Northwest Conservation Tillage Handbook Series No. 17
Chapter 5 - Weed Control Strategies, December 1999
Water Use and Growth of Russian Thistle
After Wheat Harvest
William Schillinger, research agronomist, Department of Crop and Soil
Sciences, Washington State University, Lind; Frank Young, research agronomist,
USDA-Agricultural Research Service, Pullman; Harry Schafer, research technician,
Department of Crop and Soil Sciences, WSU, Lind; Larry McGrew, research
technician, USDA-Agricultural Research Service, Pullman.
Russian thistle (Salsola
iberica Sennen and Pau) is a major broadleaf weed in dryland crops (less
than 12 inch annual precipitation) in the Pacific Northwest of the USA.
Russian thistle frequently infests wheat (Triticum aestivum L.) and other
spring-sown crops, especially during drought. Quantitative information
on water use, biomass accumulation, and seed production of Russian thistle
after wheat harvest is lacking. In a 2-yr field study at Lind, Washington,
Russian thistle plants were allowed to grow yearly in spring wheat in
a grid pattern without competition from other weeds. Individual Russian
thistle plants used 20 gallons of soil water while growing with the crop.
From wheat harvest in early August until killing frost in late October,
each Russian thistle used an additional 27 gallons of soil water. Water
use occurred within a 5-ft radius of the Russian thistle. Spring wheat
competed with Russian thistle for water at shallow soil depths; most water
use by Russian thistle was from deeper than 1.0 m. Russian thistle dry
weight increased from 0.4 to 2.8 lbs per plant between grain harvest and
killing frost. Russian thistle seeds were either not produced or germinable
until mid-September. By late October, individual plants had produced 67,000
and 25,000 seeds in 1996 and 1997, respectively. Water recharge into the
soil was reduced near Russian thistle after a winter of high precipitation
where water infiltration occurred to depths greater than 3 ft, but was
not affected the next year when winter precipitation was close to the
long-term average. In low crop residue situations, rapid post-harvest
growth by Russian thistle (before seed production) provides valuable surface
cover for erosion control, but with the prospect that soil water may be
reduced for the subsequent crop.
Russian thistle is
a summer annual weed which has long plagued crop production in arid and
semiarid regions of the western United States and Canada (Dewey, 1893).
It is the dominant broadleaf weed in the 3.5 million acre dryland (6 to
12 inch annual precipitation) crop production region of the inland Pacific
Northwest. The traditional cropping system is winter wheat with tillage-intensive
fallow in alternate years. Drawbacks to the wheat-fallow system include:
1) recurrent wind and water erosion (Papendick, 1998), 2) decline in soil
organic matter due to carbon loss by biological oxidation exceeding carbon
input from residue (Rasmussen and Parton, 1994), and 3) inefficient storage
of precipitation in the soil during the spring-summer of the fallow cycle
and the fall-winter of the crop cycle (Ramig and Ekin, 1991). Consequently,
many growers in this dryland region are increasing the intensity of spring
cereal cropping (i.e., decreasing the frequency of fallow) and reducing
or eliminating tillage.
Russian thistle presents
a formidable obstacle to successful dryland spring cropping. Spring wheat
and spring barley (Hordeum vulgare L.) have less early growth and slower
canopy closure compared with winter wheat which grows vigorously in early
spring. Infestation is most severe when crop competition is reduced by
poor stands, drought, inadequate fertility, and late growth. Russian thistle
seedlings first emerge in March or April, flower in June, and produce
seed beginning in August. Grain yield of spring cereals may be reduced
by 50% or more in severe infestations (Young, 1988). Grain quality is
also diminished when green Russian thistle biomass and seed contaminate
it and increase moisture (Holm et al., 1997). Russian thistle also infests
broadleaf crops which are needed to diversify the present cereal-only
cropping system. Herbicides for Russian thistle control in broadleaf crops
are either not labeled, have rotational restrictions, or require incorporation
and, therefore, are not compatible with no-till systems.
The root system of
Russian thistle can extend 6 ft deep and 16 ft in diameter (Holm et al.,
1997). Russian thistle is C4 plant with high water use efficiency (Dwyer
and Wolde-Yohannis, 1972). When not controlled, mature plants dislodged
from the soil by wind, decay, or tillage can scatter seed over several
miles (Stallings et al., 1995). Growers typically either till with V-shaped
sweeps or use herbicides for post-harvest Russian thistle control before
the onset of seed production. Sweep tillage cuts the Russian thistle roots,
but also buries some crop residue, and severed Russian thistle (tumble
weeds) blow away. This is a concern in low-residue situations where Russian
thistle stands have often produced more dry biomass than the crop by time
of grain harvest in late July-early August (Schillinger et al., 1999).
