| Smiley,
R.W., and D.E. Wilkins. 1992. Impact of sulfonylurea herbicides
on Rhizoctonia root rot, growth, and yield of winter wheat. Plant
Disease 76:399-404.
ABSTRACT
Chlorsulfuron
and metsulfuron-methyl were examined for their potential to predispose
winter wheat to Rhizoctonia root rot in eastern Oregon. Soil treated
or not treated with chlorsulfuron in the field was collected as
intact cores, infested with Rhizoctonia solani AG-8, R.
oryzae, or neither, and evaluated in the greenhouse for effects
on disease severity, growth, and development of winter wheat.
Seedlings in chlorsulfuron-treated soil had more severe root rot
and reduced growth, as compared to those in non-treated soil.
Eight field experiments were performed at two root-rot affected
sites to examine the effect of pre-plant and post-emergence applications
of chlorsulfuron on tilled and non-tilled soil. These studies
were performed over two crop seasons, and chlorsulfuron + metsulfuron
methyl was included during 1 yr. Seedlings always had more severe
Rhizoctonia root rot and grew less vigorously in plots treated
with sulfonylurea herbicides. With time, however, the negative
impacts dissipated and herbicide-treated plots had grain yields
that differed from non-treated plots in only 1 of 8 experiments.
Yield was increased by sulfonylurea herbicides in one experiment
and this was apparently not related entirely to differences in
weed populations. Although sulfonylurea herbicides interacted
with Rhizoctonia species to damage roots of winter wheat
seedlings, this did not have a direct relationship with the yield
of grain under the conditions studied.
Smiley,
R. W., A.G. Ogg, Jr., and R.J. Cook. 1992. Influence of glyphosate
on Rhizoctonia root rot, growth and yield of barley. Plant Disease
76:937-942.
ABSTRACT
Time
intervals between application of glyphosate to kill volunteer
cereals and weeds and then planting spring barley by direct drilling
(no-till) into Rhizoctonia-infested soil were evaluated
in field plots at Pendleton, OR and Lacrosse and Lind, WA. As
the interval was shortened from autumn to spring application,
or from 3 wk to 3 days before planting in the spring, Rhizoctonia
root rot severity increased and grain yield decreased. When glyphosate
applications were delayed until 2 to 3 days before planting (commonly
used in production of spring barley in the Pacific Northwest)
spring barley yields were reduced as much as 50% compared to when
glyphosate was applied in the autumn or early spring. Disease
was not as prevalent when glyphosate was applied 1 or 2 days after
direct drilling compared to applications made 3 days before planting.
Rhizoctonia root rot was least on spring barley when tillage or
application of glyphosate was performed in the autumn or in spring
3 wk before planting. Tilling soil 2 days before planting at one
site nullified the yield-depressing affect of a preplant glyphosate
application. These results suggest that the inoculum potential
for R. solani AG-8 as a pathogen of spring barley is strongly
influenced by the timing of volunteer cereal and weed elimination,
and that adjustments in such practices can minimize crop damage
and maximize yield.
Smiley,
R.W., and W. Uddin. 1993. Influence of soil temperature on Rhizoctonia
root rot (R. solani AG-8 and R. oryzae) of
winter wheat. Phytopathology 83:777-785.
ABSTRACT
Rhizoctonia
solani AG-8 and R. oryzae are associated with
Rhizoctonia root rot of cereals in the northwestern U.S.A. These
pathogens were evaluated in the greenhouse and field for effects
on disease severity and growth, development, and yield of winter
wheat. Experiments in the greenhouse were performed either with
pasteurized soil mixture or intact cores of natural soil collected
from the field. Soil temperatures were controlled at diurnal cycles
of 27/16, 23/11, or 19/6 C, or experiments were performed at ambient
temperatures of 28/15 C. Inocula of the Rhizoctonia
species were also placed in a band below winter wheat seed in
the field. R. solani caused moderate to severe disease
and reduced plant growth and development in all six greenhouse
and field tests. R. solani in natural soil caused more
severe root rot at low than at high temperature. R. oryzae
caused slight to moderate root rot in natural soil and severe
root rot in pasteurized soil at high temperature, but never significantly
(P<0.05) suppressed plant growth or development. Grain yields
for winter wheat growing in soil infested with R. solani,
R. oryzae, or neither pathogen were 624, 8724, and 9444
kg/ha, respectively, during one field test. The yield component
most closely associated with root rot during both field seasons
was tiller development. We conclude that R. solani AG-8
is the principal incitant of Rhizoctonia root rot on winter wheat
in the Pacific Northwest.
Lucas,
P., R.W. Smiley, and H.P. Collins. 1993. Decline of Rhizoctonia
root rot on wheat in soils infested with Rhizoctonia solani
AG-8. Phytopathology 83:260-265.
