Johnsongrass [Sorghum halepense (L.) Pers.][SORHA][CDFA list: C] Photographs

Shattercane [Sorghum bicolor (L.) Moench][SORVU] Photographs

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SYNONYMS: Complete synonymy is extensive and beyond the scope of this publication.

GENERAL DESCRIPTION: Coarse grasses with reddish to purplish-black panicles, to 2 m tall. These grasses are cultivated for food and/or forage, but have escaped cultivation and become troublesome agricultural weeds in temperate to tropical regions throughout the world. Johnsongrass and shattercane grow rapidly, are highly competitive with crops, and can be difficult to control. Infestations in crops can reduce harvest yields significantly. Both species hybridize with each other and with cultivated sorghum varieties, diminishing the quality and value of grain harvested for seed. Plants are highly variable and many regional biotypes exist. Healthy plants can provide good forage for livestock. However, foliage of johnsongrass and other sorghums can produce toxic amounts of hydrocyanic acid when exposed to frost, stressed by drought, or damaged by trampling or herbicides and may be poisonous to livestock when ingested. Some biotypes are potentially more cyanogenic. Young shoots and second growth are typically more dangerous than uncut mature plants. Dried plant material does not lose its toxicity. Well-cured hay from healthy mature plants is usually safe. Symptoms of cyanide poisoning include a bluish coloration of mucous membranes, rapid deep breathing, muscular twitching, staggering, weak and irregular pulse, and death. Sudden death without exhibiting symptoms is common. Under certain conditions, plants may accumulate toxic levels of nitrates. Weedy sorghums are subject to various bacterial, fungal, and nematode infections and serve as alternate hosts for the sorghum midge (Contarinia sorghicola) and the viruses that cause sugar cane mosaic virus, maize chlorotic dwarf virus, and corn stunt disease.

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SEEDLINGS: Resemble young corn seedlings, but can be distinguished by carefully removing young seedlings from the soil and examining the attached seed.

MATURE PLANT: Typically tufted, with tillers from the crown. Stems erect, unbranched, with solid internodes. Blades rolled in bud, flat, glabrous to sparsely hairy, especially near ligules, bright green. Margins rough. Midveins whitish, conspicuous. Ligules membranous, minutely shallow-toothed or fringed at the top. Collars broad, whitish or pale green, smooth. Auricles lacking. Sheaths open, ribbed, compressed, glabrous or sparsely hairy near blade junction, shorter than internodes, pale green to reddish.

ROOTS and UNDERGROUND STRUCTURES: Roots fibrous, branched, to depths of ~ 1.2 m. Prop roots often develop at the base of stalks, similar to those of corn. Johnsongrass has fast-growing rhizomes that produce new plants. Rhizomes ~ 1 cm in diameter, up to ~ 2 m long, whitish with large (purplish-) brown scales at the nodes, often root at the nodes. Shattercane lacks rhizomes.

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SPIKELETS/FLORETS: May-October. Panicles 10-50 cm long, initially pale green or greenish-violet, often mature to a dark reddish- or purplish-brown. Some panicles shed spikelets (shatter) at maturity. Spikelets disperse in pairs or trios. Lowest spikelet sessile, bisexual, contains 1 fertile floret (seed) and 1 tiny sterile floret. Upper spikelet(s) stalked, staminate, narrower than the fertile spikelet. Fertile spikelet (seed) ellipsoid to ovoid. Mature glumes leathery, thicker than lemma, glossy, reddish-brown to black, glabrous to pubescent. Lower glume tightly encloses upper glume and florets. Lemma awns bent, twisted, early deciduous. Self-fertile or out-crossing.

POSTSENESCENCE CHARACTERISTICS: Foliage is killed by frost. Dead stems with seed heads may persist through the cold season.

HABITAT: Disturbed sites, roadsides, fields, agronomic and vegetable crops. Grow best on fertile, well-drained soils in warm temperate to sub-tropical regions where some warm season moisture is available.

DISTRIBUTION: Throughout much of the U.S., except some northern states.

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PROPAGATION/PHENOLOGY: Panicles retain seed or shed seed near the parent plant (shatter). Seed disperses to greater distances with wind, water, agricultural activities, and animals. Some seed survives ingestion by birds and mammals. Unlike commercial sorghums, glumes tightly enclose seeds and can protect seeds from decomposition in the soil for several years. Photosynthesis is by the C4 pathway.

MANAGEMENT FAVORING/DISCOURAGING SURVIVAL: Cleaning agricultural machinery after use in infested fields and confining livestock that has had access to mature sorghums for about 1 week can prevent introduction of weedy sorghum seeds into uninfested fields.

SIMILAR SPECIES: Fall panicum [Panicum dichotomiflorum Michaux][PANDI] is a summer annual, to 1 m tall, that resembles johnsongrass. Nodes and internodes of fall panicum give the plant a zig-zag appearance. Unlike weedy sorghums, fall panicum has ligules that consist of a fringe of hairs and are not membranous at the base. Fall panicum seedlings are smaller than those of Sorghum and have short hairs on the lower side of the leaf blades.

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