Fall options to control johnsongrass

Erin Burns<burnser5@msu.edu>, Michigan State University Department of Plant, Soil and Microbial Sciences - November 01, 2023

Johnsongrass rhizomes are not very cold tolerant. Take advantage of Michigan winter temperatures to help reduce its population.

Closeup of a johnsongrass rhizome. — Johnsongrass rhizome. Photo by Connor Purvis.

Johnsongrass (Sorghum halepense) is an aggressive perennial weed that is difficult to control given its extensive rhizome system. However, its rhizomes are also one of johnsongrass’ largest weaknesses because they are not very cold tolerant. Therefore, fall tillage practices that bring rhizomes to the soil surface and expose them to freezing winter temperatures may reduce the population over time. However, like other perennial weeds, tillage will cut rhizomes into small pieces that can then be spread throughout the field. Properly cleaning equipment after tillage is important in preventing the spread of johnsongrass into non-infested fields.

Furthermore, scouting after fall tillage is important to make a timely spring herbicide application. Repeated spring tillage to a 6-to-8-inch depth has also been shown to increase herbicide efficacy by making new growth emerging from small rhizomes more susceptible to herbicide application. Additionally, johnsongrass seeds cannot successfully emerge when buried at least 12 inches deep; thus, in fields with severe infestations, aggressive deep tillage, e.g. moldboard plow, may be another control tactic. Fall applications of glyphosate can be effective on new growth after harvest, however a good rule of thumb for successful control is to only apply glyphosate when the daily temperature is 50 degrees Fahrenheit or higher.

Fall cover crop planting is becoming more common in Michigan. Currently, little research has been performed on the impact of cover crops on johnsongrass infestations. However, it would not be expected for cover crops to suppress johnsongrass due to its extensive rhizome system.

Johnsongrass weeds growing in a corn field. — Johnsongrass infestation in corn in southwest Michigan. Photo by Erin Burns, MSU.

It is hard to control johnsongrass once it is well-established. Taking control of johnsongrass before it takes control of your non-infested fields is a high priority. Effective johnsongrass programs take an integrated approach:

Prevent johnsongrass from becoming established in new fields by preventing the spread of rhizomes from infested to non-infested areas, cleaning equipment and harvesting infested fields last.
Control johnsongrass in fence rows and ditch banks, which can be common sources of new infestations.
If johnsongrass does appear in a new field, focus on controlling it prior to establishment as herbicides are more effective on seedlings than on plantlets growing from rhizomes. Amazingly, johnsongrass plants emerging from seeds can produce rhizomes in three to four weeks.
Consider fall tillage to bring rhizomes to the soil surface.
Disk multiple times in the spring prior to herbicide application followed by a two-pass program with full labeled rates (Table 1).

Overall, keep in mind that dense infestations of johnsongrass did not develop over one season but over many. It will take patience and persistence over many seasons to control well-established johnsongrass populations.

*Table 1. Effective johnsongrass herbicide programs in corn. (See the Michigan State University Extension Weed Control Guide for Field Crops for rate information and details.)**
Herbicide—Soil-applied	Site of Action No.**	Seedling Efficacy	Rhizome Efficacy	Corn Height/Stage
Balance Flexx	27	Good	Fair	Effective preemergence, may be applied postemergence from spike through V2.
Corvus	2, 27	Good	Fair	Effective preemergence, may be applied postemergence from spike through V2.
Herbicide—Postemergence	Site of Action No.**	Seedling Efficacy	Rhizome Efficacy	Corn Height/Stage
Accent Q	2	Excellent	Good	20 inches tall or V6 20–36 inches tall, use drop nozzles
Beacon	2	Good	Fair	4–20 inches tall Drop nozzles can be used up to tassel emergence
Capreno	2, 27	Excellent	Good	V1 to V5
Revulin Q	2, 27	Excellent	Good	20 inches tall or V6 Drop nozzles can be used up to 30 inch tall or V8
Steadfast Q	2, 2	Excellent	Good	20 inches tall or V6
Glyphosate	9	Excellent	Excellent	30 inches tall or V8 30 to 48 inches drop nozzles only
Liberty	10	Good	Fair	Emergence up to V6 Drop nozzles until 36 inch tall

* See factsheet Johnsongrass Management in Soybeans for soybean herbicide programs.
** In Michigan, we have populations of johnsongrass that are resistant to Group 2 (ALS-inhibiting herbicides). In other regions of the United States, Group 9 (glyphosate) resistant populations have been discovered. See MSU Plant & Pest Diagnostics to learn more about herbicide resistance screening.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).