Johnson grass (Sorghum halepense) is an invasive plant species, considered to be one of the top ten noxious weeds for all the annual agricultural crops. In the 19th century, it was introduced as a forage crop in South California from Turkey. Later, it caused major agricultural losses due to its high growth rate and good flourishing ability in the natural environment and farmlands. This plant is a known invasive, and in this article we will talk about how to get rid of Johnson grass.
Johnson grass can easily thrive in drought and cold conditions and has good pathogen resistance which makes it difficult to manage and control. Therefore, there is a need to take the necessary precautionary steps and measures to promote sustainable agriculture and to avoid major crop losses. To achieve the goal, it is essential to know about the life cycle and physical characters of this invasive plant species.
Johnson grass description
Johnson grass belongs to the Poaceae family, also referred to as the grass family. The fast grown, perennial grass species is a major threat to the agricultural crops and for the animal livestock as well. The species was named after the scientist Colonel William Johnson, who introduced the species in Alabama. Johnsongrass is a herbicide-resistant crop, and has been associated with a dramatic increase in growth throughout the United States and is regarded as the worst weed in 53 countries.
It easily reproduces into a new plant by seeds or underground by rhizomes, this makes it difficult to get rid of johnson grass.
Distribution and Natural habitat of johnson grass
Johnson grass is native to the Mediterranean region and West Asia. It has a worldwide distribution and is found across all the continents, including the Middle East and Europe except Antarctica.
The highly competitive invasive crop has excellent adaptive ability and reproduces to dense colonies in a variety of habitats such as wetlands, disturbed soils, grasslands, cracks between sidewalks, stream bottoms, open forests, irrigation ditches and fields.
How to identify johnson grass
Johnson grass is a summer perennial grass with reddish to purplish panicles. The rhizome can spread up to an area of 200 ft.
Johnson grass contains thick fibrous roots and horizontal thick rhizomes which tend to stay close to the surface in case of moist soil. The root color changes from white to creamy, and orange scales develop as the plant gets mature.
Leaves of Johnson grass are 0.5 to 1 inch wide and have the ability to grow up to 12 to 30 inches long. The leaves are arranged alternately, are hairless and have a distinct white midrib.
The flowers of Johnson grass are loose, with purplish, hairy panicles. The flowering takes place from May to October. Seeds are reddish-brown in color and no more than 1/8 inch long.
The crop reproduces by rhizomes and seeds. Each node of rhizome can grow new shoots and roots. Seeds remain dormant in the soil until favorable conditions arrive. This makes it difficult to get rid of johnson grass.
The rhizome of the Johnsongrass starts to reproduce in early spring and leaves develop until late spring. The dates of seedling and rhizome emergence can vary in warmer areas (early to late March) and cooler areas (late March to mid April). Germination takes place within two weeks.
The plant begins to flower in July and keeps growing until frost hits. It has the ability to produce up to 80,000 seeds in a single season. They can remain dormant up to 20 years but usually germinate and develop an extensive rhizome system to reproduce in the following season. In six weeks seedlings establish a mature and viable rhizome system.
Uses of johnson grass
In scarcity, raw or cooked seeds of Johnson grass are edible. The seeds can be used like rice or cereal or can be ground into flour to bake bread or cake etc.
Johnson grass has excellent forage characteristics, contains 55 to 60% total digestible nutrients and 10 to 14% crude protein. The crop has the potential biomass of up to 19 tonnes/hectare of yields.
Johnson grass has been reported as depurative, demulcent, cyanogenetic, poison, diuretic and tonic. It is a folk remedy for urinary and blood disorders.
Why is johnson grass invasive?
The toxic level of Cyanide Compounds
Even though healthy crops of Johnson grass can be used as forage, it can cause crucial effects on animal livestock due to the rapid growth and release of toxins the soil. In stress conditions such as cold, extreme heat, physical stresses (wilting) or drought it produces a cyanide compound. This can be detrimental to grazing animals.
The toxin can cause neurological damage which ultimately leads to death. Try to avoid feeding Johnson grass to your cattle to prevent serious consequences.
Accumulation of Nitrates
Johnson grass accumulates a high level of nitrates which is lethal for animal livestock. This can cause nitrate poisoning in sheep and cattle. In the gastrointestinal tract, these nitrates are converted to nitrites and then to methemoglobin that is unable to carry oxygen to tissues. As a result, the animal starts to suffocate. This includes an elevated heart rate and fast breathing through the mouth.
