Lamb’s Quarter is a common weed species in a varieties of regions. The Lamb’s Quarter growing degree day model developed as part of the CROPTIME project at Oregon State University, uses heat units and time as a method to estimate plant phenological stages through the growing season. This can be helpful to time herbicide applications before flowering occurs.
Calculating Growing Degree Days
For this model, a lower temperature threshold of 42F and an upper threshold of 95F is used to calculate growing degree day accumulation beginning when the first cotyledon is observed. Growing degree days can be calculated from daily high and low temperatures, or via the Pest Prophet app, which uses hourly temperature data for a given field. The first flower will occur at 596 GDD (F) with average viable seed at 1462 GDD (F).
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