Corn Herbicides and Rotation to Cover Crops

Consider the corn herbicide program you used in 2017 before you plant a fall cover crop. Most small grains are fine, but legumes and radish can be problematic.
Corn Herbicides and Rotation to Cover Crops - News

Updated: September 7, 2017

Corn Herbicides and Rotation to Cover Crops

Beautiful oat cover crop in late fall. Photo credit W.S. Curran.

With silage harvest underway a number of farmers are considering cover crop establishment this fall. Remember that some herbicides can persist and potentially influence successful cover crop establishment. Both the 2017/18 Agronomy Guide (Table 2.1-12) and the 2017 Mid-Atlantic Weed Management Guide (Table 1-6), contain a table titled Corn herbicide half-lives and their potential to injure fall-established cover crops that include the major corn herbicide restrictions and guidelines. Remember that cash crop rotation restrictions may be due to the concern for herbicide residues accumulating in forage or feed rather than carryover injury. Cover crops that are not harvested can be planted after any herbicide program, but the grower assumes the risk of crop failure. For a more complete listing, refer to the Penn State Agronomy Guide or the Mid-Atlantic Weed Management Guide.

Corn herbicide half-lives and their potential to injure fall-established cover crops.

This table does not directly address preharvest establishment of cover crops such as interseeding or aerial seeding, which may be more restrictive.

Trade NameCommon NameNormal Rate/AcreHalf-life (days)1Fall-established Cover Crops: OK to plantFall-established Cover Crops: Concern forOther
2,4-D 4S2,4-D1–2 pt7All grassesWait 30 days before planting sensitive broadleavesAmine formulations more water soluble and can leach into seed zone
Accent 75DF/Steadfast75DFnicosulfuron/ nicosulfuron+ rimsulfuron0.66 oz/0.75 oz21Fall cereal grains, ryegrassSmall-seeded legumes, mustards, sorghum2More persistent in high pH soils (> 7)
Armezon/Impact 2.8SCtopramesone0.75 fl oz14Wheat, barley, oats, and rye are allowed after 3 months; ryegrass should also be OKAlthough many broadleaves are restricted, Impact does not have much soil activityWe have not seen this herbicide carry over in the Mid-Atlantic region
Atrazine 4Latrazine1–2 qt15–90Sorghum speciesCereals, ryegrass, legumes, and mustardsMore persistent in high pH soils (> 7); rates < 1 lb/acre can allow more flexibility; half-life in Mid-Atlantic probably closer to 30
Balance Pro 4L/Balance Flexx 2L (Prequel also contains isoxaflutole)isoxaflutole3 fl oz/6 fl oz50–120Fall cereals grainsCereals, ryegrass, legumes, and mustards15 inches of cumulative precipitation required from application to planting rotation crops except soybean, barely, wheat, sorghum, and sunflower
Callisto 4L (includes Acuron, Acuron Flexi, Halex GT, Harness Max, Instigate, Lexar, Lumax, Resicore, Revulin, Solstice, Zemax, etc.)mesotrione3–6 fl oz10–50All grassesSmall-seeded legumes, mustardsSequential applications (PRE fb POST) increase the potential for injury
Capreno 3.45SCtembotrione + thiencarbazone3 fl oz15Wheat, triticale, ryeSmall-seeded legumes, mustards, sorghum15 inches of cumulative precipitation required from application to planting rotation crops except wheat
Clarity/Banvel 4S (DiFlexx, Distinct, Engenia, Status, Xtendimax/Fexapan)dicamba16–24 fl oz5–14All cropsOnly at high rates or less than 120 days after applicationAnything can be planted after 120 days with 24 fl oz/acre or less
Corvus 2.63SCisoxaflutole + thiencarbazone5.6 fl oz50–120Wheat, triticale, ryeSmall-seeded legumes, mustards, sorghum15 to 30 inches of cumulative precipitation from application to planting for sensitive crops
Dual II Mag 7.62E/Cinchmetolachlor1.67 pt15–50Almost anythingAnnual ryegrass or other small-seeded grassesHigher rates and later applications more of a potential problem
Glyphosate 4Lglyphosate0.75–1.25 lb473AllNoneGlyphosate does not have soil activity at normal use rates
Gramoxone 2Sparaquat2 pt1,0003AllNoneParaquat does not have soil activity at normal use rates
Harmony 50WDGthifensulfuron1/8 oz12No restrictions for wheat, barley, and oatsNone with 45-day waiting intervalHarmony Extra also contains tribenuron
Harness 7E (Degree, Surpass, Warrant)acetochlor2 pt10–20Most crops should be fineFood or feed residues rather than crop injury may be a concernNonfood/feed winter cover crops are allowed after corn harvest
Laudis 3.5SC (DiFlexx Duo)tembotrione3 fl oz14Cereal grains after 4 monthsUnknown; small-seeded legumes, mustards could be a problemOther crops may be seeded after a successful field bioassay
Liberty 2.34Lglufosinate22–36 fl oz73AllFood or feed residues rather than crop injury may be a concernGlufosinate does not have soil activity at normal use rates
Metribuzin 75DF (Sencor)metribuzin0.33 lb14–60Cereal grains and ryegrassSlight risk for small-seeded legumes and mustardsNonfood/feed winter cover crops allowed
Outlook 6E (Armezon Pro)dimethenamid16 fl oz20Most crops should be fineFood or feed residues rather than crop injury may be a concernNonfood/feed winter cover crops should be OK after corn harvest
Peak 57WG (and Spirit)prosulfuron1 oz9–152Cereal grains and sorghum are labeled, other grassesSmall-seeded legumes, mustardsMore persistent in high pH soils (> 7)
Permit/Sandea 75DFhalosulfuron2/3 oz9–27Cereal grains and sorghum after 2 mo. and other grassesSmall-seeded legumes, mustardsHalosulfuron also an ingredient in Yukon
Prowl H2O 3.8CSpendimethalin3 pt44Cereal grainsSmall-seeded legumes and annual ryegrassWe have not seen this herbicide carry over in Mid-Atlantic; nonfood/feed winter cover crops should be OK
Python 80WDG (Hornet and SureStart)flumetsulam1 oz14–120Cereal grainsSmall-seeded legumes, mustards, and annual ryegrassCover crops and forage grasses are restricted for 9 months
Resolve 25DF (Resolve Q)rimsulfuron2 oz2–4Based on the short half-life, most fall cover crops should be OK in Mid-AtlanticNoneMore persistent in drought conditions
Sharpen 2.85SC (Verdict)saflufenacil3 fl oz7–35AllNoneThis product has been reported more persistent in western Canada
Simazine 4L (Princep)simazine1–2 qt60Sorghum speciesCereals, ryegrass, legumes, and mustardsSoil pH > 7
Stinger 3S (Hornet, Resicore, SureStart)clopyralid5 oz40All grassesSmall-seeded legumes
Zidua (Anthem)pyroxasulfone0.13320Most crops should be fineFood or feed residues rather than crop injury may be a concernNonfood/feed winter cover crops should be OK after corn harvest

1 The herbicide half-life is defined as the time it takes for 50 percent of the herbicide active ingredient to dissipate. See the “Managing Herbicides” section for additional information. Herbicide half-life estimates are derived for the WSSA Herbicide Handbook and other scientific literature.
2 Common small-seeded legumes include alfalfa, clovers, and hairy vetch.
3 This herbicide does not have soil residual activity at normal application rates.

Authors

Managing weedy plants in agroecosystems Conservation tillage and cover crops Herbicide use Integrated weed management Weed management in organic cropping systems

More by William S. Curran, Ph.D.