News

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.

Updated:

September 20, 2017

Skip to the end of the images gallery

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

Skip to the beginning of the images gallery

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 Name	Common Name	Normal Rate/Acre	Half-life (days)¹	Fall-established Cover Crops OK to plant	Fall-established Cover Crops Concern for	Other
2,4-D 4S	2,4-D	1–2 pt	7	All grasses	Wait 30 days before planting sensitive broadleaves	Amine formulations more water soluble and can leach into seed zone
Assure II/Targa 0.88E	quizalofop	8 oz	60	Most broadleaves	All grasses if less than 120 days or at high rates	Plant anything after 120 days
Authority 75DF (Authority First, BroadAxe, Sonic, Spartan)	sulfentrazone	4 oz	32–302	Cereals and ryegrass	Small-seeded legumes, mustards, sorghum2	Labeled on tobacco, sunflowers, transplanted tomato
Classic 25DF (Authority XL, Canopy, Envive, Fierce, Fierce XLT, Synchrony, Trivence, Valor XLT, etc.)	chlorimuron	0.5–2 oz	40	Cereals and ryegrass	Small-seeded legumes, mustards, sorghum	More persistent in high-pH soils (> 7) and with higher soil applied rates
Dual II Mag 7.62E/Cinch	metolachlor	1.67 pt	15–50	Almost anything	Annual ryegrass or other small-seeded grasses	Higher rates and later applications more of a potential problem
FirstRate 84WDG (Authority First, Sonic)	cloransulam	0.3 to 0.6 oz	8–33	Wheat, triticale, rye	Small-seeded legumes, mustards, sorghum	The restriction for transplanted tobacco is 10 months for 0.3 oz/acre; sugarbeet and sunflower have a 30-month restriction
Glyphosate 4L	glyphosate	0.75–1.25 lb	473	All	None	Glyphosate does not have soil activity at normal use rates
Gramoxone 2S	paraquat	2 pt	1,0003	All	None	Paraquat does not have soil activity at normal use rates
Harmony 50WDG	thifensulfuron	1/8 oz	12	No restrictions for wheat, barley, and oats	None with 45-day waiting interval	Harmony Extra also contains tribenuron
Liberty 2.34L	glufosinate	22–36 fl oz	73	All	Food or feed residues rather than crop injury may be a concern	Glufosinate does not have soil activity at normal use rates
Metribuzin 75DF (Sencor)	metribuzin	0.33 lb	14–60	Cereal grains and ryegrass	Slight risk for small-seeded legumes and mustards	Nonfood/feed winter cover crops allowed
Outlook 6E (Verdict)	dimethenamid	16 fl oz	20	Most crops should be fine	Food or feed residues rather than crop injury may be a concern	Nonfood/feed winter cover crops should be OK after corn harvest
Prowl H2O 3.8CS	pendimethalin	3 pt	44	Cereal grains	Small-seeded legumes and annual ryegrass	We 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)	imazethapyr	4 fl oz	60–90	Wheat, triticale, rye, alfalfa, clover	Oats, sorghum, mustards	Any crop can be planted 40 months after Pursuit application
Python 80WDG	flumetsulam	1 oz	14–120	Cereal grains	Small-seeded legumes, mustards, and annual ryegrass	Cover crops and forage grasses are restricted for 9 months
Raptor 1E	imazamox	5 fl oz	20–30	Wheat, triticale, rye, alfalfa, clovers	Slight risk for mustards	Most cash crops allowed 9 months following application
Reflex 2E/Flexstar 1.88E (Warrant Ultra)	fomesafen	1.5 pt	100	Cereal grains	Small-seeded legumes, mustards, sorghum	Since fomesafen is often applied postemergence, soil activity can surprise users
Scepter 1.5AS	imazaquin	0.66 pt	60–90	Cereal grains	Small-seeded legumes, mustards	Carryover much more of a risk with drought
Select 2E	clethodim	10 oz	3	All broadleaves	None assuming at least 30 days	Plant anything after 30 days
Sharpen 2.85SC (Optill, Verdict, Zidua Pro)	saflufenacil	3 fl oz	7–35	All	None	This product has been reported more persistent in western Canada
Valor 51WDG (Afforia, Envive, Fierce, Surveil, Trivence, Valor XLT, etc.)	flumioxazin	2.5 oz	12–20	All grasses	Small-seeded legumes and mustards	Based on the half-life, all nonfood/feed winter cover crops should be OK
Warrant	acetochlor	2 pt	10–20	Most crops should be fine	Food or feed residues rather than crop injury may be a concern	Nonfood/feed winter cover crops are allowed after corn harvest
Zidua (Fierce, Anthem, etc.)	pyroxasulfone	0.133	20	Most crops should be fine	Food or feed residues rather than crop injury may be a concern	Nonfood/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.

Agenda

Authors