ABSTRACT
Soils
collected from two sites were used for up to six successive plantings
of wheat in the greenhouse. Soils were infested before each of
the first four plantings with Rhizoctonia solani AG-8
or R. oryzae, or left noninfested. R. solani
stunted seedlings during the first planting. After a second or
third crop, depending upon the soil origin, shoot weights were
significantly higher in infested soils than in controls. Shoot
growth was never suppressed when soils were infested with R.
oryzae. Disease suppressiveness tests performed during a
fifth crop demonstrated that successive plantings of wheat into
soils infested with R. solani AG-8 caused a decline
of the disease. Both a susceptible host (wheat) and virulent pathogen
(R. solani AG-8) were necessary to achieve disease suppressiveness.
In contrast, R. oryzae did not induce soil suppressive
to R. solani. Induction of Rhizoctonia root rot decline
occurred earlier in tilled than non-tilled soil, and rates of
applied nitrogen had little effect on the decline process.
Smith,
J.D., K.K. Kidwell, M.A. Evans, R.J. Cook, and R.W. Smiley. 2003.
Evaluation of spring cereal grains and wild Triticum germplasm
for resistance to Rhizoctonia solani AG-8. Crop Science
43:701-709.
ABSTRACT
Rhizoctonia
root rot, caused by Rhizoctonia solani Kühn AG-8 (Anastomosis
Group 8), is a yield-limiting disease of direct-seeded cereals
in the Pacific Northwest (PNW) region of the USA, and to date,
no resistant Triticum germplasm has been identified. The
objective of this research was to identify potential sources of
genetic resistance among selected members of the primary, secondary
and tertiary gene pools of wheat (Triticum aestivum L.)
for use in cultivar improvement. Members of the primary gene pool
(spring wheat germplasm, synthetic hexaploids, triticale (X Triticosecale
spp.), Triticum turgidum var. durum (Desf.) Bowden
[= T. turgidum subsp. durum (Desf.) Bowden],
secondary gene pool [Aegilops cylindrica Host., Dasypyrum
villosum (L.) P. Candargy], and tertiary gene pool (Hordeum
vulgare L.) of wheat were screened for disease response to
two isolates (C1 and D2) of R. solani AG-8 in controlled
environment assays. Variation for magnitude of susceptibility
to both isolates was detected, but no sources of resistance were
identified among primary or tertiary gene pool members. Isolate
D2 generally produced more severe disease than isolate C1, with
the exception of the most susceptible accessions for which both
isolates caused equally severe disease. All accessions of D.
villosum exhibited some level of seedling resistance to isolate
C1, and 73% also displayed a resistance response to isolate D2.
All D. villosum/durum amphiploids, as well as Chinese Spring/D.
villosum addition lines, were susceptible to both isolates.
Differences in disease response between the two isolates suggest
that varying levels of virulence, or aggressiveness, exist among
R. solani AG-8 isolates.
Smith,
J.D., K.K. Kidwell, M.A. Evans, R.J. Cook, and R.W. Smiley. 2003.
Assessment of spring wheat genotypes for disease reaction to Rhizoctonia
solani AG-8 in controlled environment and direct-seeded
field evaluations. Crop Science 43:694-700.
ABSTRACT
Rhizoctonia
root rot, caused by Rhizoctonia solani Kühn AG-8,
is a yield limiting disease of direct-seeded cereal grains. Twenty-one
adapted spring wheat (Triticum aestivum L.) genotypes
from the U.S. Pacific Northwest were evaluated for two crop years
in a split-plot field study with high and low levels of pressure
from Rhizoctonia root rot. The high-inoculum treatment consisted
of plots planted the previous fall with a 3:1 mixture of winter
wheat and oat grains colonized by the pathogen, followed by a
pre-plant, non-selective herbicide application 6 to 10 days before
planting the following spring. The low-inoculum treatment was
neither inoculated nor planted with a green bridge host the previous
fall, and received the non-selective herbicide application in
the fall, as well as prior to planting in the spring. Genotypes
also were assayed for disease reaction in controlled environment
(CE) assays. The objectives of this study were to (1) determine
whether adapted spring wheat genotypes vary in susceptibility
to Rhizoctonia root rot in inoculated field trials; and (2) evaluate
whether disease ratings obtained by CE analyses are predictive
of disease ratings or genotype performance in the field. Average
disease ratings of field entries in the high-inoculum treatment
were 2.1 times greater than those from the low-inoculum treatment
(P< 0.05), however, disease pressure was low in both
years. The yield average of entries in the high-inoculum treatment
was 87% of that of entries in the low-inoculum treatment (P<
0.001). Adult plant heights also were 5 cm shorter (P<
0.001), heading date was slightly delayed (P< 0.05),
and grain protein content decreased slightly (P< 0.05)
in the high-inoculum compared to the low-inoculum treatment. However,
test weight was not affected by inoculum level. A statistically
significant, negative association (r=-0.6, P< 0.0001)
between disease rating and grain yield was detected. Based on
significant grain yield differences between entries in the high-
and low-inoculum treatments, variation for reaction to R.
solani exists among adapted spring wheat germplasm. Even
though yield rankings among genotypes did not generally shift
dramatically between inoculum treatments, several genotypes were
more responsive to pathogen pressure than others. As a group,
soft white genotypes appeared to be more severely impacted by
the high-inoculum treatment than were hard red genotypes. Disease
reaction differences were not detected among genotypes in CE assays,
and field and CE disease ratings were not correlated (r=0.23,
P =0.32), indicating that growth chamber assays were
not prognostic of genotype performance in response to pressure
from Rhizoctonia root rot in the field.
