Kochia Description : Cotyledons of kochia seedlings are stalkless, elliptical, 0.18 inch long by 0.1 inch wide and softly hairy, with dull green upper surfaces and sometimes bold pink or Managing Kochia Kochia ( Kochia scoparia ), also known as summer cypress and burning bush, is a weed on the increase in parts of Manitoba, particularly in the southwest region of the province. It Kochia Mature kochia plant growth above the wheat canopy near time of harvest in Colorado. Photo credit: Eric Westra, Colorado State University. Biology Weed biology often informs
Description: Cotyledons of kochia seedlings are stalkless, elliptical, 0.18 inch long by 0.1 inch wide and softly hairy, with dull green upper surfaces and sometimes bold pink or magenta on the underside. Stems are hairy and green to reddish in color. Young leaves are lanceolate 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 feet tall, pyramidal to round, and bushy, with a soft, airy texture. Plants look blue to gray-green during the growing 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 inches long by 0.13–0.25 inch 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 inch-long flowers occur singly or in clusters of two to six in leaf axils of the upper stems or in short spikes with long, white hairs and a 0.13–0.5 inch-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 inch, 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 inch-long, linear leaves. Common lambsquarters (Chenopodium album L.) has broader, diamond-shaped leaves and is a hairless species with a white or pink-dusted leaf surface, especially when the plant is young.
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. 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. 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. Avoid uncompetitive crops such as flax or beans. 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. Yellow sweetclover significantly reduced kochia population when grown as a green manure fallow in Alberta.
Kochia is more abundant in no-till than in conventional-tillage systems, in part because of its ability to germinate in cool soil associated with crop residue at the soil surface. Management including carefully targeted tillage operations were most effective for reducing kochia populations. 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. 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. Cool-season crops like wheat, however, will compete better with kochia, a warm-season weed, when planted during the cool weather of spring.
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’s three-leaf stage gave 66% and 62% control of kochia, respectively. Spike tooth harrowing at both the three- and five-leaf stage increased control to 82%, but a second tine weeding at the five-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. 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. This indicates that many of the early maturing seeds could be captured during combine harvesting of grain and, with prompt cleanup of the field after harvest, could prevent further seed production that year. Plants remaining after grain harvest can produce many seeds, so destroy kochia re-growth before the first killing frost. Avoid irrigation practices that increase soil salinity, as this will favor kochia relative to crops. After a field has been cleaned up, a snow fence can prevent the majority of mature plants from rolling in from adjacent infested areas.
Origin and distribution: Kochia is native to eastern Europe and western Asia. It occurs throughout southern Canada and the United States except parts of the Southeast, but it is particularly a problem in the Great Plains and Intermountain 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.
Seed weight: Population mean seed weights vary from 0.2–0.85 mg.
Dormancy and germination: Kochia seeds have little dormancy and germinate greater than 75% at temperatures from 41–95°F, but germination is inhibited at 104°F. Alternating temperature does not enhance germination. Germination is very rapid, with seedlings commonly breaking through the seed coat within 24 hours at 68–77°F. Light is not required for germination. 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 parts per million salt. High salt conditions reduce germination less at high temperatures than at low ones. Kochia can germinate at a wide range of pH from 2–12.
Seed longevity: Most kochia seeds either germinate or die in their first year. In undisturbed soil, up to 3% can survive two to three years when buried at 12 inches, but survival is much poorer near the soil surface. In the western United States 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. Seed placement from the soil surface to a depth of 4 inches had little effect on seed mortality in these experiments.
Season of emergence: Most seedlings emerge early in spring, but some emerge later following rains. In Colorado, for example, 80% of seedlings emerged between April 11 and June 20, with emergence commencing when the average daily air temperature was 49°F, a finding consistent with research showing emergence commencing when the soil temperature reached 50°F. Populations from several Great Plains states had different emergence patterns, suggesting different emergence biotypes that would require location-specific management tactics. Post-emergence herbicides have selected for late emerging biotypes.
Emergence depth: Seedlings emerge best from the top 0.4 inch, and few emerge from deeper than 0.8 inch. Seedlings establish better from seeds on the soil surface than at 0.1 inch.
Photosynthetic pathway: C4
Sensitivity to frost: Seedlings in spring have tolerated a nighttime temperature of 9°F, but six-week-old plants that were cold acclimated for three weeks did not survive 18 hours at temperatures of 22°F or lower.
