Disease Triangle
Turfgrasses are susceptible to more than 70 diseases, which develop from an interaction between a susceptible plant (host), a disease-causing organism (pathogen), and an environment that favors the pathogen to infect and incite disease in the host.
Disease Management Triangle
Disease management may also be conceptualized as a triangle. Following proper diagnosis, plant diseases may be managed or controlled by manipulating the host, the pathogens and/or the environmental conditions. Hosts may be manipulated by replacing a susceptible turfgrass species or cultivar with a resistant alternative. Contact Forest Green Lawn Services today to schedule your FREE lawn analysis.
Gray Snow Mold
Hosts:
Diagnosis:
Environment:
Cultural Controls:
- All cool season turfgrasses
- Bentgrass, annual bluegrass, and perennial ryegrass are particularly susceptible
Diagnosis:
- Circular straw-colored patches of turf usually less than 10 inches in diameter, evident after snow-melt
- Orange, brown to black sclerotia form on leaves
Environment:
- Snow-cover is required for disease development
- Disease is severe when snow-cover exceeds 90 days
Cultural Controls:
- Avoid a fertility program that results in lush, fast-growing turf in late fall and winter
- Maintain potassium levels according to soil tests
- Use snow fence, hedges, or knolls to prevent snow from accumulating excessively on turf
- Use dark-colored organic fertilizers or composts to melt snow in spring
- Physically remove snow in spring
- Prevent compaction of snow during winter
Spring Dead Spot
Hosts:
Environment:
- Bermudagrass
- Circular patches of straw-colored turf up to several feet in diameter, evident after winter dormancy
- Roots at edges of patches are dark brown to black
Environment:
- Disease is severe where average daily temperature in November is < 60°F (16°C).
- Poor surface and subsurface drainage
- Thatch > 1/2-inch thick
- Disease is more severe on soils low in potassium and on turf that receives excess nitrogen during late summer and fall
- Maintain balanced fertility throughout the growing season
- Maintain moderate to high levels of phosphorus, potassium, and minor elements according to soil test
- Improve surface and sub-surface drainage
- Limit thatch thickness
Rust
Hosts:
Diagnosis:
Environment:
Cultural Controls:
- Creeping bentgrass and annual bluegrass
Diagnosis:
- Red-brown powdery masses of spores on leaf blades or leaf sheaths
Environment:
- Temperatures of 68° - 86°F (20° - 30°C)
- Disease is severe on turf subjected to drought stress, low mowing, shade or poor air circulation
Cultural Controls:
- Disease is more severe under low nitrogen conditions
- Maintain balanced fertility throughout the growing season
- Reduce shade and increase air circulation
- Mow at recommended height
- Avoid drought stress
- Avoid irrigation in late afternoon or in evening prior to midnight
Cool Season Pythium
Hosts:
Diagnosis:
Environment:
Cultural Controls:
- All common species of turfgrasses
Diagnosis:
- Can be difficult to diagnose; microscopic examination of roots and crowns may be necessary
- Symptoms resemble other patch diseases or dormant turf
- Slow return from dormancy in the spring
- Later spring symptoms include patchy turf with yellowish-orange to reddish-brown discoloration
- Fall patches can be quite obvious with chlorotic tan and brown coloration
Environment:
- Daytime temperatures from 50° - 70°F (10° - 21°C) and
- Nighttime temperatures from 45° - 55°F (7° - 13°C)
- Cool, wet weather
- Poor drainage and excessive irrigation
- Critical times for disease: early spring after snow melts and late autumn
- Highly maintained turf most susceptible
Cultural Controls:
- Improve drainage and do not overwater
- Promote good air circulation
- Increase mowing height
Powdery Mildew
Hosts:
Diagnosis:
Environment:
Cultural Controls:
- Kentucky bluegrass, fine-leaf fescue, and bermudagrass
Diagnosis:
- White, powdery masses of fungal spores scattered over surface of leaves
Environment:
- Disease is severe in shaded areas at temperatures of 60° - 72°F (15° - 22°C)
- High humidity is required for infection, but leaf wetness is not essential
Cultural Controls:
- Disease is more severe under excess nitrogen conditions
- Maintain balanced fertility throughout the growing season
- Reduce shade and increase air circulation
- Plant shade tolerant cultivars and species
Pink Snow Removal
Hosts:
Diagnosis:
Environment:
Cultural Controls:
- All cool season turfgrass
- Bentgrass, annual bluegrass, and perennial ryegrass are particularly susceptible
Diagnosis:
- Salmon colored to red-brown patches of turf 1 to 8 inches or more in diameter; common after 60 days or more of snow cover
Environment:
- Disease is common after at least 60 days of snow cover, but pathogen can infect turf in absence of snow
- Disease is particularly severe when snow covers unfrozen ground
Cultural Controls:
- Disease is more severe on fast-growing, lush turf that receives high nitrogen and low potassium in late fall
- Maintain balanced fertility
- Use snow fence, shrubs, or knolls as wind-breaks to prevent excess snow from accumulating
- Prevent snow compaction by machinery or skiers
- Melt snow in spring with organic fertilizers
- Physically remove snow in spring
- After snow melts, to prevent Fusarium Patch, decrease shade and increase air circulation to enhance drying of turf; avoid application of lime if possible
- Avoid irrigation in late afternoon or in evening prior to midnight
- Mow at recommended height
"Helminthosporium" Leaf Spot
"Helminthosporium" Leaf Spot
Hosts:
Diagnosis:
Environment:
