Kochia

Bassia scoparia (L.) A.J. Scott = Kochia scoparia (L.) Schrad.

Images above: Upper left: Kochia older seedling (Anita Dille, Kansas State University). Upper right: Kochia plant (Wale Osipitan). Bottom: Kochia flowering stem (Anita Dille, Kansas State University).

Identification

Other common names:  summer-cypress, belvedere, burning-bush, fireball, Mexican fireweed, belevedere, mock cypress, red belevedere, belevedere-cypress, red belvedere, broom-cypress

Family:  goosefoot family, Chenopodiaceae

Habit:  Tall, much branched, taprooted summer annual herb.

Description:  Cotyledons of kochia seedlings are stalkless, elliptical, 0.18” (0.5 cm) long by 0.1” (0.3 cm) wide, and softly hairy, with dull green upper surfaces and may be bold pink or magenta on the underside.  Stems are hairy and green to reddish in color.  Young leaves are lance to wide-thumb shaped, pointed at the tip, red-tinged underneath, gray-green above due to the presence of numerous soft hairs, and initially have a whorled leaf arrangement like a basal rosette.  Mature plants are highly branching, 1-6.5 ft (0.3-1.8 m) tall, pyramidal to round, and bushy, with a soft, airy texture. Plants look blue to gray-green during the season, turning red-green or red-purple in the fall.  Stems are red tinged and more or less hairy.  Alternate leaves are narrow, 1-2” (2.5-5 cm) long by 0.13-0.25” (0.3-0.6 cm) wide, and are attached by short stalks.  Soft hairs are present on the untoothed leaf edges, leaf undersides and typically on upper leaf surfaces.  Leaves decrease in size higher up on stems.  The root system is a taproot with branched fibrous roots.  The stem of the mature, dry plant breaks free from the root to become a tumbleweed in the fall.  Green, petal-less, 0.13” (0.3 cm) long flowers occur singly or in clusters of 2 to 6 in leaf axils of the upper stems or in short spikes with long, white hairs and a 0.13-0.5” (0.3-1.3 cm) long leaf-like bract below each flower cluster.  Seeds are contained in papery bladders derived from the green portion of the flowers.  Seeds are egg shaped with many irregularities and no bigger than 0.1” (0.25 cm), with a gritty, bumpy, dull, grooved surface; they range in color from transparent brown with yellow spots to dark red-brown or black.

Similar species:  Russian-thistle (Salsola tragus L.) has narrower, needle-like leaves at all stages compared to kochia.  Forage kochia [Bassia prostrata (L.) A.J. Scott] is a perennial, semi-evergreen species with 1-5” (2.5-13 cm) linear leaves.  Common lambsquarters (Chenopodium album L.) has broader, diamond-shaped leaves, and is a hairless species with white or pink-dusted leaf surface, especially when the plant is young. 

Management

Kochia relies primarily on prolific seed production and abundant seedling emergence for population growth, suggesting that management of these life stages will have the greatest impact on controlling this species (Osipitan et al. 2019).  Because kochia seeds survive for a short time in the soil, preventing seed production for just a single year will largely control even severe infestations (Dille et al. 2017, Murray 2003).  Two or three years of vigilance can essentially eradicate the population.  Consequently, rotating fields into a hay crop for a few years should be highly effective for managing kochia.  Winter cereals are good competitive crops when they establish a vigorous leaf canopy by the time kochia emerges in spring (Kumar et al. 2019).  Spring wheat that is planted during the primary emergence period of kochia and harvested while kochia is vegetative or beginning to flower can eliminate seed production (Mosqueda et al. 2020).  Avoid uncompetitive crops such as flax, beans, or sugar beet (Mosqueda et al. 2020, Murray 2003).  Growing a fall-established triticale-legume cover crop mix in a wheat-fallow system in Kansas effectively suppressed kochia without adversely affecting the following wheat crop (Petrosino et al. 2015).  Yellow sweetclover significantly reduced kochia population when grown as a green manure fallow in Alberta (Blackshaw et al. 2001). 

Kochia is more abundant in no-till than conventional-tillage systems, in part because of its ability to germinate in cool soil associated with crop residue at the soil surface (Friesen et al. 2009, Kumar et al. 2019).  Management including carefully targeted tillage operations were most effective for reducing kochia populations (Osipitan et al. 2019).  Because seeds need to be within the top inch or less of soil to successfully emerge and because seeds buried more deeply often germinate and die, inversion tillage is an effective control measure (Schwinghammer and Van Acker 2008).  Because the peak of emergence occurs early in the spring, delaying tillage and planting will decrease the current year’s infestation, even if tillage is shallow (Beck 1964, Dille et al. 2017, Eberlein and Fore 1984, Kumar et al. 2019).  Cool-season crops like wheat, however, will compete better with kochia, a warm-season weed, when planted during the cool weather of spring (Nord et al. 1999).  