Therefore, dead Russian thistle may be an important source of surface
cover for erosion control, especially if beginning a 13-mo-long fallow
cycle. In addition, increased quantities of residue enhance over-winter
water storage (Papendick and Miller, 1977). When post-harvest control
is with herbicides, Russian thistle generally remain anchored in the soil
or trapped by standing stubble or snow.
For growers to convert
from traditional winter wheat-fallow to more intensive farming involving
spring crops, further understanding of the ecology and management of Russian
thistle is needed. The objective of this study was to determine the effects
of individual Russian thistle plants when allowed to grow uncontrolled
in spring wheat and after crop harvest on: i) the extent and pattern of
soil water extraction and impact on over-winter soil water content, ii)
post-harvest Russian thistle dry biomass accumulation and, iii) timing
and magnitude of Russian thistle seed production.
and Field Layout - A 2-year field study was conducted from
February 1996 to March 1998 at the Washington State University Dryland
Research Station at Lind, WA. The soil is a deep (more than 6 ft to bedrock)
Shano silt loam. Average annual precipitation is 9.61 inches, which is
less than any other state or federal non-irrigated crop research facility
in the United States.
In late February
of 1996 and 1997, 12 oz. glyphosate (Roundup) was applied (in stubble)
to control winter annual grass weeds and volunteer wheat before planting
spring wheat. Plots were tilled with a duck-foot cultivator with an attached
4-bar harrow, and fertilized with a Solution 32 blend of 50 lbs N, 16
lbs P, and 10 lbs S per acre. In mid-March of each year, hard red spring
wheat (cv. Butte 86) was sown at 70 lbs per acre with a double-disc drill
in 6-inch-wide rows. When wheat tillered in mid-to-late April, paper cups
were placed over 100 juvenile Russian thistle in a 20 x 20-ft grid (one
plant every 400 square feet). Unprotected Russian thistle were killed
with 12 oz./acre of bromoxynil. Russian thistle that germinated later
were removed by hand. Wheat was harvested with a combine cutting 12 inches
above the ground on 1 August both years. About 20% of total Russian thistle
green biomass was removed from the top of each of the 100 plants during
Use - Within 2 days after wheat harvest, aluminum access
tubes were installed at distances of 1, 2, 3, 5, and 10 feet from the
base of individual Russian thistle plants. The experimental design was
a randomized complete block with 6 replications (i.e., individual Russian
thistle plants), with each block containing the set of 5 access tubes.
The access tube located 10 ft from each plant was the control treatment
from which we assumed no water extraction by Russian thistle would occur.
At about 13-day intervals
from the first week of August until after killing frost in late October,
soil volumetric water content was measured in 6-inch increments to a depth
of 6 ft by neutron attenuation (Gardner, 1986). Overall mean water use
by the six individual Russian thistle on each sampling date was determined
by summing water depletion for each distance (compared with the control
treatment located 10 ft from each target Russian thistle) and using conversion
factors to calculate the surface area represented by the respective access
tubes. Neutron access tubes located 1, 2, 3, and 5 ft from individual
Russian thistle plants represented surface areas of 7 ft2, 13 ft2, 19
ft2, and 40 ft2, respectively (79 ft2 collectively). Access tubes remained
in place over the winter, until soil water recharge was measured in late
February or in March of the following year.
An analysis of variance
(ANOVA) was conducted for soil water on every measurement date for each
6-inch depth increment as well as the entire 6 ft soil profile. Treatments
were considered significantly different at P < 0.05. Treatment means
for all ANOVA in this study were separated using Fisher's protected least
Use - At spring wheat harvest on 1 August in 1996 and 1997,
individual Russian thistle plants had already used 19 gallons or more
water (Fig. 1). Spring wheat competed with Russian thistle for water at
shallow soil depths, as evidenced by no differences in soil water content
among access tube treatments in early August until depths of 2.5 ft in
1996 and 4 ft in 1997 (data not shown). However, Russian thistle had already
depleted soil water below these depths at harvest. These data agree with
scanner rhizotron root observations in a separate study at Lind in 1997
showing prolific lateral rooting of Russian thistle at soil depths of
2 ft and below (W.L. Pan, unpublished data).
Measured water extraction
by Russian thistle was always greatest closest to the plant and decreased
proportionate to distance from the plant on all August-to-October sampling
dates during both years (data not shown). Whereas spring wheat extracts
water relatively inefficiently from soil depths deeper than 4 ft, Russian
thistle aggressively reduced soil water content at 1 ft from the plant
to 5% by volume throughout the entire 6 ft profile in 1996 and to a depth
of 4.5 ft in 1998 (data not shown). Individual Russian thistle did not
extract water beyond a 5-ft radius of the base of the plant, as there
were no significant water differences at any depth or on any sampling
date between measurements obtained 5 ft and 10 ft from the Russian thistle
plants. In both years, Russian thistle depleted soil water until killed
by hard (250F) frost on 23 October in 1996 and 25 October in 1997 (Fig.
