Reports on Plant Diseases |
RPD No. 412 - Rusts of Turfgrasses
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June 2000
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[ Symptoms ] [ Disease Cycle
] [ Control ]
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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.
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Click on images for
larger version
Figure 1. Leaf
rust on
bluegrass showing advancing
stages of infection.
Figure 2. Bluegrass
attacked by rust.
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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.
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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).
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.
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Click on images for
larger version
Figure 3. Leaf
rust infecting tall
fescue leaves; the leaf to the right
is healthy (courtesy L.T. Lucas).
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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.
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.
In 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.
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.
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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.
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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.
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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.
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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.
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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.
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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.
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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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[ Figure 1 ] [ Figure
2 ] [ Figure 3 ] [ Figure
4 ] [ Figure 5 ] [ Table
1 ] [ Table 2 ]
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