C.V. Eberlein and ZQ Fore

University of Minnesota, St Paul, Mn

North Dakota State University, Fargo, N.D.

KOCHIA ,also known as Mexican fireweed, burning bush, summer cypress or belvedere, is an annual weed that was introduced to North America as an ornamental. Kochia, which is possibly native to south and eastern Russia, was brought to North America from Europe and grown as an ornamental hedge around gardens, or used for backdrop plantings because of its dense, conical shape and attractive red color in the late fall (Beck 1964; Stevens 1965). Kochia has since escaped from cultivation and developed extensive stands in cultivated fields, along roadsides, and in waste areas throughout much of America.

KOCHIA, a member of the Chenopodiaceae or goosefoot family is a herbaceous dicot which reproduces by seed. Depending on growing conditions, kochia may range in height from 6 inches to more than 6 feet. It is highly variable in form. When grown in competition with other plants, kochia is erect and may grow to 7 feet tall; when grown without competition, it assumes a more bushy habit, typically reaching heights of 3 to 4 feet. Leaves of kochia are linear to narrowly lanceolate in shape, 1 to 2 inches long, alternate, hairy and sessile. Plants from the western U.S. are usually more hairy and have shorter leaves than midwestern plants. Small, green, apetalous flowers are found in clusters in the axils of upper leaves and in terminal spikes. Seeds are about 1/16 inch long, brown with yellow markings, oval, flattened and grooved on each side. A gragile, star-shaped hull may enclose the seed. Kochia typically produces 14,600 seeds per plant. (Stevens, 1932

Bell and Nalewaja (1972) studied floral induction in several selections of kochia and found that kochia is a short day plant. The critical light period at which floral induction occurred varied from 13 td 15 hours among kochia selections. The time from emergence to flowering varied from 57 to 100 days with some of earliest selections capable of producing seed before the harvest of small grains and flax. According to the authors, Kochia in North Dakota has been considered a weed problem in late crops such as sugarbeets and soybeans; however, the potential for early seed production suggests it could become an increasing problem in small grains and flax.

KOCHIA possesses the tumbleweed characteristic, an effective adaptation for seed dispersal. In autumn, an abscission zone develops at the stem base of a kochia plant. Becker (1978) studied the abscission zone in kochia and found that abscission was not related to the development of an abscission layer or to chemical dissolution of pectic materials, but rather to a gradual loss in stem flexibility and increase in brittleness of the abscission zone. He explains that brittleness of the abscission zone and rigidity of the stem are related to the amount and distribution of capillary water in the plant. Capillary water is believed to act as an energy absorbing medium in the plant which increases the ability of the stem and abscission zone to absorb wind-generated forces without tissue injury. However, flexibility and energy absorbing capacity of the stem and abscission zone decrease in the fall as capillary water decreases, and strong winds may result in rupture of the brittle abscission zone tissues. Kochia then tumbles with the wind, dropping seeds along its path.

KOCHIA germinates very early in the spring and seedlings are apparently quite tolerant to frost. Stevens (1965) reported that on April 19, 1953, a temperature of 9 F caused "some but not extensive" damage to kochia seedlings. In laboratory studies, kochia seeds germinated well (76 % or better) over a temperature range of 39 to 106 F. Optimum temperature for germination were reported to be 61 F in one study and alternating temperatures of 59/86 or 68/86 F in other research.

The ability of kochia seeds to germinate early in the spring may lead to control problems. Kochia is susceptible to several broadleaf herbicides when young. However, because of its early germinating characteristic, it may be in an advanced stage of growth at the time of herbicide application, which may result in poor control. On the other hand, delayed seeding may be an effective means of controlling kochia in areas with an adequate growing season.

KOCHIA is common in dry areas throughout the Great Plains and western regions of the U.S. Adaptations, such as its tumbleweed characteristic, drought tolerance, and salt tolerance, have probably helped the spread of kochia to drier areas. Stevens (1965) for example, reported that kochia was relatively rare in cultivated fields in North Dakota in the early 1920s, but during the drought years of the 1930s, spread rapidly and became 'abundant" in fields. A similar rapid increase in kochia populations during the 1930s was also noted by Gates (1941) in Kansas. According to Becker (1978), this increase in kochia population during dry years was repeated in Colorado, and North Dakota in the 1950s, and again in North Dakota and South Dakota during the dry summer of 1976. Becker (1978) suggests that these trends in kochia population may be related to soil moisture stress an the resulting reduced competition from crop plants.

Several characteristics of kochia germination aid its ability to establish under dry conditions. Fvetts and Burnside (1972) studied kochia germination under various moisture stress, salinity and pH conditions. They found that kochia showed good tolerance to moisture stress during germination, with 45% of the stressed seeds still able to germinate at 13.2 bars of osmotic pressure. Kochia seeds were also found to germinate well at salt concentrations as high as 10,000 ppm salt, so kochia seedings should be able to establish in highly saline soils. In addition, kochia has fairly broad tolerance to pH during germination. It was able to germinate 60 % or more over a pH range from 2 to 8. However, as pH was increased from 8 to 10, percent germination dropped rapidly.

Rooting characteristics of kochia also add to its ability to withstand drought. Root studies on plants growing without competition and under favorable moisture conditions showed that at maturity, kochia had a root profile 22 ft wide and over 7 feet deep (Davis et al., 1967) However, a Kansas study conducted in 1956 during a severe drought showed that roots of kochia growing in a sorghum field penetrated vertically to 16 feet (Phillips and Launchbaugh, 1958) When roots were excavated in September, the soil was at or below the permanent wilting percentage from the surface to at least 6 ft. At this time, kochia was still green and continuing limited growth, while the sorghum was dead.

Another interesting characteristic of kochia is the limited longevity of kochia seed in the soil. Seed burial studies in Nebraska (Burnside et al. 1981) showed that kochia germination dropped from 40 % initially to 5 % after one year of burial, and to nearly 0 %after two years of burial. The lack of seed survival in the soil has important ramifications for genetic shifts in kochia populations. If, for example, some biotypes of kochia were susceptible to a given control practice, the tolerance types could replace the susceptible biotypes more rapidly than if kochia seed was long-lived, because, little, if any, seed of the susceptible biotype would survive after only a few years of burial.

And variation in response to herbicides does exist in kochia. Johnson and Wood (1976) found triazine resistant kochia along the Union Pacific Railroad in Idaho, where atrazine has been used for total vegetation control for 13 years. Burnside et al. (1979) also reported that triazine resistant kochia biotype had been found along railroad rights-of-ways in several locations. According to LeBaron and Gressel (1982) infestations of trazine resistant kochia now extend along several railroad lines in at least 11 states. Research by Salhoff and Martin (1980) showed that triazine resistant kochia biotypes were more susceptible to contro with 2,4-D ester than triazine susceptible biotypes. The triazine resistant biotypes were also less competitive for light and nutrients than triazine susceptible biotypes.

Bell and Nalewaja (1972) found variation among kochia selections in tolerance to 2,4-D and Banvel (dicamba), with some selections much more tolerance to 2,4-D or Banvel than others. The response of a give selection to 2,4-D was generally independent of the response to Banvel, though some selections responded similarly to both herbicides. In general then, if the continuous use of 2,4-D resulted in a more 2,4-D tolerant kochia population, the population would not necessarily be more Banvel tolerant. Rotating herbicides would reduce the possibility of an increase in the proportions of plants tolerant to 2,4-D or Banvel.