For various reasons, you may need to make “a game-time decision” on whether to plant corn or soybeans this spring. In that case, it is best to apply a flexible herbicide program that allows planting of either crop.
A limited number of corn and soybean herbicides allow you to switch crops if necessary. Here is a list of herbicides that can be used preplant in both corn and soybeans. Be careful of application rates and wait periods that may differ for each crop.
Also, keep in mind that some of these products and active ingredients are available in generic alternatives.
Burndown
Here are products for burndown:
2,4-D LVE. When applied at 1 pint an acre, there is a seven-day waiting period for soybeans. This is also the safest use in corn. If applying 1 quart, wait at least 15 days to plant soybeans.
Basis Blend. Apply at 0.825 to 2.5 ounces an acre in burndown programs before corn emergence. Corn injury may occur under cool, wet conditions, so the 1.5-ounce rate is a good compromise. In soybeans, apply 0.825 ounces at least 15 days before planting. Tank-mix to enhance control. It provides some weedy grass control and fair-to-good burndown activity on several key broadleaves.
Elevore. Either corn or soybeans can be planted 14 days after application when applied at 1 fluid ounce an acre. However, corn can be planted after three days if seed is planted at least 1.5 inches deep and completely covered. It provides control of glyphosate-resistant marestail.
Glyphosate. This can be used burndown and post in glyphosate-resistant crops. Increase the rate to 1.5 pounds an acre for larger weeds.
Gramoxone. You can increase the rate to 2.7 pints an acre for larger weeds. You can tank-mix with metribuzin, plus 2,4-D, and still be able to plant corn or soybeans. This mixture provides better burndown activity than paraquat alone.
Harmony/Extra, Audit 1:1 and other thifensulfuron + tribenuron mixes. These can be added to the 2,4-D or glyphosate burndown at 0.45 to 0.90 ounces an acre for both corn and soybeans. You must wait seven days to plant soybeans and 14 days for corn. Without glyphosate, it provides average (70% to 80%) control on many key broadleaves and no grass control, With glyphosate, it improves control of curly/broadleaf dock, wild garlic, common groundsel, field pansy and Canada thistle.
Liberty 280. This is labeled up to 43 fluid ounces an acre in the burndown application. Liberty is most effective on small, actively growing weeds under warm temperatures. Use sufficient carrier volume (minimum 15 GPA, 20 GPA is better) and spray nozzles to get thorough droplet coverage of the weeds.
Reviton. This can be used in a burndown program before field corn or soybeans. Corn can be planted immediately after application. Wait seven days to plant soybeans if using 2 to 3 fluid ounces (0 days at 1 fluid ounce). It has a low use rate (1 to 3 fluid ounces an acre) and can be tank-mixed with other herbicides, especially glyphosate. MSO or COC, plus AMS, must be added to the spray solution. Reviton is similar to Sharpen and is less active on marestail, but it has better activity on field pansy/violet, primrose and some grasses compared to Sharpen.
Sharpen. This is labeled for both corn and soybeans. Use only one fluid ounce an acre in soybeans for burndown if planting soybeans immediately. Higher rates can be used, but be aware of planting restrictions for soybeans. Corn can be planted immediately at any labeled rate. Always add MSO and AMS as the adjuvants to the spray tank for optimal weed control.
Grass residual
Here are products primarily for grass residual:
Group 15 products (s-metolachlor/Dual, etc.; acetochlor/Enversa, Warrant, etc.; and Outlook). These can be used in both corn and soybeans for residual grass, yellow nutsedge and some small-seeded broadleaf control.
Broadleaf residual
Here are products for broadleaf residual:
Lorox. This can be used in both corn and soybeans. It primarily provides control of annual broadleaves, but it can suppress certain annual grasses.
Metribuzin. This product was labeled preemergence at up to 5.3 ounces an acre on medium-textured soils with greater than 2% organic matter as part of the burndown program in either crop.
Python. This is effective on several annual broadleaf weeds and can be used in both corn and soybeans. The use rate range is 0.8 to 1.14 ounces an acre (up to 1.33 ounces in soybeans).
Valor. It can be used in both corn and soybeans. Corn may be planted seven days after application at the 2 ounces-an-acre rate (requires minimum 25% surface residue and 0.25 inches of rainfall between application and planting). Do not tank-mix with common grass herbicides (Dual, Outlook, etc.) in soybeans due to injury concerns.
Grass and broadleaf residual
Here are products for grass and broadleaf residual:
Verdict. This is a mixture of the active ingredients found in Sharpen and Outlook. The most common application rate is 13 fluid ounces an acre for corn and 5 fluid ounces an acre for soybeans.
Zidua and Anthem Maxx/Flex. This can be used in the burndown mix, and either corn or soybeans can be planted and will provide control of many annual weeds.
Fierce. This can be used in both soybeans and no-till or minimum-till corn to control many annual grasses and broadleaves. In corn, you must wait at least seven days to plant corn after application.
Combinations that include a grass product (Dual, Outlook and Warrant/Enversa), plus Python, would also provide residual grass and broadleaf control for both corn and soybeans.
You must know what weeds cause problems and understand that, in some cases, multiple trips across the field for better weed control might be more economical to ultimately protect and improve crop yields.
But don’t forget, one-pass burndown/residual herbicide programs may have a fit in certain situations.