Fall Cultivation and Fertilization to Reduce Winterhardiness of Leafy Spurge (Euphorbia esula)

Abstract

Reduced-tillage practices have allowed leafy spurge to infest cropland. The reduction in leafy spurge infestation and winterhardiness by fall tillage, N application, or herbicide treatment was evaluated. Cultivating leafy spurge twice each fall for 3 yr provided complete control. Cultivation followed by N application at 225 kg ha−1reduced the stand by 85% after 3 yr, whereas N applied alone had little effect. Picloram plus 2,4-D at 0.6 plus 1 kg ha−1reduced the infestation to 65% of the untreated control after 2 yr but then the infestation declined rapidly to 1% after a third application. Leafy spurge cold tolerance decreased as root depth increased. The GR50and LT50, the temperatures required to reduce total dry weight and survival, respectively, by 50% varied by root depth and treatment. For example, the LT50and GR50for untreated leafy spurge averaged −19 and < −20 C for crowns, respectively, compared to the −16 and −18 C for roots from 0 to 15 cm deep and −13 and −12.5 C for roots from 15 to 30 cm deep. The GR50and LT50temperature after 2 yr of treatment was reduced to 0 C by two cultivations in fall or picloram plus 2,4-D. Carbohydrate content was not a good indicator of winterhardiness. Cultivation reduced the leafy spurge root system faster than herbicide treatment especially at the 15- to 30-cm depth.