ISSUE 3   May 27, 2010


The NDSU Weed Science home page listed on the front and back cover of the weed guide is

The most current version of the weed guide can be found at this site with the new 2010 herbicide prices listed in the Herbicide Compendium.

Herbicide prices are averages of four different suppliers. Many herbicide prices remain the same or had a significant reduction in price. The price of many brands of generic herbicides were reduced. The price of most adjuvants remained the same or increased slightly.

Many herbicides are now available through generic trade names. Many brand names of generic herbicides are listed in the Herbicide Compendium which may be helpful if you hear of new name but not sure what the active ingredient is.

Most generic 3 lb ae/gallon glyphosate formulations are in the $12 to $15/gallon range.

Rich Zollinger
NDSU Extension Weed Specialist



The goal of all growers should be to maximize glyphosate activity whenever it is applied to Roundup Ready crops. This goal should maximize profitability and weed control and reduce the risk for herbicide resistance. Below are the most important management strategies for improving glyphosate activity. For additional information, consult pages 69 to 71 in the 2010 North Dakota Weed Control Guide and pages 52 and 53 in the 2010 Sugarbeet Production Guide.

1. Apply glyphosate to small (1 to 3") annual weeds.

2. Apply glyphosate to perennial species in the bud to early-flowering stage of development.

3. Apply the most effective rate for the most difficult to control species in the field. For many annual species the minimum rate of glyphosate should be 0.75 pounds acid equivalent/acre (lb ae/A). Species such as lambsquarters, velvetleaf, wild buckwheat, common ragweed, common mallow, smartweeds, horseweed/marestail, biennial wormwood, dandelion, and waterhemp are more difficult to control with glyphosate. Consider using the maximum single-use rate of glyphosate for these species in Roundup Ready crops, especially if a reduction in control has been observed previously. Glyphosate should be applied at greater than 0.75 lb ae/A to improve control of perennial species. Multiple glyphosate applications usually improve control of most species, especially perennial species.

4. Always add ammonium sulfate (AMS) to glyphosate mixtures. Ammonium sulfate should be added at a minimum of 4 pounds per 100 gallons of spray mixture (lbs/100 gal) for most of North Dakota. Higher rates of AMS will be needed if water hardness is greater than 1600 ppm.

5. Allow at least a 6 hour rainfree period for all glyphosate formulations to maximize activity. A shorter rainfree period can be acceptable for the most susceptible species. Lambsquarters control is usually reduced if the rainfree period is less than 6 hours.

6. Apply glyphosate during the warmest and most humid weather conditions to maximize activity.

7. Most glyphosate formulations include a nonionic surfactant (NIS) in the formulation. Consult page 71 in the 2010 North Dakota Weed Control Guide concerning glyphosate formulations and the following web address for information about glyphosate formulations labeled for Roundup Ready sugarbeet: Some glyphosate formulations do not include NIS (non-loaded). For these formulations add a quality NIS product at 0.5 to 1.0 % v/v. Some weed species, especially lambsquarters, can be more effectively controlled with the addition of NIS at 0.25 %v/v to "loaded or full adjuvant load" glyphosate formulations and 0.25 to 0.375 %v/v to "partial–loaded" glyphosate formulations. Some glyphosate formulations prohibit the use of additional NIS.

8. Glyphosate activity is influenced by the time of day of the application. Maximum activity occurs between 10:00 AM and 4:00 PM. Velvetleaf and common and giant ragweed control may be the most negatively affected by the time of the glyphosate application.

9. Application of glyphosate in low water volumes improves glyphosate activity. However, when spraying large weeds and/or dense weed canopies, higher spray volumes usually improves glyphosate activity.

10. Glyphosate is strongly and irreversibly absorbed to clay particles and organic matter. Therefore dust of any amount, especially initiated by the wheels of the sprayer, will cause a reduction in glyphosate activity. The best methods for decreasing this problem are to drive slower and make sequential applications perpendicular to the previous application or off-set sequential application by a few feet compared to the previous application.

11. When mixing other herbicides with glyphosate, add the most effective adjuvant for the herbicide being added. This strategy will maximize the activity of the herbicide(s) being added to the glyphosate mixture. If the herbicide being added to the glyphosate mixture recommends the addition of an oil adjuvant for maximum activity, then add a High Surfactant Oil Concentrate (HSOC). This is important because most oil adjuvants antagonize glyphosate activity. Current NDSU research indicates that not all HSOC’s perform equally. Purchase a good quality HSOC and apply at 0.75 to 1.25 pt/A.

Jeff Stachler
Agronomist - Weed Science

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