Shattercane

Images above: Upper left: Shattercane immature plant (Antonio DiTommaso, Cornell University). Upper right: Shattercane unopened panicles (Joseph DiTomaso, University of California, Davis). Bottom: Shattercane open panicle (Scott Morris, Cornell University).

Identification

Other common names:  sorghum, black amber cane, wildcane, milo, chicken corn

Family:  grass, Poaceae

Habit:  Tall, upright annual grass.

Taxonomic note:  The taxonomic status of shattercane is controversial.  Some recent authors have used Sorghum bicolor (L.) Moench nothosubsp. drummondii (Steud.) de Wet ex. Davidse for shattercane (DeFelice 2006, Schmidt et al. 2018), but USDA and WSSA use Sorghum bicolor (L.) Moench ssp. drummondii (Nees ex Steud.) de Wet & Harlan to refer to sudangrass (USDA Plants, WSSA).  All competent authorities agree that shattercane is differentiated from domestic sorghum only at the subspecies level.

Description:  Seedlings are similar in appearance to corn.  Leaves are rolled in the bud, and the ligule is a translucent fringed membrane.  The collar is whitish, and auricles are absent.  Early leaves are 0.08-0.2” (0.2-0.5 cm) wide by 1.6-7” (4-18 cm) long and usually hairy at the base and otherwise hairless.  Sheaths may or may not have hairs.  Mature plants tiller to form clumps, and can reach 8 ft (2.4 m) in height.  The stems are erect, unbranched, hairless, and may have purple spots.  Sheaths are smooth and open, with occasional scattered hairs near the collar.  Auricles are absent.  The ligule is a fringed, translucent membrane up to 0.2” (0.5 cm) long.  Blades are 1-2 ft (30-60 cm) long by 1-4” (2.5-10 cm) wide, hairless to sparsely hairy, and have a prominent, pale green to white midvein.  The roots are fibrous and branching, and brace roots develop at the base of the stem.  The inflorescence is a compact to open, 3-20” (8-50 cm) long panicle with whorled and upright branches that turns from green to reddish brown as it matures.  Spikelets are paired, and each spikelet has one fertile and one infertile flower.  The fertile flower is stalkless and 0.16-0.24” (0.4-0.6 cm) long with a 0.25-0.5” (0.6-1.3 cm) long awn, whereas the infertile flower is stalked and lacks an awn.  As with all grasses, seeds are covered with a thin, tight, hard layer of fruit tissue.  Seeds are red to black, 0.1-0.17” (0.25-0.43 cm) wide, oval, and flattened.  The seeds fall readily when ripe, and panicle branches may become fragile and break when mature.  

Similar species:  In domestic sorghum [Sorghum bicolor (L.) Moench ssp. bicolor], the short stem (rachilla) that attaches the seed to the main stem of the inflorescence breaks to free the seed during combining.  In most biotypes of shattercane, a special layer of cells forms at the tip of the rachilla, which causes the seed to fall off spontaneously when ripe (Horak and Moshier 1994).  In a few biotypes the rachilla itself becomes fragile at maturity and breaks spontaneously.  Johnsongrass [Sorghum halepense (L.) Pers.] is similar to shattercane, but is a perennial with large, scaly rhizomes and narrower (0.5-2” = 1.3-5.1 cm wide) leaves than shattercane.  Seedlings of shattercane and Johnsongrass are nearly indistinguishable, but if removed from the soil the attached seed coat may be used to differentiate them.  Johnsongrass seeds are much smaller than shattercane seeds, just 0.06-0.08” (0.15-0.2 cm) wide.  Corn (Zea mays L.) seedlings may be distinguished from shattercane by the larger attached seed of corn.

Management

Prevent movement of shattercane into uninfested fields by cleaning combines and tillage equipment.  If shattercane is not already present in a field, avoid growing sorghum of any sort on that field.  Essentially all sorghum seed contains at least a few seeds of shattering off-types that will introduce the weed to that field.  If you have a compelling reason to grow sorghum on an uninfested field, plan to hand rogue out off-type individuals after the inflorescence has emerged, but before they set seed.  If plants have flowered, remove the cut plants from the field.

