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All
commonly grown turfgrasses in the Midwest — bluegrasses, fescues,
ryegrasses, zoysiagrasses, and bermudagrass — are attacked
by one or more rust fungi in the genus Puccinia (Table
1). Other rust genera (Uromyces and Physopella)
attack turfgrasses outside of the Midwest. Bentgrasses are usually
not affected. Rust fungi are obligate parasites and infect only
living grass plants. Two or more rusts may attack the same grass
plant at the same time. Grass plants are most easily infected under
stressful growing conditions.
Rusts
are most severe when water and fertility are less than adequate
for good growth. Most rust problems occur on Kentucky bluegrass,
perennial ryegrass, tall fescue, and zoysiagrass. These diseases
occur throughout the United States wherever susceptible grasses
are grown.
Most
rusts do not usually become a growth-limiting problem until mid
to late summer during extended, warm to hot, humid, but dry periods
when grass grows slowly or not at all and nights are cool with heavy
dews. Some cultivars of Kentucky bluegrass (such as Birka, Campus,
Delft, Eclipse, Lovegreen, Merion, Mystic, Prato, Touchdown, and
Windsor), several of the newer perennial ryegrasses (Derby, Manhattan,
Pennfine, and Regal), zoysiagrasses, Pennlawn creeping fescue, and
Sunturf bermudagrass are particularly susceptible.
Severe
rust infection causes many grass blades to turn yellow to brown,
wither, and die. Such turf may be thinned and weakened and also
be more susceptible to winter-kill, drought, weed invasion, and
other diseases. Like powdery mildew, rusts are often more serious
in the shade.
Symptoms
Shortly after infection, a close examination of the grass blades
and leaf sheaths will show small light yellow flecks. These
soon enlarge. In several days, the epidermis ruptures and tears
away to expose the round, oval, or elongated powdery, spore-filled
pustules, which may be reddish to chestnut brown, brownish yellow,
bright orange, or lemon yellow (Figures 1 and 2). |
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on image for larger version
Figure 1. Leaf Rust on Bluegrass Showing Advancing
Stages of Infection
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Figure 2. Bluegrass Attacked by Rust
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The
powdery material rubs off easily on hands, shoes, clothing,
and animals. Where severe, rust-affected leaves or even entire
plants may turn yellow (orange on zoysiagrasses), wither, and
die. Severely rust-infected turf soon takes on a reddish brown
to yellowish or orange appearance, depending on the rust involved.
Affected turf becomes weakened, chlorotic, thin, and unsightly. |
Disease
Cycle
The cycle of development for these rust fungi is very complex
because of the many species involved (about 30 in the United
States, see Table
1, Figure 4 and Figure 5.) and the numerous alternate
hosts, mostly woody shrubs and herbaceous ornamentals. The alternate
hosts are not believed to play an important role in the disease
development of the rust fungi that attack turfgrasses. |
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Figure 3. Leaf Rust Infecting Tall Fescue Leaves; the
Leaf to the Right is Healthy (courtesy L.T. Lucas)
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Figure 4. Fifteen species of Puccinia that cause rust
diseases of turfgrasses; for each species the urediospores
are on the left and the teliospores are on the right (after
Cummins) Drawing by Lenore Gray
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The
yellow-orange to rust-colored powdery material that rubs off
is composed of tremendous numbers of microscopic spores (urediospores,
uredospores, or urediniospores; Figure 4 and Figure 5) the reproductive
structures of the rust fungi (Puccinia species). A single
pustule may contain 50,000 or more spores, each capable of producing
a new infection. These spores are readily disseminated by air
currents, water, shoes, turf equipment, infected sod, plugs,
or sprigs. Some spores land on susceptible leaf tissue, where,
in the presence of moisture, they germinate by developing germ
tubes that penetrate the grass leaves and sheaths through open
pores (stomates) and cause infection. Most spores do not successfully
reach a turf plant. A new generation of rust pustules and urediospores
appear 7 to 15 days later, depending largely on the temperature.
Urediospores constitute the repeating stage of the rust fungus.
