Beneficials Sweet on Alyssum

July 22, 2009

INTERPLANTING SWEET alyssum (Lobularia maritima) is an excellent way to promote natural biocontrol of a wide array of landscape, orchard, field and garden pests like aphids, stinkbugs, leaf and fruit worm caterpillars, etc. Companion planting has ancient roots, figuring in the writings of the Greek Theophrastus in 300 B.C. and the Roman Pliny (Plinius Secundus) in 1 A.D. Though popular in organic gardening and farming, floral interplants escaped serious scientific scrutiny until recent years.

Australia’s wine grape growers are among those who take their sweet alyssum companion plantings very seriously. At Australia’s EH Graham Centre for Agricultural Innovation ecological engineers and entomologists like Geoff Gurr of Charles Sturt University are fine-tuning companion planting. Firstly, you need to choose companion interplants that supply nectar, shelter and other resources to beneficial predators and parasites but not to pest species.

The Aussies focused their scientific studies on a Trichogramma species parasitizing and destroying the eggs of the lightbrown apple moth (Epiphyas postvittana), a key pest of Australian vineyards. In “clean” vineyards where weeds and ground covers are destroyed by herbicides or cultivation, biocontrol species like Trichogramma may survive as few as two days, versus three days with water only and up to 20 days with sweet alyssum (the best ground cover tested). Alyssum flowers doubled the number of moth eggs parasitized over a 10 day period. In contrast, when the alyssum plants were deflowered the Trichogramma perished and there was little biocontrol.

But there is more to the story. “Not only is plant species important, but the cultivar within the species is critical,” Gurr told an Entomological Society of America annual meeting. For example, Trichogramma survive far longer on white-flowered alyssum cultivars compared to purple and other colors. Alyssum also boosted predators without aiding the apple moths, which was not the case for every ground cover interplant tested.

Most landscape and cropping systems have not been subjected to the same level of ecological and laboratory investigation as Australian wine grapes. Thus, Rincon-Vitova and other insectaries selling beneficial insects generally recommend blends of flowering plants supplying floral nectar throughout the season.

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