If your johnsongrass is subjected to any of these conditions, keep cattle away for about a week to allow the prussic acid to dissipate. For more information on nitrate and prussic acid poisoning, and testing plants for these compounds, please see the following two articles by Clay Wright in the Ag News and Views archives:.
Chan Glidewell. Positive aspects of johnsongrass As far as nutritive value is concerned, johnsongrass is tough to beat. Negative aspects of johnsongrass Johnsongrass is on the noxious weed list in several U. For more information on nitrate and prussic acid poisoning, and testing plants for these compounds, please see the following two articles by Clay Wright in the Ag News and Views archives: Drought-Induced Poisonings are Dangerous to Livestock August ; and Rethinking Nitrate and Prussic Acid "Quick" Tests September Smaller, younger growth plants, especially those plants that are less than a foot tall produces much more of the toxin than do older, more mature plants,.
Ruminant animals cattle, sheep and goats appear to be the most susceptible to prussic acid poisoning. Reports of poisoning in swine and horses are rare. Also younger calves that are still nursing are much more susceptible to this toxin than are older, more mature cattle; although older cattle can be poisoned if they eat enough of the plants. Drinking soon after eating these plants raises the likelihood of poisoning. Symptoms of prussic acid poisoning include anxiety, progressive weakness and labored breathing, gasping, increased pulse rate, muscular twitching and convulsions, and death may follow rapidly when lethal amounts of HCN are consumed.
However, the dead animals may be found without visible symptoms of poisoning. Animals affected by prussic acid poisoning may be treated with a sodium nitritesodium thiosulfate combination. It must be injected intravenously and very slowly.
The dosage and method of administration are critical. Fortunately, prussic acid soon turns into a gas and disappears into the air. So wait 3 to 5 days after a freeze before grazing the Johnsongrass.
Because the concentration of prussic acid can vary in the plant, It is difficult to say how much must be consumed before it is lethal. Today, Johnsongrass is found in all states except Minnesota, and is considered a noxious weed in 19 states NRCS, It also serves as a host for several insects, disease pathogens and nematodes of corn and sorghum.
A Johnsongrass seedling can resemble a corn or sorghum seedling; however, its stems and leaves are narrower and completely hairless.
In any developmental stage, Johnsongrass leaves have a very distinct and prominent white mid-vein, which differentiates it from most other grasses Figure 2a. Adult plants can range in height from 2. Johnsongrass is a bunch-type grass, tillering from the crown of the plant.
The flower head is a panicle highly branched and can reach up to 1. It has a green central stalk i. The branches are perpendicular to the stem at the bottom and parallel at the top, resulting in a pyramidal-shaped head Figure 2b.
The seeds, which are very small 2 to 3 mm and egg-shaped, attach to the lateral branches and turn from greenish-violet to dark reddish-brown when mature. Both roots and rhizomes i. Most other grass species that resemble Johnsongrass do not contain rhizomes. Rhizomes are white to brown in color and may contain purple spots and nodes covered by brown scaly sheaths Figure 2c. The leaf collar, where the leaf sheath and leaf blade meet, can serve as a useful identification tool.
Pulling the collar back and detaching it from the stem will reveal the presence of a toothed membrane called the ligule. With age, some ligules may develop a fringe of hairs in the upper portion Figure 2d. Johnsongrass is an aggressive perennial. Either new shoots from rhizomes or new seedlings will sprout during early to mid-spring. Seeds start to germinate when soil temperatures reach 70 F; however, new shoots from rhizomes will sprout when soil temperatures are 60 F.
Sprouts from rhizomes develop faster than seedlings by taking advantage of rhizome carbohydrates accumulated during the winter. Plants start to produce new rhizomes after five to seven true leaves have developed. This occurs approximately three to six weeks after emergence.
Flowering will commence six to nine weeks after emergence, and viable seeds will be produced two to three weeks after flowering. During the fall, Johnsongrass growth ceases when soil temperatures return to 60 F, turning the plant dormant. In Oklahoma, Johnsongrass will start to grow by the end of March, and new rhizomes will start to develop by the end of April.
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