Drought tolerance: Kochia is very drought tolerant, and historically infestations have tended to increase during drought periods to the exclusion of other weed species. Drought tolerance is partially due to an extensive root system; under favorable moisture conditions the roots penetrate 7 feet, and under drought conditions they can penetrate up to 16 feet. Kochia is less drought tolerant under high-salt soil conditions.
Mycorrhiza: Kochia is not mycorrhizal.
Response to fertility: Kochia is highly responsive to N, and its productivity continues to increase up to very high N application rates (480 pounds per acre). Plants can absorb up to 90% of available soil nitrogen. 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. High soil P levels will suppress growth.
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.
Response to shade: Compared with cropped sunflowers, kochia is relatively intolerant of shade.
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. Plants that are cut off by a combine produce many seeds that remain in place since the truncated plant does not break off and tumble.
Time from emergence to reproduction: Kochia plants flower 57–109 days after emergence. It flowers in response to decreasing day length, with shorter light periods and longer times from emergence required for more southerly populations (e.g., New Mexico as compared to South Dakota).
Pollination: Kochia commonly self-pollinates but has a moderate rate of outcrossing by wind and bee dispersed pollen.
Reproduction: Kochia typically produces 10,000–30,000 seeds per plant, with the potential for up to 100,000 seeds per plant. Greater than 99.9% of seeds are retained on plants at wheat harvest, suggesting the potential for removal and destruction of seeds at harvest. However, plants re-growing following combine harvest of grain can produce 2,600–4,000 seeds each.
Dispersal: Mature kochia break off near the base of the stem and roll as tumbleweeds, dispersing seeds as they bounce along over long distances if unobstructed. As a result, kochia has the highest rate of spread of any introduced weed in the western United States. 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. The seeds also disperse in irrigation water.
Common natural enemies: Kochia appears to be free of damaging diseases and insect herbivores in North America, although grasshoppers do eat it.
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. 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. Kochia can be toxic to livestock if it composes more than 50% of the diet for several weeks, particularly if it is fed fresh. Note that “forage kochia” [Bassia prostrata (L.) A.J. Scott] is a perennial shrub suitable for forage in western rangeland 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.
Weed Characteristics Summary Table
|Growth habit||Seed weight (mg)||Seed dormancy at shedding||Factors breaking dormancy||Optimum temperature for germination (F)||Seed mortality in untilled soil (%/year)||Seed mortality in tilled soil (%/year)||Typical emergence season||Optimum emergence depth (inches)|
|Photosynthesis type||Frost tolerance||Drought tolerance||Mycorrhiza||Response to nutrients||Emergence to flowering (weeks)||Flowering to viable seed (weeks)||Pollination||Typical & high seed production (seeds per plant)|
|C4||moderate||high||no||high||8–16||–||self, can cross||20,000 & 100,000|
General: The designation “–” signifies that data is not available or the category is not applicable.
Growth habit: A two-word description; the first word indicates relative height (tall, medium, short, prostrate) and second word indicates degree of branching (erect, branching, vining).
Seed weight: Range of reported values in units of “mg per seed.”
Seed dormancy at shedding: “Yes” if most seeds are dormant when shed, “Variable” if dormancy is highly variable, “No” if most seeds are not dormant.
Factors breaking dormancy: The principle factors that are reported to break dormancy and facilitate germination. The order of listing does not imply order of importance. Abbreviations are:
scd = seed coat deterioration
cms = a period subjected to cold, moist soil conditions
wst = warm soil temperatures
at = alternating day-night temperatures
Optimum temperature range for germination: Temperature (Fahrenheit) range that provides for optimum germination of non-dormant seeds. Germination at lower percentages can occur outside of this range. The dash refers to temperature range, and the slash refers to alternating day/night temperature amplitudes.
Seed mortality in untilled soil: Range of mortality estimates (percentage of seed mortality in one year) for buried seeds in untilled soil. Values were chosen where possible for seeds placed at depths below the emergence depth for the species and left undisturbed until assessment. Mortality primarily represents seed deterioration in soil.
Seed mortality in tilled soil: Range of mortality estimates (percentage of seed mortality in one year) for seeds in tilled soil. Values were chosen for seeds placed within the tillage depth and subjected to at least annual tillage events. Seed losses are the result of dormancy-breaking cues induced by tillage, germination and deterioration of un-germinated seeds.
