Herbicide Protocol

Herbicide approaches:  Matrix SG (active ingredient rimsulfuron) applied via chemigation is the only currently-approved herbicide program for management of branched broomrape in CA.

Note: while Matrix and similar herbicides are commonly sprayed PRE or POST emergence for weed control in tomato, these spray-applications DO NOT provide control of broomrape.  Instead, broomrape control is achieved with the herbicide injected into the subsurface drip irrigation system so that it is placed directly in the soil surrounding the tomato roots where it can kill broomrape seed at germination or shortly after attachment to the tomato.

Growing Degree Day Calculator
  1. Matrix chemigation for management of broomrape in tomatoes is allowed by a Section 24(c) Special Local Need Label (EPA Reg No. 352-768; SLN#303093).
    1. Consult the SLN label for details:
      1. Matrix is applied three times at 1.33 oz Matrix/A (total of 4.0 oz/season).
      2. Label rec: apply at approximately 30, 50, and 70 days after transplanting
      3. Inject Matrix into the chemigation/fertigation system at approximately the midpoint of the irrigation set to limit movement of the herbicide beyond the tomato root zone.
        1. The amount of water and injection time may vary depending on the irrigation system and soil type.  The goal is to get uniform distribution of the herbicide across the field and move it through the tomato root zone at each application.
      4. Ensure sufficient water at the end of the irrigation set to flush the herbicide from the system.
    2. Limitations:
      1. Do not apply more than 4.0 oz/A Matrix on tomato during the same year
      2. Do not make more than 3 applications of Matrix per year
      3. Preharvest Interval: do not apply within 45 days of harvest

Note: After the 24c label was approved, UC research showed that earlier treatment timing (e.g., ~20, 30, and 40 days after transplanting) improved broomrape control in some situations. Current UC recommendations are to use the GDD model (linked) rather than relying solely on days since transplanting to better account for the rate of broomrape development earlier and later in the season

Note: Matrix chemigation has provided greater than 80% suppression of broomrape in multiple years of small-plot research trials in a highly-infested research site in Yolo County, California.  Anecdotal evidence suggests that the commercial growers get even better results, presumably due to more uniform applications that can be made at field scale.  This is currently our best option for reducing the establishment of early-stage populations of broomrape!

  1. Chemigation Recommendations
    1. High Risk Fields:  Highly recommend using the Matrix chemigation protocol in all high risk fields.
    2. Designated Zone:  Strongly encourage the use of the Matrix chemigation protocol in all tomato fields in the designated zone to reduce risk of broomrape establishment.
    3. Outside Designated Zone: Consider adopting Matrix chemigation as a prophylactic treatment to reduce risk of successful establishment of initial introductions.

To assist with timing of broomrape management operations, researchers at UC Davis have developed a growing degree–day–based web tool. After entering your planting date and location, this decision-support tool uses information from the nearest weather station to calculate degree-day accumulation and predicts key broomrape growth stages to guide the timing of chemigation, scouting, and roguing operations.