Corn, Soybean, Wheat, and Alfalfa Field Guide

NO-TILL PERENNIAL WEED CONTROL

Perennial weeds will increase as the amount of tillage is decreased. The optimum time to control many perennials, such as hemp dogbane, quackgrass and Canada thistle, is in the fall, especially in mowed (before Aug. 1) wheat stubble, when herbicide can be translocated to the roots and rhizomes with downward-moving energy reserves. Rotation of crops and herbicides can be an effective means of control. Following is a review of some of the more persistent perennials and herbicide programs that have proven to be effective. Always add Ammonium Sulfate (AMS) to glyphosate products at 17 pounds/100 gallons of water for perennial weed control. Applying glyphosate in spray volumes of 5 to 10 gallons per acre can increase weed control.

Glyphosate rates will be expressed as pounds acid equivalent per acre (lb ae/A). Gylphosate at 0.75 lb ae/A is equal to 26.0 oz/A of Roundup Ultra Max (3.75 lb ae/gal) and 1.0 qt/A of Touchdown, Roundup Ultra, Roundup Original, Glyphomax Plus, Glyphosate Original and most other 3.0 lb ae/gal gylphosate formulations. Gylphosate at 1.5 lb ae/A is equal to 52.0 oz/A of Roundup Ultra Max and 2.0 qt/A of Touchdown, Roundup Ultra, Roundup Original, Glyphomax Plus, Glyphosate Original and most other 3.0 lb ae/gal glyphosate formulations. Read all glyphosate labels to determine whether a surfactant is needed.

Quackgrass

• Apply glyphosate in the spring when quackgrass is at least 8 to 12 inches tall, or fall after harvest before the killing frost with at least 6 to 8 inches of regrowth. Rates: glyphosate (0.75 lb ae/A).
• Other materials include:
  • Accent, Beacon and Steadfast POST on corn. Roundup Ultra on Roundup Ready corn.
  • Assure II, Fusilade DX, Fusion & Select POST on soybeans. Roundup Ultra on Roundup Ready soybeans.

Canada Thistle

• Fall Treatment with at least 8 inch tall plants:
  • glyposate (1.13 lb ae/A)
  • dicamba (1 to 2 qt/A) (Check recrop restrictions)
  • glyphosate - spot treatment - 2% solution.
• Stinger (0.67 pt/A) POST on corn.
• Glyphosate (0.75 lb ae/A) applied at bud to flower stage of growth on Roundup Ready corn or soybeans
• Other materials include: Basagran, Distinct, Hornet, Laddok and Marksman POST on corn. Basagran and First Rate POST on soybeans and Synchrony STS POST on STS soybeans.

Bindweeds

• In wheat stubble before killing frost:
  • glyphosate (2.25 to 3.0 lb ae/A)
  • glyphosate - spot treatment - 2-3% solution.
  • glyphosate + 2,4-D ester (1.5 lb ae/A + 1.5 pt/A)
  • dicamba (1 to 2 qt/A) alone or in combination with glyphosate.
• Apply glyphosate (1.5 lb ae/A) at flower stage on Roundup Ready soybeans
• Other materials include: dicamba, 2,4-D, Exceed + dicamba and Marksman POST on corn. Glyphosate on Roundup Ready corn. Blazer, Cobra, Flexstar, Reflex POST on soybeans.

Hemp Dogbane

• In wheat stubble before killing frost:
  • glyphosate (2.25 to 3.0 lb ae/A)
  • glyphosate - spot treatment - 2-3% solution
  • glyphosate + 2,4-D ester (1.5 lb ae/A + 1.5 pt/A.)
• Apply glyphosate at highest possible rate at bud to flower stage on Roundup Ready corn or soybeans.
• Other materials include: 2,4-D, Accent + dicamba, dicamba, Beacon + 2,4-D, Distinct (6.0 oz/A), Exceed + 2,4-D, Marksman, Spirit + 2,4-D or combinations of dicamba + 2,4-D POST on corn.

Common and Honeyvine Milkweed

• In wheat stubble before killing frost:
  • glyphosate (2.25 lb ae/A)
  • glyphosate - spot treatment - 2-3% solution.
  • glyphosate + 2,4-D ester (1.5 lb ae/A + 1.5 pt/A).
• Apply glyphosate at highest possible rate at bud to flower stage on Roundup Ready corn or soybean.
• Other materials include: same as hemp dogbane.

