halepense (L.) Pers.][SORHA][CDFA list: C] Photographs
[Sorghum bicolor (L.) Moench][SORVU] Photographs
Complete synonymy is extensive and beyond
the scope of this publication.
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.
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.
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.
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.
CHARACTERISTICS: Foliage is killed by frost. Dead stems with seed
heads may persist through the cold season.
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.
much of the U.S., except some northern states.
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.
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.
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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