Herbicide Options for Planting Forage Cover Crops after Corn and Soybean

Herbicide Options for Planting Forage Cover Crops after Corn and Soybean March 18, 2016

Cover crop adoption is continuing to increase throughout Nebraska. Respondents to the 2015 cover crop survey conducted during Nebraska extension meetings indicated the top five desired benefits from cover crops are

  • building soil organic matter,
  • reducing soil erosion,
  • increasing soil water-holding capacity,
  • producing forage, and
  • improving soil microbial biomass.

While all of these benefits will improve cropping system productivity and sustainability over time, the direct economic value of cover crops is difficult to determine. For this reason, many producers are grazing or haying cover crops to offset the expense while still capturing the longer term benefits. An important consideration of using these forage cover crops following corn or soybean is that herbicide label rotation restrictions from the agronomic crop MUST be followed to avoid potential carryover to animals consuming this forage. The recommendations in this article are for forage cover crops because the requirements to integrate them in a herbicide program are most restrictive.

Herbicide Label Plant-Back Restrictions

Most herbicide labels list crop rotation intervals or plant-back restrictions that limit how soon a subsequent crop can be planted after a herbicide application. It is important to note that this is different from the grazing or forage restrictions posted on a herbicide label for crops to which a herbicide is directly applied. When planning a fall-planted forage cover crop following corn or soybean, a herbicide crop rotation interval or plant-back restriction should be short enough to allow the forage cover crop to establish before winter. If the forage cover crop species you intend to plant is not listed on the label, you must follow the rotation restriction listed for “other crops.” In addition, the rotation restriction for a forage cover crop mixture is dictated by the species in the mixture with the longest restriction. Meeting these restrictions can become challenging as replant restrictions may fall outside the ideal fall planting window. Hail or other crop damage, seed corn, and silage corn all provide opportunities for earlier forage cover crop planting; however, care must still be taken to observe herbicide plant-back restrictions.

Herbicide persistence in the soil is affected by several environmental factors and ultimately, herbicide residues can inhibit forage cover crop growth or cause crop failure. Furthermore, herbicide residues can be taken up into forage cover crops and either be directly toxic to livestock or accumulate in their fat, meat, milk, or other tissues and pass into the human food supply. For labeled crops, studies have been conducted to identify safe replant intervals that prevent bioaccumulation of herbicides. In the case of non-labeled crops such as many cover crops or “other crops,” these tests were not conducted. In this case, labels list the longest plant-back restriction where herbicide companies can be confident potential herbicide carry-over effects are negligible. Without crop-specific tests, the risk for herbicide toxicity to animals consuming cover crop forage or herbicide residues in human food is unknown.  

As a point of clarification, if cover crops will NOT be harvested or grazed, they can be planted before the label replant restriction allows. Growers would assume the risk for cover crop failure. However, if cover crops are to be used as a forage, planting before the label replant restriction permits violates federal law. An Environmental Protection Agency (EPA) registered herbicide label is a legal document and must be followed.

Plant-back restrictions of forage cover crops will limit herbicides that can be used in corn and soybean cropping systems. Many pre-emergence herbicides that allow fall planting of a forage cover crop have a four-month restriction interval. To compensate for this, consider planting forage cover crops in the earliest planted, sprayed, and harvested fields. Additionally, to avoid selection for herbicide-resistant weeds due to repeated application of the same herbicide, fields in which forage cover crops are planted should be rotated so that a broader range of herbicides can be used during the non-forage cover crop year.

It can be challenging to decipher herbicide label information when deciding which herbicides to use with forage cover crops.  Restrictions are listed for common pre-emergence and post-emergence corn and soybean herbicides. When tank-mixing herbicides, follow the most restrictive interval listed on all the labels.

Integrating forage cover crops into your cropping system can provide economic and agronomic benefits. To maximize these benefits, it is important to consider how your herbicide program may impact the use of forage cover crops in your cropping system.

For more information on cover crop termination methods and crop insurance, see the United States Department of Agriculture’s (USDA) Risk Management Agency (RMA) resource 2016 Cover Crops Crop Insurance, Cover Crops and NRCS Cover Crop Termination Guidelines.

Disclaimers

Herbicide information compiled here is intended to be as accurate as possible at the time of publication; however, refer to current herbicide labels for the latest and most detailed information.

Reference to commercial products or trade names in this publication is made with the understanding that no discrimination is intended and no endorsement by Nebraska Extension is implied.


