Weed Control
By: Willie Holmon
Soil Conservationist

What is a weed? A weed is any plant that cause problems, annoyance, or discomfort or becomes a nuisance by destroying food and fiber products, causing structural damage, or creating a poor environment for other plants.

Importance:

Weeds compete with forages for light, moisture, nutrients, which reduces total production and may result in stand loss.  Typically for every pound of weed produced, a pound of forage is lost in native pastured and two to three lbs. of forage is lost in improved pastures.  Weeds can also prevent newly planted perennial forages from becoming established and result in a stand failure, due to the perennial forages having a lower seeding vigor.  Annual weeds complete their life cycle in one year and produce most of their growth early in the season, whereas perennial plants are slower to develop.  Controlling weeds can increase forage production and hasten the establishment time, which can allow for sooner and greater utilization by livestock resulting in increased profit.

Controlling Weed

 The first step to controlling a weed is to properly identify it.  However, there are many weeds and it is difficult to know them all.  Fortunately weeds can be classified and managed by their life cycle and growth habit.  The first step is to determine if the weed is an annual or perennial.  The second step is to determine if the weed is a grass, broadleaf, or sedge-like.   Most pasture herbicides only control broadleaf weeds and have no activity on grassy or sedge-like weeds.  (Note: It is very difficult to control a grassy weed in a grass forage).  Finally, determine if the weed is cool-season (germinating in the fall) or warm-season (germinating in spring, growing throughout the summer).  For more information on weed identification visit web page: http://www.nobel.org

Chemical Weed Control

There are many herbicides on the market and occasionally the label changes, so it is imperative that the user carefully read the most up to date label prior to use, because the label is the law.  The label should state which crops it can be used on, which weeds it controls, as well as any restrictions.  Herbicides are applied either pre-emergence or post-emergence.  That means they are applied either before or after weeds emerge from the soil and begin to grow.  Pre-emergence herbicides kill weeds shortly after they germinate or emerge through the soil surface.  Post-emergence herbicides control weeds that are already growing and easily visible.  Some herbicides are applied to the soil and are taken up by seedling plant roots or shoots. They are said to have soil activity.  Herbicides that are applied to plant foliage have foliar activity.  Some herbicides have both.  Herbicides with a high degree of soil activity usually are applied pre-emergence.  

Proper Timing

The best time to spray depends on the weed.  Annual broadleaf weeds such as annual broomweed, bitter sneezeweed, and woolly croton should be sprayed in the early spring (May) when they are small and actively growing.  Some perennials like western ragweed should also be sprayed in early spring. However, some perennial broadleaf weeds like Texas bullnettle, western horsenettle, or silverleaf nightshade should be sprayed later (early June) when they are blooming partially due to when their carbohydrates are moving down into the root system, but also because of their late and indeterminate short emergence from the soil.  Cool-season weeds (grasses and broad-leaves) should be sprayed with glyphosate +2,4-D in late February while forage is dormant if it is grown for hay production.

Also, if annual broadleaf weeds are present, Cimmerian can be used to control these weeds when they are small and actively growing.  If broadleaf weeds are still present once the grasses reach the 5^th leaf stage, the other pasture herbicides (2, 4-D, Weedmaster, Grazon P+D) maybe used to control these weeds.

Weed Control Workshop

Please mark your calendar for a green milkweed control demonstration April 5, 2005 at the pavilion at Honey Grove off HWY 82 next to the golf club lake.  This is one of our worst and hardest to kill weeds in North Texas.

 For more information on weed control or the seminar, call the USDA-NRCS office in Bonham at 903-583-9513 x3.