Typical emergence season: Time of year when most emergence occurs in the typical regions of occurrence for each weed. Some emergence may occur outside of this range.
Optimum emergence depth: Soil depths (in inches below the soil surface) from which most seedlings emerge. Lower rates of emergence usually will occur at depths just above or just below this range.
Photosynthesis type: Codes “C3” or “C4” refer to the metabolic pathway for fixing carbon dioxide during photosynthesis. Generally, C3 plants function better in cooler seasons or environments and C4 plants function better in warmer seasons or environments.
Frost tolerance: Relative tolerance of plants to freezing temperatures (high, moderate, low).
Drought tolerance: Relative tolerance of plants to drought (high, moderate, low).
Mycorrhiza: Presence of mycorrhizal fungi. “Yes” if present; “no” if documented not to be present, “unclear” if there are reports of both presence and absence; “variable” if the weed can function either with or without, depending on the soil environment.
Response to nutrients: Relative plant growth response to the nutrient content of soil, primarily N, P, K (high, moderate, low).
Emergence to flowering: Length of time (weeks) after emergence for plants to begin flowering given typical emergence in the region of occurrence. For species emerging in fall, “emergence to flowering” means time from resumption of growth in spring to first flowering.
Flowering to viable seed: Length of time (weeks) after flowering for seeds to become viable.
Pollination: “Self” refers to species that exclusively self-pollinate, “cross” refers to species that exclusively cross-pollinate, “self, can cross” refer to species that primarily self-pollinate, but also cross-pollinate at a low rate, and “both” refers to species that both self-pollinate and cross-pollinate at relatively similar rates.
Typical and high seed production potential: The first value is seed production (seeds per plant) under typical conditions with crop and weed competition. The second value, high seed production, refers to conditions of low density without crop competition. Numbers are rounded off to a magnitude that is representative of often highly variable reported values.
Eberlein, C.V. and Z.Q. Fore. 1984. Kochia biology. Weeds Today 15: 5–7.
Friesen, L.F., H.J. Beckie, S.I. Warwick and R.C. Van Acker. 2009. The biology of Canadian weeds. 138. Kochia scoparia (L.) Schrad. Canadian Journal of Plant Science 89: 141–167.
Moore, J., J. Dodd, S. Lloyd, C. Hanson, T. Grice and J. Thorpe. 2003. Kochia (Bassia scoparia). Weed Management Guide.
Petrosino, J.S., J.A. Dille, J.D. Holman and K.L. Roozeboom. 2015. Kochia suppression with cover crops in southwestern Kansas. Crop, Forage & Turfgrass Management 1(1): 1–8.
Schwinghammer, T.D. and R.C. Van Acker. 2008. Emergence timing and persistence of kochia (Kochia scoparia). Weed Science 56: 37–41.
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Kochia (Kochia scoparia), also known as summer cypress and burning bush, is a weed on the increase in parts of Manitoba, particularly in the southwest region of the province. It is a weed native to Asia and central Europe, and was introduced to Canada as an ornamental planting by European immigrants. It can be difficult to manage, mostly because of its ability to spread and quickly establish itself as a major weed, particularly during drought years.
A provincial weed survey conducted in 1997 ranked kochia as the 14 th most abundant weed in southwest Manitoba, an increase from the 26 th position where it was ranked in a 1986 survey. It was ranked 24 th and 30 th in the central and northwest regions, respectively, in 1997. Kochia was not observed in the eastern or interlake regions of the 1997 weed survey. Although not a predominant weed throughout Manitoba, it is a serious problem in the southwest region and in localized areas of central Manitoba, particularly on saline soils.
Kochia is a summer annual broadleaf weed that reproduces only by seed. Depending on growing conditions, it may range in height from 6 inches to 6 feet. When grown in competition with other plants, it grows upright and may reach 6 feet in height. When competition is absent it is bushy in nature, typically reaching heights of 3 to 4 feet.
The undersides of kochia cotyledons on seedlings are usually bright pink in colour. Adult kochia plants have many branches with stems that are often red-tinged. There are numerous, hairy, pale green leaves with an alternate arrangement and tapered to points at the tips. The leaves often turn purplish-red in the fall. Flowers are small and green and found in clusters in the axils of upper leaves and on short, dense spikes. Kochia seeds are nearly oval, 1.5 to 2.0 mm long, flattened with a groove on each side and dull brown in colour with yellow markings. Normally, kochia seeds are not threshed out but are enclosed in a chaffy, paper-like “hull”.