Displaces Native Crops
Johnson grass aggressively spreads over the land and disrupts the native plant vegetation. It is reported to reduce soybean and corn yields up to 40% and 30% respectively. This plant has the capability to rapidly alter the diversity and to create a monoculture due to its highly competitive potential.
High Adaptive Ability
As one of the worst noxious weeds, johnson grass can grow and flourish in a wide range of habitats. Its excellent thriving and adaptive ability in different conditions makes it a potential threat for the agricultural crops. This aggressive crop can significantly cause hazards in poorly managed ecosystems.
Host of Crop Pathogens
Johnson grass acts as a host for a number of plant pathogens also called allergens. The plant produces a phytotoxic effect (growth-inhibiting) on other plant and significantly reduces their yield and causes millions of dollars in losses. Due to multiple risk factors and the effects of this invasive plant species, the U.S Department of Agriculture is trying to find methods to get rid of johnson grass.
Herbicide Resistant Crop
Johnson grass is resistant to most of the herbicides such as some variations of glyphosate. Due to its rapid growth rate and herbicide resistance, it is extremely difficult to eradicate from an infested land. Therefore the process requires persistence, vigilance and good handling strategies to get rid of johnson grass.
How does johnson grass spread?
Johnson grass is a prolific weed with effective dispersal techniques. Pollination takes place through the wind. A new plant can reproduce from seed or rhizomes. Each node or segment of the weed has the potential to develop into shoots and roots. However, rhizomes sprout faster than seeds. The seed can stay dormant in the soil for up to 20 years.
The eradication of this invasive crop is immensely difficult due to its fast growth, adaptive ability and capability to thrive in a wide range of environments.
How to get rid of Johnson grass?
Johnson grass eradication and removal from an infested land is extremely difficult due to the large number of seed production, seed longevity, rapid growth, herbicide resistance and high dispersal rate. However, management depends on the invasiveness of the crop in a particular area.
Several control methods can be helpful to prevent the invasion of johnson grass such as burning, torching, tilling and plowing, mowing, grazing and treatment with herbicides.
An integrated strategy should be employed to gain effective outcomes. Our focus should be:
- Control and prevention of seed exposure
- Depletion of the existing rhizomes and seeds
- Destroying the seedling and rhizome before the next growth season
The complete eradication and removal of johnson grass can be extremely difficult if not handled properly. We are going to share the most effective methods to get rid of johnson grass:
Pulling and digging
Keep a close eye on your yard at every growing season and continue the practices of digging and pulling the weed. Try hand weeding or pulling whole weeds without leaving fragments when there are new sprouts and soil is soft. Finally pull all the plant parts out carefully and dispose of them.
If the land is mowed regular for at least two years the weed growth will be stunted and rhizomes will be concentrated near the ground surface. It may deplete the rhizomes energy and suppress weed growth. Mowing is done when plants are 8 to 12 inches tall with an interval of 2 to 4 weeks. The technique will kill the seedlings but the rhizomes may still remain unaffected.
Tilling and Plowing
Johnson grass can be controlled by repeated tilling every few weeks during summer. In winter, freezing out rhizomes can also help to control the infestation. After the fall season, when frost begins, plow up the roots and rhizome of the weed to expose them to cold temperatures.
A propane torch can also be used to control johnson grass. The technique can be used every two weeks or monthly to weaken the growth of rhizomes or to manage seedlings.
Grazing of johnson grass can also be used to prevent a larger infestation. Care should be taken that when you use Johnson grass as a forage it should not be stressed by physical or environmental factors. As johnson grass under stress condition accumulates a high level of nitrate and hydrocyanic acid which is lethal for animal livestock. Therefore, it is not a recommended control method due to its potential dangers.
Many herbicides are available to get rid of johnson grass. The selection of herbicides is critically important for desirable results.
Glyphosate (Roundup®) is a systemic herbicide, that produces effective results after the treatment. The herbicide is applied to actively growing, 6 to 24 inches tall plants, or the plants that are at the boot stage. Dalapon (Dowpon ®) is also commercially used to control johnson grass. However, guidelines and manuals should be followed for effective results.
Acetolactate synthase inhibitors (ALS)
Application of Acetolactate synthase inhibitors (such as rimsulfuron, imazethapyr, nicosulfuron), also referred to as acetohydroxy acid synthase, is also found to be effective to control johnson grass. The herbicide should be applied with nonionic surfactant three weeks after mowing for better outcomes.
Acetyl CoA Carboxylase inhibitors (ACCase)
Acetyl CoA Carboxylase inhibitors like clethodim, sethoxydim and fluzifop can also be used to control the infestation of johnson grass. These herbicides come in various formulations. Read the instructions before the application of herbicide.