1). Individual plants had removed an average of 47 gallons of residual
soil water by late October (Fig. 1), in addition to most of the August-through-October
precipitation (2.4 inches in 1996 and 1.8 inches in 1997). The 47 gallons
amounts to 0.9 inch of soil water from within the 79 ft2 extraction zone
of each Russian thistle, or 25,000 gallons per acre if plants were uniformly
spaced 10 ft apart. The loss of this quantity of soil water would reduce
grain yield of a subsequent wheat crop by about 6 bushels per acre according
to Leggett (1959).
Fig. 1. Post-harvest
soil water use by undisturbed Russian thistle in spring wheat stubble
from wheat harvest in early August until killing frost in late October
in 1996 and 1997. Within-year means followed by the same letter are not
significantly different at the 5% probability level.
Soil Water Recharge - In the Pacific Northwest, soil water
recharge occurs during fall and winter. Precipitation at Lind between
1 October and 1 March was 9.48 inches in 1996-1997 and 5.51 inches in
1997-1998, compared with the 80-year average of 5.28 inches. Surface soils
were only briefly frozen during both winters, and water did not runoff
from the site either year. After the wet 1996-1997 winter, partial soil
water recharge had occurred to a depth of at least 6 ft and soil water
content in the control treatment 10 ft from the Russian thistle plant
was significantly higher than other treatments (data not shown).
1 October-1 March was close to the long-term average in 1997-1998 and
soil water recharge was much less than in the previous wet winter (data
not shown). Uniform, but meager, water recharge occurred in all treatments
in the top 2.5 ft of soil, but decreased sharply below this depth. There
were no significant differences at any depth or in total profile water
among the treatments in late February 1998. Because Russian thistle extracts
water from below the rooting depth of spring wheat, these data suggest
that soil water storage may not be adversely affected by Russian thistle
during "average" years when over-winter recharge occurs to only
3 ft or less.
Accumulation, Seed Production, and Germination - Dry biomass
of individual Russian thistle plants averaged over 2 years was 0.4 lbs
just after spring wheat harvest but increased rapidly thereafter (Fig.
2). In 1996, dry biomass accumulation peaked by 22 September, but continued
steadily until late October in 1997. During both years, final dry weight
exceeded 2.7 lbs per plant (Fig 2).
Russian thistle did
not produce seed until mid-to-late September in 1996, whereas plants had
already produced some seed at the time of spring wheat harvest in early
August in 1997 (Table 1). Total Russian thistle seed production per plant
in 1996 (58,350) and 1997 (25,070) were much greater than that reported
following spring wheat at Lind (17,400) by Young (1986). In that (1986)
study, a frost killed the Russian thistle plants on 23 September whereas
the growing period extended until the end of October in both 1996 and
1997. Russian thistle is an indeterminate plant which will continue to
grow and produce seed until the temperature drops to about 250F for one
night or just below 320F for several successive nights (Young et al.,
1995). Although Russian thistle produced seed by early August in 1997,
seeds were not germinable until 9 September (Table 1). Germination increased
from 23% for seed collected on 9 September to 48% for seed harvest on
31 October. Although the germination data were only obtained in one year,
these results agree with other studies in the Pacific Northwest (Young
and Whitesides, 1987) and other regions of the world (Holm et al., 1997;
Young and Evans, 1972) that germination increases with after- ripening
in the field.
Fig. 2. Post-harvest
dry biomass accumulation of Russian thistle plants when allowed to grow
undisturbed and without competition in spring wheat stubble from early
August until late October in 1996 and 1997. Within-year means followed
by the same letter are not significantly different at the 5% probability
Within column means followed by the same letter are not significantly
different at the 0.05 probability level
AND MANAGEMENT RECOMMENDATIONS
Water is the most
limiting factor in dryland crop production regions where Russian thistle
is the dominant broadleaf weed. Russian thistle aggressively extracted
soil water, beyond the available range of spring wheat as well as from
deeper soil depths than spring wheat, until the weed was finally killed
by frost. Russian thistle plants produced an average 46,000 seeds between
early August and late October, but seeds were either not produced or germinable
in appreciable quantities until mid-September.
A management option
for erosion control in extreme low-crop-residue situations is to allow
Russian thistles to grow for a period of time after wheat harvest prior
to germinable seed production. In this study, an average of 1.6 lbs dry
biomass per Russian thistle (about 885 lbs per acre) was produced during
this 5 to 7 week post-harvest window. However, Russian thistle used 0.35
inch of soil water to produce this biomass, which could reduce the subsequent
wheat yield by about 2.5 bushels per acre.
