Weed Control In Forage Crops

Introduction
Weed control is essential in forage production due to the high investment costs and potential negative impacts of weeds, including:
  • Reduced yield from competition for water, nutrients, and sunlight.
  • Lower forage quality and increased disease/insect problems.
  • Premature stand loss and harvesting difficulties.
  • Presence of unpalatable or poisonous species.
 
Weed Management Principles
Focus on cultural practices first, followed by chemical control when necessary. A vigorous, dense forage stand is the best defense against weeds.
Key Cultural Practices:
  • Fertilize based on soil tests.
  • Use well-adapted, vigorous varieties.
  • Buy weed-free seed.
  • Cut forage at proper growth stages.
  • Control insects and diseases promptly.
  • Rotate crops to break weed cycles.
 
Weed Control in New Seedings
  • Critical Period: First year—seedlings grow slowly and are easily outcompeted.
  • Site Selection: Avoid fields with heavy infestations or herbicide carryover risk.
  • Fertilization: Maintain proper nutrient levels for competitive stands.
  • Clipping/Mowing: Effective for annual broadleaf weeds; remove residues to prevent smothering.
  • Herbicides: Used to reduce competition during establishment; refer to the Field Guide to Crop Protection for recommended products.
 
Site Selection
  • Choose fields with minimal history of persistent weeds (e.g., thistle, dandelion, quackgrass).
  • Be aware of herbicide carryover from previous crops, which can injure new forage seedlings.
  • Consult Manitoba Agriculture offices or product labels for herbicide carryover information.
 
Fertilization
  • Apply nutrients based on soil test recommendations during establishment and throughout the stand’s life.
  • Goal: Create a competitive forage stand to suppress weed emergence.
  • Note: Proper fertility does not eliminate established weeds, especially in thin stands.
 
Cutting – New Stands
  • Clipping/mowing controls weeds like common cocklebur by removing leaves and lateral buds.
  • Annual broadleaf weeds are easier to control than grasses (which have crown buds near soil surface).
  • Mow low for effectiveness; legumes like alfalfa tolerate low clipping.
  • Remove heavy residues to avoid smothering forage seedlings.
 
Herbicides for New Seedings
  • Designed to reduce competition from fast-growing weeds during establishment.
  • Benefits: Improved stand longevity and higher yields in subsequent years.
  • Caution: Forage grasses are sensitive to herbicides used for legumes; no products registered for legume-grass mixtures.
  • Refer to Field Guide to Crop Protection (Forage Crops Chart) for recommended herbicides.
 
Maintaining Established Stands
  • Established forages compete well but weeds invade as stands age.
  • Timely mowing and herbicide use can prolong stand life.
  • Control weeds along borders and adjacent fields to prevent seed spread.
Clipping:
  • Hay mowing can weaken perennials by reducing food reserves.
  • Post-grazing mowing prevents seed production.
Herbicides:
  • Options available for dormant, non-dormant, or between-cutting applications.
  • Consider weed species, crop tolerance, grazing restrictions, and cost.
 
Scouting
  • Identify weeds early to prevent severe infestations.
  • Winter annuals (e.g., stinkweed, flixweed) appear in early spring; summer weeds (e.g., wild oat, lamb’s quarters) after first harvest.
  • Estimate weed density by sampling random sites (one per 10 acres).
  • Record species and size at each site.
 
Summary
Effective weed control in forage crops combines preventive cultural practices, timely mowing, and judicious herbicide use. Early scouting and integrated management are key to maintaining productive, high-quality forage stands.