Postemergence Control of English Ivy (Hedera helix L.) and Moisture Effects on Preemergence Weed Control with Flumioxazin

Abstract

English ivy (Hedera helix L.) is an invasive vine in at least 28 states in the United States. This species has excellent environmental adaptability, grows as a ground cover and climbs into tree canopy. More potential herbicides for English ivy control were registered in 2000’s. Four experiments were conducted to evaluate English ivy response to old and new postemergence herbicides in different season applications with a series of application rates. Results indicated English ivy was not controlled by aminopyralid and fluroxypyr (i.e. experiment I & II). Metsulfuron provided excellent control of English ivy when the rate was above 0.21 kg ha-1 at any application timing (i.e. experiment II, III & IV). Sulfometuron provided excellent control in summer application (experiment III), but not in spring application (experiment IV). The old herbicides, i.e. glyphosate and 2,4-D (2,4-Dichlorophenoxyacetic acid), usually provided better control at the higher rates. However, the best control was obtained with summer application. Therefore, we assumed that higher temperatures perhaps reduce English ivy tolerance to the herbicides. Another research component was to evaluate the effect of substrate moisture on preemergence weed control with flumioxazin. Flumioxazin is a commonly used herbicide in nursery production for preemergence weed control. Moisture is an important component to activate preemergence herbicides; however, this aspect had not been investigated in soilless substrate. The objective of this research was to evaluate the influence of both pre-application moisture levels and post-application irrigation levels in the preemergence control of hairy bittercress (Cardamine hirsuta L.) and spotted spurge (Chamaesyce maculata L.) with flumioxazin in a pine bark substrate. Similar experiments were conducted. Treatments were a factorial arrangement: three pre-application moisture levels (dry, medium and wet), two flumioxazin formulations (granular and spray), two flumioxazin rates [0.28 and 0.42 kg ha-1 (0.250 and 0.375 lb ai A-1)] and four post-application irrigation levels [0.6, 1.3, 2.5 and 5.1 cm (0.25, 0.50, 1.00 and 2.00 in)]. Each pot was overseeded with 25 weed seeds after herbicide application. Weed germination was counted weekly, and shoot fresh weights were taken after the last weed count. Results showed pre-application moisture did not affect the flumioxazin efficacy. The spray formulation provided maximum reduction of weed counts, regardless of rate, pre-moisture level or post-irrigation level. Conversely, the granular formulation was less effective, and the higher rate was generally more effective than lower rate. For granular herbicides, more water was needed to break the herbicide coating. This process is likely improved by higher temperature.