Reduced crop quality weed seeds and foreign material can reduce the market grade of crops weed seeds and foreign material may be moist and cause storage problems

Weed Biology

Weed and Crop Life Cycles

Weed Seeds

Weed Interference

Weed Management Strategies

Prevention

Eradication

Control

Methods of Weed Control

Cultural weed control

Mechanical weed control

Biological weed control

Chemical weed control: Some chemicals have carryover problems: Atrazine (AAtrex), Lasso

Herbicide Application Methods

Preplant

Preemergence

Postemergence

Keys to Successful Weed Management with Herbicides

Weed ID is Key

Herbicide selection

Herbicide application

Hybrid/Variety Interactions with Herbicides

Most effective weed control = Combination of cultivation and chemicals

Timing of Weed Control

Knezevic et al. 2003 (Nebraska)

Species Shifts

What will happen to RR technology?

Volunteer corn in corn and soybeans fields will affect yields if density levels are high and left uncontrolled. In soybeans fields there are herbicides effective in controlling glyphosate or non-glyphosate resistant corn plants. In corn it becomes more problematic if the volunteer plants from the previous crop are glyphosate resistant and growing in a glyphosate resistant field.

Cultivation is the only practical means available to remove these volunteer plants. The yield impact can approach 13% under extremely high density levels. Studies from Iowa State show a 1.3% yield loss with a volunteer plant every ten feet of row. In many fields there are clumps and individual plants scattered about. University studies show 0.5% yield loss with 500 volunteer plants per acre up to 1.5% loss at 2000 plants per acre. If there are clumps in the field, then yield losses range from 1.2% per 500 clumps per acre to 2.4% per 1000 clumps per acre. An acre is 208.7 feet by 208.7 feet.

Cultivation

Most farmers cultivate row crops at least once, many cultivate twice
Research shows cultivation may increase yields as much as 10-20% on soils that tend to crust
Cultivation breaks up crust and improves rainfall infiltration
Cultivation dries out upper 2-3 in of soil more rapidly, but it also breaks up capillary pathways that extend into the soil
Cultivation stirs the soil, which can increase microbial oxidation and release of nutrients
Breaking a crust to increase water infiltration can reduce soil erosion

Chemicals

Banding herbicides at planting is an excellent practice

Offers protection in a wet spring
Banding saves dollars
Usually use ½ to 1/3 as much chemical in comparison with broadcasting
Banding with the planter controls weeds in the row, cultivation later controls weeds between rows

Broadcasting

Uniform weed control throughout a field, but more chemical applied/a means more expense
Many herbicides (except "burn down" or contact herbicides) lose effectiveness in a dry spring
Herbicide management is very important
On continuous corn, many farmers rotate herbicides from year to year
Heavy rates of some herbicides may damage corn
Hybrids may differ in tolerance
Environmental conditions important

Weed Control and Tillage Systems

Reducing or eliminating tillage can alter weed populations
Perennial weeds are often more prevalent in no-till systems than in moldboard and chisel systems
Higher rates of chemicals are often required as tillage is reduced because residue ties up chemicals
Uniform incorporation/distribution of herbicides is usually more difficult as amount of surface residue increases

Weed Control and Crop Rotations

Continuous corn: Weed control in reduced till fields can be as dependable as in conventional fields since the same herbicides and mechanical cultivation can be used

Corn-soybean rotations: If soybean was the previous crop in a reduced tillage system, much of the surface residue is buried with the first tillage operation. Therefore, uniform incorporation of herbicides is not much of a problem when following soybeans

No till: Weed control depends entirely on herbicides. A higher level of herbicide management is required

Herbicides requiring incorporation are not used
Both preemergence and postemergence herbicides are required

Herbicide Resistance

List of herbicide resistance weeds

http://www.weedscience.org/in.asp (from Robert Gunn)

Herbicide Resistant Crops
Herbicide Resistant Weeds
Management of Resistance

Weeds cause harvest problems

Lower stems of some weeds are very thick and woody at maturity (velvetleaf, sunflower) can be tough on a combine
If there are many weeds, and the weeds are tough, may have to wait for a killing frost to combine soybeans
May have to operate the combine at a reduced ground speed, and at the same time increase combine rpm's
Too much weed trash may plug the sieves, and soybeans may be lost out of the back end of a combine

Problem weeds in WI

annual grasses (barnyard grass, crabgrass, downy brome, fall panicum, foxtails, longspine sandbur, prairie cupgrass, shattercane, wild proso millet, witchgrass, wooly cupgrass)

large-seeded broadleaf weeds (cocklebur, common sunflower, devil's claw, eastern black nightshade, puncture vine, smartweed, velvetleaf, Venice mallow)

perennial grasses (johnsongrass, quackgrass, wirestem muhly)

annual broadleaves (common ragweed, lambsquarter, Pennsylvania smartweed, redroot pigweed, waterhemp)

perennial broadleaves (field bindweed, hedge bindweed, swamp smartweed, woolyleaf bursage)

small-seeded broadleaf weeds (kochia, lambsquarters)

How to calibrate a sprayer

Calibrating a boom sprayer is not as difficult as it sounds. Although there are many methods to use, the method described below for broadcast applications is simple and requires few calculations.

To calibrate your sprayer you need a measuring tape, a watch capable of indicating seconds, and a measuring jar graduated in ounces. A pocket calculator also will be handy. What follows is a calibration process:

Fill at least half the tank with water.
Run the sprayer, inspect it for leaks, and make sure all vital parts function properly.
Measure the distance in inches between the nozzles. Then measure an appropriate distance in the field based on the nozzle spacing (204, 136 and 102 ft for nozzle spacings of 20, 30 and 40 inches of nozzle spacing, respectively).
Drive through the measured distance in the field at your normal spraying speed, and record the travel time in seconds. Repeat this procedure and average the two measurements.
With the sprayer parked, run the sprayer at the same pressure level and catch the output from each nozzle in a measuring jar for the travel time required in Step 4.
Calculate the average nozzle output by adding the individual outputs and then dividing by the number of nozzles tested. If an individual sample collected is more than 10 percent higher or lower than the average nozzle output rate, check for clogs and clean the tip, or replace the nozzle.
Repeat steps 5 and 6 until the variation in discharge rate for all nozzles is within 10 percent of the average.
Then, the final average output in ounces is equal to the application rate in gallons per acre (Average output in ounces = Application rate in GPA).
Compare the actual application rate with the recommended or intended rate. If the actual rate is more than 5 percent higher or lower than the recommended or intended rate, you must make adjustments.
You can start the adjustments by changing the pressure. Lowering the spray pressure will reduce the spray delivered; higher pressure means more spray is delivered. Don't vary from the pressure range recommended for the nozzles used.
You also can correct the application error by changing the actual travel speed. Slower speeds mean more spray is delivered; faster speeds mean less spray is delivered.
If these changes don't bring the application rate to the desired rate, then you may have to select a new set of nozzles with smaller or larger orifices.
Recalibrate the sprayer (repeat steps 5 through 12) after any adjustment.

Weed Management