Electrical weed control of herbicide-resistant Italian ryegrass ( Lolium multiflorum ) in orchard systems

Abstract

Italian ryegrass is a significant weed in Oregon, and resistance to multiple herbicide sites of action is widespread. Nonchemical tools are needed to improve management of Italian ryegrass in orchard systems. Field studies were conducted in Oregon to evaluate electrical weed control (EWC) of Italian ryegrass at two voltage ranges (3.9 kV and >5.0 kV) and multiple energy rates generated by varying travel speed. Energy was the primary factor affecting EWC efficacy. Control increased with increasing operational energy rate and, in two studies conducted when Italian ryegrass was at tillering to stem elongation stages, visible estimates of control reached 70% to 80% at 67.5 to 168.8 kJ m ⁻² , corresponding to travel speeds of 0.8 to 0.32 km h ⁻¹ . Control was lower in a third study when plants were at a more advanced growth stage. Plant density was not consistently reduced, indicating that a single EWC application suppressed growth but did not consistently kill Italian ryegrass plants. When energy was increased shoot and inflorescence dry weight and inflorescence number were reduced, indicating lower reproductive output among surviving plants. Voltage effects were limited and inconsistent across studies. These results indicate that EWC can suppress herbicide-resistant Italian ryegrass and reduce reproductive output in orchard systems, but a single treatment does not provide complete control. Growers will likely need to repeatedly apply EWC or to integrate it with other weed control tactics to improve suppression and reduce reproductive output.