Timing of Early Weed Control Practices by Growing Degree Days

Farmers producing crops organically or with few herbicide options must control very small weeds early in the growing season.  We compared weed control using propane flaming to weed control with rotary hoeing, and we evaluated the use of growing degree days (GDD) to optimize rotary hoe timing. Propane flaming was not effective on grassy weed species in our research. Common lambsquarters, redroot pigweed, and velvetleaf were easier to control by flaming than common ragweed and common purslane. Flaming was more effective in the morning through mid-afternoon; evening flaming was not effective. In dry beans the most effective weed control treatments were rotary hoeing three times or a treatment of flaming once prior to dry bean emergence, followed by rotary hoeing twice. Timing rotary hoe passes every 300 GDD (base 3.3 C) from the time of dry bean planting resulted in fewer passes compared with rotary hoeing every 7 day or every 150 GDD, and weed control and bean yields were similar to the weed-free treatment in one of two years.