Tables of herbicide restrictions for various categories are available in a mobile/web friendly format (below) or in a print-friendly PDF format (red button).


Table 1a Plant-Back Restrictions for Cool-Season Forage Cover Crops after Pre-Emergence Herbicide Applications in Corn
MONTHS REQUIRED BETWEEN PRE-EMERGENCE HERBICIDE APPLICATION IN CORN AND PLANTING OF FORAGE COVER CROP1
HerbicideAnnual
Rye
BarleyCereal
Rye
CloverField PeaOatsRadishTriticaleTurnipVetchWheat
Anthem2 4 4
Anthem Maxx3 4 4
Balance Flexx 4 4
Callisto 4 4 0 4 4
Cinch4 4.5 4.5 4.5 4.5
Cinch ATZ
Confidence/ Confidence Xtra5 4
Corvus 4 4
Degree/ Degree Xtra6 4
Dual II Magnum7 4.5 4.5 4.5 4.5 2 2 4.5
G-Max Lite
Guardsman Max
Harness/ Harness Xtra8 4
Hornet 4 4 4 4
Instigate 4 4 4 4 4
Lumax EZ 4.5 4.5 4.5
Outlook 4 4 4 4
Parallel 4.5 4.5 4.5 4.5
Prequel 4
Prowl H2O9 4 4
Resolve 4
Sharpen10 0 0 2 0 0
Sure Start II 4
Surpass/ Surpass NXT11 4
Topnotch 4
TripleFLEX12 4
Valor13 4 3 3 4 3 4 4 4 4 4 1
Verdict 4 4 4 4
Zemax14 4.5 4.5 4.5 4.5
Zidua15 4

Table 1b. Plant-Back Restrictions for Warm-Season Forage Cover Crops after Pre-Emergence Herbicide Applications in Corn
MONTHS REQUIRED BETWEEN PRE-EMERGENCE HERBICIDE APPLICATION IN CORN AND PLANTING OF FORAGE COVER CROP1
HerbicideChickpeaCowpeaPearl MilletProso MilletSorghum
Anthem2
Anthem Maxx3
Balance Flexx
Callisto 0 0
Cinch4 0
Cinch ATZ 0
Confidence/ Confidence Xtra5
Corvus
Degree/ Degree Xtra6 0
Dual II Magnum7
G-Max Lite 0
Guardsman Max 0
Harness/ Harness Xtra8 0
Hornet
Instigate 4 4
Lumax EZ 0
Outlook
Parallel
Prequel
Prowl H2O9
Resolve
Sharpen10 2 0 0 0
Sure Start II
Surpass/ Surpass NXT11
Topnotch
TripleFLEX12
Valor13 4 3 4 4 1
Verdict
Zemax14 0
Zidua15
 
