Field Scouting

Green crop field with black trash bags and orange cone by dirt road, workers far away
Scouting

and Roguing

Black and white trash bags on dirt, black bags overflowing with broomrape

 

GDD Calculator

Field Scouting/Rogueing 

Scouting fields to identify early-stage infestations and removing broomrape plants before they produce seeds is critical to keeping new infestations in check. A single plant can shed dozens of seeds in its early stages, quickly escalating to thousands as it matures.

  • Field staff and equipment operators should be trained on the identification of broomrape and encouraged to report it to their supervisors.
    • Regular operations such as irrigation monitoring, hand weeding, cultivating, and vine training all present opportunities for field personnel to see and identify broomrape plants and infested fields or areas of fields.
       
  • Scout and rogue fields to identify early-stage infestations and remove as many broomrape plants as possible BEFORE they set seed.  In UC research, broomrape emergence typically has started approximately 400 GDD (growing degree days) after transplanting and flowering begins around two weeks later and many continue for several weeks. 

Note: A single broomrape plant can have dozens of stems, each with multiple purple flowers.  On an individual stem, the lower flowers mature first and the upper flowers mature later and each of these can make a seed capsule with many seeds.  As the plants mature, the individual stems and seed capsules begin to dry and can shed mature seed; an individual broomrape plant can make thousands of seeds that can drop to the soil or be picked up with the harvested tomato vegetation.

Best current practice for effective management is 'rogueing'; the careful removal of the entire broomrape plant, including as much of the belowground point of attachment to the host root as feasible.

  1. DO NOT simply hoe out broomrape stems and leave them in the field, as they may have already produced viable seed on the earliest flowers shortly after emergence.
  2. Place plant material in sturdy plastic bags and remove from the field while taking care to avoid dropping seed and plant fragments.  After removal, rogued plant material can be disposed of by:
    1. Bringing bags directly to the landfill in a closed or carefully tarped load to minimize the risk of spreading seed.
    2. Leaving bags in the sun for a minimum of several days to “solarize” (achieve high temperatures inside the bag to kill seed; clear bags work better than black) and then landfilled.
    3. Incinerating on site if allowed by your local Ag Commissioner and air quality regulation requirements.  It is recommended to landfill any remaining ash and debris in case of incomplete burning of some material.
  3. Do not compost rogued plant material -even after solarization or burning- in order to reduce the risk of spreading viable seed if composting is incomplete.

Scouting and Rogueing Recommendations

  • All Zones:  Recommend that all growers with compliance agreements train field staff and equipment operators on broomrape identification and reporting processes.
  • High Risk Fields:   Recommend high risk fields scouted and rogued twice, approximately 6-8 weeks after transplanting and again approximately three weeks later.
  • Designated Zone:  Encourage scouting of all tomato fields in designated zone.
  • Outside Designated Zone:  Encourage scouting of field edges and near entry points in fields outside the designated zone as these are relatively higher risk of early 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.

Growing Degree Day Tool