This FAQ complements the voluntary compliance agreement framework developed by the CDFA Broomrape Board. UC researchers will continue to update these recommendations based on new findings and industry feedback. For questions or to request a field visit, contact your local farm advisor or the UC Broomrape research team.
- Q: What is branched broomrape?
- Branched broomrape (and other broomrapes) are parasitic plants that attach to the roots of other “host” plants. These plants do not have chlorophyll or a real root system of their own, instead they are completely dependent on extracting water and nutrients from the host. Parasitism by broomrape can greatly reduce the productivity and yield of the host plant. It doesn't damage crops like a weed you can spray and walk away from - it hijacks the plant before symptoms are even visible. By the time you see broomrape above ground, the yield loss is already underway. Broomrape seed only germinate if they receive a signal that there is a suitable host root nearby, else the seed can stay dormant in the soil for decades.
- Q: What crops and weeds are affected by broomrape in California?
- As of 2025, the only crop known to be affected by branched broomrape in California is tomato, primarily in the southern Sacramento Valley counties. Broomrape has been observed on some weedy plants common to the region, particularly nightshades. However, information in the scientific literature indicates that branched broomrape has a fairly wide host range that includes several important annual broadleaf crops grown in California. Greenhouse testing at UC Davis with broomrape seed collected in California indicates that the population has some ability to parasitize many crops, but that tomato is the most sensitive so far. Although broomrape has not been reported in the central and southern San Joaquin Valley thus far, there is no information to suggest that the weed could not also become established in that region.
- Q: When do you expect to see broomrape plants in tomatoes in California?
- The lifecycle of branched broomrape begins with germination, followed very quickly by attachment of the broomrape root to a host root. After attachment, an underground mass of tissue forms and after a period of time multiple shoots grow towards the soil surface and emerge. These above-ground stems can flower and set seed within a few weeks of emergence. Broomrape seed can only germinate in the presence of a host root, so germination cannot happen before tomato transplanting in the spring. Research data at UC Davis suggests that germination and early attachments begin a few weeks after transplanting but that emergence of the stems aboveground begins around 4-6 weeks after transplanting. The length of the period of emergence can vary among years and even planting dates within a year and this is thought to be due to soil-temperature conditions affecting germination.
- Q: Why should I care about broomrape?
You should care because:
It’s highly aggressive and nearly invisible early on. A single plant can produce thousands of tiny seeds that stay viable in soil for decades.
There’s no silver bullet. Control requires early detection, sanitation, and coordinated management, not just a one-time herbicide, cultural practice or genetic solution. Although these types of solutions are being researched and worked on at UC Davis and other institutions, with industry support, there is not expected to be one size fits all easy management fixes in the near or medium term.
It can trigger regulatory action. Even though compliance agreements are just rolling out in 2025, they’re the bridge to keeping harvests flowing in future seasons. A confirmed broomrape finds without a mitigation plan, per these Compliance Agreements, could result in a hold order that delays or halts harvest.
It’s already here and spreading. Infestations have been confirmed in multiple counties. Once introduced, it’s difficult and expensive to avoid and manage around.
Perhaps most critically, yield impacts in countries where broomrape has been allowed to establish are severe. In regions of southern Europe, the Middle East, and North Africa, broomrape infestations have caused up to 70% yield loss in tomato crops. In some cases, entire fields are abandoned due to the impracticality of continued production. California’s aggressive, science-driven response is about avoiding that future, preserving both productivity and profitability.Perhaps most critically, yield impacts in countries where broomrape has been allowed to establish are severe. In regions of southern Europe, the Middle East, and North Africa, broomrape infestations have caused up to 70% yield loss in tomato crops. In some cases, entire fields are abandoned due to the impracticality of continued production. California’s aggressive, science-driven response is about avoiding that future, preserving both productivity and profitability.
- Q: How should I scout for broomrape?
- Broomrape plants are short and do not usually extend above the tomato canopy and can be challenging to see. Training equipment operators, weeding crews, and other field personnel to identify and report broomrape is recommended. The broomrape plants are pale yellow in color (they do not have chlorophyll and are not green plants) and have lavender or light purple flowers arranged on each stem. Multiple stems from a single attachment often look like “clumps” of broomrape plants emerging in a small area. Since broomrape is attached to tomato roots and the bulk of the tomato root system is near the buried drip lines, most broomrape emergence within or very near the tomato row in single row planted beds and or on the side of the row nearest the drip line in two-row planting configurations. Because broomrape emergence can extend for several weeks and the above ground portion of the lifecycle is relatively short, fields may need to be scouted multiple times within a season.
- Q: Should my level of concern change depending on where I farm?
Whether or not you've seen broomrape on your farm, your level of concern should reflect:
Your geographic proximity to known infestations. If you farm in or near designated zones (outlined in CDFA's Designated Zone Map), your exposure risk is higher.
Your equipment movement patterns. If you share equipment with other growers, lease land, or move between regions, you're more likely to unknowingly transport seeds.Your long-term business outlook. Even if you’re not directly impacted today, your processor, transporter, or neighboring grower might be. Industry-wide coordination helps maintain market access and avoid fragmented regulation.
The bottom line: broomrape is not just someone else’s problem. It’s an emerging industry issue that demands proactive, regionally informed vigilance. The earlier we act, the better chance we have of avoiding the costly outcomes seen elsewhere in the world.
- Q: What makes a field "high-risk"?