Cultural Controls:
Hosts:
- Bluegrass, bentgrass, fescue, perennial, ryegrass, bahiagrass, bermudagrass, zoysia, and buffalograss
Diagnosis:
- Round to oval chocolate-brown spots on leaves
- Spots may have tan centers
Environment:
- Temperatures of 77° - 95°F (25° - 35°C)
- Disease severity increases with increase in temperature
- More than 10 hrs. of leaf wetness per day for several days
Cultural Controls:
- Disease is more severe under excess nitrogen conditions
- Maintain balanced fertility throughout the growing season
- Reduce shade and increase air circulation
- Avoid irrigation in late afternoon or in evening prior to midnight
- Limit thatch thickness
- Mow at recommended height
- Use light-weight mowing equipment to reduce stress
- Plant resistant cultivars
Take-All Patch
Hosts:
Diagnosis:
Environment:
Cultural Controls:
- Only bentgrasses are highly susceptible
Diagnosis:
- Wilted to bronze or brown circular patches of turf up to several feet in diameter
- Roots along margins of patches are dark brown
Environment:
- Disease develops rapidly on cool, wet soils with pH > 5.5
- Disease can be more severe on sandy soils
Cultural Controls:
- Disease is more severe under low or unbalanced fertility conditions
- Fertilize with acid-forming sources of nitrogen such as sulfur-coated urea
- Maintain moderate levels of phosphorus, potassium and minor elements according to soil tests
- Improve surface and subsurface drainage
- Avoid use of lime if pH > 5.0
- Avoid heavy, frequent irrigation
Necrotic Ring
Hosts:
Kentucky bluegrass, fine-leaf fescue, annual bluegrass, and rough bluegrass.
Diagnosis:
Necrotic ring spot first appears as small patches 6 in. to 1 ft (15 cm to 0.3 m) in diameter. When the fungus is actively attacking the Kentucky bluegrass plants in the fall of the year, dark red blades of grass can be seen in the patches. The pathogen attacks root systems in the spring and fall, and in the summer, infected plants begin to wilt in patches. Patches eventually turn straw colored, and older patches (2 yrs +) appear as a "frog-eye" with a center of healthy turf surrounded by a ring of dead turf.
Necrotic ring spot occurs in the cool regions of the world where Kentucky bluegrass (a primary host) is grown. The fungus achieves maximum growth at temperatures between 68° and 82° F (20° and 28° C). The pathogen is active in the cool weather of the spring and fall, even though symptoms are seen in the warm weather of the summer. The fungus is thought to move among the turf stand by growing along the surface of roots and rhizomes.
Environment:
Summer symptoms are the result of the inability of the turfgrass to take up adequate amounts of water during the summer stress period because the fungus has destroyed the root system during the cool weather. One way to keep the weakened plants alive during the summer is through the use of light, daily irrigation. Turf should be irrigated daily with between 0.1 and 0.2 in. (0.25 and 0.5 cm) of water, preferably applied between noon and 4:00 P.M. This rate can be doubled during periods of prolonged droughts.
Adequate levels of nitrogen should also be used in the management of necrotic ring spot. Improved Kentucky bluegrass cultivars require 4-6 lb (2 to 2.9 kg) of actual nitrogen per 1000 ft2 (100 m2) per season. Slow-release nitrogen fertilizers such as Turf Restore, Nature Safe, Lawn Restore, IBDU, UF, etc., are more effective in managing the disease than fast-release fertilizers like urea. Complete fertilizers (N-P-K) with slow-release nitrogen carriers are the most effective.
Kentucky bluegrass, fine-leaf fescue, annual bluegrass, and rough bluegrass.
Diagnosis:
Necrotic ring spot first appears as small patches 6 in. to 1 ft (15 cm to 0.3 m) in diameter. When the fungus is actively attacking the Kentucky bluegrass plants in the fall of the year, dark red blades of grass can be seen in the patches. The pathogen attacks root systems in the spring and fall, and in the summer, infected plants begin to wilt in patches. Patches eventually turn straw colored, and older patches (2 yrs +) appear as a "frog-eye" with a center of healthy turf surrounded by a ring of dead turf.
Necrotic ring spot occurs in the cool regions of the world where Kentucky bluegrass (a primary host) is grown. The fungus achieves maximum growth at temperatures between 68° and 82° F (20° and 28° C). The pathogen is active in the cool weather of the spring and fall, even though symptoms are seen in the warm weather of the summer. The fungus is thought to move among the turf stand by growing along the surface of roots and rhizomes.
Environment:
Summer symptoms are the result of the inability of the turfgrass to take up adequate amounts of water during the summer stress period because the fungus has destroyed the root system during the cool weather. One way to keep the weakened plants alive during the summer is through the use of light, daily irrigation. Turf should be irrigated daily with between 0.1 and 0.2 in. (0.25 and 0.5 cm) of water, preferably applied between noon and 4:00 P.M. This rate can be doubled during periods of prolonged droughts.
Adequate levels of nitrogen should also be used in the management of necrotic ring spot. Improved Kentucky bluegrass cultivars require 4-6 lb (2 to 2.9 kg) of actual nitrogen per 1000 ft2 (100 m2) per season. Slow-release nitrogen fertilizers such as Turf Restore, Nature Safe, Lawn Restore, IBDU, UF, etc., are more effective in managing the disease than fast-release fertilizers like urea. Complete fertilizers (N-P-K) with slow-release nitrogen carriers are the most effective.
