Soybean Herbicides and Rotation to Cover Crops

Consider the soybean 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.
Soybean Herbicides and Rotation to Cover Crops - News

Updated: August 16, 2018

Soybean Herbicides and Rotation to Cover Crops

Rye cover crop in early November. Photo credit: W.S. Curran.

With soybeans beginning to turn yellow and dropping leaves, 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 2.1-13) and the 2017 Mid-Atlantic Weed Management Guide (Table 1-6), contain a table titled “Soybean herbicide half-lives and their potential to injure fall-established cover crops” which includes 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.

Soybean herbicide half-lives and their potential to injure fall-established cover crops.
This table does not directly address perharvest establishment of cover crops such as interseeding or aerial seeding, which may be more restrictive. See Table 1-6 of the 2017 Mid-Atlantic Weed Management Guide.

Trade NameCommon NameNormal Rate/AcreHalf-life (days)1Fall-established Cover Crops
OK to plant
Fall-established Cover Crops
Concern for
Other
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
Assure II/Targa 0.88Equizalofop8 oz60Most broadleavesAll grasses if less than 120 days or at high ratesPlant anything after 120 days
Authority 75DF (Authority First, BroadAxe, Sonic, Spartan)sulfentrazone4 oz32–302Cereals and ryegrassSmall-seeded legumes, mustards, sorghum2Labeled on tobacco, sunflowers, transplanted tomato
Classic 25DF (Authority XL, Canopy, Envive, Fierce, Fierce XLT, Synchrony, Trivence, Valor XLT, etc.)chlorimuron0.5–2 oz40Cereals and ryegrassSmall-seeded legumes, mustards, sorghumMore persistent in high-pH soils (> 7) and with higher soil applied rates
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
FirstRate 84WDG
(Authority First, Sonic)
cloransulam0.3 to 0.6 oz8–33Wheat, triticale, rye Small-seeded legumes, mustards, sorghumThe restriction for transplanted tobacco is 10 months for 0.3 oz/acre; sugarbeet and sunflower have a 30-month restriction
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
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 (Verdict)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
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
Pursuit 2S (Authority Assist, Optill, Zidua Pro)imazethapyr4 fl oz60–90Wheat, triticale, rye, alfalfa, cloverOats, sorghum, mustardsAny crop can be planted 40 months after Pursuit application
Python 80WDGflumetsulam1 oz14–120Cereal grainsSmall-seeded legumes, mustards, and annual ryegrassCover crops and forage grasses are restricted for 9 months
Raptor 1Eimazamox5 fl oz20–30Wheat, triticale, rye, alfalfa, cloversSlight risk for mustardsMost cash crops allowed 9 months following application
Reflex 2E/Flexstar 1.88E (Warrant Ultra)fomesafen1.5 pt100Cereal grainsSmall-seeded legumes, mustards, sorghumSince fomesafen is often applied postemergence, soil activity can surprise users
Scepter 1.5ASimazaquin0.66 pt60–90Cereal grainsSmall-seeded legumes, mustardsCarryover much more of a risk with drought
Select 2Eclethodim10 oz3All broadleavesNone assuming at least 30 daysPlant anything after 30 days
Sharpen 2.85SC (Optill, Verdict, Zidua Pro)saflufenacil3 fl oz7–35AllNoneThis product has been reported more persistent in western Canada
Valor 51WDG (Afforia, Envive, Fierce, Surveil, Trivence, Valor XLT, etc.)flumioxazin2.5 oz12–20All grassesSmall-seeded legumes and mustardsBased on the half-life, all nonfood/feed winter cover crops should be OK
Warrantacetochlor2 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
Zidua (Fierce, Anthem, etc.)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

1The 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.

2Common small-seeded legumes include alfalfa, clovers, and hairy vetch.

3This herbicide does not have soil residual activity at normal application rates.

Authors

William S. Curran, Ph.D.