Shatter cane (Sorghum bicolor)

Description:

Shattercane is the weedy form of grain sorghum (Sorghum bicolor), the same species grown as a crop ? but this off-type drops its seed before harvest, which is how it got its name [2][4][5]. It is a fast-growing summer annual that shoots up to about 8 feet and competes hard with corn and soybeans, and most infestations began when shattercane seed contaminated fields planted to cultivated sorghum [1][2]. MISIN tracks it because it spreads readily on farm equipment and in water, and because ? like other sorghums ? it can poison livestock with cyanide when the plants are frosted or drought-stressed [1][3].

Habit:

Shattercane is a tall, erect annual grass that reaches about 8 feet, with smooth, unbranched stems that sometimes show purple spotting [1]. Before it produces a seed head it looks strikingly like a corn plant, which is exactly why it is easy to miss in a cornfield [2]. Its leaves are much wider than most grasses ? 1 to 2 feet long and 1 to 4 inches across ? hairless to sparsely hairy, with a prominent pale green to white midrib running down the center [1]. Where the leaf meets the stem there is a fringed, see-through membrane (the ligule) up to about 1/5 inch long [1].

Once it heads, identification is easy. The seed head is a loose, branching cluster 3 to 20 inches long with whorled, upright branches, green at first and turning reddish-brown as it ripens [1]. The seeds are oval, flattened, and red to black, and ? the key trait ? they fall away readily as soon as they are ripe, with the seed-head branches becoming brittle and breaking [1].

Look for it in mid to late summer, when it towers above a crop canopy with its open, reddish seed head. That is also the moment to act, because once the seed shatters it is already in the soil [1].

At-a-glance cues:

1. Tall annual grass to about 8 feet with smooth, unbranched stems, sometimes purple-spotted ? corn-like before it heads [1][2]
2. Unusually wide leaves, 1 to 4 inches across, with a prominent pale green to white midrib [1]
3. Loose, branching seed head 3 to 20 inches long, green turning reddish-brown [1]
4. Oval, flattened, red-to-black seeds that drop readily when ripe [1]

Leaves:

1. Blades: 1 to 2 feet long and 1 to 4 inches wide ? much wider than most grasses [1]
2. Surface: hairless to sparsely hairy [1]
3. Midrib: prominent, pale green to white, running down the center of the blade [1]
4. Ligule: a fringed, translucent membrane up to about 1/5 inch long where the blade meets the stem [1]
5. Sheaths: smooth and open, occasionally hairy near the collar [1]

Stems:

1. Habit: an erect summer annual growing to about 8 feet, corn-like in appearance before heading [1][2]
2. Form: unbranched and hairless [1]
3. Color: green, sometimes marked with purple spots [1]
4. Roots: fibrous ? it does not produce creeping underground stems (rhizomes) [1]

Flowers:

1. Seed head: a compact to open branching cluster (panicle) 3 to 20 inches long [1]
2. Branching: branches whorled and upright [1]
3. Color: green at first, turning reddish-brown as it matures [1]
4. Timing: heads form in mid to late summer on this summer annual [1][2]

Fruit and seeds:

1. Seeds: oval and flattened, about 1/10 to 1/6 inch wide [1]
2. Color: red to black at maturity [1][2]
3. Shattering: seeds fall readily as soon as they ripen, and the seed-head branches turn brittle and break ? the trait the plant is named for [1][2]
4. Dispersal: seed moves on tillage and harvest equipment, with livestock, and in irrigation water and runoff [1]

Habitat:

Shattercane descends from cultivated and wild sorghum, and most infestations trace back to shattercane seed contaminating fields planted to cultivated sorghum varieties [2]. It occurs throughout the United States and into southern Ontario and Quebec, but it is most problematic in the Midwest [1].

It is overwhelmingly a plant of cultivated ground. It grows in and along corn and soybean fields, field edges, and the disturbed margins around them, and it moves along the routes farm equipment and irrigation water travel [1][2].

Reproduction:

Shattercane is a summer annual that reproduces only by seed [1][2]. For anyone managing land, the spread routes are practical ones: seed rides on tillage and harvest equipment moving between fields, passes through livestock, and washes along in irrigation water and runoff [1]. That is why an infestation often shows up first along a field entrance or a water course.

Its defining habit is in the name. As soon as the seed ripens, it falls ? the seed-head branches go brittle and break apart, dropping seed before a crop is harvested [1][2]. So by the time a combine goes through, the plant has already restocked the soil.

