California: Update on curly top virus

Following the detection of a large number of beet leafhoppers, a pest emergency has been declared in both Kerns and Fresno counties allowing growers temporary use of neonicotinoid pesticides.

The Curly Top Virus can stunt tomato plant growth and significantly reduce yields of the plants they infest.  It is  spread by a small insect known as the Sugar Beet Leaf Hopper. In the spring, when the rains stop and the foothills dry out, the Leaf Hopper migrates down to irrigated fields in search of food. Beyond tomatoes, beet leafhoppers are known to target many crops, including cantaloupe, cucumber, peppers, spinach, squash and watermelon. In 2013, it caused major damages to the processing tomato crop, reducing the size of the crop significantly. 

In order to protect California’s crops, each year the state-administered Beet Curly Top Virus program (see  https://www.cdfa.ca.gov/plant/ipc/curlytopvirus/ctv_hp.htm) enables early detection and treatment when necessary with a program to sprays hill regions, road sides and fallow fields to control the pests.

Until recently, curly top mainly affected the Centre and South tomato production areas of California, but in 2021 and 2022 unusual outbreaks affected the northern production areas, as reported by Melgarejo et al. (see reference and link to article below).  

After a 2023 crop which experienced minimal damages from the curly top virus, largely thanks to the wet conditions throughout the season, it appears that a large number of potentially virus-carrying beet leafhoppers could pose a threat to the tomato industry in Central and Southern California in 2024. However, new regulations were adopted by the California Department of Pesticide Regulations in January 2024 limiting the use of neonicotinoid pesticides in the production of certain agricultural commodities, including tomatoes for processing because these may present hazards to honeybees and other pollinators. Following this restrictions, growers are limited in effective pesticides they can use.

Consequently, in order to combat the beet leafhopper, the County of Fresno has declared a pest emergency on April 17 allowing the commercial growers to use neonicotinoid pesticides as an emergency measure in 2024. The County of Kerns had taken a similar measure on April 9. These two counties represent nearly a quarter of the total production of tomatoes in California.

For more information:
Tomas A. Melgarejo, Margaret K. Cespedes, Li-Fang Chen, Thomas Turini, Patricia A. Lazicki, Amber Vinchesi-Vahl, Robert L. Gilbertson, Unusual outbreaks of curly top disease in processing tomato fields in northern California in 2021 and 2022 were caused by a rare strain of beet curly top virus and facilitated by extreme weather events, Virology, Volume 591, 2024, 109981, ISSN 0042-6822,
Full article:  https://doi.org/10.1016/j.virol.2024.109981 

Sources: CDFA, Science Direct, Bakersfield.com