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MANAGEMENT IMPLICATIONS OF
YELLOW STARTHISTLE ADAPTATIONS
IN THE PACIFIC NORTHWEST
Gary L. Kiemnec
Michael L. Mcinnis
evaluated (Coombs and others 1987). Fungal rust (Puccinia jaceae) is being investigated as a method of control
of starthistle. The spread of disease depends on climatic
factors, which can vary considerably from year to year.
ABSTRACT
Yellow starthistle (Centaurea solstitialis) management
must take into account the environmental variables that can
be used to assist in control of this weed. Biological factors
affecting starthistle growth are discussed with emphasis on
the planting of desirable grasses to compete with starthistle.
Using such a method would require a grass that can effectively compete for water by early growth and good lateral
root spread. Suroival characteristics of starthistle seed are
also discussed.
WATER
In arid environments water availability is a limiting factor in the successful spread of yellow starthistle. If an understanding of the water needs of yellow starthistle can
be achieved, some appropriate management choices could
be made in control efforts.
Competition for water may provide a means for control
of yellow starthistle. Desirable grasses can create competition for water, but the soil volumes from which water is
extracted by grasses and starthistle must overlap. However, in the first year, many grasses grow more in a vertical direction than in a horizontal spread (Troughton 1957),
and thus do not provide for competition in the interplant
area.
Initial grass establishment in an area already infested
with starthistle is difficult due to the different growth characteristics of yellow starthistle compared to arid grasses.
In the initial year, annuals such as yellow starthistle will
have faster growth than perennials since they are trying
to produce seeds while the perennials are trying to produce
a greater root system. Water competition by the grasses
will not be grea~in fact, starthistle will be more competitive for available water in the surface soil and perhaps in
the subsoil, as studies have shown starthistle to produce a
long taproot (Sheley and Larson 1992).
Only after the grass stand has established will competition be effective. Given this observation, it becomes necessary to reduce the competitive edge that yellow starthistle
has through application of mechanical control, for example,
tillage, and/or chemical control (herbicides). Picloram
(4-am.ino-3,5,6-trichloropicolinic acid) has been beneficial in
this respect (Larson and Mcinnis 1989). Other herbicides
such as clopyralid (3,6-dichloropicolinic acid), 2,4-D (2,4dichlorophenoxyacetic acid), dicamba (3,6-dichloro-o-anisic
acid), chlorsulfu.ron (2-chloro-N[( 4-methoxy-6-methyl-1,3,5
triazin-2-yl) aminocarbonyl]-benzenesulfonamide), and
metsulfuron (methyl 2-[[[[(4-methoxy-6-methyl-1,3,5triazin-2-yl)-amino]carbonyl]amino]sulfsonyl]benzoate)
can be effective but have different effects on desirable
grasses (Northam and Callihan 1989).
From the foregoing discussion two grass characteristics
are critical to successful grass establishment and competition against yellow starthistle: (a) fast growth rate; and
(b) large root system with good lateral spread.
INTRODUCTION
Plants are adapted to surviving and spreading in certain
environments. A number of environmental or ecological
factors that favor or restrict survival are present at any
one time, to varying degrees and levels of interactions. The
aboveground factors include biology, gas, and light, while
soil factors include biology, nutrients, and water. Manipulation of these factors may provide for management of yellow starthistle (Centaurea solstitialis L.).
ATMOSPHERIC GAS
Atmospheric gas concentration does not change to any
large degree over the growing season, and practically cannot be manipulated so as to be used ~s a management tool.
Carbon dioxide levels are not changeable in the short term.
Over the past 30 years, the atmospheric carbon dioxide level
has been increasing (Miller 1990). It is unknown at this
time what the long-term effect of increased carbon dioxide
levels will be on weed species competitiveness.
BIOLOGY
Biological factors include insect and disease pests that
will attack starthistle and also other plants that limit its
competitivene88 in the environment. Seed head fly (Urophora sirunaseva) has been successfully introduced into
Oregon, but its ability to control starthistle has yet to be
Paper presented at the Symposium on Ecology, Management, and Restoration oflntermountain Annual Rangelands, Boise, ID, May 18-22, 1992.