Kochia Germination And Growth
Kochia seeds are short lived in the soil, with most of the seeds dying after one year. Therefore, most kochia problems result from plants that set seed the previous year. Kochia germinates in the early spring and is quite tolerant of frost. Because of its early germination, it is often in advanced stages of growth when other broadleaf weeds are ready to spray. Although kochia mainly germinates in the early spring, additional flushes can germinate throughout the growing season making it difficult to control.
Kochia is tolerant of drought and saline soils, and does well under growing conditions considered poor for most crops. It is quick to invade and establish itself on saline spots within fields. Under drought conditions, kochia roots can penetrate to a depth of 10 feet or more in the soil. Its extensive root system explains its ability to withstand drought and also explains why kochia is a predominant weed during drought years.
Kochia is a competitive weed. Kochia densities of 21 plants per m 2 have caused yield losses in wheat of approximately 33%, while extreme infestations of 195 plants per m 2 have reduced wheat yields by 73%.
Kochia seed production ranges from 15,000 to 25,000 seeds per plant. Kochia is often referred to as a “tumbleweed” because the stem breaks off at the base of the plant in the fall allowing it to roll across fields like a large ball, which is an important way of spreading its seeds.
Kochia As Feed
Kochia has been used as a livestock feed during feed shortages resulting from drought. As a forage crop, kochia is noteworthy because it has good drought tolerance, salinity tolerance, good leafiness, high yields, and has high protein and carbohydrate content.
Kochia can, however, be harmful or toxic to cattle if it comprises a large portion of the diet. It contains a number of toxic substances including saponins, alkaloids, oxalates and nitrates. Animals that consume large amounts of the weed may exhibit a range of health problems and have lower rates of gain. Therefore, no more than 50 percent of the ration should consist of kochia.
Kochia is considered a noxious weed in Manitoba, and preventing kochia seed set and spread are important aspects of the Noxious Weeds Act. This must be considered if using kochia as feed or when buying hay with kochia mixed in it.
Management of Kochia
Planting crop seed free of kochia will help prevent its introduction and keep kochia populations in check. Kochia falls within class 6, ‘other weed seeds’ of the Canada Seeds Act. This means that even certified crop seed may legally have some kochia seed in it, so be sure to check your seed source if kochia is a concern.
As kochia germinates early in the spring, delayed seeding and pre-seeding tillage or pre-seeding herbicides will help reduce in-crop weed densities. Crop rotations that use a combination of early and late sown crops and alternating seeding dates on individual fields will help keep kochia populations in check. Because the majority of kochia seeds don’t live for more than one year, preventing seed production for a single year will help reduce kochia problems. Mowing or cutting for feed are effective ways of controlling kochia seed production, as long as the plants have not yet set seed.
A recent weed survey comparing zero and conventional tillage crop production systems shows that zero tillage could be an important tool for kochia management. Average kochia densities were 16.3 plants per m 2 in conventional till fields and only 0.4 plants per m 2 in zero till fields. Kochia is a shallow germinator and prefers drier, warmer soils which may explain why lower densities were found in the cool, moist soils of zero till fields. Refer to the factsheet “Weed Management – Comparing Zero and Conventional Tillage” for more information.
Fall tillage for kochia control is usually not necessary as kochia is a spring germinator and seedlings do not survive the winter, but it may be important for controlling escaped plants or late germinating weeds that are about to set seed.
A number of herbicides are registered for control of kochia. The key to success with most of these products is to spray early. Remember that kochia is one of the first weeds to emerge in the spring and is usually well advanced by the time other broadleaf weeds are ready to spray. Choose a herbicide that provides the widest possible window of application for kochia and the other weeds in your field. Good spray coverage is important for heavy infestations of kochia, especially when using contact herbicides.
Preharvest glyphosate (Roundup, Touchdown) treatments may be effective if kochia has set seed but is not yet mature. Immature seed will absorb glyphosate which can affect kochia seed viability. Usually, however, preharvest glyphosate is economical only if perennial weeds are present, as most field crops are normally cut before kochia seeds become mature and viable. Similarly, post-harvest herbicide treatments are not likely to be worthwhile unless other weeds are present or kochia is about to set seed.
