In summary, this study provides the first information on agronomic
aspects of strip intercropping transplanted romaine lettuce
with alyssum for biological control of aphids in organic systems in
replacement arrangements and novel additive arrangements. AlyssumDMwas
highly correlated with open inflorescences of alyssum,
and alyssum flower production increased with alyssum transplant
density. Lettuce was more competitive and productive than alyssum
in terms of shoot DM at the densities evaluated. Additive intercropping
appears to be a more efficient intercropping approach to produce
alyssum floral resources for beneficial insects. More research
is needed (1) to determine the minimum number of open inflorescences
of alyssum per ha necessary to achieve consistent biological
control of aphids in lettuce, (2) to understand adult hoverfly movement
into and within lettuce fields and if biological control of aphids
is influenced by insectary arrangement (i.e. scattered versus concentrated
alyssum strips), (3) to compare the effectiveness of insecticides
versus biological control of aphids with alyssum intercrops
in conventional lettuce, and (4) to determine if there are yield advantages
in additive intercropping systems. Furthermore, it would also
be useful to know if the agronomic aspects of intercropping alyssum
and lettuce differ in transplanted versus direct-seeded production
systems. A novel approach for intercropping alyssum and lettuce
in direct-seeded fields would involve seeding a desired mixture of
pelleted alyssum and pelleted lettuce seed.