Pythium ultimum and Rhizoctonia solani. In greenhouse experiments with a nonsterile soilless mix, G. virens controlled damping-off of zinnia, cotton and cabbage. It was the most effective at controlling disease of 50 isolates of fungi and bacteria tested. Twenty isolates of G. virens varied in their efficacy in controlling the damping-off fungi; some were able to control Pythium, but not Rhizoctonia, and vice versa.
Disease control lasted for at least two months when G. virens was introduced with the pathogen and the mix was planted with zinnia seeds at intervals. These tests showed G. virens would be useful in the greenhouse production of bedding plants.
A commercial formulation of G. virens strain G1-21 is now available (SoilGardŽ by Thermo Trilogy, Columbia, MD) for control of damping-off and root rots of ornamental and food crop plants grown in greenhouses, nurseries, and interior gardens.
Lumsden, R. D. and J. C. Locke. 1989. Biological control of damping-off caused by Pythium ultimum and Rhizoctonia solani. Phytopathol. 79(3): 361-366.
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