Companion planting guide › Sweet alyssum with lettuce for aphid control

Sweet alyssum with lettuce for aphid control: does it work?

Proven Consistent benefit shown in replicated field research or long-running extension trials.

Alyssum flowers feed hoverflies whose larvae eat lettuce aphids; USDA-ARS found sparse alyssum plantings controlled aphids in organic romaine.

1. Brennan E.B. (2013). Agronomic aspects of strip intercropping lettuce with alyssum for biological control of aphids. Biological Control 65:302–311 (USDA-ARS Salinas).
2. Ag Alert (Mar 19, 2014), reporting USDA-ARS researcher E. Brennan's decade-long alyssum study.

Mechanism

Insectary: pollen and nectar for hoverflies (Syrphidae), whose larvae are aphid predators.

What the research found

• Organic growers in California typically devote 5–10% of lettuce area to alyssum strips (Brennan 2013).
• Additive intercropping (alyssum added without removing lettuce) produced 2–15 open inflorescences per head; lettuce heads were slightly smaller with lower N, showing competition (Brennan 2013).
• In the long-term ARS study, about 500–1,000 alyssum transplants per acre spread through the field gave aphid control without reducing marketable head weight (Brennan, reported in Ag Alert 2014).

Caveats

Evidence is from coastal California lettuce. Flowering must coincide with pest pressure. Alyssum competes for nitrogen.