Herbicide Residue Considerations for Fall Cover Crop Establishment

Cover Crops in Corn Stalks

Herbicides with residual that are used in corn and soybeans can affect the establishment of fall-planted cover crops, and should be taken into account when planning cover crop practices and selecting species. Soil characteristics and weather also play a role in the persistence of residual herbicides, which can vary by field and year. More information is needed on rotational intervals for many cover crop species, and this information is often not included on herbicide labels. University weed scientists have studied the effect of residual herbicides on some of the most popular cover crop species in order to provide this information to growers. In general, residual herbicides that control grass weeds can hinder establishment of grass cover crop species. Broadleaf cover crop species are most impacted by group 2 (ALS inhibitors), 5 (PSII inhibitors), 14 (PPO inhibitors), and 27 (HPPD inhibitors) herbicides (Purdue University).

            A multi-state study found that the general order of sensitivity of cover crops to herbicide carryover, from greatest to least sensitive, is:

  • Tillage radish > Austrian winter pea > crimson clover = annual ryegrass > winter wheat = winter oats > hairy vetch = cereal rye.

Soybean herbicides that tended to be most injurious were:

  • Fomesafen, pyroxasulfone, imazethapyr, acetochlor, and sulfentrazone.

Corn herbicide treatments that were most injurious to cover crops were:

  • Topramezone, mesotrione, clopyralid, isoxaflutole, pyroxasulfone, and nicosulfuron

(University of Missouri).

Below is a table of commonly used corn and soybean herbicides, the fall cover crops that are safe to plant in rotation, and cover crop species that may be injured following these herbicides (Adapted from Lingenfelter D. and Curran W., Penn State University).

 

Herbicide

Fall cover crops:

safe to plant

Fall cover crops:

potential for injury

2,4 - D

All grasses

30 days before sensitive broadleaves

nicosulfuron/ nicosulfuron+ rimsulfuron

Fall cereal grains, ryegrass

Small-seeded legumes*, mustards, sorghum

topramezone

Wheat, barley, oats, rye, and ryegrass after 3 months

Many broadleaves are restricted, does not have much soil activity

atrazine

Sorghum species

Cereals, ryegrass, legumes, and mustards

isoxaflutole

Fall cereals grains

Cereals, ryegrass, legumes, and mustards

mesotrione

All grasses

Small-seeded legumes, mustards

tembotrione + thiencarbazone

Wheat, triticale, rye

Small-seeded legumes, mustards, sorghum

dicamba

All crops

Only at high rates or less than 120 days after application

isoxaflutole + thiencarbazone

Wheat, triticale, rye

Small-seeded legumes, mustards, sorghum

metolachlor

Almost anything

Annual ryegrass or other small-seeded grasses

glyphosate

All

None

paraquat

All

None

thifensulfuron

No restrictions for wheat, barley, and oats

None with 45-day waiting interval

acetochlor

Most crops should be fine

Food or feed residues rather than crop injury a concern

tembotrione

Cereal grains after 4 months

Unknown; small-seeded legumes, mustards could be a problem

glufosinate

All

Food or feed residues rather than crop injury a concern

metribuzin

Cereal grains and ryegrass

Slight risk for small-seeded legumes and mustards

dimethenamid

Most crops should be fine

Food or feed residues rather than crop injury a concern

prosulfuron

Cereal grains and sorghum are labeled, other grasses

Small-seeded legumes, mustards

halosulfuron

Cereal grains and sorghum after 2 mo., other grasses

Small-seeded legumes, mustards

pendimethalin

Cereal grains

Small-seeded legumes and annual ryegrass

flumetsulam

Cereal grains

Small-seeded legumes, mustards, and annual ryegrass

rimsulfuron

Based on short half-life, most fall cover crops should be OK

None

saflufenacil

All

None

simazine

Sorghum species

Cereals, ryegrass, legumes, and mustards

clopyralid

All grasses

Small-seeded legumes

pyroxasulfone

Most crops should be fine

Food or feed residues rather than crop injury a concern

quizalofop

Most broadleaves

All grasses if less than 120 days or at high rates

sulfentrazone

Cereals and ryegrass

Small-seeded legumes, mustards, sorghum

chlorimuron

Cereals and ryegrass

Small-seeded legumes, mustards, sorghum

cloransulam

Wheat, triticale, rye

Small-seeded legumes, mustards, sorghum

imazethapyr

Wheat, triticale, rye, alfalfa, clover

Oats, sorghum, mustards

flumetsulam

Cereal grains

Small-seeded legumes, mustards, and annual ryegrass

imazamox

Wheat, triticale, rye, alfalfa, clovers

Slight risk for mustards

fomesafen

Cereal grains

Small-seeded legumes, mustards, sorghum

imazaquin

Cereal grains

Small-seeded legumes, mustards

clethodim

All broadleaves

None assuming at least 30 days

saflufenacil

All

None

flumioxazin

All grasses

Small-seeded legumes and mustards

            Cover crops provide a multitude of benefits and their use is becoming an increasingly popular practice in Ohio. Including cover crops in rotation with agronomic crops to realize these benefits costs time and money. It is important to evaluate the potential risk of herbicide residue on the establishment of cover crops in order to ensure success. Residual herbicides applied at the time of planting typically interfere with cover crop establishment less than those applied POST. Weather can affect the persistence of herbicides also, especially rainfall in summer.  The risk of residual herbicides affecting cover establishment will be higher in areas that have been dry since herbicide application.  Risk will be lower where the herbicide application was followed by some wet weather to get herbicide degradation started, compared with an application during prolonged dry weather.  One of the least problematic cover crop species is cereal rye, which can be successfully established following a late corn or soybean harvest, and is tolerant to a most of the most commonly used corn and soybean herbicides. Weed control should continue to be the priority in selecting herbicides, and cover crop species selection should be based on potential injury and goals for the use of cover crops.  The introductory section of the “Weed Control Guide for Ohio, Indiana, and Illinois” has some of the same information presented here, and OSU weed scientists also summarize this in a video: https://www.youtube.com/watch?v=ylr0zGnXMfs

The following resources contain information on residual herbicides and cove crops also:

https://extension.psu.edu/corn-herbicides-and-rotation-to-cover-crops https://extension.psu.edu/soybean-herbicides-and-rotation-to-cover-crops

https://ipm.missouri.edu/IPCM/2020/3/coverCropTermination-KB/

https://ag.purdue.edu/btny/weedscience/Documents/covercropcarryover.pdf

Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.

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