Yellow witchweed - Alectra vogelii
Effective: April 24, 2015
Taxonomic Position: Lamiales : Scrophulariaceae
Pest Type: Plants
Pest Code (NAPIS): PEUAZBA
This pest is a member of the following surveys: Soybean
These Approved Methods are appropriate for: 2025, 2024, 2023, 2022, 2021, 2020, 2019, 2018, 2017, 2016
Pest Information
CAPS Pest Datasheet: https://download.ceris.purdue.edu/file/4464
Pest Tracker: https://pesttracker.org/pest/PEUAZBA
Hosts Identified in the CAPS Host Matrix:
Cowpea; Soybean
Pest is vectored by:
No known vector.
Survey

Approved Method(s)
Method Detail NAPIS Survey Method
Visual Collect suspect plants. See the visual inspection excerpt from the guidelines. 3031 - General Visual Observation
Method Notes:
Because seeds are very small and could easily be transported on gear or clothing, samples should be collected carefully and double-bagged, and all gear and clothing should be cleaned to prevent introduction of weed seeds to new fields by surveyors.

Survey Recommendations
The following are recommendations for executing the survey using the approved methods for pest surveillance. The recommendations are developed through literature review and consultation with subject matter experts.
Signs:
Roots are bright orange below soil surface. Stems and leaves are conspicuously hairy. The dust-like seeds are covered with indentations.
Symptoms:
Stunted crop plants with smaller leaf area, shorter leaf petioles, and increased shoot/root ratios.
Time of Year to Survey:
The best time to survey is likely 12 to 14 weeks after warm-season crops are planted, when flowers and mature shoots are most likely to be visible. Seeds can germinate whenever soil conditions are warm and moist and host plants are available. Shoots are first produced 7 to 8 weeks after germination, and flowers are produced 9 to 10 weeks after germination. Emergence can, however, take three months after germination.
Survey Site Selection:
Surveys should target fields of suitable hosts or fallow fields that are growing in well-drained soils such as sand and sandy-loams. In Africa, A. vogelii infestations are typically on annual cropping and in semi-arid areas with a 4 to 6 month growing season below a mile in altitude.

Climatic preference estimates (CABI, 2023):
- Mean annual rainfall: 20 to 40 inches
- Mean annual temperature: 66 to 78ºF
- Mean maximum temperature of hottest month: 84 to 100ºF
- Mean minimum temperature of coldest month: 42 to 60ºF
- Absolute minimum temperature: 26 to 32ºF
Sample Collection Instruction:
Samples should be collected carefully and double-bagged. Clean all gear and clothing to prevent spreading seeds to new fields.
Key Diagnostic or Identification

Approved Method(s)
ID/Diagnostic:
Morphological: Characteristics of the flowers, leaves, seeds, and roots can be used to distinguish A. vogelii.

The Federally Noxious Weeds Disseminules of the U.S. provides keys and fact sheets that can help identify seeds of Federally Noxious Weeds, including Alectra spp. (Scher and Walters, 2015).
Identification Resources:
The Federal Noxious Weeds Disseminules of the United States provides keys and fact sheets that can help identify seeds of Federal Noxious Weeds, including Alectra spp. (Scher et al., 2015). It does not, however, show seeds of A. vogelii specifically.
Mistaken Identities:
This weed can be confused for other Striga species and symptoms on host plants are similar to nutrient deficiencies.
Notes:
Send to an approved botanist for identification.
References
  1. Scher, J. L. and D. S. Walters. 2015. Federal Noxious Weed Disseminules of the U.S., Edition 2.2. California Department of Food and Agriculture, and USDA APHIS Identification Technology Program.
  2. Scher, J. L. and D. S. Walters. 2015. Federal Noxious Weed Disseminules of the U.S., Edition 2.2. California Department of Food and Agriculture, and USDA APHIS Identification Technology Program. Alectra Fact Sheet.

If you are unable to find a reference, contact STCAPS@usda.gov. See the CAPS Pest Datasheet for all references.