- In the 2025 compliance agreements developed by the CDFA Broomrape Board and industry stakeholders, the term “high-risk field” replaces what was historically labeled as an “infested field.” This change isn’t just semantics, it reflects a practical, grower-supported shift in how the industry is managing the presence and spread of broomrape. A “high-risk field” is one where there is either a known detection of branched broomrape or a reasonable likelihood of exposure—for example, through shared equipment, soil movement, or proximity to past detections. Importantly, this classification does not require a grower to confirm or declare an infestation in order to participate. The focus is not on fault or declaration—it’s on coordinated management.
- Q: How does broomrape spread?
Broomrape spreads in ways that are deceptively simple and dangerously effective. The plant produces tiny seeds (less than 0.3 mm) that are not visible to the naked eye, and a single plant can produce up to 100,000 seeds in one season. These seeds are incredibly resilient, capable of surviving dormant in soil for decades while waiting for the right chemical signals from host roots to germinate.
Once broomrape is present in a field, it spreads through three main pathways:
- Contaminated Soil Movement
Soil is the primary vehicle for broomrape seed spread. Any activity that moves soil between fields, such as tillage, harvest, transport, or even irrigation runoff, can carry seeds. Contaminated soil stuck to boots, tires, or equipment can travel miles before being deposited in a new location.
- Equipment (particularly those that are used on multiple operations) Contamination
Harvesters, trailers, tractors, transplanters, etc. that are not thoroughly cleaned can carry broomrape seed from infested fields and regions to clean ones. Even a thin layer of soil or a small amount of plant debris can be enough to establish a new infestation.
- Field-to-Field Human Activity
Field crews, crop consultants, and even visitors can unintentionally transfer seeds on their footwear or clothing. This makes crew hygiene and training especially important, particularly during the periods when these activities are common – like during hand weeding.
- Contaminated Soil Movement
- Q: What about seed imports or wind?
- Imported seed lots were once a suspected pathway, but the 2024 genetic analysis of broomrape populations across California found strong evidence that infestations stem from a single historical introduction, not multiple reintroductions from contaminated seed stock. Imported seed is still worth screening carefully, but it's not the dominant risk today. Wind and water are minor contributors. Broomrape seed isn’t adapted for long-distance wind dispersal. While heavy rain could move seed within a field, it’s not considered a major mechanism for regional spread.
- Q: Why is it so persistent?
- Broomrape’s survival strategy hinges on its seed longevity and stealth. Because it parasitizes the host underground, you might never know it’s there until the damage is done. And by the time above-ground shoots emerge, it’s already tapped into your crop’s vascular system. Preventing spread isn’t about a single action - it’s about building habits: cleaning equipment, isolating high-risk fields, scouting early, and coordinating as an industry.
- Q: Where did broomrape come from? Should I worry more about my rotations with seed supply from other countries or about the movement we have been doing internally and unknowingly in California?
Branched broomrape was first detected in California nearly a century ago—with documented outbreaks in the 1920s, 1950s, and 1970s—and has resurfaced in the modern era with detections since 2009, most recently in Yolo, San Benito, and San Joaquin Counties. Recent populations genetic research (Schneider, 2024) provides important new insights. By analyzing broomrape DNA from both contemporary field detections and CA specimens dating back to the 1920s, researchers found strong evidence that the genetic similarity of samples over time are not repeated introductions via imported seed, but rather a persistent seed bank re-emerging under favorable conditions.
This has two big takeaways for growers:
- Worry less about seed imports. The data show no link between California's current infestations and broomrape populations in Chile or elsewhere. The California group is genetically distinct and has not been reintroduced from overseas sources in recent decades.
- Worry more about what’s already here—and how it's moving within the state. Broomrape likely persisted undetected for years in low populations and was inadvertently spread between fields and counties via equipment, soil, trailers, and even boots. This internal movement is now the primary driver of risk.
The good news? This finding means California still has a chance to contain the problem before it reaches the scale seen elsewhere. But it also means that local decisions matter. If contaminated equipment or soil moves from a high-risk area to a clean field, that’s how new infestations start.
Bottom line: the greatest risk isn’t imported—it’s internal. Preventing spread today depends on sanitation, scouting, and early detection
- Q: I’ve heard Matrix herbicide is effective on broomrape. How do I apply it to control this unusual weed?
- Matrix is commonly used in tomato for control nightshades and other weeds as a PRE or POST foliar spray. Foliar treatments of Matrix have NOT BEEN EFFECTIVE for branched broomrape control. The use pattern for control of broomrape with Matrix is described in a 24c Special Local Needs label that was approved in 2023. In this use pattern, Matrix is injected into the drip irrigation system (chemigation) at a rate of 1.33 oz/A three times after tomato transplanting during the period of time when broomrape seed are germinating and attaching to the tomato root. Current recommendations are for these treatments to be applied at approximately 20, 40, and 60 days after transplanting. See here for a more complete description.
- Q: Does QAC sanitizer kill broomrape seed on field equipment?
- Quaternary Ammonium Compound (QACs) have been shown to make broomrape seed unable to germinate in lab tests at UC Davis and are the recommended method for sanitizing field equipment to reduce the risk of spreading seed among fields and regions. A major caveat to this recommendation, though, is that QACs are deactivated in the presence of soil and plant debris. Therefore, field equipment MUST be physically cleaned, preferably with air compressors and power washing BEFORE sanitizers are applied as the final step in the cleaning process. Simply applying QAC sanitizers to equipment covered in large amounts of soil and plant debris is likely not effectively killing seed (or other pathogens of concern) on field equipment. See here for a more complete description.
- Who can I contact for questions about broomrape?
- If you have questions about broomrape, you can email the CDFA or reach out to your local California farm advisor.