Because kochia emerges only from the top inch of soil, tine weeding is effective against this weed in both small grains and row crops.  For example, harrowing of spring wheat and barley with either a tine weeder or a spike-tooth harrow at the crop 3-leaf stage gave 66 and 62% control of kochia, respectively (Wright et al. 1992).  Spike tooth harrowing at both the 3 and 5-leaf stage increased control to 82%, but a second tine weeding at the 5-leaf stage did not improve control.  None of the weeding treatments affected yield of either crop despite about 19% damage when harrowing was done twice.  Pre-emergence tine weeding or rotary hoeing would probably provide additional control.  Due to its small seed reserves, kochia starts slowly, but it grows rapidly once established (Nord et al. 1999).  Consequently, burying in-row kochia seedlings with soil as soon as the crop will tolerate it could be effective.

In the northern Great Plains, seeds mature after the time of small grain harvest (Burton et al. 2017, Eberlein and Fore 1984).  This indicates that many of the early maturing seeds could be captured during combine harvesting of grain (Burton et al. 2017) and, with prompt clean up of the field after harvest, could prevent further seed production that year.  Plants remaining after grain harvest can produce significant quantities of seeds, so it is important to destroy kochia regrowth before the first killing frost (Mickelson et al. 2004).  Avoid irrigation practices that increase soil salinity as this will favor kochia relative to crops (Murray 2003).  After a field has been cleaned up, a snow fence can prevent the majority of mature plants from rolling in from adjacent infested areas (Murray 2003).  

Ecology

Origin and distribution:  Kochia is native to eastern Europe and western Asia.  It occurs throughout southern Canada and the U.S.A. except parts of the southeast (USDA Plants), but is particularly a problem in the Great Plains and inter-mountain West.  In addition to North America, it has spread widely in Europe, China and Japan, and has been introduced into Africa, Argentina, Australia, and New Zealand.  (Friesen et al. 2009, Moore et al. 2003)

Seed weight:  0.20 mg (Zhao 2011), 0.47-0.74 mg (Thompson et al. 1994), 0.54 mg (Mohler unpublished data), 0.85 mg (Stevens 1932).

Dormancy and germination: Kochia seeds have little dormancy and germinate greater than 75% at temperatures from 39-95 °F (4-35 °C) (Al-Ahmadi and Kafi 2007, Dille et al. 2017, Eberlein and Fore 1984, Everitt et al. 1983, Khan et al. 2001, Kumar and Jha 2017, Yadav et al. 2023), but germination is inhibited at 104 °F (40 °C) (Al-Ahmadi and Kafi 2007, Everitt et al. 1983).  Alternating temperature does not enhance germination (Everitt et al. 1983, Kumar and Jha 2017).  Germination is very rapid, with seedlings commonly breaking through the seed coat within 24 hr at 59-79 °F (15-26 °C) (Al-Ahmadi and Kafi 2007, Steppuhn and Wall 1993, Yadav et al. 2023).  Light is not required for germination (Everitt et al. 1983).  Kochia seeds can germinate in soil that is too dry for establishment of drought tolerant crops, and kochia can also germinate in solutions of up to 10,000 ppm salt (Everitt et al. 1983, Evetts and Burnside 1972, Steppuhn and Wall 1993, Yadav et al. 2023).  High salt conditions reduce germination less at high than at low temperatures (Khan et al. 2001).  Kochia can germinate at a wide range of pH from 2 to 12 (Everitt et al. 1983).

Seed longevity:  Most kochia seeds either germinate or die in their first year (Dille et al. 2017, Friesen et al. 2009, Schwinghammer and Van Acker 2008).  In undisturbed soil, up to 3% can survive 2 to 3 years when buried at 12” (30 cm), but survival is much poorer near the soil surface (Zorner et al. 1984, Burnside et al. 1981).  In the western U.S.A. and Canada, seeds buried in fall had good viability in the early spring when emergence typically occurs, but they suffered high mortality over summer months and had low viability by fall (Beckie et al. 2018, Dille et al. 2017).  Seed placement from the soil surface to 4” (10 cm) depth had little effect on seed mortality in these experiments.

Season of emergence:  Most seedlings emerge early in spring, but some emerge later following rains (Dille et al. 2017, Doll 2002, Eberlein and Fore 1984, Kumar et al. 2018, Moore et al. 2003, Murray 2003, Werle et al. 2014).  In Colorado, for example, 80% of seedlings emerged between 11 April and 20 June, with emergence commencing when the average daily air temperature was 49 °F (9.5 °C) (Anderson and Nielsen 1996), a finding consistent with research showing emergence commencing when the soil temperature reached 50 °F (10 °C) (Undersander et al. 2000).  Populations from several Great Plains states had different emergence patterns, suggesting different emergence biotypes that would require location-specific management tactics (Kumar et al. 2018).  There has been a shift toward later germination and emergence patterns in biotypes resistant to post-emergence herbicides (Beckie et al. 2018, Kumar et al. 2019).

Emergence depth:  Seedlings emerge best from the top 0.4” (1 cm) and few emerge from deeper than 0.8” (2 cm) (Undersander et al 2000, Schwinghammer and Van Acker 2008).  Seedlings establish better from seeds on the soil surface than at 0.1” (0.3 cm) (Everitt et al. 1983, Schwinghammer and Van Acker 2008).