Smiley,
R.W. 1996. Diseases of Wheat and Barley in Conservation Cropping
Systems of the Semi-Arid Pacific Northwest. American Journal of
Alternative Agriculture 11:95-103.
ABSTRACT
Diseases
continue to be important constraints to production of wheat and
barley in conservation cropping systems of the semi-arid Pacific
Northwest. Several diseases are more damaging in high- than low-residue
seedbeds, and in crops planted during early autumn to reduce soil
erosion during winter. This is particularly true for nonirrigated
winter wheat in rotation with summer fallow in low rainfall zones
(250-400 mm). Changes in cropping systems in the region have made
management of diseases and maintenance of yield goals and farm
profitability more challenging because disease management is often
more complex and expensive for conservation- than inversion-tillage
systems. Management practices being developed to meet this challenge
are reviewed for diseases that are particularly troublesome in
conservation farming systems of the Pacific Northwest.
Smiley,
R.W., H.P. Collins, and P.E. Rasmussen. 1996. Diseases of wheat
in long-term agronomic experiments at Pendleton, Oregon. Plant
Disease 80:813-820.
ABSTRACT
Diseases
of winter wheat were evaluated over 3 years in four long-term
(27- to 60-year) cropping system experiments. Disease incidence
and severity were evaluated with respect to seasonal precipitation
and soil chemical and microbiological parameters. Take-all and
eyespot were associated with increasing precipitation, and Rhizoctonia
root rot and Fusarium crown rot were favored by drought. Eyespot
and crown rot increased with rate of applied nitrogen and were
inversely proportional to soil pH. Surface residue from previous
crops had variable effects on diseases. Crown rot increased with
amount of surface residue and was directly correlated with soil
organic nitrogen and carbon. Surface residue also had a variable
effect on Rhizoctonia root rot, depending on magnitude of soil
microbial respiration; root rot increased directly with amount
of residue in a wheat-summer fallow rotation and was unaffected
by residue and/or tillage in a wheat-pea rotation. Repeated burning
of wheat stubble caused variable disease response, depending on
precipitation and nitrogen rate. At high fertility, burning suppressed
Pythium root rot and Rhizoctonia root rot, and enhanced eyespot
and take-all. Effects of crop rotations on diseases appeared related
to soil microflora effects on pathogen survival or virulence.
Rhizoctonia root rot was most damaging in wheat-fallow rotation,
Pythium root rot in wheat-fallow and annual wheat, and eyespot
and crown rot in annual wheat. Diseases were collectively least
prevalent where nitrogen in a wheat-fallow rotation was applied
as pea vines or manure, rather than as inorganic fertilizer. Diseases
also were generally less damaging in a wheat-pea rotation than
in annual wheat or wheat-fallow rotation. Soilborne plant pathogenic
fungi appeared to suppress wheat yield by 3 to 12%. Long-term
experiments provided insights to crop management and seasonal
effects that are unlikely to be identified in short-term experiments.
Paulitz,
T.C., R.W. Smiley, and R.J. Cook. 2002. Insights into the prevalence
and management of soilborne cereal pathogens under direct seeding
in the Pacific Northwest, USA. Canadian Journal of Plant Pathology
24:416-428.
ABSTRACT
Direct
seeding or no-till leaves the soil undisturbed, except where the
seed is planted and the soil fertilized. It offers several advantages
in small-grain cereal production, including reduction in labor
and other operating costs, reduction in soil erosion, and improvement
of soil quality. However, only about 10% of small grains in the
U.S.A., and 6% of the small grains in the Pacific Northwest region
of the U.S.A. are currently direct seeded. Root diseases are major
constraints to adoption of direct seeding; they increase because
of lack of tillage, increased crop residue left on the surface,
and typically cooler and wetter soil conditions in the spring.
This review covers some recent research on the four most important
root diseases of cereals in the Pacific Northwest and their causal
agents. These diseases are rhizoctonia root rot and bare patch
[Rhizoctonia solani AG-8, Rhizoctonia oryzae],
pythium damping-off and root rot [Pythium spp.], take-all
[Gaeumannomyces graminis var. tritici], and
fusarium foot rot [Fusarium pseudograminearum and Fusarium
culmorum]. We discuss how these diseases are affected by
direct seeding and the impact of management strategies, including
crop rotation, residue management, control of inoculum from volunteers
and weeds, fertilizer placement, genetic tolerance, biological
control, development of natural suppressiveness, and prediction
of risk through DNA-based detection methods.
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