Date of Award


Degree Name

MS in Agriculture - Plant Protection Science


College of Agriculture, Food, and Environmental Sciences


David H. Headrick

Advisor Department

Horticulture and Crop Science

Advisor College

College of Agriculture, Food, and Environmental Sciences


The efficacy of two different autonomous Ultraviolet-C (UV-C) units on two spotted spidermite, Tetranychus urticae Koch (Acari: Tetranychidae), and greenhouse whitefly, Trialeurodes vaporariorum. (Hemiptera: Aleyrodidae). was tested in four commercial strawberry fields in California.

In 2020, California strawberry growers used 12 million pounds of active ingredients (AIs) to keep pests under economic thresholds. While pesticides are an important part of an integrated pest management program, their use poses threats to the environment and human health. To protect agricultural workers, the public and the environment, regulators in California have consistently limited or removed the use of certain pesticide AIs. For strawberry growers in the state, this trend signifies that reliance on pesticides may not be a sustainable approach. Resistant pest populations further intensify the need for more sustainable pest control measures. Tetranychus urticae populations in California strawberry production have documented resistance to at least three AIs; abamectin, bifenazate, and hexythiazox. Trialeurodes vaporariorum populations in California strawberry production have documented resistance to five AIs; imidacloprid, thiamethoxam, dinotefuran, acetamiprid, and chlorpyrifos.

To address this issue, stakeholders must invest in research and development of new non-chemical control methods. One of these methods is the use of autonomous UV-C for pest control. These systems emit UV-C radiation, which affects the cellular and genetic structure of organisms, leading to detrimental effects. One unit, by Tric Robotics, emits an avg of 250 J m−2 of UV-C irradiation and was tested in three different strawberry fields. Another unit by Saga Robotics emits an avg of 200 J m−2 was tested on a single field different from the first three. In each field, a plot was treated with UV-C twice weekly at night. Untreated controls were not possible with this study, so UV-C has been tested against each grower’s standard (GS) treatment. Twenty leaflets from the middle and 20 bottom tier of the strawberry plant canopy were collected weekly to assess the presence of T. urticae and T. vaporariorum. Samples were compared using Kruskal-Wallis rank sum tests with Bonferroni adjusted Dunn tests in the R statistical environment. The data showed that UV-C may be an effective tool for the control of certain T. vaporariorum stages in strawberry. Follow-up studies with untreated controls are needed to validate the efficacy of UV-C on T. urticae and further validate the positive results observed on T. vaporariorum.