Common Dandelion

• In wheat stubble during mid-October:
  • glyphosate (1.13 to 1.5 lb ae/A)
  • glyphosate + 2,4-D ester (0.75 lb ae/A + 1.5 pt/A).
  • 2,4-D ester (1.0 qt/A to 1.5 qt/A).
• Apply 2,4-D ester (2 pt/A) in the spring after soil temperatures are above 50°F and 14 days before planting corn and 30 days before planting soybeans.
• Apply glyphosate (0.75 lb ae/A or 1.5 lb ae/A) POST on Roundup Ready corn or soybeans, respectively.
• Other materials include: Gramoxone Max + 2,4-D ester + Canopy XL or Sencor applied early preplant to soybean. 2,4-D ester (1.5 pt/A) + Balance Pro (2.2 to 3.0 oz/A) + atrazine applied preplant to corn. 2,4-D, dicamba, Distinct, Hornet and Marksman POST on corn. Liberty (34 oz/A)or Liberty ATZ POST on Liberty Link corn. Classic (0.75 oz/A) or Synchrony STS on STS soybeans.

Common Pokeweed

• In wheat stubble before killing frost with plants at least 18 inches tall.
  • glyphosate (1.13 to 1.5 lb ae/A).
  • glyphosate - spot treatment - 2% solution.
  • glyphosate + 2,4-D ester (0.75 lb ae/A + 1.5 pt/A).
• Apply glyphosate (0.75 or 1.5 lb ae/A) on Roundup Ready corn and soybeans, respectively, when plants are at least 30 inches tall or near bud stage.
• Other materials include: Beacon, Exceed, Permit or Spirit + Banvel (0.5 pt/A) POST on corn when pokeweed is at least 18 inches tall. Synchrony STS on STS soybeans.

Johnsongrass

• In wheat stubble before killing frost with plants at least 24 inches tall:
  • Glyphosate (0.75 lb ae/A)
  • Glyphosate - spot treatment - 2 % solution
• Apply Accent, Beacon, Celebrity Plus, or Steadfast POST on corn with johnsongrass greater than 8 inches tall.
• Apply glyphosate (0.75 lb ae/A) POST on Roundup Ready corn or soybean with johnsongrass greater than 15 inches tall.
• Apply Assure II, Fusilade DX, Fusion, or Select POST on soybeans with johnsongrass 10 to 20 inches tall.
• Apply Lightning POST on Clearfield corn with johnsongrass less than 8 inches.

WEED RESPONSE TO BURNDOWN HERBICIDES

This table gives a general comparative rating of “burndown” herbicides used in no-till corn and/or soybean production. Under unfavorable conditions, some herbicides may not perform as well as indicated below. Under very favorable conditions, control may be better than indicated. Soil type, rate of herbicide, weed stage of growth and environmental conditions all interact to influence herbicide performance.

Weed control rating:
9 = 85 to 100%; 8 = 75 to 85%; 7 = 65 to 75%; 6 = 55 to 65% control; and NR = not recommended.

Weed control of 5 or less is rarely significant. These treatments are rated for control of existing vegetation only. The use of crop oil, surfactants or fertilizer solutions generally increases burndown activity of these herbicides. Check label for recommended rates and type of additives. For best results use the liquid form of Atrazine.

SOIL SAMPLING IN NO-TILL

Research indicates that phosphorous (P) and potassium (K) layers or concentrates are near the soil surface in notillage and reduced tillage systems. Because of this stratification of nutrients, split sampling can be used to see if corrective action is necessary.

The routine method of sampling no-tillage fields is as follows:

1. 0-2 inch sample to check for soil pH and lime requirement. When nitrogen fertilizers such as urea or (UAN) solutions are applied to the surface in no-till systems, the surface few inches can become acid very quickly. This can affect both herbicide activity and plant growth.
2. 0-8 inch sample to check for all nutrient requirements.
   Sample can be split into a top 4" section and a bottom 4" section if so desired.

P AND K SOIL TEST LEVELS FOUND AT VARIOUS DEPTHS IN THE SOIL (CRUZ, 1982)