Herbicide Tolerance and Weed Control of Longleaf Pine Native Understory Species

Abstract

The restoration of longleaf pine (Pinus palustris) is an important environmental issue due to the shrinking size of this once dominant forest type. The restoration of this ecosystem requires the presence of native understory species such as wiregrass (Aristida beyrichiana), muhly grass (Muhlenbergia capillaris), yellow Indian grass (Sorghastrum nutans), Florida ticktrefoil (Desmodium floridanum), narrow-leaf sunflower (Helianthus angustifolius) and many others. The commercial propagation of these understory species is a relatively new aspect of nursery management, which subsequently means that nursery managers have little knowledge on how to grow and propagate these plants, and also how to control unwanted weeds amongst them as well. In addition, the use of herbicides as part of ecological restoration of longleaf has been reported to decrease seedling survival. These trials will examine the effects of several herbicides applied at varying rates to further evaluate their effect upon the selected understory plants. These herbicides include: atrazine (AAtrex®), imazapyr (Chopper®), imazamox (Clearcast®), lactofen (Cobra®), s-metolachlor (Dual Magnum®), oxyflurofen (Goal 2XL® and Goaltender®), pendimethalin (Prowl H2O®), imazapic (Plateau®), imazethapyr (Pursuit®), halosulfuron-methyl (Sedgehammer®), sulfentrazone (Spartan Charge®), dicamba + 2,4-D (Weedmaster®) and butyric acid (2,4-DB®). For both the seed production study and the grass seedling study, successful herbicide treatments were identified that are tolerated by the native plant species and effective on target weed species. The successful herbicide treatments for the native plant seed production include atrazine, dicamba + 2,4-D, imazapic, and sulfentrazone. The successful treatments for the native grass seedlings include halosulfuron-methyl, lactofen, pendimethalin and a low rate of oxyfluorfen. These treatments will provide nursery managers and plant growers with proven tools which can be used to grow native plants and aid longleaf pine restoration initiatives. Additionally, an indicator species, sorghum, was identified as a potential imazapyr bioassay. This indicator species will allow land managers and foresters to easily and efficiently determine if a site that has been treated with imazapyr is safe to plant longleaf pine seedlings.