Herbicide Resistance In Kochia
Kochia resistance to Group 2 herbicides exists in Manitoba. Group 2 herbicides include products such as Refine Extra, Ally, Pursuit, and Odyssey (refer to tables for additional Group 2 products). Herbicide resistance in kochia developed on fields where there was repeated use of Group 2 herbicides over several seasons.
A small number of resistant populations were identified in the early 1990’s, but there has been little work to determine the spread of kochia since. It is possible that herbicide resistance in kochia has spread and is a more serious problem than it was at the beginning of the 1990s.
The best way of delaying resistance development in kochia is to rotate broadleaf herbicides. It is important that the same Group of herbicides is not used more frequently than one year in three on the same field. There are a number of broadleaf herbicides from different Groups that can be used for control of kochia (refer to tables). Herbicide rotation should be used as part of a long term, integrated weed management strategy (refer to the publication “Integrated Weed Management – Making it Work on Your Farm” for more information).
If you notice patches of kochia in your field, and you sprayed under good growing conditions at the correct weed stage using full recommended herbicide rates, consider collecting some kochia seed for herbicide resistance testing. At present, Ag Quest based out of Minto, Manitoba offers commercial herbicide resistance testing.
A Plan For Kochia
Consider the following points as you develop your kochia management strategy:
Mature kochia plant growth above the wheat canopy near time of harvest in Colorado. Photo credit: Eric Westra, Colorado State University.
Weed biology often informs management decisions. Weed management practices that disrupt the weed’s life cycle by targeting weak points will result in better weed control. The biology of kochia is particularly problematic because of its ability to emerge in early-spring, grow rapidly, and tolerate heat, drought, and saline soil conditions. The spread of kochia, including widespread herbicide-resistant biotypes, is facilitated by obligate outcrossing and tumbleweed physical seed dispersal mechanisms. Small emerging kochia seedlings have leaves that are densely covered in small, fine, white hairs in what is commonly referred to as the button stage. Herbicide applications during button stage are discouraged (as often stated on herbicide label) as leaf hairs can reduce foliar absorption of herbicides by suspending droplets above the leaf cuticle on the leaf hairs.
Around two weeks after seedling emergence, leaf hair density decreases as leaves grow. After the button stage, kochia leaves maintain fine leaf hairs on the bottom of the leaf, while leaf tops are smooth. It is common to see high seedling densities, especially around the location where the parent plant was growing before detaching from the soil when mature. This is often referred to as a “kochia mat.”
Kochia leaves are alternate with simple blades that are highly pubescent and arise on erect, highly branched stems. Kochia flowers are inconspicuous without petals, and on a given flower the stigmas emerge prior to anther development which facilitates cross pollination between plants. Flowers develop in clusters in the axils of upper leaves and in terminal spikes. Seeds are around 1.5 mm long and develop in star shaped fruit that are brown and flattened. Kochia has a shallow taproot which can be easily pulled or hoed out at early growth stages. Once fully matured, an abscission layer near the soil surface allows for whole plants to detach and bounce across the landscape dropping seed in a wind-driven process known as ‘Tumble mechanism’.
Kochia is a summer annual broadleaf weed species native to Eurasia and was introduced to the Americas as an ornamental in the mid to late 1800s by European immigrants. Ornamental kochia escaped cultivation and formed naturalized populations that now occur throughout most of the continent, especially in arid and semiarid environments. The ability to grow in dry, saline soils has led to adaptation and widespread distribution of kochia in the arid west and semi-arid Great Plains.
Kochia growth and architecture is highly influenced by inter and intraspecific competition. When growing with competing vegetation, growth is more erect, single stemmed and taller; when growing in the absence of competing vegetation, it is more bushy and multi-branched with a larger plant diameter. In moderately dense kochia stands that promote erect, taller primary axis growth, plants can get over six feet tall. While in low competition environments high light intensity suppresses apical dominance and lateral growth resulting in plants typically around three feet tall with oval growth forms and a diameter similar to its height.
Where is kochia a problem?
Kochia is common in rangeland, pastures, and crop production systems where it has adapted and thrives in semiarid to arid regions of North America. It is also commonly found along roadsides, ditch banks, railroad tracks, and in other disturbed sites as a ruderal species. Kochia is competitive in cropping systems due to its ability to germinate and emerge early at low soil temperatures, grow rapidly, and tolerate heat, drought, and saline soil conditions. In areas at high risk of saline seep development, dense kochia patches are a common indicator of increasing soil salinity in crop fields. With further herbicide-resistance development, kochia is becoming more problematic in chemical-fallow fields.