Photosynthetic pathway:  C4 (Elmore and Paul 1983, Friesen et al. 2009)

Sensitivity to frost:  Seedlings in spring can tolerate a nighttime temperature of 9 °F (-13 °C) (Eberlein and Fore 1984), but 6-week-old plants that were cold acclimated for 3 weeks could not survive 18 hours at temperatures of 18 °F (-8 °C) or lower (Cici and Van Acker 2011).

Drought tolerance:  Kochia is very drought tolerant (Friesen et al. 2009), and historically infestations have tended to increase during drought periods to the exclusion of other weed species (Murray 2003).  Drought tolerance is partially due to an extensive root system; under favorable moisture conditions the roots penetrate 7 ft and under drought conditions they can penetrate up to 16 ft (Eberlein and Fore 1984, Phillips and Launchbaugh 1958).  Kochia is less drought tolerant under high-salt soil conditions (Steppuhn and Wall 1993).

Mycorrhiza:  Kochia is not mycorrhizal (Friesen et al. 2009, Pendleton and Smith 1983).

Response to fertility:  Kochia is highly responsive to N and its productivity continues to increase up to high N application rates (480 lb/A = 538 kg/ha) (Blackshaw et al. 2003, Lugg et al. 1983).  Plants can absorb up to 90% of available soil nitrogen (Blackshaw et al. 2003).  Kochia only responds to P when soil levels are very low, although very low soil N fertility increases the range of P application rates to which kochia responds (Blackshaw et al. 2004, Lugg et al. 1983).  High soil P levels will suppress growth (Undersander et al 2000).

Soil physical requirements:  Kochia is most common in dry pastures, rangelands and cropland with alkaline soils.  It does not occur on highly acidic soils.  It tolerates a wide range of soil types and is well adapted to saline soils. (Friesen et al. 2009, Steppuhn et al. 1993, Undersander et al 2000)

Response to shade:  Compared with cropped sunflower, kochia is relatively intolerant of shade (Durgan and Dexter 1985).  Kochia seed production was reduced more by tall crops such as corn and wheat than shorter crops such as sugar beet and beans (Mosqueda et al. 2020).

Sensitivity to disturbance:  Kochia regrows profusely after cutting by producing branches from axillary buds.  For example, when grown for hay it is typically mowed four times during the growing season (Undersander et al. 2000).  Plants that are cut off by a combine will produce many seeds that remain in place since the truncated plant does not break off and tumble (Mickelson et al. 2004).

Time from emergence to reproduction:  Kochia plants flower 57 to 109 days after emergence (Doll 2002, Eberlein and Fore 1984, Friesen et al. 2009).  It flowers in response to decreasing day length, with shorter light periods and longer times after emergence required for more southerly populations (e.g. New Mexico as compared to South Dakota) (Bell et al. 1972).

Pollination:  Kochia commonly self-pollinates, but has a moderate rate of outcrossing by wind and bee dispersed pollen(Beckie et al. 2016, Friesen et al. 2009, Mulugeta et al. 1994)

Reproduction:  Kochia typically produces 10,000 to 30,000 seeds per plant (Friesen et al. 2009, Stevens 1932, Thompson et al. 1994), with the potential for up to 100,000 seeds per plant (Beckie et al. 2016).  Greater than 99.9% of seeds are retained on plants at wheat harvest, suggesting the potential for removal and destruction of seeds at harvest (Burton et al. 2017).  Plants re-growing following combine harvest of grain can produce 2,600 to 4,000 seeds each (Mickelson et al. 2004).

Dispersal:  Mature kochia break off near the base of the stem and roll as tumble weeds, dispersing seeds as they bounce along over long distances if unobstructed (Beckie et al. 2016, Eberlein and Fore 1984, Moore et al. 2003).  As a result, kochia has the highest rate of spread of any introduced weed in the western U.S.A. (Forcella 1985).  Some kochia seeds can pass through the rumen of cattle unharmed and can be expected to move about with the cattle and be spread with manure (Blackshaw and Rode 1991).  The seeds also disperse in irrigation water (Kelly and Bruns 1975, Wilson 1980).

Common natural enemies:  Kochia appears to be free of damaging diseases and insect herbivores in North America, although grasshoppers do eat it (Undersander et al 2000).

Palatability: The palatability and nutritional value of kochia for livestock is better than that of some grasses, such as bromegrass, but less than that of alfalfa (Undersander et al. 2000).  Plants contain up to 25% protein, and biotypes have been investigated as forage species on arid saline soils which are not suitable for common forages (Steppuhn et al. 1993, Undersander et al. 2000).  Kochia can be toxic to livestock if it composes more than 50% of the diet for several weeks, particularly if it is fed fresh (Burrows and Tyrl 2006, Friesen et al. 2009).  Note that "forage kochia" [Kochia prostrata(L.) A.J. Scott] is a perennial shrub suitable for forage in western rangeland (Kettle and Davison 1998) and should not be confused with the weedy annual kochia described here.

Note:  Kochia pollen is an important allergen and a common cause of allergic sensitization (Friesen et al. 2009).

References:

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