Crop, Soil, and Environmental Sciences
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University of Arkansas
Fayetteville, AR 72701
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Weed control

 

WEEDS


A. What's wrong with weeds besides being ugly?
   1. Decrease forage yield - lower carrying capacity
 Competition - light, water, nutrients, space.
   2. Decrease animal performance
 Lower nutritive value at more mature stages and weeds mature fast
 Toxic to animals
 Off flavor in milk - wild garlic, bitterweed
 Pinkeye, mouth sores
   3. Decrease value of hay
 Customer wants a particular product
 Grasses increase fiber content of legume hay
 Mature stems are uneaten
 Weed seeds spread in hay
Note:  On marginal soils, "weeds" can be a desirable forage, but 
controlled grazing is essential to exploit their goodies.
B. Weed avoidance through management - cheapest, best
   1. Plant clean seed
   2. Encourage vigorous forage growth
   3. Do not over- or undergraze the forage you are trying to encourage
C. Weed control
   1. Cultural practices
 Promote vigorous growth of desirable forage
 Mowing - brush hog before seed set, harvest for hay
 Grazing - use intensive rotational stocking (short-duration with high
stocking density) to control weeds that are less palatable than the
preferred forage, such as dock, smartweed, ragweed, bitterweed, or that
are at a competitive disadvantage when the forage is allow rapid,
uninterrupted recovery.  Use continuous stocking to control weeds that are
more palatable than the forage and that need a rest period for
carbohydrate replenishment, such as johnsongrass (if you really want to
get rid of it).  The idea is to use defoliation frequency and intensity to
shift the balance in favor of your preferred forage.
   2. Chemical control - see extension pubs for more info
 Weed susceptibility and crop tolerance
 Calibrate sprayer - active ingredient sound equipment, markers
 Use surfactant with paraquat and Ally/Cimarron
 Spray young active growth
 Watch the weather!
 Animal withdrawal periods varies with the herbicide
 Restricted use - applicator's license
See Handouts on herbicides and pasture weed control
CONSULT UA PUBLICATION MP44 FOR HERBICIDE RECOMMENDATIONS
This extremely informative publication is updated every March
 HERBICIDES
MP-44 manual for Arkansas
Broadleaf control
*   2,4-D:   Broadleaf control.  Different formulations, e.g. Weedar64
*   Weedmaster:   2,4-D amine + dicamba; Broadleaf control
*   Ally:   Broadleaf and bahiagrass control in bermudagrass, not thistle
*   Grazon P+D:   picloram (P) + 2,4-D (D)
Nonselective herbicides
   Roundup (glyphosate):  kills most plants, annuals and perennials
   Gramoxone (paraquat):  burns back tops, kills annuals
Brush control
   Grazon P+D:   picloram (P) + 2,4-D (D)
   Crossbow:   trichlopyr + 2,4-D
 These are leachable to ground water.
   Remedy:  triclopyr
There are other chemicals for brush control listed in MP44
Spot spraying - localized infestations of brush, horsenettle,
johnsongrass.  Hand-directed nozzle sprayer.
Ropewick application - wipe on concentrated herbicide with rope wick 
boom.  Usually use glyphosate diluted 1 part herbicide:2 parts water.
If using generic, be sure to add surfactant.  Monsanto's Roundup includes
surfactant already.