Weed Emergence Scouting Tool

Project Director: Melissa Widhalm, Purdue University

Funded in 2023

U.S. corn and soybean production systems are heavily reliant on post-emergence applied herbicides. However, overuse of post-emergence herbicides combined with frequent resprays to control weed escapes has resulted in the rapid spread of herbicide-resistant weeds, necessitating increased use of soil residual herbicides with different sites of action and pre-plant tillage to provide additional control measures before the crop is planted. Soil residual herbicides work by getting into the soil solution and coming into contact with a germinating weed seedling right after the germination process has initiated. Freshly germinated weed seeds are also very susceptible to tillage control measures. Understanding and communicating to farmers and spray applicators about when weeds will be germinating and when peak weed emergence will occur allows for more timely applications of soil residual herbicides and the use of tillage to control germinating weed seedlings.

We propose to develop the Weed Emergence Scouting Tool (WEST). This product will be a real-time tool for monitoring first and peak emergence of giant ragweed and waterhemp in the Midwest to support more effective weed management with soil residual herbicides or tillage. Past research has identified the emergence sequence for numerous weed groups based on growing degree day (GDD) accumulations, but weed management historically has not utilized temperature-based scouting protocols. The WEST will integrate weed emergence and management knowledge with high-resolution weather and climate data to develop a first-of-its-kind tool that supports timely soil residual herbicide use and tillage.


  • Gathering field observations of first and peak emergence for giant ragweed and waterhemp and comparing results to known emergence sequences
  • Developing the Weed Emergence Scouting Tool (WEST), which includes GDD-based weed emergence climatology, real-time emergence tracking, and user-submitted emergence observations
  • Disseminating the WEST to key audiences across the region