Reports of previously unknown diseases, sightings in areas where diseases have not been seen previously and other news of turfgrass diseases
Read this story in GCM's digital edition
note: Each year, GCM publishes reports of previously unknown diseases, sightings in
areas where diseases have not been seen previously and other news of turfgrass
diseases. The following reports were previously published in the journal Plant Disease.
report of Curvularia inaequalis
and Bipolaris spicifera causing
leaf blight of buffalograss in Nebraska
Patches of thinning buffalograss are the result of leaf blight caused by Curvularia and Bipolaris species in mid-summer in Lincoln, Neb.
Photos by B.S. Amaradasa
Buffalograss (Buchloe dactyloides [Nutt.] Engelm.) is
a warm-season turfgrass native to the mid-plains of North America having exceptional
heat, cold and drought tolerance. In the past few decades, many turf-type
buffalograss cultivars have been commercially released. During the summer of
2011, foliar blight was observed on buffalograss lawns in Lincoln and Waverly,
Neb. Disease symptoms were common when buffalograss was growing above 86 F (30
C) and in drought conditions. Disease symptoms began as dark brown, oblong leaf
spots, followed by leaf tip dieback and eventual blighting of entire tillers.
Leaf infections would progress into patches of thinning turf.
Diseased leaf pieces were cultured and observed
under a microscope to identify the causal organisms. Two fungal species having conidial
morphology of Curvularia and Bipolaris were isolated. Colonies of Curvularia isolates grown on potato dextrose agar at 77 F
(25 C) appeared velvety and dark greenish to grayish black after one week,
were brownish gray with olive-green margins. The two species were identified as
inaequalis (Shear) Boedijn and Bipolaris spicifera (Bainier) Subram.
Leaf spots and leaf tip dieback are initial symptoms
of buffalograss leaf blight.
Conidia of C. inaequalis were mostly straight to slightly curved, 17.4 to
37.1 × 7.2 to 12.6 micrometers, pale brown to brown, and three to four septate.
Conidia of B. spicifera were 18.5 to 30.3 × 7 to 11.4 micrometers, ellipsoidal or oblong,
light brown and three-septate. DNA testing was used to confirm the identity of
the two pathogens. Pathogenicity of the two species was tested on the
buffalograss cultivar Prestige. Stolons of Prestige were established in 4-inch (10-centimeter)
square pots filled with potting medium. The pots of buffalograss were kept in
an 86 F greenhouse with a 12-hour photoperiod for 12 weeks. One isolate of each
species representing each collection site (two isolates per each species) was
cultured on potato dextrose agar plates, and conidial suspensions of 1.5 × 106
spores/milliliter in sterile water were prepared. Each isolate was inoculated
to three pots of Prestige by spraying 15 milliliters of spore suspension per
pot. Control pots of Prestige were sprayed with water. Pots were sealed in
transparent plastic bags, and every other day, the bags were opened for a few
hours and the plants were sprayed with water to encourage infection. Isolates
inaequalis were more virulent, with initial symptoms of foliar spots
appearing seven days after inoculation, followed by leaf tip dieback and
necrosis of infected tillers. Bipolaris spicifera isolates induced similar symptoms 14 days after
inoculation. Control pots were asymptomatic. Curvularia inaequalis and B. spicifera were successfully re-isolated
from symptomatic tissue. To our knowledge, this is the first report of
identification of foliar blight causal pathogens on buffalograss in Nebraska.
Source: Plant Disease, February
2014, 98(2):279. http://dx.doi.org/10.1094/PDIS-05-13-0487-PDN
B.S. Amaradasa, Ph.D., is a post-doctoral
research associate and K. Amundsen, Ph.D., is an assistant
professor in the department of agronomy and horticulture, University of
Nebraska, Lincoln, Neb.
report of Ustilago cynodontis
causing smut of bermudagrass in Washington
Bermudagrass (Cynodon dactylon) is an important
perennial turf and forage grass that is typically grown in warm, tropical and subtropical
climates. Smutted inflorescences of bermudagrass were observed and collected in
Benton County, Wash., in October 2012 in an unmanaged, naturalized area located
near the banks of the Columbia River and adjacent to large expanses of managed
turf containing bermudagrass. The climate in this area is favorable to
bermudagrass because of the relatively mild winters and hot, dry summers that
usually occur in this region.
Healthy (left) and diseased (right) bermudagrass inflorescences collected from a naturalized riparian area in Washington state. The diseased inflorescences on the right were found to be infected with
bermudagrass smut, which is caused by the fungus Ustilago cynodontis.