1 A zero indicates no replant restrictions are required following herbicide application.  A dash indicates the restriction for that herbicide-species combination is too long to allow for planting of that forage cover crop species within the same growing season as the corn crop.
2 Wheat may be planted as a cover crop when Anthem is applied at a rate of 9.75 oz/ac or less. Field pea may be planted when Anthem is applied at a rate of 3.25 oz/ac or less.
3 Wheat may be planted as a cover crop when Anthem Maxx is applied at a rate of 4.875 oz/ac or less. Field pea may be planted when Anthem Maxx is applied at a rate of 1.625 oz/ac or less.
4 To avoid injury in rotational alfalfa or clover, do not apply more than 1.9 lbs active ingredient per acre (2.0 pints of Cinch) in the previous crop, and do not make lay-by or other post-emergent applications in the previous crop.
5 Following harvest of food crops treated with Confidence/Confidence Xtra, only non-food or non-feed cover crops (with the exception of wheat) may be planted. Do not graze or harvest rotational cover crops (with the exception of wheat) for food or animal feed for 18 months following the last application of Confidence/Confidence Xtra. This prohibition does not apply to nongrass animal feeds, which may be planted nine months after the last application of Confidence/Confidence Xtra.
6 Following harvest of food crops treated with Degree/Degree Xtra, only non-food or non-feed cover crops (with the exception of wheat) may be planted. Do not graze or harvest rotational cover crops (with the exception of wheat) for food or animal feed for 18 months following the last application of Degree/Degree Xtra. This prohibition does not apply to nongrass animal feeds, which may be planted 9 months after the last application of Degree/Degree Xtra.
7 Intervals are for rates of Dual II Magnum applied at not more than 1.33 pint/ac pre-emergence in corn. A second application of Dual II Magnum or other herbicides containing Dual II Magnum (S-metolachlor) is prohibited when planting forage double crops in fall.
8 Following harvest of food crops treated with Harness/Harness Xtra, only non-food or non-feed cover crops (with the exception of wheat) may be planted. Do not graze or harvest rotational cover crops (with the exception of wheat) for food or animal feed for 18 months following the last application of Harness/Harness Xtra. This prohibition does not apply to nongrass animal feeds, which may be planted nine months after the last application of Harness/Harness Xtra.
9 When applied at a rate of 3.2 pts/ac.
10 Sharpen can be applied pre-emergence in corn at 2 to 3 fl oz/ac depending on organic matter content of the soil. Crop rotation intervals listed are for a rate of 3 fl oz/ac.
11 Following harvest of food crops treated with Surpass/Surpass NXT, only non-food or non-feed cover crops (with the exception of wheat) may be planted. Do not graze or harvest rotational cover crops (with the exception of wheat) for food or animal feed for 18 months following the last application of Surpass/Surpass NXT. This prohibition does not apply to nongrass animal feeds, which may be planted nine months after the last application of Surpass/Surpass NXT.
12 Following applications of TripleFLEX, when annual rainfall or irrigation is less than 15 inches on soils with less than 2% organic matter, alfalfa, clover, and vetch should not be planted until 18 months after treatment.
13 When applied at a rate of 2 oz/ac or less. At least one inch of rainfall/irrigation must occur between application of Valor and planting of wheat or sorghum or injury may occur. Intervals for all crops marked (4) require soil be tilled prior to planting; otherwise, the interval is eight months. See herbicide label for rotation intervals for applications greater than 2 oz/ac.
14 Grain sorghum must be treated with a safener to tolerate S-metolachlor.
15 When applied at a rate of 3 oz/ac or less. See herbicide label for rotation intervals for each rate of Zidua use.

Table 2a. Plant-Back Restrictions for Cool-Season Forage Cover Crops after Post-Emergence Herbicide Applications in Corn
MONTHS REQUIRED BETWEEN PRE-EMERGENCE HERBICIDE APPLICATION IN CORN AND PLANTING OF FORAGE COVER CROP1
HerbicideAnnual
Ryegrass
BarleyCereal
Rye
CloverField
Pea
OatsRadishTriticaleTurnipVetchWheat
Aim 0 0 0 0 0 0 0 0 0 0 0
Armezon 3 3 3 3 3 3
Basis Blend 3 3 3 3 3
Beacon2 3 3 3
Buctril3 1 1 1 1 1 1 1 1 1 1 1
Cadet 0 0 0 0 0 0 0 0 0 0 0
Callisto 0 0
Callisto GT
Clarity4 3 3 3 3 3
Dicamba5 3 3 3 3 3
DiFlexx6 2 2 2
Expert
Glyphosate 0 0 0 0 0 0 0 0 0 0 0
Halex GT
Harmony SG 1.5 0 1.5 1.5 1.5 0 1.5 0 1.5 1.5 0
Impact 3 3 3 3
Liberty 280 2.3 2.3 2.3 2.3 2.3 2.3 2.3
Permit 2 2 2 2 2 2
Require Q7 3
Resolve Q 3
Resource 1 1 1 1 1 1 1 1 1 1 1
Solida8 3
Solstice 0
Spirit 3 3 3 3 3
Status9 1 1 1 1 1
Warrant10
Yukon 2 2 2 2 2 2

Table 2b. Plant-Back Restrictions for Warm-Season Forage Cover Crops after Post-Emergence Herbicide Applications in Corn
MONTHS REQUIRED BETWEEN PRE-EMERGENCE HERBICIDE APPLICATION IN CORN AND PLANTING OF FORAGE COVER CROP1
HerbicideChickpeaCowpeaPearl MilletProso MilletSorghum
Aim 0 0 0 0 0
Armezon 3 3
Basis Blend 3 3
Beacon 2
Buctril 3 1 1 1 1 1
Cadet 0 0 0 0 0
Callisto 0 0
Callisto GT 0
Clarity 4 3 3
Dicamba 5 3 3 0.5
DiFlexx 6 2
Expert 0
Glyphosate 0 0 0 0 0
Halex GT 0
Harmony SG 1.5 1.5 1.5 1.5 1.5
Impact
Liberty 280
Permit 2 2 2
Require Q 7
Resolve Q
Resource 1 1 1 1 1
Solida 8
Solstice 0 0
Spirit
Status 9 1 1 1
Warrant 10 0
Yukon 2 2 2