What is the emergence pattern of kochia?
Kochia has a wide window of emergence due to the unique ability to germinate at low temperatures as early as January and continue to emerge throughout the summer into July. High seedling emergence in early spring and continued emergence into mid or late-summer means kochia must be managed from early spring through late summer. Kochia seed does not generally exhibit innate dormancy so mature seeds are readily germinable and will germinate rapidly under favorable conditions, prolonging the emergence period.
What is the lifecycle of a kochia plant like?
Kochia can germinate in low temperatures early in the spring with emergence extending into July. Kochia will grow vegetative throughout the spring and summer before flowering; it can produce copious amounts of pollen. In the fall, fully senesced mature kochia plants will detach at the soil surface and tumble across the landscape, dropping seeds with each impact, in a wind-driven process that spreads seeds long distances.
Figure adapted from Loux et al. 2006. Photo credit: Eric P. Westra and Phillip Westra (Kochia streak picture), Colorado State University.
How does kochia spread?
Kochia physically spreads seeds via a tumbling mechanism where the senesced (mature) plant’s stem breaks at the soil surface, which allows the plant to roll across the landscape in the fall dropping seed along the way in a wind-driven process. Studies have shown that kochia tumbleweeds can move up to 3,280 feet (plants were stopped at fence line at this distance), and pollen from kochia can move up to 315 feet, allowing for the rapid physical spread and genetic exchange between individuals.
How many seeds can kochia produce and how long can those seeds survive?
Kochia is a prolific seed producer. Seed production per plant can vary widely depending on stand density and the extent of intra- and interspecific competition. Seed production of field-grown kochia has been shown to range from 2,000 to 30,000 seeds per plant, with an average of around 14,000 seeds per plant. More recent evaluations of seed production from kochia growing in sugarbeets have shown that individual kochia plants can produce over 100,000 seeds per plant. Kochia seed is relatively short lived in the soil with a mean seed bank longevity of 1-2 years. Kochia seedlings typically cannot emerge from greater than two inches deep in the soil.
What other biological weaknesses does kochia have that can be targeted with management techniques?
The weakest points in a kochia plant’s life cycle are the seed and seedling growth stage. The seeds are short-lived and germinate rapidly under favorable conditions in the top two inches of the soil. Management efforts should focus on suppressing weed seed germination and seedling emergence through strategic tillage, preemergence (PRE) herbicides, and competitive crops. The wind-driven tumbleweed dispersal mechanism allows the use of fence lines or physical barriers to minimize the movement of kochia between fields, although an extensive build up of kochia tumbleweeds on fences can occur. Planting a few rows of a stiff stemmed crop like corn or sorghum along field borders of the prevailing winds can help prevent kochia tumbleweeds from dispersing their seeds in the field. An unharvested strip of small grains can be left as a kochia barrier, too, though it is not as effective as corn.
This graph shows documented cases of herbicide-resistant kochia in the US that have been reported to the International Herbicide-Resistant Weed Database, www.weedscience.org. Both resistance to a single herbicide group, as well as resistance to multiple herbicide groups, are displayed. Contact your local extension office for details about resistance in your area and management options.
*Herbicide names listed are representative products that contain specific active ingredients. Last updated on: 8-10-2020
Integrated Weed Management Strategies
Cultural Tactics: Focusing on control of emerged seedlings prior to planting through strategic shallow-tillage (e.g. Undercutter/V-blade) to remove germinated seedlings where acceptable can help manage early emerging kochia. Establishing competitive crops using optimum planting dates, row spacing, seeding rates, and competitive varieties that close their canopy faster can help crops to compete with kochia, especially during early critical weed free periods. Establishing competitive crops such as winter wheat has been shown to reduce kochia biomass in field studies by over 99% compared to treatments without wheat. Mowing kochia closer to flowering has been shown to reduce seed densities the following year by 98% and reduce biomass by 33% compared to a non-mowed control in a surface mining reclamation project. Chemical fallow is commonly used in the high plains, however the development of herbicide-resistance to commonly used fallow herbicides allows for maximum kochia growth and seed production in the absence of plant competition. Kochia that are able to grow in chemical fallow can rapidly spread a resistance trait through both seed and pollen dispersal. Resistance to glyphosate (RoundUp) is commonly seen in chemical fallow with the meandering trails of kochia throughout the field
Cover Crops: Fall-sown cover crops can compete with both late-fall and early-spring emerging kochia to help minimize kochia growth and biomass production. Fall-sown triticale has been shown to reduce kochia densities by 78 to 94% and biomass by 98% compared with kochia in chemical fallow. Because kochia and spring-planted cover crops both germinate at the same time in early spring, spring-planted cover crops are not effective at reducing kochia densities or biomass. This emphasizes the value of fall-sown cover crops for kochia suppression. Fall-sown cover crops that produce the most biomass are most effective at suppressing kochia. However, evaluation of cover crops for weed suppression in semiarid environments has concluded that growing cover crops instead of fallowing is not beneficial if there is insufficient moisture for the subsequent cash crop at planting. However, if adequate precipitation or irrigation is present, cover crops can reduce soil moisture evaporation and help conserve moisture for crop establishment.