Where the weed is already present, management of the shattercane seed bank is critical.  A season-long tilled fallow can reduce shattercane seed by 91% (Martin and Roeth 1980), but this may not be sufficient to make this approach worthwhile.  In regions with mild winters, leave seeds on the soil surface until spring to maximize seed predation.  In regions where the soil freezes, shallowly incorporate the seed to insure they imbibe and thereby become subject to damage by freezing.  Avoid deep burial in the fall as that will decrease the number of freeze-thaw cycles the seeds experience and may prevent freezing altogether.  In the spring, bury the seeds deeply by moldboard plowing to reduce emergence.  Although a few will return to the surface with next year’s tillage, the mortality rate of shattercane seeds is sufficiently high that most will not.  Although shattercane continues to emerge through the summer, most seedlings appear in late spring and early summer, so delaying tillage and planting can reduce shattercane density in the crop (Fawcett 1981).

Since many shattercane seedlings will emerge from below the working depth of a rotary hoe or tine weeder, the objective of in-row weeding must be to break or bury the seedlings rather than uprooting them.  A tine weeder is better for these purposes.  Plant soybeans at high density to allow for more aggressive weeding and consequently greater soybean stand loss.  If conditions are favorable for continued shattercane emergence, a late tine weeding at the first to second trifoliate stage of the soybeans can be useful for removing new seedlings close to the row.  Since shattercane can emerge late into the summer, delay the lay-by cultivation as long as is practical.  If shattercane is a severe problem on the farm, consider obtaining a weed puller, electric discharge weeder or a mower to top the shattercane after it emerges above the crop.  Since shattercane generally overtops grain sorghum, at least the first two options can be effective for managing the weed in sorghum (Fawcett 1981).  A mower that removes tops of the weed will be most effective after the inflorescence has emerged, but before the flowers have opened.

A dense, vigorous crop of winter grain or early planted spring grain will be well established by the time shattercane emerges and will suppress the weed (Fawcett 1981).  Since small grains are harvested before shattercane goes to seed, clean-up fields with tillage or mowing after harvest to prevent seed production and, in conjunction with good seed bank management, reduce the severity of an infestation.  Harvesting corn or sorghum for forage before shattercane sets seed can also interrupt the life cycle of the weed (Horak and Mosher 1994).  Although some shattercane seeds will likely survive through rotation with alfalfa, many will not, and in any case, repeated mowing will prevent further seed production by the weed during the alfalfa portion of the rotation.

Ecology

Origin and distribution:  The first shattercane varieties originated in northern sub-Saharan Africa along with domesticated sorghum (De Wet 1978).  It probably emerged multiple times and has further evolved through multiple hybridizations between it, domesticated and wild Sorghum species around the world.  It has been introduced into semi-arid areas of Asia, Europe, Australia and North America (Horak and Moshier 1994).  It occurs throughout the U.S.A. and in southern Ontario and Quebec in Canada (USDA Plants) but is most problematic in the Midwest.

Seed weight:  13-20 mg, without glumes (Fellows and Roeth 1992), 19-22 mg (Schmidt et al. 2018).

Dormancy and germination:  A moderate proportion of the seeds are capable of germination immediately after falling from the parent plant.  Late emerging plants produce a higher proportion of dormant seeds, and the proportion of dormant seeds probably also varies among populations.  Removal of glumes or slight damage to the seed coat (scarification) decreases dormancy.  The optimal temperature for germination is 77-95 °F (25-35 °C) (Horak and Moshier 1994, Sahoo et al. 2010), and germination is poor at temperatures below 59 °F (15 °C) (Peacock 1982).  Temperature fluctuations promote germination, and consequently, shade inhibits emergence by reducing temperature fluctuations (Kegode et al 1998).  After burial, light promotes germination of seeds in some populations (Jacques et al. 1974) but not in others (Horak and Moshier 1994).  Nitrogen fertilization does not promote germination (Horak and Moshier 1994). 