Gary L. Kiemnec is Associate Professor, Department of Crop and Soil
Science, and Michael L. Mcinnis is Associate Professor, Department of
Rangeland Resources, Oregon State University, Corvallis, OR 97850.
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In the soil seed bank, starthistle seeds lose viability with
time (Joley and others 1992; Northam and others 1989).
However, some seeds can remain viable for years (Northam
and others 1989). Even if seed rain can be prevented, tillage of an infested site would bring buried, viable seeds to
a germinable position.
NUTRIENTS
Limited experimentation with fertilizer application to
help in grass establishment has shown that competition
from grass has not been increased to the point where starthistle populations have been adversely affected (Larson
and Mcinnis 1989; Prather and others 1988). Not enough
work has been done to identify whether this effect is one
of water and/or nutrient competition. These experiments
have broadcast the fertilizer, thus providing a uniform distribution of nutrients that would benefit the starthistle to
the same or greater degree compared to grasses. If starthistle root growth is faster than grass root growth, then
the soil volume explored by starthistle would be greater
than that of the grasses and would therefore benefit more
than grass from added nutrients.
·
Additionally, starthistle may be more efficient than
grasses at removing nutrients from the soil. If nutrients
are to be added to give an advantage to grasses the nutrients should be banded with, or close to, the seed. It might
be anticipated (but not proven) that uniform (broadcast)
fertilizer applications on older grass stands would assist
competition from grasses.
Expectations would be that, if competition is used as a
control method, eradication would not be the end result.
Some survival of yellow starthistle would be expected.
REFERENCES
Coombs, E. M.; Brown, R. E.; Hawkes, R. B. 1987. Biological control of weeds in the state of Oregon-an update.
In: Proceedings of 36th annual meeting of the Oregon
Society ofWeed Science. Clackamas, OR: 33-40.
Joley, Donald B.; Maddox, D. M.; Supkoff, David M.;
Mayfield, Aubrey. 1992. Dynamics of yellow starthistle
(Centaurea solstitialis) achenes in field and laboratory.
Weed Science. 40: 190-194.
Larson, L.; Kiemnec, G. Yellow starthistle germination
under stressed conditions in field and growth chamber
experiments. [In review].
Larson, L.; Mcinnis, M. L. 1989. Response of yellow starthistle and grass biomass to grass, picloram, and fertilizer combinations. Weed Technology. 3:497-500.
Miller, G. T., Jr. 1990. Resource conservation and management. Belmont, CA: Wadsworth Publishing Company.
546p.
Northam, F. E.; Callihan, R. H.1989. Effects of eleven
herbicides on a yellow starthistle community. In: Res.
Prog. Rep. Western Society ofWeed Science. Honolulu,
HI: 81-83.
Northam, F. E.; Prather, T. S.; Callihan, R. H. 1989. Viability and germination of buried yellow starthistle seed.
In: Res. Prog. Rep. Western Society ofWeed Science.
Honolulu, HI: 124-126.
Prather, T. S.; Callihan, R. H.; Thill, D. C. 1988. Revegetating yellow starthistle infested land with intermediate wheatgrass. In: Res. Prog. Rep. Western Society of
Weed Science. Fresno, CA: 68-69.
Sheley, R.; Larson, L. 1992. Life strategy attributes of
yellow starthistle: a discussion. In: Ecology and management of rangeland weeds. Spec. Rep. 897. Corvallis,
OR: Agricultural Experiment Station, Oregon State
University: 2-5.
Troughton, Arthur. 1957. The underground organs of
herbage grasses. Reading, England: Lamport Gilbert &
Company. 163 p.
SOIL
The geographic spread of starthistle depends on the interaction between climate and soil factors. Whether starthistle
can survive under stresses such as salt and/or water is important in determining its areal spread.
Seed germination is the first step in establishment. Research has shown that starthistle germination can take
place under saline soil conditions (Larson and Kiemnec,
in preparation). Seedling survival under salt stress has
yet to be determined, thus establishment in saline soils
is still in question. Water stress on germination can be
imposed by exposure of seed to polyethylene glycol (PEG).
Yellow starthistle germination can occur at stresses of
-0.5 MPa. Germination differences between plumeless
and plumed seed under stressed or nonstressed conditions
suggest that starthistle seed may be able to survive through
dispersal in time, thus making a long-time infested site especially difficult to manage.
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