An Illustrated Guide to ARIZONA WEEDS

The University of Arizona Press




JOHNSONGRASS-Sorghum halepense (L.) Pers.

DESCRIPTION-Johnsongrass is a prohibited noxious weed in Arizona. It is a coarse perennial, 3 to 7 feet high, and very leafy, spreading by seeds and by an extensive system of underground rhizomes. The bright green leaf blades are up to 2 feet long, and 1/4 to 3/4 inch broad. The many-branched flowering tops are loose, open, and 1/2 to 2 feet long. The drooping branches come off 2 or 3 at a joint, and are naked below.

The spikelets occur in pairs, but in threes at the tips of the branches, 1 (or 2) is stalked and bears stamens only, while the other is stalkless, thickened, and fertile. The fertile spikelet is about l/4 inch long, and has a twisted, once-bent bristle about 1/2 inch long. The dark reddish brown grains are nearly 1/8 inch long without the hull.

DISTRIBUTION-Johnsongrass is one of the most abundant and vicious weeds throughout the state, serious in all important summer crops. It may be found along irrigation ditches, cultivated fields, and moist waste places of any type; 100 to 6,000 feet elevation; flowering April to November. This weed can completely take over agricultural lands unless constant control methods are practiced. Its stout underground stems may be 2 1/2 feet deep, and the grains may lie dormant for many years, making complete eradication almost impossible.

POISONOUS PROPERTIES-Johnsongrass ordinarily is good feed, but some- times the plant, particularly the leaves, contain hydrocyanic (prussic) acid, a cyanide type of poisoning. Any factor which interrupts normal growth may cause the release of HCN within plants. Rapid growth of new leaves, wilting due to drought, frost, freezing, cutting, or trampling are the most dangerous events.

Copyright (c) 1972 The Arizona Board of Regents

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