The control timing follows directly: remove plants before the seed head ripens and shatters in late summer. Because it is an annual with no creeping underground stems, a plant removed before it seeds is gone for good ? there is nothing left below ground to regrow [1].

Impact and Damage:

The most serious risk shattercane poses is to livestock. Like other members of the sorghum family, it contains dhurrin, a compound that releases hydrogen cyanide ? prussic acid ? when the plant's tissues are damaged or stressed [3]. Freezing, drought stress, wilting, and young regrowth all raise the danger, and frozen plants can keep releasing cyanide for several days afterward [3]. Cattle and sheep are at greater risk than horses or pigs, because the microbes in a ruminant's stomach break the plant cells open quickly [3]. Signs can appear within 15 to 20 minutes and include bright pink gums, rapid heartbeat, labored breathing, and muscle tremors, and poisoning can kill within minutes [3]. Anyone with grazing animals should keep them off frosted or drought-stressed sorghum.

Its other major impact is agricultural. Shattercane grows fast and tall ? up to about 8 feet ? so it overtops corn and soybeans and competes aggressively with them [1][2]. It is also stubborn to control: after years of repeated use of the same products, soil microbes adapted and began breaking some herbicides down so quickly that they stopped working on it [2]. Because the seed shatters before harvest and travels on equipment, an infestation in one field readily seeds the next [1][2].

Its footprint is mainly on farmland rather than in wild habitat ? it is a weed of cultivated ground and field margins, most troublesome across the Midwest [1].

Similar species:

Shattercane is most often mistaken for two things: another sorghum, and the crop it is growing in.

Johnsongrass (Sorghum halepense) is the closest relative and the main point of confusion, since the two have a similar growth habit [2]. The decisive difference is underground: Johnsongrass is a perennial that spreads by thick creeping rhizomes, while shattercane is an annual with no rhizomes at all [1][2]. Shattercane also has noticeably wider leaf blades and larger, rounder seeds.

Corn (Zea mays) is the other common mix-up, because young shattercane is an erect, corn-like plant and blends into a crop row before it heads [2]. Once it produces its loose, branching, reddish seed head it is unmistakable ? corn bears a tassel at the top and ears along the stalk, never an open shattering panicle [1].

Monitoring and rapid response:

Signs to watch for:

1. In mid to late summer, a tall grass to about 8 feet overtopping a crop, with a loose reddish-brown branching seed head [1]
2. Unusually wide leaves (1 to 4 inches) with a pale white midrib, and stems that may be purple-spotted [1]
3. Corn-like young plants standing out of place along field edges, entrances, and ditches [2]

What you can do:

1. Pull, hoe, or cut plants out before the seed head ripens. Because shattercane is an annual with no creeping underground stems, a plant removed before it seeds is finished ? nothing regrows from below ground [1].
2. Time it to beat the shatter. Once the seed ripens it drops on its own, so removing plants after that point does nothing to stop reseeding [1][2].
3. Bag and remove any seed heads rather than dropping them in place, and do not compost them.
4. Clean tillage and harvest equipment before moving between fields ? equipment is a main way the seed travels [1].
5. Keep grazing animals off shattercane that has been frosted, drought-stressed, or is in young regrowth, because of the cyanide risk [3].
6. For a farm or natural area crew: scout and pull scattered plants before heading, prioritize new patches along field entrances and water courses where seed arrives first, and repeat through the season since plants emerge over time [1][2].

When to call a professional:

1. Large, established infestations across cropland, or situations where past control has stopped working ? some products have lost effectiveness against it over years of repeated use [2].
2. Any suspected livestock poisoning, which is a veterinary emergency ? contact a veterinarian immediately [3].
3. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. Cornell University College of Agriculture and Life Sciences, Weed Science. Shattercane (Sorghum bicolor). cals.cornell.edu
2. Iowa State University Extension and Outreach, Integrated Crop Management. Shattercane. crops.extension.iastate.edu
3. University of Nebraska?Lincoln Extension. Cyanide Poisoning (NebGuide G2184). extensionpubs.unl.edu
4. Integrated Taxonomic Information System. Sorghum bicolor (L.) Moench, TSN 42108. itis.gov
5. Plants of the World Online. Sorghum bicolor (L.) Moench. Royal Botanic Gardens, Kew. powo.science.kew.org

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