(Adapted from the Wisconsin Soy Sentinel 2008)

 

Glyphosate has been the herbicide of choice for soybean weed control for a decade and for good reason. It controlled weeds well without injuring soybeans and its price kept dropping, which made the choice easier. However, the trend of low priced glyphosate changed in 2008. Glyphosate prices have spiked because of reduced glyphosate supplies and increased demand.

 

Does this change how glyphosate is used in soybeans? Glyphosate will still be the backbone for most soybean weed control programs, but the higher price may have a couple consequences. First, some people may be tempted to reduce glyphosate rates, which may lead to poor control if the weeds are too large when sprayed. Some people also suggest that reduced rates may contribute to a shift towards more tolerant weeds. Regardless of price, apply the glyphosate rate that is appropriate for the weed species and size in soybean fields. Avoid the temptation of reducing rates below those needed for effective control just to save costs.

 

The second consequence of higher glyphosate prices is that it may open the door for some other herbicide options. Consider the preemergence (PRE) herbicides. The cost of several PRE herbicides that are recommended as foundation treatments in Roundup Ready soybeans may be similar to the current cost of glyphosate. “Foundation treatments” often refer to PRE herbicides that are applied at lower rates to provide early season weed suppression. They can help to control weeds that might be tougher to control with glyphosate alone or provide early season weed suppression so that glyphosate can be applied closer to soybean canopy closure. As a result, more consistent and higher levels of weed control are typical (based on university test results).  Adding a PRE herbicide also brings another herbicide mode of action into the weed management program, which may reduce the selection pressure for glyphosate-resistant weeds.

 

Conditions where 2 glyphosate applications may be required:
30-inch row soybeans Weeds with extended emergence (ie waterhemp, giant ragweed) Tough to control weeds (ie giant ragweed, lambsquarters)
Standard 2 pass glyphosate*	PRE herbicide* and POST glyphosate
$12 + $12 = $24/a	$12 + $12 = $24/a
*Actual costs will vary depending on herbicide and rate, but can be very similar.

Most of the foundation herbicide programs have been promoted to improve broadleaf weed control and many of the common options are listed below. Some other herbicides provide effective control of a mix of broadleaf and grass weeds while others are primarily effective on grass weeds. In the table below, the ingredients of premixed herbicides are provided as a guide to help understand these herbicides and their performance. More information on these herbicides, their use, and weed control ratings can be found in the 2008 Pest Management in Wisconsin Field Crops bulletin, which can be ordered or viewed at http://learningstore.uwex.edu/

 

Common Preemergence (PRE) Soybean Herbicides
Primarily Broadleaf Herbicides	Grass and Broadleaf Herbicides
Authority First or Sonic (Authority + FirstRate)	Boundary (Dual II Magnum + Sencor)
Authority MTZ (Authority + Sencor)	Prefix (Dual II Magnum + Flexstar)
Enlite (Classic + Valor SX + Harmony)	Prowl H2O
Envive* (Classic + Valor SX + Harmony)
FirstRate	Primarily Grass Herbicides
Gangster (Valor SX + FirstRate)	Dual II Magnum
Python	Intrro
Sencor	Outlook
Valor SX	Sequence (Dual II Magnum + glyphosate)
Valor XLT* (Valor SX + Classic)
*Southern WI only

Glyphosate is only one of many items with a rapidly changing price. The prices of crops, fertilizers, seed, fuel, and land are all in flux and it may be tempting to cut costs. However, remember that the goal of a weed management program is to protect yield. The old saying about being penny wise and pound foolish certainly applies to weed management. Herbicides are a wise investment. This investment may now include more than just glyphosate. The price increase of glyphosate should make us consider if other herbicide options have a fit in soybean systems and provide benefits to improve overall weed management.