Mechanical: Early spring tillage prior to crop planting provides good control of early emerging seedlings. Less intensive, shallower ridge tillage has been shown to increase kochia densities up to 50 fold, which can be used to promote spring germination and emergence for subsequent control. If herbicide resistance becomes a major issue in a given field, strategic deep tillage (e.g. moldboard plowing) (> every five years) can help reduce population numbers by inverting the soil and burying kochia to a depth where it is no longer able to germinate or remain viable (since average viability is two years). Studies have shown that preplant plowing can reduce kochia densities by 4.5 and 45 fold compared to disk or ridge tillage, respectively, showing the impact of burying kochia more than two inches deep. Mowing kochia before or during flowering is an effective strategy to reduce seed production. However, regrowth can occur which may require repeated mowing depending on time of year.
Chemical: Kochia has evolved resistance to several different herbicide modes of action (MOAs) (resistance to multiple MOAs within populations has been documented) which limits the use of those herbicide groups on certain populations. It is necessary to know if resistance to certain MOAs is present in a given population to formulate a successful herbicide program.
Chemical-fallow control of kochia is often where herbicide resistance, especially to glyphosate, is observed. Herbicide resistant populations are readily visible, with meandering trails of individuals (resistant progeny seed dropped as the parent plant tumbles across a field in the fall) surviving chemical applications in fallow fields. With increased glyphosate-resistant kochia in fallow, alternative auxin herbicides such as dicamba (Clarity) or fluroxypyr (Starane Ultra) are commonly used. However, resistance is continuing to evolve to these herbicides as selection pressure switches from glyphosate to auxin herbicides.
Whether entering a fallow or cropping rotation, starting clean by removing weeds and planting into weed-free fields is critical to minimize weed competition for resources. Burndown products that contain glyphosate (RoundUp), glufosinate (Liberty), or paraquat (Gramoxone) are effective at controlling smaller emerged kochia prior to planting or entering a fallow period. Diversifying weed management strategies for kochia are essential to preserve and extend the longevity of currently effective chemical control methods.
Within crops there are many PRE and POST herbicide options available for kochia control, however, herbicide resistance present at the field level will dictate efficacy of these products. Herbicide applications to kochia should be avoided during the early button stage due to dense leaf hairs that can reduce foliar adsorption. Reducing seed germination with PRE herbicides, as well as targeting smaller, more vulnerable kochia seedlings, should be the focus of chemical control programs.
Herbicide resistance to group 2 (ALS), group 9 (EPSPS-inhibitor on the plot), group 5 (PSII), and group 4 (Synthetic Auxins) has resulted in a need to start clean with PRE herbicides as the foundation for kochia control programs. Examples include products that contain pyroxasulfone (Zidua) or s-metolachlor (Dual II Magnum), sulfentrazone (Spartan), HPPD-inhibitors (eg isoxaflutole or mesotrione), metribuzin (Sencor), saflufenacil (Sharpen), dicamba (PRE), and atrazine (depending on if triazine resistance is present) or combinations of above. Postemergence herbicides that contain glyphosate (RoundUp), glufosinate (Liberty), dicamba, fluroxypyr (Starane Ultra), mesotrione (Callisto), tembotrione (Laudis), bromoxynil (Buctril), pyrasulfotole, atrazine, or combinations of the above, are effective at controlling susceptible kochia populations in various crops or fallow. Diversifying chemical control tactics and targeting smaller, more vulnerable growth stages can help reduce herbicide resistance development in kochia.
Biological: There are currently no biological control agents for kochia. Kochia is so ubiquitous that biological control is not a realistic option.