Tiny Weed Threatens California Tomatoes

California’s tomato industry, which supplies 95 percent of the nation’s processed tomatoes and a significant portion of the world’s crop, faces a formidable threat in Orobanche ramosa, a parasitic weed. This invasive plant has re-emerged in tomato fields across several Central Valley counties, sparking concerns that it could decimate a significant portion of this vital crop. 

Think of all the tomato products used that could be affected by tomato shortages. Popular food dishes like pizza, pasta, ketchup, and many other sauces would be impacted, creating a potential economic impact on our farming industry, groceries, and restaurant sectors. Grocers and restaurants would need to raise prices to accommodate, directly impacting consumers with another price increase. As small as the Orobanche Ramona plant is, the impact on tomato crops would be devastating.

In 2018, California contributed to over 90 percent of the 12 million tons of tomatoes grown in the United States, highlighting this industry’s crucial role in our state’s agricultural economy. Unfortunately, Orobanche ramosa, commonly known as branched broomrape, is listed as an “A” noxious weed by the California Department of Food and Agriculture (CDFA). The discovery of this weed in California tomato fields triggered quarantine measures and crop destruction without harvesting, resulting in substantial economic losses for farmers.

The impact of Orobanche ramosa on tomato yields can be devastating. In regions where this parasitic weed is prevalent, yield reductions range from moderate to a staggering 80%, depending on factors such as infestation levels, host plant types, and environmental conditions. Controlling Orobanche ramosa presents significant challenges due to its unique biology and complex life cycle. “Much of its life cycle occurs beneath the soil surface, making it difficult to detect and control before causing harm to host plants. Most of the damage occurs before you can see it,” said Brad Hanson, a professor of Cooperative Extension in plant sciences, who is extensively involved in the Orobanche research at UC Davis. 

In a UC Davis report, “Parasitic Weeds Threaten Tomato Plants on California Farms,” researcher Emily Dooley stated, ”There’s a lot of ripples to the problem. We could see it spread to other crops and other regions in the state if it’s not managed.” 

Additionally, the short period between emergence and seed dispersal complicates detection and control efforts. The weed’s tiny seeds — smaller than finely ground pepper — can survive in the soil for many decades and be carried by wind, water, soil transfers, and even footwear. Because the weed is considered a quarantine pest in California, crops must be destroyed once a case is reported, and no susceptible crops can be planted for the next two years. 

Efficiently managing Orobanche ramosa necessitates a long-term, integrated approach that involves a deep understanding of the weed’s biology and disseminating effective management practices to all stakeholders, in which Western Plant Health members are directly involved. 

WPH member companies highlight the dangers of failing to control this parasitic weed. “If left unchecked, this weed will extend beyond tomato fields. It could spread to other crops and regions within the state, impacting farmers and their workers and communities reliant on agriculture and the broader food industry.”

UC Davis researchers are conducting experiments on controlled crop areas to find an effective and long-lasting solution to eradicating the weed. Last year, CTRI (California Tomato Research Institute) and UC Davis Plant Science Researchers got state permission for a herbicide treatment that, in trials, has reduced Orobanche emergence fourfold. “That management treatment has been used extensively by growers this year,” said Zach Bagley, managing director for the CTRI.

California’s tomato future lies with researchers at UC Davis and WPH members who support the farming community and tomato industry. Their work is critical in developing strategies to eliminate Orobanche ramosa and safeguard California’s vital tomato industry. The outcome of this research effort will have far-reaching implications, affecting not only the availability of tomatoes but also the prices of the countless products that rely on this essential ingredient.

Harvesting ripe tomatoes in an agricultural field


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