1 A zero indicates no replant restrictions are required following herbicide application.  A dash indicates the restriction for that herbicide-species combination is too long to allow for planting of that forage cover crop species within the same growing season as the corn crop.
2 Injury may occur if dry weather prevails during much of the time between Beacon application and seeding of winter cereals or other crops.
3 Do not cut crop for feed, fodder, or graze within 45 days of application.
4 Sorghum may be planted 15 days after Clarity application of 8 oz/ac; all other intervals are for rates of 24 oz/ac or less. See label for rotation intervals at rates of more than 24 oz/ac.
5 Sorghum may be planted 15 days after Dicamba application of 8 oz/ac; all other intervals are for rates of 24 oz/ac or less. See label for rotation intervals at rates of more than 24 oz/ac.
6 When applied at a rate of 24 oz/ac or less. See label for rotation intervals at rates of more than 24 oz/ac.
7 When applied at a rate of 4 oz/ac.
8 When applied at a rate of 1 oz/ac.
9 If at least 1 inch of rainfall or overhead irrigation has been received following the last application of Status (less than or equal to 5 oz/ac only), alfalfa, cereal grain crops, and sorghum may be planted 30 days after the rainfall/irrigation event.
10 When planting sorghum, use only seed properly treated with seed protectant or safener.

Table 3a. Plant-Back Restrictions for Cool-Season Forage Cover Crops after Pre-Emergence Herbicide Applications in Soybeans
MONTHS REQUIRED BETWEEN PRE-EMERGENCE HERBICIDE APPLICATION IN CORN AND PLANTING OF FORAGE COVER CROPA
Annual
Ryegrass
BarleyCereal
Rye
CloverField
Pea
OatsRadishTriticaleTurnipVetchWheat
AnthemB 4 4
Anthem MaxxC 4 4
Authority Assistd 4 4
Authority Elite 4.5 4.5 0 4.5 4.5
Authority First 4
Authority Maxx 4 4 4
Authority MTZ 4 4 4
Authority XL 4 4
Boundary 4.5 4.5
Canopy 4 4 4 4
Commande 0/9f
Dimetric DF 4 4
Dual II Magnumg 4.5 4.5 4.5 2 4.5
Enlite 4 4 3
Envive 4 4 4 4
FirstRate 4
Gangster 3
Optill 4 4 4
Optill PRO 4 4 4
Outlook 4 4 4
Prefix 4.5 4.5 4.5
Prowl H2Oh 4 4
Pummel 4.5
PursuitI 4 0 0 4
Python 4 4 4 4 4
Rowelj 4 3 3 4 3 3 4 1 4 1
Rowel FX 4 4 4 4
Sharpenk 4 0 0 2 4 2 0 0 4 4 4
Sonic 4
Surveil Co Pack 3
Torment 4 4 4 4
Trivence 4 4
Valor SXl 3-4 3-4 3-4 3-4 1-9 1-9
Valor XLTm 4 4 4
Vise 4.5 4.5 4.5
Warrant 4
Warrant Ultra 4 4 4