This cycle of spore production, release, penetration, and infection
may be repeated a number of times during the summer and fall,
or until environmental conditions become unfavorable for the
growth and reproduction of the rust fungus. |
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mild climates, the rust fungi overwinter as dormant mycelium
and as urediospores in or on infected turfgrass foliage and
equipment. In Illinois, rust fungi usually overwinter as dormant
mycelium within living grass leaves and crowns. When the temperature
(usually between 60° and 90°F or 15° to 32°C)
and moisture conditions are conducive to regrowth of the mycelium
and germination of the urediospores, the leaves and leaf sheaths
become infected and a new generation of redial pustules and
their urediospores are formed. These spores are readily transported
over long distances by air currents, and those from southern
regions of the United States may serve as sources of windblown
inoculum for northern regions, where mycelium and urediospores
cannot survive the winter. |
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on image for larger version
Figure 5. Twelve species of rust fungi that cause rust
diseases of turfgrasses; for each species the urediospores
are on the left and the teliospores are on the right (after
Cummins) Drawing by Lenore Gray
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Most
rust fungi also produce another spore type, teliospores (Figure
4 and Figure 5), when the leaves senesce or dry slowly. The brown
to black telial stage is minor on mowed turfgrasses grown under
a good cultural management program. The teliospores, if produced,
may serve as overwintering structures in the north, germinating
in the spring to produce a third spore type, basidiospores. Basidiospores
are transported by air currents to the leaves of nearby, alternate
hosts (mostly woody shrubs and herbaceous ornamentals), where they
may germinate and infect resulting in two more spore types, pycniospores,
and later, the aeciospores. Cluster cups or aecial form on the alternate
hosts and release aeciospores which are then capable of infecting
grass plants giving rise to urediospores, thus completing the disease
or life cycle. The urediospores are most important in infection
of mowed turfgrasses.
Infection
for most rusts is favored by 4 to 8 hours of low light intensity,
temperatures of 70° to 75°F (21° to 24°C), and high
humidity, heavy dews, or light rains followed by 8 to 16 hours of
high light intensity, temperatures of 80° to 95° F (27°
to 35°C), and slow drying of leaf surfaces. Stripe or yellow
rust is active in northern states in early spring and fall. Along
the Pacific Coast it is active during the winter months.
Control
- Plant rust-resistant grasses, blends, or mixtures locally adapted
for your area. Check with your area Extension office or Extension
turf specialist for suggested grass species and cultivars to grow.
Kentucky bluegrass cultivars with moderate to good resistance
to one or more rust include A-20 and A-34 (Bensun), Adelphi, Admiral,
America, Apart, Aquila, Argyle, Aspen, Banff, Bayside, Bonnieblue,
Bono, Bristol, Brunswick, Challenger, Charlotte, Classic, Columbia,
Enmundi, Enoble, Escort, Fylking, Geronimo, Glade, Harmony, Holiday,
Majestic, Midnight, Mona, Monopoly, Mosa, Mystic, Nassau, Nugget,
Parade, Park, Piedmont, Plush, Ram I, Rugby, Sasta, Sydsport,
Trenton, Vantage, Victa, Wabash, and Welcome (see Table
2).
Other resistant grasses include Ensylva, Flyer, and Shadow fine-leaved
fescues; All-Star, Birdie II, Blazer, CBS II, Citation II, Cowboy,
Dasher, Delray, Elka, Fiesta, Gator, Loretta, Manhattan II, Omega
II, Palmer, Pennant, Prelude, Premier, Repell, Tara, and Yorktown
perennial ryegrasses. Emerald and Meyer zoysiagrasses are very
susceptible; Belair has some resistance. Bermudagrass, Italian
or annual bluegrass, and tall fescue cultivars also differ in
resistance. Common and many hybrid bermudagrasses are tolerant
or resistant while the hybrid Sunturf is very susceptible.