Seed longevity:  Shattercane is genetically diverse and seed survival in soil varies with the biotype present.  Long term survival in soil depends on the tight glumes that enclose the seed of most populations (Fellows and Roeth 1992).  Seeds buried at 8.7” (22 cm) under sod remained viable for as long as 13 years.  Over 30% remained viable for 8 years, but viability declined rapidly after that (Burnside et al. 1977).  In a subsequent experiment, viability of seeds buried 8” (20 cm) declined to 37-43% after the first year, and only 0-3% were viable after 5 years (Burnside et al. 1996).  In another experiment, 1% of seeds from plants with open inflorescences survived for three years at 3-6” (7.5-15 cm), but survival increased with burial at greater depths.  Seeds from compact inflorescences did not survive more than 1 year unless deeply buried (Jacques et al. 1974).  In experiments in Nebraska, only 11-17% of seeds buried 1-5” (2.5 to 12.5 cm) in November survived until March, and most of the remaining died within the next year (Teo-Sherrell and Mortensen 2000).  Covering seeded areas with clear plastic increased winter soil temperatures and seed survival, so over-winter seed survival is probably greater in milder climates.  Freezing greatly decreases viability (Peacock 1982, Kegode and Pearce 1998).  Progeny of outcrossed populations derived from grain sorghum and weedy shattercane had smaller, less tightly adhering glumes than shattercane and were unable to survive one Nebraska winter on the soil surface (Schmidt et al. 2018).

Season of emergence:  Shattercane begins to emerge in late spring and can continue to emerge throughout the summer (Kegode et. al 1998, Doll 2002).

Emergence depth:  Shattercane emerges best from the top 1-2” (2.5-5 cm), but 10-50% of seeds placed at 4” (10 cm) can successfully produce seedlings (Kegode et. al 1998).  Emergence has been observed from depths of more than 6” (15 cm) (Jacques et al. 1974, Defelice 2006).

Photosynthetic pathway:  C4 (Elmore and Paul 1983)

Sensitivity to frost:  Shattercane is killed by frost and is injured by temperatures below 55 °F (13 °C) (Peacock 1982).

Drought tolerance:  Shattercane is moderately drought tolerant (Defelice 2006).  If seed set is reduced by drought during flowering, side inflorescences can form to partially compensate for the loss (Berenguer and Faci 2001).

Mycorrhiza:  The species is mycorrhizal (Ames et al. 1984). 

Response to fertility:  Recommended rates of balanced N-P-K increased productivity of forage sorghum by 45% relative to no fertilizer (Pholsen and Suksri 2004, Ramanjaneyulu et al. 2007).  In competition with corn, shattercane took up significant amounts of nitrogen and subsequently reduced corn yields (Hans and Johnson 2002).

Soil physical requirements:  Shattercane grows best on irrigated bottomlands.  It does well on soil textures ranging from very fine sandy loam to silty clay loam (Burnside et. al 1977) and heavy clay (Patil and Sheelavantar 2006).

Response to shade:  The species is intolerant of shade, but due to rapid early growth supported by large seed reserves and its potentially tall height, it can often avoid shade by overtopping competing crops.

Sensitivity to disturbance:  In Nebraska, plants cut before August will regrow and produce viable seeds before frost (Roeth et al. 1996).

Time from emergence to reproduction:  Shattercane in Wisconsin flowered 11 weeks after emergence (Doll 2002).  In Nebraska, shattercane produced seeds in 8 to 9 weeks.  Seeds became viable 10 days after anthers emerged, and shattering occurred 9-12 days later (Horak and Moshier 1994).   Shattercane plants that emerged as late as July in Nebraska were still able to produce viable seeds before a killing frost (Defelice, 2006). 