Table 3b. Plant-Back Restrictions for Warm-Season Forage Cover Crops after Pre-Emergence Herbicide Applications in Soybeans
MONTHS REQUIRED BETWEEN PRE-EMERGENCE HERBICIDE APPLICATION IN CORN AND PLANTING OF FORAGE COVER CROPA
ChickpeaCowpeaPearl MilletProso MilletSorghum
Anthem B
Anthem Maxx C
Authority Assist D
Authority Elite
Authority First
Authority MAXX
Authority MTZ
Authority XL
Boundary
Canopy
Command E
Dimetric D F
Dual II MagnumG 2 4.5 2
Enlite
Envive
FirstRate
Gangster ——
Optill 4
Optill PRO
Outlook 4
Prefix 4.5
Prowl H2O h
Pummel
Pursuit i 4
Python 4
Rowel j 4 4 4 4
Rowel FX
Sharpen k 4 4 0 0 4
Sonic
Surveil Co Pack
Torment 4 4
Trivence
Valor SX l 4-10 4-10
Valor XLT m
Vise 4.5
Warrant
Warrant Ultra 4
a A zero indicates no replant restrictions are required following herbicide application. A dash indicates the restriction for that herbicide-species combination is too long to allow for planting of that forage cover crop species within the same growing season as the corn crop.
b Wheat may be planted when Anthem is applied at less than 9.75 oz/ac. Field pea may be planted when Anthem is applied at less than 3.25 oz/ac.
c Wheat may be planted when Anthem Maxx is applied at less than 4.875 oz/ac. Field pea may be planted when Anthem Maxx is applied at less than 1.625 oz/ac.
d Intervals for cereal rye and wheat are 18 months for Minnesota and North Dakota, north of Highway 210. Do NOT feed treated soybean forage or hay to livestock.
e Do not graze or harvest for food or feed cover crops planted less than 9 months after treatment with Command.
f Peas may be planted immediately following application when Command is applied at less than 0.5 lb/ac; otherwise, the interval is nine months.
g Intervals are for rates of Dual II Magnum applied at NOT more than 1.33 pint/ac. A second application or other herbicides containing S-metolachlor is prohibited when planting forage double crops in the fall.
h When applied at a rate of 3.2 pts/ac.
i This will restrict the post-emergence application of Pursuit in soybean if growers intend to plant alfalfa, cereal rye, clover, or wheat in the fall.
j A rotational interval for most cover crops is four months if soil is tilled prior to planting, and eight months if no tillage is performed. See herbicide label for instructions.
k Can be applied at 1 fl oz/ac if the organic matter content of the soil is less than 2%. This herbicide will provide limited broadleaf control at this rate. Coarse soils with less than 2% organic matter require a minimum preplant interval of 30 days for planting soybean.
l Rotation intervals for Valor SX vary depending on the applied rate of herbicide; see label for full restrictions.
m Valor XLT in Nebraska can only be applied in soybean fields south of route 30 and east of route 281.

Table 4a. Plant-Back Restrictions for Cool-Season Forage Cover Crops after Post-Emergence Herbicide Applications in Soybeans
MONTHS REQUIRED BETWEEN PRE-EMERGENCE HERBICIDE APPLICATION IN CORN AND PLANTING OF FORAGE COVER CROPA
Annual
Ryegrass
BarleyCereal
Rye
CloverField
Pea
OatsRadishTriticaleTurnipVetchWheat
Assure II 0
Cadet 0 0 0 0 0 0 0 0 0 0 0
Classic b 3 3 3 3 3
Cobra 2 2 2 2 2 2
Extreme 0
Fusilade DX 2 2 2 2
Glyphosate 0 0 0 0 0 0 0 0 0 0 0
Harmony SG 1.5 0 1.5 1.5 1.5 0 1.5 0 1.5 1.5 0
Liberty 70 days 70 days 70 days 70 days 70 days 70 days 70 days
Poast Plus 1 1 1 0 1 1 1 1 1
Pursuit 0
Raptor 0 3
Resource 1 1 1 1 1 1 1 1 1 1 1
Select Max 1 1 1 0 0 1 0 1 0 1 1
Synchrony 3 3 3 3 3 3
Targa 0 0 0
Torment
Ultra Blazer c 100 days 40 days 40 days 100 days 100 days 40 days 100 days 40 days 100 days 100 days 40 days

Table 4b. Plant-Back Restrictions for Warm-Season Forage Cover Crops after Post-Emergence Herbicide Applications in Soybeans
MONTHS REQUIRED BETWEEN PRE-EMERGENCE HERBICIDE APPLICATION IN CORN AND PLANTING OF FORAGE COVER CROPA
ChickpeaCowpeaPearl MilletSorghum
Assure II 0 0
Cadet 0 0 0 0
Classic b 0
Cobra 2 2
Extreme 0
Fusilade DX 2 2
Glyphosate 0 0 0 0
Harmony SG 1.5 1.5 1.5 1.5
Liberty 70 days 70 days
Poast Plus 1 1 1
Pursuit 0 0
Raptor 0
Resource 1 1 1 1
Select Max 1 0 1 1
Synchrony 3
Targa 0
Torment 0
Ultra Blazer c 100 days 100 days 40 days 100 days
a A zero indicates no replant restrictions are required following herbicide application. A dash indicates the restriction for that herbicide-species combination is too long to allow for planting of that forage cover crop species within the same growing season as the corn crop.
b Classic should be applied early post-emergence to meet the three-month interval for planting listed forage cover crops in fall. cApplication rate should not be more than 1.5 pint/acre. Soybean cannot be used for livestock grazing or feeding after application of Ultra Blazer.