Keys to Cost-Effective Weed Control in Pastures
Herbicides are most cost effective when sprayed at the right rate and the right time. Below are tips that
will allow you to get the most control from your herbicide/weed control investment.






Identify your problem weed species and select the herbicide that will provide a satisfactory level
of control in a cost effective manner.
Calibrate your sprayer before use. Calibration pre vents waste and added expense of over
application and reduced control from under application. Get the most from your investment,
calibrate.
Spray at the right time. Most broadleaf weeds should be controlled when they are small and
actively growing. In northeastern Oklahoma, May is a good time to utilize weed control.
Beware drought stressed and/or bigger more mature weeds will be harder to control. Higher
rates of chemical will be needed to successfully control mature weeds.
Follow label instructions for application and mixing. With ground broadcast, apply between 10
and 20 gallons of total spray per acre. Use the recommended surfactant listed on the label.
Surfactants will aid in improving herbicide effectiveness.
Read and follow all herbicide label instructions. Do not use products off label. If you have
questions, contact your herbicide representative or dealer or contact your local county OSU
Extension educator.
Warm Season – Annual Forage Crops
Sudan grass and sorghum sudan grass hybrids
There is little yield variance between sudangrass or sorghum sudangrass hybrids. Forage sorghum was
crossed with sudangrass to increase leafiness and yield while minimizing seed set.
Plant sorghum sudangrass or sudangrass on a soil site with a pH of 5.5 or above. Drill rate of seed is 2025 lbs/acre or 35 lbs/acre is broadcast. Recommended seeding depth is ½ to one inch, plant in May.
Provide phosphorus and potassium as called for by soil test. Apply fifty actual pounds of nitrogen per
acre at planting (110 lb/acre of 46-0-0 fertilizer). After each harvest, reapply another 50 pounds actual
nitrogen per acre.
You can begin grazing when sudan reaches 24 inches in height. Harvest for hay when it reaches a height
of three feet or when in the boot stage of growth.
When grazed, prussic acid and nitrate poisoning can be problems. Hay should be tested for problem
nitrate levels.
Pearl Millet
Pearl Millet does not contain prussic acid and will tolerate low pH soils. Drilling rate is 15 pounds/acre
or broadcast at 25 pounds/acre. Plant in May through early June. Ideal plant depth is ¾ to 1 inch.
Apply phosphorus and potassium according to soil test and 60 lb/acre/actual nitrogen at establishment,
then 50 lb/acre of actual nitrogen after each cutting.
You can begin grazing when millet reaches 20 inch height. Harvest for hay at 30 to 36 inches. Do not cut
below 8 inches.
Crabgrass
Seed in May by drilling 3 to 4 pounds per acre at a depth of no more than one-half inch.
At establishment, apply phosphorus and potassium according to soil test plus 40 lbs/acre of actual
nitrogen (87 lb/acre of 46-0-0 fertilizer). After first cutting, apply 60 lbs/acre of actual nitrogen (or 130
lb/acre of 46-0-0 fertilizer). Hold off grazing until plants reach an 8 inch height. Harvest for hay in the
boot stage, about 12 inches in height. Lowest cutting height is 3 inches.
Crabgrass is highly palatable and stocker cattle can gain over 2 pounds/day on this forage. A high
quality forage, best utilization is when grazing will be with a rotational system.
In the Tulsa area, crabgrass, sudangrass and pearl millet yields are expected to run in a range of 1-3
ton/acre for crabgrass and 2 to 4 ton/acre for sudan and pearl millet.
Cowpeas and Soybeans for Forage
Cowpeas (black eyed peas) a non-bloating legume, should be planted in May at a rate of 20 pounds/acre
at a one inch depth. Apply phosphorus and potassium as called for by soil testy. Soil pH for cowpeas
can range from 5.5 to 7.
Cowpeas will reach maturity in about 90 days. Yield potential should be in a range of 2-4 ton per acre.
Crude protein content will be expected to run from 12 to 16%. Can be planted in combination with
sudan or millet.
Soybeans
Ideally, plant in May at a seeding rate of about 50 pounds/acre. Apply phosphorus and potassium at
planting. With traditional soybeans, select a full season variety. Soybean may be grouped or harvested
from the flowering stage to 90 percent pod fill. Forage quality will be similar to alfalfa hay.
Expect yields from 2 to 4 ton/acre.
Forage soybeans, tall growing forage soybeans are now available. Selected for forage production, these
beans have performed well in several southwestern state’s university tests. Yields over 5 tons per acre
have commonly been reported.
Stocking Rate - How Big are Your Cows
How big are your cows? What do they weigh? In the 60’s a good 1000 lb. cow was considered good
sized, however, by the late 70’s cow size increased dramatically with 1200 lb. cows becoming common
on farms and ranches. Today mature cows often weigh 1300 lbs. or more.
Why weigh your cow? Because most of us that guess cow weights do. Cow size has been found to
strongly correlate with a cows daily forage intake. As a rule of thumb, a spring calving cow will eat 3.0%
of her body weight daily if forage is available during the summer.
If your average mature cow weight is 1300 pounds, expect her to eat 39.0 lbs. of forage per day (1300
lbs. x 3.0% = 39.0). If we take her daily expected forage intake (39.0 lbs.) times a 180 day summer
grazing season, then she will need 7020 pounds of forage (or 3.51 tons) for that time period. If she has a
calf at side we can expect the calf to consume 7.5 pounds/day of grass for the 180 day summer period
or 1350 lbs. (0.68 ton). Together the pair need 4.19 ton of forage for summer grazing.
We expect a good stand of non-fertilized Bermuda grass to produce a ton of forage during a summer
growing season (180 days). Of the ton of forage produced, plan on utilizing 60 percent of that
production (0.6 ton) leaving the remainder to maintain the resource. If we divide the 4.19 tons of
forage required by the 1300 pound cow and calf for the summer by the amount of forage per acre
available for grazing/acre (0.6 T) then we find that we should allot the pair 6.98 acres for the summer.
Below is a chart showing different cow weights, expected intake with a calf at side, and the amount of
acres required for the pair grazing non-fertilized Bermuda grass.
Cow Weight, pounds
1100
1200
1300
1400
Tons forage required
per pair 180 days
3.65
3.92
4.19
4.46
Acres of Bermuda required
Non-fertilized
6.08
6.53
6.98
7.43
This chart points out that if you underestimate cow weight you can overstock a pasture in short order.
Overstocking not only can reduce cattle performance, it can damage your forage resource (pasture) for
future use. Knowing your cow’s average body weight is a mnajor step in keeping your stock rate correct
and maintaining pasture condition.
Cow intake of a forage will vary with plant maturity and plant species. For example, a cow on a wheat
straw or mature grass hay will be hurried to consume 2% of their body weight while the same cow will
easily consume 3% of her body weight in alfalfa hay. Forage physical properties, dry matter and protein
content will all effect cow intake. Fetus size can also effect intake, larger fetuses, less space for rumen
expansion.
Cow size, forage quality and physical properties, nutrient passage rate, supplement and stage of
pregnancy all effect a cow’s forage intake.