Photo credit: Rebekah D. Wallace, University of Georgia, Bugwood.org
Johnsongrass can have negative economic impacts as an agricultural weed of corn and soybeans. There are herbicide resistant strains in the United States which can increase the cost of agricultural production. It is also an alternate host to pests that affect corn, can be toxic to grazing animals, and can invade native habitats and outcompete native plants. It is not clear how hardy Johnsongrass may be in Minnesota, so reporting any populations found will aid in understanding its possible impacts in Minnesota.
Johnsongrass is a perennial grass that spreads by underground rhizomes. Plants can grow up to 8 to 12 feet tall.
Leaves and stem
Leaves can grow up to 1 inch wide and 20 inches long. There is a conspicuous white line down the center of the leaf (the midvein). At the point where the leaf and stalk meet, there is a small growth called a ligule. Johnsongrass ligules are about 1/10 of an inch long and have short hairs.
Many small flowers (florets) make up an inflorescence that can be up to 24 inches long. Overall it can have a pyramid-like shape. On the small florets is a lower bract called a lemma. Johnsongrass lemmas usually do not have awns (small spines), but sometimes they do have short, twisted awns.
Johnsongrass seeds are 1/10 of an inch long, oval, and brown. The bracts covering the seeds are generally covered in short, fine hairs.
Johnsongrass can form a dense network of rhizomes (an underground stem that sends out roots and shoots).
Johnsongrass is a perennial grass. It is not clear how cold hardy Johnsongrass rhizomes may be in Minnesota so it is possible that in Minnesota seed production would be the main way that plants would persist.
Origin and spread
Johnsongrass is native to southern Eurasia. Johnsongrass was introduced to the southeastern United States in the early 1800s for forage. By 1900, Johnsongrass was considered a weed in the United States and was the subject of the first United States federal weed control funding. It is generally found in states to the south of Minnesota.
Refer to EDDMapS Distribution Maps for current distribution.
Don't be fooled by these look-alikes
- Shattercane, Sorghum bicolor, (non-native) – Johnsongrass is a Sorghum species and there has been extensive agricultural breeding and hybridization of Sorghum species making it challenging to distinguish species. Shattercane is an annual grass and does not produce rhizomes, unlike Johnsongrass which produces rhizomes. Shattercane has wider leaves and larger seeds than Johnsongrass.
- Indiangrass, Sorghastrum nutans (native) – Indiangrass has short rhizomes and does not have the prominent white mid-vein in the leaf that Johnsongrass has.
- Switchgrass, Panicum virgatum (native) – Switchgrass leaves are narrower (less than 0.6 inches wide) than Johnsongrass leaves, and switchgrass has no hairs on the seed coverings.
- Non-native weedy annual grasses, such as proso millet, Panicum miliaceum, and Barnyard grass, Echinochloa crus-galli – there are many annual grasses that people may encounter. The University of Minnesota Extension Annual Grass Weeds webpage has diagrams of grass identification characteristics and photos and identification explanations for a variety of grass species.
- Regulatory classification
This species is a Minnesota Department of Agriculture Prohibited Noxious Weed on the Eradicate List meaning that the above and below ground parts of the plant must be destroyed. Additionally, no transportation, propagation, or sale is allowed.
- Threat to Minnesota
- Johnsongrass can have negative economic impacts as an agricultural weed of corn and soybeans. There are herbicide resistant strains in the United States which can increase the cost of agricultural production.
- It is an alternate host to pests that affect corn.
- Johnsongrass can be toxic to grazing animals.
- It can invade native habitats and outcompete native plants.
- Its seeds spread by water, wind, ingestion by birds and cattle, and through contamination of hay, grain, and equipment.
- What you should do
One way that invasive plant seeds and fragments can spread is in soil. Sometimes plants are planted purposefully. You can prevent the spread of invasive plants.
- REMOVE plants, animals and mud from boots, gear, pets and vehicles.
- CLEAN your gear before entering and leaving the recreation site.
- STAY on designated roads and trails.
- PLANT non-invasive species.
- Native substitutes
- Control methods
Mechanical control can be done by cutting or pulling the plant by hand or with equipment such as rakes or cutting blades. Be aware that root fragments are likely to break off and remain in the soil and create new plants so mechanical control alone may not be enough. Follow Minnesota Department of Agriculture noxious weed disposal guidance for the pulled plants. Avoid mowing once the plants have gone to seed (generally July-November).
Herbicide control can be done using systemic herbicides which are taken up by plants and move within the plant, which can kill leaves, stems, and roots. April-May and September-November are the best times for foliar herbicide applications. Since Johnsongrass is known to develop herbicide resistance, work with the Minnesota Department of Agriculture and University of Minnesota Extension on herbicide suggestions for your situation. In small infestations, using a weed torch may be an option for control without herbicides.
- Identification and management of Johnsongrass (Minnesota Department of Agriculture)
- Identification and management of Minnesota Noxious Weeds (MN Department of Transportation)
- Management of Johnsongrass (University of Missouri Extension)
- Identification of Johnsongrass – Mistaken Identity Guide (USDA NRCS and partners)