Photos courtesy of Jeremiah Dung
The infected plants occurred in patches alongside
healthy plants, and several disease foci were observed along a 328-foot (100- meter)
transect of non-contiguous bermudagrass. The disease was severe wherever it occurred.
Diseased inflorescences were distorted, frequently failed to fully emerge and develop,
and were covered with black-brown teliospores, which serve as resting spores of
the fungus. Teliospores (n = 80) were irregularly globose to subglobose, 5.3 to 7.0 × 4.5 to
6.2 micrometers (mean 6.4 × 5.9 micrometers) and 6.2 to 8.8 × 5.3 to 7.0
micrometers (mean 7.0 × 6.5 micrometers), with a smooth wall approximately 1
micrometer thick, and were consistent with previous descriptions of Ustilago cynodontis teliospores.
Teliospores germinated within 24 hours when plated on 0.2% malt agar at 61 F
(16 C) and produced four-celled basidia in an arrangement also consistent with U. cynodontis. Basidia gave rise
to lateral and terminal, ovoid-tolong ellipsoidal basidiospores. Basidiospores budded
or germinated by hyphae and produced lateral or terminal aerial sporidia.
Collectively, the morphology of the teliospores, basidia and sporidia were
similar to previous descriptions of U. cynodontis.
DNA was extracted from sporidia of three single-spored
isolates grown in malt extract broth. Genetic testing of the three isolates showed
that they exhibited 99% to 100% identity with U. cynodontis strains previously deposited in GenBank.
Representative specimens were deposited in the WSU Mycological Herbarium as WSP
72345 to WSP 72348.
This is the first report of U. cynodontis causing smut on
bermudagrass in Washington state and represents the northernmost record of this
fungus in North America. The occurrence of U. cynodontis in Washington suggests that the pathogen may
exist in other hot and dry areas of northwestern North America where
bermudagrass can be associated with recreational, landscape or natural settings.
Source: Plant Disease, February
2014, 98(2):280. http://dx.doi.org/10.1094/PDIS-05-13-0560-PDN
J.K.S. Dung, Ph.D., is an assistant professor in the department of
botany and plant pathology, Central Oregon Agricultural Research Center, Oregon
State University, Madras, Ore.; L.M. Carris, Ph.D., is an associate professor
in the department of plant pathology, Washington State University, Pullman, Wash.;
and P.B. Hamm is station director and professor emeritus in the department of
botany and plant pathology, Hermiston Agricultural Research and Extension
Center, Oregon State University, Hermiston, Ore.
spot disease on the oceanside sedge Trichophorum cespitosum
homoeocarpa is a fungal pathogen that causes dollar spot disease on more than
40 plant species, mostly in the family Poaceae, and is considered the most
widespread pathogen of golf course turfgrasses in the St. Lawrence River
Dollar spot lesions on tufted bulrush (Trichophorum cespitosum) on the seashore near Peggys Cove, Nova Scotia, Canada.
Photos by T. Hsiang
In June 2011, lesions were observed on tufted
bulrush, Trichophorum cespitosum (Poales, Cyperaceae), on the seashore near Peggys
Cove, Nova Scotia, Canada. Single bunches had up to 40% of the leaves affected.
The foliar symptoms were large hourglassshaped lesions, up to 2 inches (5
centimeters) long, with a straw-colored portion capped at two ends by dark zone
lines on surrounding green foliar tissue. These lesions were similar to dollar
spot lesions found on turfgrasses such as Kentucky bluegrass (Poa pratensis).
A fungus was isolated from symptomatic leaf
segments and, after three days of growth on nutrient agar at room temperature,
white fluffy mycelia covered the entire petri dish. Brown columnar structures
began to form in the colony centers after seven days with abundant aerial
growth, and cultures became cinnamon-colored after 14 days. Dark brown or black
substratal stroma were formed on or in the agar, and cultures appeared dark brown
from the bottom.
DNA was extracted and amplified using ribosomal
DNA primers ITS1 and ITS4, and the DNA fragment sequenced (GenBank Accession
No. KF447776). The sequence showed a top match of 522/524 bp identity with the
ITS sequence of an isolate of S. homoeocarpa, with the next 40 top matches also identified as S. homoeocarpa. This was an
unexpected finding, so attempts were made to test the ability of this isolate
to cause disease on turfgrasses.
Dollar spot lesions on Kentucky bluegrass
(Poa pratensis) in mid-summer.