In the wheat-summer
fallow rotation, we feel the best post-harvest management strategy in
low-crop-residue situations with heavy Russian thistle infestation is
to apply a fast-acting herbicide. Herbicide should be applied 10 to 14
days after wheat harvest when Russian thistle begins rapid regrowth (Young,
1986). This will halt soil water use and seed production and dead Russian
thistles will be kept in place as source of residue for erosion control.
In addition, over-winter soil water storage will likely be augmented due
to the additional soil surface cover. Post-harvest sweep tillage to sever
the roots of Russian thistle is not advised when residue is lacking as
dislodged plants will be wind-blown from the field. In the spring of the
fallow cycle, primary tillage with non-inversion wide-blade sweeps may
be followed by 2 or 3 secondary tillage operations with rodweeders in
late spring and summer to control Russian thistles and other weeds. This
method has proven to consistently retain more than the minimum 350 lbs
per acre surface cover (Schillinger et al., 1999) required for highly
Post-harvest control of Russian thistle before germinable seed production
is especially important when the ensuing crop will be spring wheat. Wind
erosion is less a factor when spring cropping compared with summer fallow,
thus either herbicide or sweep tillage are acceptable post-harvest Russian
thistle management options. Spring wheat sown i) early and with minimum
soil covering the seed for fast emergence and, ii) on narrow (6 to 9 inch)
row spacing, will increase the crop's competitiveness with Russian thistle.
On-going research to suppress Russian thistle by spring wheat varieties
with rapid and prostrate early growth habit, and effective in-crop herbicides
with short-term residual activity, will help make spring cropping an increasingly
viable option for inland Pacific Northwest drylands.
Dewey, L.H. 1893.
The Russian thistle and other troublesome weeds in the wheat region of
Minnesota and North and South Dakota. USDA Farmers' Bull. 10. 16 p.
Dwyer, D.D. and K.
Wolde-Yohannis. 1972. Germination, emergence, water use, and production
of Russian thistle. Agron. J. 64:52-55.
Gardner, W.H. 1986.
Water content. p.493-544. In A. Klute (ed.) Methods of soil analysis.
Part 1. 2nd ed. Agron. Monogr. 9. ASA and SSSA, Madison, WI.
Holm, L., J. Doll,
E. Holm, J. Pancho, and J. Herberger. 1997. Salsola kali L. p. 708-721.
In World weeds: Natural histories and distribution. John Wiley & Sons,
Leggett, G.E. 1959.
Relationships between wheat yield, available moisture and available nitrogen
in eastern Washington dry land areas. Wash. Agr. Exp. Sta. Bull. 609:1-16.
Papendick, R.I. 1998.
Farming with the wind: Best management practices for controlling wind
erosion and air quality on Columbia Plateau croplands. Washington State
Univ. College of Agric. and Home Econ. Misc. Pub. no. MISC0208.
and D.E. Miller. 1977. Conservation tillage in the Pacific Northwest.
J. Soil Water Cons. 32:49-56.
Ramig, R.E., and
L.G. Ekin. 1991. When do we store water with fallow? Columbia Basin Agric.
Res., Oregon Agric. Exp. Stn. Rpt. 860:56-60.
and W.J. Parton. 1994. Long-term effects of residue management in wheat-fallow:
I. Inputs, yield, and soil organic matter. Soil Sci. Soc. Am. J. 58:523-530.
R.I. Papendick, R.J. Veseth, and F.L. Young 1999. Russian thistle skeletons
provide residue in wheat-fallow cropping systems. J. Soil Water Cons.
D.C. Thill, C.A. Mallory-Smith, and L.W. Lass. 1995. Plant movement and
seed dispersal of Russian thistle (Salsola iberica). Weed Sci. 43:63-69.
Wallace, A., W.A.
Rhods, and E.F. Frolich. 1968. Germination behavior of Salsola as influenced
by temperature, moisture, depth of planting, and gamma irradiation. Agron.
Young, J.A. and R.A.
Evans. 1972. Germination and establishment of Salsola in relation to seedbed
environment. I. Temperature, after ripening, moisture relations of Salsola
seeds as determined by laboratory studies. Agron. J. 64:214-218.
Young, F.L. 1986.
Russian thistle (Salsola iberica) growth and development in wheat (Triticum
aestivum). Weed Sci. 34:901-905.
Young, F. L. 1988.
Effect of Russian thistle (Salsola iberica) interference on spring wheat
(Triticum aestivum). Weed Sci. 36:594-598.
Young, F., R. Veseth,
D. Thill, W. Schillinger, and D. Ball. 1995. Managing Russian thistle
under conservation tillage in crop-fallow rotations. Pacific Northwest
Ext. Pub. 492. Univ. of Idaho, Oregon State Univ., and Washington State
Young F.L. and R.E.
Whitesides. 1987. Efficacy of postharvest herbicides on Russian thistle
(Salsola iberica) control and seed germination. Weed Sci. 35:554-559.
Conservation Tillage Handbook Series publications are jointly produced
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