Reducing ragweed in pastures
By Noel Mues
UNL Extension Educator
Ragweed growth has exploded in many of our pastures during recent years, according to Bruce Anderson, UNL Extension forage specialist. This major source of hay fever can reach 1' to 6' in height, depending on the taxonomy. There are three different kinds of ragweed--common ragweed, western ragweed and giant ragweed--and all are responsible for ragweed allergy.
Under the right conditions, there's one characteristic of giant ragweed that you can't miss: namely, its height. It is not uncommon for giant ragweed to stand 6 feet tall or more. The stalk on such a plant will be thicker than a broom handle and may bear many large branches. However, giant ragweed is otherwise unremarkable, even as weeds go. It bears inconspicuous yellow flowers; nor does its foliage offer much interest.
Common ragweed is indigenous to North America. It can be found in every state in the U.S. except for Alaska, and it is widespread in Canada, too. The plant thrives in disturbed soils and is frequently found along roadsides.
Timely spring rains have encouraged germination and seedling growth. Dry conditions during the fall contribute to seed development; and drought conditions during previous years weakened competition from desirable grasses.
Both, common ragweed, which is an annual, and western ragweed, which is a perennial, can be held in check by using similar methods of control. However, common ragweed is controlled more easily with grazing management or herbicides than western ragweed. Western ragweed has the ability to reproduce by rhizomes (underground stems) or seeds.
Research and observation both show that ragweed problems are greater in pastures that fail to maintain competition from a full leaf canopy of grass during late May through late June. If you experienced ragweed problems the past couple of years, look for tiny plants or seedlings underneath the 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 problems with ragweed. This includes increasing grass growth with fertilizer and thickening stands by seeding, but most important of all is to avoid grazing heavily in areas with ragweed problems. If you do graze heavily or cut hay, treating with herbicides like 2,4-D or Grazon or Milestone or Weedmaster after grazing or cutting gives good control of ragweed seedlings and small plants. And if ragweed gets away, shredding in September can reduce seed production.
It takes time, and a well-planned approach, to control ragweed. With proper grazing, appropriate use of herbicides and timely shredding it can be done.