Integrating Cover Crops in No-till Corn and Soybean to Diversify Herbicide-Resistant Weed Management in the Mid-Atlantic

Open Access
Bunchek, Jess Marie
Graduate Program:
Master of Science
Document Type:
Master Thesis
Date of Defense:
August 30, 2018
Committee Members:
  • William Curran, PhD, Thesis Advisor
  • David Mortensen, PhD, Thesis Advisor
  • John Wallace, PhD, Committee Member
  • John Tooker, PhD, Committee Member
  • Charles White, PhD, Committee Member
  • weed science
  • weed management
  • integrated weed management
  • cover crops
  • herbicide resistance
  • agroecology
  • conservation tillage
  • glyphosate
  • horseweed
  • pigweed
Widespread adoption of genetically-engineered, herbicide-resistant (HR) crops have simplified crop rotation diversity and the use of single-tactic, herbicide-based weed management programs. These practices have resulted in an HR weed epidemic, where glyphosate-resistant weeds are especially problematic. Glyphosate-resistant weeds like horseweed [Conyza canadensis (L.)] and pigweeds (Amaranthus spp.) threaten grower productivity and long-term efficacy of common agronomic herbicides. Thus, integrated weed management (IWM) programs that implement both ecological- and herbicide-based tactics are needed in no-till annual grain systems to (1) manage current HR weeds, (2) reduce HR selection pressure for evolution of resistance to other herbicides, (3) preserve effective herbicide technology, (4) enhance environmental stewardship, (5) safeguard soil conservation gains, and (6) maintain farm profits and productivity. To address these goals, we established three field studies at two sites in the Mid-Atlantic and identified combinations of cover crop and herbicide tactics that achieve effective season-long annual weed management, minimize HR selection pressure, and increase sustainability by reducing herbicide inputs. The first two studies assessed the complementarity of cover crops treatments and herbicide programs in corn and soybean, where integrating a cover crop treatment combined with applying a spring, pre-plant burndown herbicide application as well as a POST-emergent application provided the most effective season-long annual weed control. The third study assessed cover crop treatments and varied management practices, such as planting and termination dates, on HR selection pressure reduction at the time of herbicide applications. While cover crops intercepted a portion of the burndown herbicide application from reaching the soil surface, weeds were effectively controlled by the cover crops before the application, thus reducing the HR selection pressure.