Rehabilitation of Perennial Pepperweed Infested Habitats Perennial pepperweed (Lepidium latifolium), also referred to as tall whitetop, is native to eastern Europe and Asia and was accidentally introduced into North America early in the 20th century. A member of the mustard family, this weed has spread to portions of all western states and adjacent Canada. In the Intermountain Area, perennial pepperweed first became established in riparian and wetland areas. It spread to native hay meadows and alfalfa (Medicago saliva) fields. Native hay meadows located on flood plains are particularly susceptible to perennial pepperweed invasion (Figure 1). The weed is highly adapted, but not restricted to growth on salt affected soils and soils with sodium hazards. Perennial pepperweed plants can produce large quantities of viable seeds that can reach 16 billion seeds/acre. The plants have an extensive creeping root system with the ability of very small fragments of these roots producing new plants. This makes mechanical control by tillage virtually impossible
By Charlie D. Clements and Dan N. Harmon
as following mechanical tillage can result in a significant increase in perennial pepperweed density and cover. The invasion of native hay meadows by perennial pepperweed is a threat to the range livestock industry of the Intermountain Area because these meadows are a critical portion of the forage base for both hay production and grazing of crop aftermath. Perennial pepperweed can be partially suppressed by grazing, but if grazing is deferred for hay production the plants become quite woody and the resulting hay is of very poor quality. If herbicidal weed control is practiced on these meadows with near mono-cultures of perennial pepperweed, spontaneous regeneration of the meadow is very slow and re- invasion of perennialweed will occur. This makes seeding of a perennial forage species necessary. The choice of revegetation for these seasonally dry meadows with salt affected soils is limited, with tall wheatgrass (Elytrigia elongata) being the
Figure 1. Former irrigated hay field infested with a dense stand of perennial pepperweed.
most widely used species. The standard herbicide for control of perennial pepperweed has traditionally been 2,4-D [(2,4-dichorophenoxy) acetic acid]. More recently, herbicides of the sulfonylurea family, especially chlorsulfuron {2-chloro-N-[(4- methoxy-6-methyl-1, 3, 5-triazin, 2-yl) - aminocarbony] benzenenesulfonamide } have been found to be very effective for the control of perennial pepperweed. Both 2,4-D and chlorsulfuron can be applied at appropriate rates and kill perennial pepperweed in established stands of meadow species and not injure the perennial grasses and grass-like species. To give the perennial grass plants a chance to biologically suppress perennial pepperweed, repeated herbicide applications are necessary over the seedling stands. This obviously requires the use of a selective herbicide. We tested mechanical (discing), biological (goats) and chemical (herbicides), as well as a combination of these treatments to control perennial pepperweed infestations (Figure 2). In all we had a combination of 52 treatments. Here we report on what we consider the more important portions. Discing, conducted in late May and early June, initially reduced perennial pepperweed cover from 95% cover down to 5% cover, but by the end of summer (October) perennial pepperweed cover was up to 30% and reached 100% the following July. Discing in early May followed by the application of herbicides [2-4D 2.2 kg/ha (2 lbs/ac), or Chlorsulfuron (Telar®XP) 0.11 kg/ha (0.10 lbs/ ac)] initially appeared to be very effective as perennial pepperweed leaves looked very necrotic. Even though perennial pepperweed failed to seed due to the combination of discing and spraying, perennial pepperweed became productive and vigorous by the following July and cover increased to more than 20%. There were no significant differences in cover between the combination of discing and herbicide application and that of herbicide application by itself.
24 FEBRUARY 2022
The Progressive Rancher
www.progressiverancher.com
