lettuce infected with downy mildew

Lettuce downy mildew caused by Bremia lactucae is an important disease that can significantly reduce the quality and marketability of lettuce. This disease is controlled using fungicides, by modifying the environment to reduce humidity, and by planting varieties containing downy mildew resistance (Dm) genes. B. lactucae evolves rapidly resulting in new races leading to the breakdown of resistance in downy mildew resistant (DMR) lettuce varieties, and fungicide resistance, threatening the available control methods.

In March 2021 the tospovirus Impatiens necrotic spot virus (INSV) was identified in lettuce fields in the Yuma growing region. This is a new disease for iceberg lettuce growers in Arizona. How the virus was introduced into Yuma County has not been determined and the impact is difficult to predict. INSV is reported to infect hundreds of plant species including ornamentals, crops and weed species. Symptoms include necrotic spots, tip dieback, stunting, yellowing and death. The disease is vectored by thrips, primarily by western flower thrips.

Fusarium wilt of lettuce is severely impacting productivity of the Arizona lettuce industry. The disease, caused by a soil-residing fungus that once established may persist in soils indefinitely, has spread widely throughout Arizona's lettuce growing regions since it was first identified in Arizona in 2001. Romaine cultivars can tolerate the pathogen better than head lettuce, but even with this tolerance, romaine crop losses occur in fields with high disease pressure. Currently, there is no effective treatment to mitigate the disease in lettuce.

This project addresses the number one priority issue from the 2018 Arizona Iceberg Lettuce Research Council (AILRC) survey: Disease Control and Management. The Yuma Center of Excellence for Desert Agriculture (YCEDA) was established to be responsive to the critical needs of the production agriculture industry.  Fusarium wilt of lettuce is one of the challenges prioritized by YCEDA stakeholders, and we are working on several fronts to investigate strategies to control this disease.

field work at the trial site

This project addresses the number one priority issue in the 2018 AILRC survey: Disease Control and Management. Fusarium wilt of lettuce caused by the soil-residing fungus Fusarium oxysporum f.sp. lactucae (fol) has increasingly become a problem in iceberg lettuce in Arizona, causing significant losses in early season iceberg lettuce crops.

Fusarium wilt of lettuce field trial

Since 2015, The Yuma Center of Excellence for Desert Agriculture (YCEDA) has managed Fusarium wilt of lettuce field trials evaluating commercial and pre-commercial lettuce cultivars for resistance to Fusarium wilt, chemical and biological crop protection products for disease suppressing activity, and cultural management methods.

Fusarium wilt of lettuce continues to be a growing threat to the competitiveness of the Arizona iceberg lettuce industry, and unlike most plant diseases, there is no known treatment to control this soil-borne disease completely.  The Yuma Center of Excellence for Desert Agriculture (YCEDA) is leading multiple projects conducting research to find solutions to this plaguing problem.  The objectives of this project were developed based upon findings from our 2016 study, “Advancing Fusarium wilt management in lettuce",  which revealed the need for more precise and reproducible methods for inocu

Prior to submitting the proposal, Lettuce Fusarium Wilt Trials and Analysis, to the AZ Department of Agriculture's Specialty Crop Block Grant Program, YCEDA convened a meeting with members of the production Ag industry to receive guidance and ensure the research would address industry needs. $69,000 was awarded to continue efforts to mitigate Fusarium Wilt of lettuce. 

November 2105 International Symposium on Fusarium Wilt of Lettuce in Yuma, AZ

The 2015 Conference on Excellence in Desert Agriculture focused on Fusarium wilt of lettuce. The Yuma Center of Excellence for Desert Agriculture (YCEDA) brought together the world's foremost researchers and industry professionals to share their knowledge on this insidious disease. The purpose of hosting this conference was twofold: (1) to share and disseminate information from academia and industry and (2) to build a collaborative road map for future endeavors to control Fusarium wilt and increase productivity and profitability.

October 2016 FW Conference in California

A 2016 Fusarium conference for researchers and industry was held in the Salinas area to advance the priority suggestions from the 2015 symposium. Breakout sessions focused on future research projects and field evaluation of resistant varieties and crop protection products. Attendees were able to tour the area's lettuce industry and research institutions.

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