Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 27, 2013
Publication Date: April 6, 2013
Citation: Brennan, E.B. 2013. Agronomic aspects of strip intercropping lettuce with alyssum for biological control of aphids. Biological Control. 65(3):302-311. Interpretive Summary: Lettuce is the most economically important vegetable crop in Monterey county on the central coast of California with annual production value of more than one $ U.S. billion. Beneficial insectary plants are species planted in or around fields to provide habitat and food for beneficial insects. Alyssum is a common insectary plant that is intercropped with organic lettuce to control aphids that are the primary insect pests in this region. Agricultural land rent in the primary lettuce growing regions of central coast of California is high, and thus for alyssum insectaries to be economical, growers need to minimize the amount of area allocated to insectaries. A 2-year study at the USDA-ARS in Salinas, California investigated novel intercropping patterns for organic lettuce and alyssum. The study identified more efficient intercropping patterns that will allow farmers to maximize lettuce yields and obtain the pest control benefits of alyssum. These results will benefit organic farmers, and may also help conventional farmers minimize pesticide use in lettuce.
Technical Abstract: Organic growers in California typically devote 5 to 10% of the area in lettuce (Lactuca sativa L.) fields to insectary strips of alyssum (Lobularia maritime (L.) Desv.) to attract syrphid flies (Syrphidae) whose larvae provide biological control of aphids. A 2-year study with organic romaine lettuce in Salinas, California investigated agronomic aspects of monoculture lettuce and lettuce-alyssum strip intercropping on beds in five replacement intercropping treatments (RIT) and two additive intercropping treatments (AIT). The monoculture and RIT had 65333 transplants ha-1 and the AIT had the monoculture density interspersed with 1600 or 5333 alyssum transplants ha-1. Alyssum replaced 2 to 8% of the lettuce plant ha-1 in the RIT. Due to increased competition, alyssum transplants produced less shoot dry matter (DM) in the AIT (18 g) than RIT (31g). The number of open inflorescences of alyssum increased with alyssum DM, and ranged from 2-15 open inflorescences head-1 of lettuce among treatments. Lettuce plant DM was lower in AIT (38 g) than RT (40-51 g), and monoculture lettuce had greater N concentration than some RIT and both AIT. At the same lettuce density, N content of lettuce was approximately 30% greater and lettuce C:N was lower in L100 than the AIT indicating that lettuce and alyssum competed for N in the AIT. Estimated yields of large lettuce (=50 g DM head-1) were greatest in a RIT where lettuce and alyssum alternated within both lines, however, total yields of large and small lettuce (38-49 g head-1) were greatest in the AIT where lettuce densities were greatest. Practical aspects of implementing lettuce-alyssum strip intercropping and alternative approaches to maximize intercropping efficiency are discussed.