Tall fescue cultivars with improved crown rust resistance include
Adventure, Apache, Falcon, Jaquar, Mustang, and Olympic. Resistance
to rusts is limited by the presence of numerous physiological
races of the rust fungi. A cultivar in one location may be resistant
whereas it appears susceptible in another turfgrass area.
- Fertilize to keep grass growing at a steady rate, about an inch
a week, during summer or early fall droughts. The growth of grass
blades pushes the rust-infected leaves outward, where they can
be mowed off and removed. To increase vigor, maintain a proper
balance of nitrogen, phosphorus, and potassium (N-P-K), according
to local recommendations and a soil test report. These recommendations
will vary with the grasses grown and their use. Do not overfertilize,
especially with a readily available high-nitrogen source. Keep
the phosphorus and potassium levels high.
- During summer or early fall droughts, water established turf
thoroughly early in the day so that the grass can dry before night.
Water infrequently and deeply, moisten in the soil at each watering
to a depth of 6 inches or more. Avoid frequent light sprinklings,
especially in the late afternoon or evening. Free water on the
leaf surface for several hours enhances development of rusts and
many other diseases.
- Increase light penetration, air movement, and rapid drying of
the grass surface by pruning or selectively removing dense trees
and shrubs bordering the turf. Space landscape plants properly
to allow adequate air movement and to avoid excessive shade.
- Remove thatch in early spring or early fall during cool weather
when it has accumulated to half an inch. Use a "vertical
mower", "power rake", "aerifier", or
similar equipment. This equipment can be rented at most large
garden supply or tool rental stores.
- Mow frequently at the weight recommended for your area and for
the grasses grown. Mow upright grasses, such as Kentucky bluegrass,
ryegrasses, and fescues, at 1½ to 3½ inches (somewhat
higher in the summer). Creeping grasses like bentgrasses, bermudagrass,
and zoysias may be mowed to one-half inch or less. Remove no more
than a third of the leaf surface at one cutting. Collect the clippings
where feasible. This eliminates a potential source of inoculum.
- Follow suggested weed-control programs for the area and for
the grasses grown.
- The cultural practices outlined above (1 through 7) should provide
for a steady, vigorous growth of grass during extended, warm to
hot, dry periods when rust attacks are most severe. If rusts are
serious year after year, these practices may need to be supplemented
by a preventive fungicide spray program. The initial application
should be made when rust is first evident on the grass blades.
Repeat applications are needed at 7- to 14-day intervals as long
as rust is prevalent. Sterol-inhibiting fungicides such as Bayleton,
will provide several weeks of protection with a single application.
For best results, apply the fungicide soon after mowing and removal
of the clipping. Good coverage of the leaf surface is necessary
for control. The addition of about a half teaspoonful of commercial
"spreader-sticker" or surfactant (about ½ to
1 teaspoonful per gal or 1 pint to 1 quart per 100 gal) such as
Plyac Non Ionic Spreader-Sticker, De-pester Spreader-Activator,
Ortho Spreader-Sticker, Triton B-1956, Bio-Film Spreader-Sticker,
Chevron Spray Sticker, Miller NuFilm-17 and NuFilm P, or X-77.
Always follow the manufacturer’s directions. For the most
effective control of rusts, uniformly spray 1000 sq ft of turf
with 2 to 3 gal of water containing one of the suggested
fungicides listed in the current edition of Illinois Commercial
Landscape and Turfgrass Pest Management Handbook.
Use the lower fungicide rates in a routine preventive program;
use the higher rates for a curative program, after the
appearance of numerous infections (light yellow flecks).
Any one of these fungicides may be alternated with another fungicide,
such as Chipco 26019, Dyrene or Dymec, Vorlan, Cleary’s 3336,
Fungo 50, Kromad, or Tersan 1991.
If Pythium blight is also a problem, alternate one of the fungicides
suggested to control rusts, with a fungicide to control Pythium.
When mixing or applying any fungicide, follow the manufacturer’s
directions and precautions carefully.
(Mention of a trade name or proprietary product does not constitute
warranty of the product and does not imply approval of this material
to the exclusion of comparable products that may be equally suitable.)
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