Pollination:  Plants are primarily self-pollinated, but cross pollination also can occur (Schmidt et al. 2013).  The pollen can blow for a mile (1.6 km) or more, which makes production of genetically pure sorghum seed difficult.  (Fawcett 1981)

Reproduction:  A shattercane inflorescence produces 500-1500 seeds so a typical plant with three heads produces about 3,000 seeds (Horak and Moshier 1994).  In Nebraska, shattercane grown in rows similarly to grain sorghum produced 1.5 to 1.9 panicles and 2,900 to 3,800 seeds per plant (Schmidt et al. 2018).

Dispersal:  Tillage machinery and harvest equipment can move seeds between fields (Fawcett 1981).  Even certified sorghum seed with a 99.95% genetic purity can introduce as many as 20 shattercane plants per acre (50 per ha) if the seed is sown at a typical 40,000/A (99,000/ha) (Horak and Moshier 1994).  Thus, even ‘clean’ sorghum seed is a potential source of shattercane introduction.  Shattercane seeds pass through cattle in a viable condition and may be present in manure or spread with the movement of livestock (Burnside et al. 1977).  Shattercane seeds float and can be carried long distances in runoff and irrigation water (Horak and Moshier 1994).

Common natural enemies:  Many birds and small mammal species feed on shattercane seeds (Defelice 2006).

Palatability:  The seeds are commonly eaten during famines in Africa.  The plant is generally palatable for ruminants but can be poisonous to horses.  Nitrate can accumulate to poisonous levels during dry summers.  Avoid grazing livestock on young stands as the seedlings contain a compound that releases cyanide when consumed (Defelice 2006).  Shattercane is not recommended for feeding poultry because its high tannin content slows growth (Douglas and Sullivan 1991).

References:

• Ames, R. N., L.K. Porter, T. V. St. John, and C. P. P. Reid.  1984.  Nitrogen sources and A' values for vesicular-arbuscular and non-mycorrhizal sorghum grown at three rates of 15N-ammonium sulphate.  New Phytologist 97:269-276.
• Berenguer, M. J., and J. M. Faci.  2001.  Sorghum (Sorghum bicolor L. Moench) yield compensation processes under different plant densities and variable water supply. European Journal of Agronomy 15:43-55.
• Burnside, O. C., G. A. Wicks, and C. R. Fenster.  1977.  Longevity of shattercane seed in soil across Nebraska.  Weed Research 17:139-143.
• Burnside, O. C., R. G. Wilson, S. Weisberg, and K. G. Hubbard.  1996.  Seed longevity of 41 weed species buried 17 years in eastern and western Nebraska.  Weed Science 44:74-86.
• Defelice, M. S.  2006.  Shattercane, Sorghum bicolor (L.) Moench ssp. drummondii (Nees ex Steud.) de Wet ex Davidse – black sheep of the family.  Weed Technology 20:1076-1083.
• de Wet, J. M. J.  1978.  Systematics and evolution of sorghum sect. sorghum (Gramineae).  American Journal of Botany 65:477-484.
• Doll, J.  2002.  Knowing when to look for what: Weed emergence and flowering sequences in Wisconsin.  Weed Science, University of Wisconsin. https://extension.soils.wisc.edu/wp-content/uploads/sites/68/2016/07/Doll-2.pdf
• Douglas, J. H., and T. W. Sullivan.  1991.  Research note: chemical composition and nutritional value of shattercane sorghum for broilers.  Poultry Science 70:408-411.
• Elmore, C. D., and R. N. Paul.  1983.  Composite list of C4 weeds.  Weed Science 31:686-692.
• Fawcett, R. S.  1981.  Todays weed: shattercane.  Weeds Today 12:11-14.
• Fellows, G. M., and F. W. Roeth.  1992.  Factors influencing shattercane (Sorghum bicolor) seed survival.  Weed Science 40:434-440.
• Hans, H. R., and W. G. Johnson.  2002.  Influence of shattercane [Sorghum bicolor (L.) Moench.] influence on corn (Zea mays L.) yield and nitrogen accumulation.  Weed Technology 16:787-791.
• Horak, M. J., and L. J. Moshier.  1994.  Shattercane (Sorghum bicolor) biology and management.  Reviews of Weed Science 6:133-149.
• Jacques, J. L., J. F. Vesecky, K. C. Feltner, and R. L. Vanderlip.  1974.  Effect of depth and duration of burial on shattercane seed.   Crop Science 14:787-789.
• Kegode, G. O., and R. B. Pearce.  1998.  Influence of environment during maternal plant growth on dormancy of shattercane (Sorghum bicolor) and giant foxtail (Setaria faberi) seed.  Weed Science, 46:322-329.
• Kegode, G. O., R. B. Pearce, and T. B. Bailey.  1998.  Influence of fluctuating temperatures on emergence of shattercane (Sorghum bicolor) and giant foxtail (Setaria faberi).  Weed Science 46: 330-335.
• Martin, A. R., and F. W. Roeth.  1980.  Field studies on shattercane control.  Proceedings of the North Central Weed Control Conference 34:51-52.
• Patil, S. L., and M. N. Sheelavantar.  2006.  Soil water conservation and yield of winter sorghum (Sorghum bicolor L. Moench) as influenced by tillage, organic materials and nitrogen fertilizer in semi-arid tropical India.  Soil and Tillage Research 89:246-257.
• Peacock, J. M.  1982.  Response and tolerance of sorghum to temperature stress.   Pp. 143-159 in L. R. House, L. K. Mughogho, and J. M. Peacock (eds), Sorghum in the Eighties, Proceedings of the International Symposium on Sorghum, Patacheru, India, November 2-7, 1981.  International Crops Research Institute for the Semi-Arid Tropics (ICRISAT): Hyderabad, India.
• Pholsen, S., and A. Suksri.  2004.  Effect of organic amendment and chemical fertilization on growth, yield and fodder quality of a forage sorghum (Sorghum bicolor L. Moench).  Pakistan Journal of Biological Sciences 7:651-657.
• Ramanjaneyulu, A. V., Y. Shivay, and G. Giri.  2007.  Partitioning of photosynthates, N and P in mustard as influenced by nutrient management in fodder sorghum (Sorghum bicolor L.) - mustard (Brassica juneca L.) cropping sequence.  Archives of Agronomy and Soil Science 53:553-565.
• Roeth, F., A. Martin, and R. Klein.  1996.  Shattercane and its control.  NebGuide, Cooperative Extension Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE.  https://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=2502&context=extensionhist
• Sahoo, L., J. J. Schmidt, J. F. Pedersen, D. J. Lee, and J. L. Lindquist.  2010.  Growth and fitness components of wild x cultivated Sorghum bicolor (Poaceae) hybrids in Nebraska.  American Journal of Botany 97:1610-1617.
• Schmidt, J. J., J. F. Pedersen, M. L. Bernards, and J. L. Lindquist.  2013.  Rate of shattercane x sorghum hybridization in situ.  Crop Science 53:1677-1685.
• Schmidt, J. J., M. K. Yerka, J. F. Pedersen, and J. L. Lindquist.  2018.  Growth, fitness, and overwinter survival of a shattercane (Sorghum bicolor ssp. drummondii) x grain sorghum (Sorghum bicolor ssp. bicolor) F2 population.  Weed Science 66:634-641.
• Teo-Sherrell, C. P. A., and D. A. Mortensen.  2000.  Fates of buried Sorghum bicolor ssp. drummondii seed.  Weed Science 48;549-554.
• USDA Plants.  USDA Natural Resources Conservation Service Plants Database.  http://plants.usda.gov
• WSSA.  Composite List of Weeds.  http://wssa.net/wssa/weed/composite-list-of-weeds/