In lettuce, previous research showed that planting sweet alyssum attracted hoverflies, a natural enemy that is an efficient predator of aphids. Flowering plants grown with an agricultural crop to attract, feed, and shelter pest natural enemies are called insectary plants. Many research studies describe positive effects of insectary plants and discuss their use to enhance biological pest management.
Natural enemies can be important for the management of aphids. The biggest issue with aphids is the indirect damage. Aphids are considered contaminants since consumers would rather not find aphids in their lettuce, dead or alive. Aphids directly damage lettuce by feeding on plants causing stunted seedlings or transplants and certain kinds of aphids carry viruses that infect lettuce. These viruses can yellow leaves and stunt plants, resulting in unmarketable lettuce. Therefore, growers should minimize the presence of aphids in lettuce fields. Compared to conventionally grown lettuce, organic lettuce growers have fewer options to manage pests and disease. More management tools are needed.
Area IPM Advisor Alejandro Del-Pozo Valdivia investigated if insectary plants can increase hoverflies and reduce aphids in organic lettuce. He set up a research trial to compare the number of hoverflies in fields without insectary plants, with one kind of insectary plant, and with more than one kind of insectary plant. Del-Pozo Valdivia also recorded the number of pest aphids in the lettuce to see if increasing hoverflies with insectary plantings reduced the numbers of aphids. He performed his research in organic Romaine lettuce fields using the insectary plant sweet alyssum by itself and sweet alyssum with other insectary plants, including cosmos and cilantro.
Using sticky traps, more pest aphids were found flying in fields without any insectary plants and fields with two or more kinds of insectary plants. Fewer pest aphids were found on sticky traps in fields with sweet alyssum by itself. Del-Pozo Valdivia inspected the lettuce for pest aphids and found that there were fewer aphids inside lettuce heads from fields with sweet alyssum alone. Similar to sticky traps, more aphids were found inside lettuce from fields without insectary plants and from fields with more than one kind of insectary plant. Hoverfly numbers were similar on sticky traps and in the lettuce for all fields.
Interestingly, Del-Pozo Valdivia did not see higher numbers of hoverflies in fields with insectary plants and no additional benefit by having more than one kind of insectary plant. He plans to continue this work in conservational biocontrol (protecting and enhancing naturally occurring beneficial insects) to find the correct mix of the different kinds of insectary plants that increase beneficial insects, reduce pests, and reduce pest damage to lettuce. His work increases grower and pest control adviser awareness of the benefits of insectary plants. Currently, insectary plants are used by organic vegetable growers on the Central Coast. It is anticipated that Del-Pozo Valdivia’s research and extension of his research results will increase grower and pest control adviser knowledge and increase their skill in using insectary plants as part of an IPM program to manage organic lettuce pests. Since Del Pozo-Valdivia’s goal is to reduce the use of broad-spectrum insecticides, he is also looking into using sweet alyssum in conventional lettuce fields to promote conservational biocontrol. Del-Pozo Valdivia’s vision is to increase the use of insectary plants combined with releases of beneficials using drones.
Long-Term Impacts
