May 14, 2010

Ragweed growth has exploded in some pastures in recent years. Timely spring rains encouraged germination and seedling growth and sunny dry falls aided seed development. To add to the problem, earlier droughts weakened natural competition.

Both common ragweed, which is an annual, and western ragweed, which is a perennial, can be controlled using similar methods; however, common ragweed is controlled more easily than western ragweed with grazing management or herbicides.

Research and observations both show that ragweed problems are worst in pastures that fail to maintain competition from a full leaf canopy of grass during late May through late June. If you had ragweed problems the past couple of years, look for tiny plants or seedlings underneath your grass during the next couple of weeks. Heavy grazing or haying during this time opens up the grass sward, letting seedlings and small plants grow rapidly.

Any management that develops and maintains a dense leaf canopy at this time helps reduce ragweed problems. This includes increasing grass growth with fertilizer and thickening stands by seeding. Most importantly, avoid grazing heavily in areas with ragweed problems. If you do graze heavily or cut hay, spraying herbicides like 2,4-D, Grazon, Milestone or Weedmaster after grazing or cutting gives good control of ragweed seedlings and small plants.

It takes time and a well-planned approach to control ragweed. With good grazing, some spraying, and timely shredding it can be done.

Bruce Anderson
Extension Forage Specialist