Two-week-old seedlings of Penncross creeping
bentgrass (Agrostis stolonifera), Touchdown Kentucky bluegrass (Poa pratensis) and Express
perennial ryegrass (Lolium perenne) were inoculated by placing 0.2- inch (5-millimeter) diameter
mycelial plugs from five-day-old cultures onto the leaves of plants grown in
small containers, and incubating under enclosed humid conditions throughout the
test. White aerial hyphae on the leaves and straw-colored leaf lesions were observed
by seven days after inoculation on Kentucky bluegrass and perennial ryegrass, but
no lesions or hyphal growth were observed on creeping bentgrass. No signs or symptoms
were observed on leaves where sterile agar plugs were used as inoculum. These
tests were repeated three times with the same results, and a positive control
was included by using an S. homoeocarpa isolate known to be pathogenic to creeping bentgrass under the
same test conditions. Disease was observed on creeping bentgrass with the control
isolate but never with the isolate from T. cespitosum. Sclerotinia homoeocarpa was reisolated from
the lesions on Kentucky bluegrass and perennial ryegrass to satisfy Koch’s postulates.
To the best of our knowledge, this is the first report of S. homoeocarpa on T. cespitosum worldwide, involving
an isolate that was found to cause disease on Kentucky bluegrass and perennial
ryegrass, but was not pathogenic to creeping bentgrass in vitro. The original
host was not used in pathogenicity tests because it is considered an endangered
species in many locations.
These findings extend the known host range of S. homoeocarpa and may indicate another
source of inoculum of this fungus, especially for oceanside golf courses. We
are continuing research to figure out why this isolate could cause disease on
tufted bulrush, perennial ryegrass and Kentucky bluegrass, yet not on creeping
bentgrass. The answers may lead to a better understanding of the genes
involved in pathogenicity and eventually help to improve disease management.
Source: Plant Disease, January
2014, 98(1):161. http://dx.doi.org/10.1094/PDIS-07-13-0703-PDN
T. Hsiang, Ph.D., is
a professor and F. Shi is a research associate in the School of Environmental Sciences,
University of Guelph, Ontario, Canada. This work was supported by the Natural
Sciences and Engineering Research Council of Canada.
of Xanthomonas translucens causing
etiolation on creeping bentgrass in Illinois, Kentucky and North Carolina
Symptoms of etiolation, which is an abnormal elongation
and yellowing of tillers, have been observed on creeping bentgrass (Agrostis stolonifera L.) putting greens
for decades; however, symptoms are typically transient and not problematic.
Reports of etiolation have become more frequent recently, and research supports
the involvement of bacteria.
Comparison of inoculated (left) to non-inoculated (right) Penn A-1 creeping bentgrass maintained in the greenhouse at 86 F. Etiolation symptoms were continually observed in turf inoculated with Xanthomonas translucens as shown here at four weeks after inoculation.
Photo by J.A. Roberts
During stressful summer periods in 2011 and
2012, 62 creeping bentgrass putting green samples were submitted to the North Carolina
State University Turf Clinic exhibiting symptoms of etiolation, chlorosis and/ or
general decline. Microscopic examination of stem and leaf tissue often showed
bacterial streaming from the xylem tissue. Symptomatic tissue was surface
disinfested in sodium hypochlorite (10% Clorox) for five minutes, blotted dry
and rinsed in sterile distilled water. Disinfested tissue was placed in a small
drop of sterile distilled water on a glass microscope slide and cut to allow
bacteria to stream into the water for two minutes.
The resulting bacterial suspension was streaked
onto three nutrient agar plates and incubated at 86 F (30 C) overnight.
Bacterial colonies varied in morphology, and those present in the greatest
number based on morphology were re-streaked to isolate individual colonies.
Bacterial isolates were tentatively identified to species using rDNA
sequencing. Sequencing results showed isolates obtained from six locations
(Illinois, Kentucky and North Carolina) having a positive match to Xanthomonas
translucens. Additional research is needed to confirm pathovar designation as X. translucens isolates were
similar to both poae and graminis pathovars.
A representative isolate was also examined for
carbon source utilization resulting in a positive identification of X. translucens. This isolate was
used to inoculate six-week-old seeded Penn A-1 creeping bentgrass plants maintained
at a height of 0.4 inch (1 centimeter) in 1.38-inch (3.5-centimeter) diameter conetainers.
Scissors were dipped in a cell suspension and used to cut healthy creeping bentgrass
plants at a height of 0.4 inch, and the remaining suspension was applied to the
foliage until runoff using an atomizer bottle. Non-inoculated plants were cut
and misted using sterile water. After inoculation, plants were placed in a
sealed clear plastic container for 48 hours and then transferred to the growth
chamber bench (86 F) receiving irrigation twice daily with distilled water.
Etiolation was rated within each of the four replicates by counting the number
of etiolated leaves that were easily observed as significantly higher than the
rest of the turf canopy.
