California Pepper Commission


Proposal Gilbertson Monitoring Thrips TSWV Development of IPM Strategy to Reduce TSWV

Project Title: Monitoring of thrips/Tomato spotted wilt virus (TSWV) in California peppers and the development of a regional IPM strategy for reducing the incidence andseverity of TSWV.


Project Leaders: Dr. Robert L. Gilbertson (Primary leader for correspondence)
Plant Pathology Department, UC Davis. Davis CA 95616
hone: 530-752-3163 FAX: 530-752-5674 e-mail:

Dr. Ozgur Batuman, Plant Pathology Department, UC Davis (

Dr. Neil McRoberts, Plant Pathology Department, UC Davis (

Dr. Brenna Aegerter, UC Cooperative Extension County Advisor, San Joaquin County (

Budget: $15,000/yr

Overall Objective:

Monitor and understand thrips population dynamics and incidence and development of Tomato spotted wilt virus (TSWV) in San Joaquin Valley pepper fields and develop a regional thrips/TSWV IPM strategy to reduce the incidence and severity of TSWV. This will also involve the assessing of a thrips degree-day model and TSWV risk index for predicting thrips and TSWV in pepper fields in San Joaquin Valley. Our long term objectives are to reduce the impact of thrips and thrips-vectored viruses on susceptible crops (i.e., tomato, pepper and lettuce) in California. We hope that by reducing thrips population levels within each crop, we can achieve a long term reduction in the incidences of thrips-vectored viruses.

Specific Objectives:

  1. Conduct surveys of selected pepper fields in San Joaquin Valley to gain insight into when and from where thrips and TSWV enters into commercial fields
  2. Assess the applicability of our degree-day model and TSWV risk index, which were developed
  3. Develop an IPM strategy for thrips and TSWV for San Joaquin Valley peppers


Thrips impact the pepper industry by (1) causing direct damage to pepper fruit through feeding damage and (2) spreading viruses (particularly Tomato spotted wilt virus [TSWV]) that cause significant yield losses. In conventional production, thrips are managed with insecticides. However, effective use of insecticides for thrips management requires accurate timing of sprays, usually in advance of population peaks, to limit feeding damage and virus transmission.

In the San Joaquin Valley, the source(s) of thrips migrating into pepper crops in the spring, both in terms of absolute numbers and the risk of vectoring TSWV, is not known. Pepper crops are thought to increase thrips and TSWV early in season, resulting in subsequent build-up in other crops (e.g., tomato). For this reason it is important to understand thrips population dynamics in pepper crops in order to reduce the impact of thrips and TSWV early in the season and develop more effective control programs. Better control of thrips in pepper and processing tomato will be mutually beneficial. Our overall goal is to determine whether the approach developed for processing tomato, which has shown some success, can be extended to peppers.

We propose to survey 3-5 pepper fields in the San Joaquin Valley with yellow sticky cards to determine thrips population dynamics and conduct regular inspections for TSWV development. We will also use our thrips degree-day model to see if we can predict peak thrips populations, and develop a risk index for pepper to predict TSWV threat in pepper fields. Because we are monitoring processing tomatoes in the area, data obtained from both crops will be useful for developing an IPM strategy. We are hopeful that the IPM strategy we have developed for processing tomatoes, which has helped reduce the incidence and severity of TSWV in Central Valley, will also work for peppers. All of the participants (Gilbertson, McRoberts, Batuman and Aegerter) are currently involved in a project funded by the California Tomato Research Institute (CTRI) to improve management of thrips-vectored TSWV in processing tomatoes in the Central Valley of California.



Tomato spotted wilt disease has the potential to cause serious losses in pepper production in California. In California, TSWV can be a very serious problem in pepper and the incidence of the disease has been increasing. It is now a serious disease of processing tomato and pepper production in many areas of the Central Valley. TSWV and possibly other tospoviruses cause spotted wilt in peppers. The virus is spread by at least 10 different species of thrips, but the Western flower thrips (Frankliniella occidentalis) is most important in California. The symptoms of the disease can vary, but young leaves develop extensive necrotic spots and streaks; eventually, young shoots may dieback and entire parts of the plant may collapse. One of the most diagnostic symptoms is chlorotic or yellow ringspots in fruit.

Tomato spotted wilt virus and the thrips vectors have a very wide host range. Tomato spotted wilt has been a difficult disease to predict and manage. One of the main reasons is that both the virus and the thrips vectors have very broad host ranges. Economic hosts include tomatoes, peppers, celery, legumes, lettuce, radicchio and many ornamentals; whereas weed hosts include nightshade, tree tobacco, sowthistle, prickly lettuce and jimson weed.

Understanding the biology of the thrips vector in critical to understanding the dynamics of tomato spotted wilt disease. TSWV is not-seed transmitted nor does it persist in debris; thus, the main means by which the virus spreads into and within pepper fields is by the thrips vector. The virus is acquired by larvae, but it is mainly spread by adults that have acquired the virus as larvae. Thus, adults can not acquire the virus, they can only transmit it.

Therefore, it is important to know when and from where adult thrips, carrying TSWV, enter pepper fields. As thrips can survive and reproduce on a diversity of plants, any of these can serve as potential sources of thrips/TSWV for peppers. Understanding the population dynamics of thrips in an area where TSWV occurs is the first step towards identifying the likely source of the vector.



Salary & benefits $9,500 (10% Project Scientist salary $7,000 and benefits $2,500)

Supplies $3,000

Travel $2,500

Total $15,000

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