Location: Crop Improvement and Protection ResearchTitle: Agronomy of strip intercropping broccoli with alyssum for biological control of aphids
Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2016
Publication Date: 2/24/2016
Citation: Brennan, E.B. 2016. Agronomy of strip intercropping broccoli with alyssum for biological control of aphids. Biological Control. 97:109-119.
Interpretive Summary: Broccoli is the second most economically important vegetable crop in Monterey county on the central coast of California with annual production value of more than $400 million from approximately 65,000 acres. Alyssum is a common insectary plant that is intercropped with organic broccoli to control aphids that are the primary insect pests in this region. Insectary plants are species planted in or around fields to provide habitat and food for beneficial insects. Agricultural land rent in this region of California is high, and thus for alyssum insectaries to be economical, growers need to minimize the amount of area allocated to insectaries. A 3-year study at the USDA-ARS in Salinas, California investigated several intercropping patterns for organic broccoli and alyssum. The study identified efficient intercropping patterns that will help farmers to maximize broccoli yields and obtain the pest control benefits from intercropping with alyssum. These results will benefit organic farmers, and may also help conventional farmers minimize pesticide use in broccoli.
Technical Abstract: Organic broccoli growers in California typically control aphids by intercropping broccoli with strips of alyssum (Lobularia maritima (L.) Desv.) which attracts hoverflies (Diptera: Syrphidae) that are important predators of aphids. A three year study with transplanted organic broccoli in Salinas, California evaluated agronomic aspects of broccoli monoculture (B100) and broccoli-alyssum strip intercropping on beds in replacement intercropping treatments where alyssum transplants replaced 4 or 8% of the broccoli transplants, and an additive intercropping treatment (B100+A100) where alyssum transplants were interspersed between broccoli without displacing it. The replacement patterns included alyssum planted on both lines of a bed (A100), beds with 50% broccoli and 50% alyssum transplants in different lines (B50A50D), and beds with 50% broccoli and 50% alyssum alternating in the same lines (B50A50S). To evaluate competition, shoot dry matter (DM) of alyssum and broccoli was measured at 36 to 43 days (harvest 1) and 59 to 66 days (harvest 2) after transplanting, and alyssum flowering was assessed at both harvests. The treatments performed consistently across years. The number of flowering alyssum shoots was highly correlated with alyssum DM. Per alyssum transplant, alyssum DM was highest in A100 and B50A50D at harvest 1, and by harvest 2 (3 to 7 days before broccoli maturity) was in order of A100 > B50A50D > B50A50S = B100+A100. Broccoli was much more competitive than alyssum and by harvest 2 produced larger broccoli shoots per transplant in B50A50S (122 g) and B50S50D (96 g) than the more ideally sized shoots (73 g) in B100 and B100+A100. The A100 pattern was the most efficient replacement intercropping strategy to provide hoverflies with floral resources through the whole season, however, additive intercropping may also be useful to augment floral resources early in the season without displacing broccoli. These results can help growers reduce the cost of alyssum intercropping in high-density broccoli systems (>100,000 transplants per ha). The practical management implications and future research needs to further improve the efficiency of these systems are discussed.