Plants inoculated with X. translucens exhibited etiolation
of the youngest leaf within 48 hours, whereas the non-inoculated plants did
not. Symptoms were similar to observations in the field, as etiolated leaves
were chlorotic and easily extracted from the turf surface. Microscopic
examination showed bacterial streaming and identification of bacteria (using
the previously described methods) was positive for X. translucens. Etiolation symptoms
persisted over multiple weeks, but a decline in turf quality was not observed.
Etiolation has been previously suggested as a
precursor to bacterial wilt, caused by X. translucens pv. poae, on annual bluegrass (Poa annua L.), and Acidovorax avenae has also been shown to
produce etiolation on creeping bentgrass. To our knowledge, this is the first
confirmation of X. translucens as a
cause of etiolation in creeping bentgrass.
Source: Plant Disease, 2014, in
Joseph Roberts, M.S., is a graduate
research assistant; Lane Tredway, Ph.D., is an associate professor; and David F. Ritchie, Ph.D., is a professor and Extension
specialist in the department of plant pathology, North Carolina State
University, Raleigh, N.C.
report of stubby root caused by Trichodorus obtusus
on zoysia and bermuda in South Carolina
Trichodorus obtusus female from South Carolina
(length = 1,235 micrometers).
Photos by Brad Shaver
In September 2011, diagnostic samples were taken
from Tifway bermudagrass (Cynodon dactylon × C. transvaalensis) tees and from
Emerald zoysiagrass (Zoysia japonica) roughs of a golf course in Charleston, S.C. Additional samples
were taken from a sod farm located near Charleston from a field of Empire
The soil was sandy loam, and the samples were
taken at a depth of 4-6 inches (10-15 centimeters) from symptomatic turf.
Symptoms on bermudagrass and zoysiagrass included stubby roots and lightly to
severely chlorotic or dead patches of irregular sizes and shapes. Nematodes
were extracted by sugar centrifugal- flotation and counted. The predominant nematode
species recovered was a stubby root nematode, Trichodorus obtusus Cobb. Nematode densities
were 30 to 170/6.1 cubic inches (100 cubic centimeters) of soil (average 94, n = 5) at the sod
farm, and 30 to 230 (average 107, n = 7) at the golf course.
Trichodorus obtusus has been reported as
a pathogen of bermudagrass in Florida, where it is more damaging than Paratrichodorus minor,
other stubby root nematode commonly associated with turfgrass. In Florida, a
density of 120 T. obtusus/6.1 cubic inches is considered high risk. We have encountered several
additional samples from across South Carolina with similar or higher densities since
our first diagnosis.
Infested soil (94 individuals/6.1 cubic inches)
collected from the sod farm was put into columns and planted with Empire sod and
maintained in the greenhouse. After 140 days, the population density increased
to an average of 230 individuals/6.1 cubic inches of soil. Plants were prone to
wilting, and new root growth showed symptoms similar to those observed in the
Root symptoms of the stubby root
nematode, T. obtusus, on zoysiagrass.
Morphologic and morphometric identification of T. obtusus was made by
examining male and female specimens in temporary water mounts. Males had
ventrally curved spicules with three ventral precloacal papillae, with the
posterior papilla just anterior to the head of the retracted spicules, one
ventromedian cervical papilla anterior to the excretory pore, and tail with
non-thickened terminal cuticle. Females had a deep, barrel- shaped, pore-like
vulva, and one or two postadvulvar lateral body pores on each side. Males and
females had distinctly offset esophagus. Females (n = 10) were 1,100 to 1,440
(1,250) micrometers long, body width 40 to 53 (45) micrometers, onchiostyle 63
to 75 (67) micrometers, and V 583 to 770 (673) micrometers. Males (n = 10) were 1,076 to 1,353
(1,222) micrometers long, body width 33 to 45 (39) micrometers, onchiostyle 62
to 69 (65) micrometers, and spicule 55 to 63 (59) micrometers.
A section of the rDNA region was sequenced from
individuals representing the two locations. A search revealed no similar sequences
to those of our two populations. As such, it appears that these are the first
sequences of this portion of the rDNA for T. obtusus, although a different, non-overlapping portion
was found under the synonym T. proximus. To our knowledge, this is the first report of T. obtusus on zoysiagrass and the
first report of the species on bermudagrass in South Carolina.
Source: Plant Disease, June 2013,
J.B. Shaver is a graduate student in plant
and environmental sciences; P. Agudelo, Ph.D., is an
associate professor and nematologist; and S.B. Martin, Ph.D., is a professor in
turfgrass pathology in the School of Agricultural, Forest and Environmental
Sciences, Clemson University, Clemson, S.C.