COMMON DISEASES
List of Lawn Information/Diseases

Necrotic Ring Spot
Necrotic Ring Spot is a root infecting fungus that affects Kentucky Bluegrass lawns. The disease survives in dead and decaying root tissues and is spread when the infected tissues are relocated by transferring soil, sod, or plugs of grass. Necrotic Ring Spot is a relatively new disease to our area. It was first noticed on a regular basis in the mid 1990's stated that the disease was not found any further north than northern Colorado. Where it is possible to trace the history of an affected lawn there is a high incidence of these lawns showing symptoms of Necrotic Ring Spot three to ten years after being sodded. Numerous times the disease could be traced to imported sod from Colorado. Many times the sod source could not be traced. This is not scientifically proven finding, only observation. Most infected lawns were sodded over hard clay soils that have little or no organic matter and/or very little preparation.

Symptoms
In the early stages, symptoms of Necrotic Ring Spot often appears as a small, scatted, circular, light gray to straw color patches. As the symptoms progress, these patches become sunken and appear as rings or arcs of dead grass. Often tufts of healthy grass remain in the center of the ring producing a "frog eye" pattern, hence the common name Frog Eye Disease. The disease spreads in April and May with the symptoms appearing when the turf is allowed to go under stress in July and August. Symptoms may increase in severity one season and lessen in another season depending upon grass stress.

Controlling Necrotic Ring Spot
The disease symptoms can be suppressed by encouraging a healthy turf with minimum stress. The following cultural practices need to be addressed to keep infected turf as healthy as possible.

  1. Core aeration once per year, spring or fall. Fall may produce a more favorable result as that is the time of vigorous root growth. Aeration improves the soil condition and encourages a healthier root system.
  2. Mow grass at a height of 3" (usually highest mower setting) the entire season except for early spring clean up.
  3. Proper irrigation, very important.
  4. Proper fertilization with 4lb of Nitrogen per 1000 square feet per season with a high percent of the fertilizer from a slow release source. Excessive fertilization with fast release nitrogen sources should be avoided.
  5. A spring and fall application of 90% sulfur granular at the rate of 5lb to 6lb per 1000 square feet.

Chemical Control

Chemical control works only in combination with cultural controls.

Rubigan applied spring and fall for two consecutive seasons is rated the number one control, but is only registered for commercial turf. Eagle, Banner, Maxx, and Cleary's 3336 applied as a spray or Eagle granules applied as a spreadable, work well if applied in April or May and again in October for two consecutive seasons.

All of the above fungicide applications need to be irrigated in.

LONG TERM SOLUTION

Fine leafed turf quality perennial rye grasses are not affected by Necrotic Ring Spot. Some of the genetically improved varieties of Bluegrass, e.g. Midnight, American, Unique, Rugby II, Odyssey, Award, show a high degree of resistance to Necrotic Ring Spot in the National Turf Grass trials. These Bluegrass varieties also show outstanding performance in the Rocky Mountain Trials. The above grasses should be used in inter-seeding or re-establishing Necrotic Ring Spot infested turf.

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Black Leaf Spot
Aspens are susceptible to many problems in the urban landscape. One of those problems is aspen leaf spot, a disease caused by fungus. Aspen leaf spot, or Marssonina leaf spot, is common on aspen trees in the late summer and autumn. A previous spring of warm, rainy conditions creates the perfect environment for the disease to spread.

Symptoms

When affected by the disease, black spots develop on aspen leaves. However, black spots may develop for a variety of reasons, so it's important to recognize all of the symptoms of aspen leaf spot. Symptoms occur between July and frost. Leaves affected with the disease will be scattered randomly throughout the tree and spots will appear randomly on the leaves. The spots are dark brown to black circles containing more rings, looking almost like a bulls-eye. Sometimes the edges of the spots may appear irregular or feathery.

Solution

To manage aspen leaf spot, rake fallen leaves in the autumn to prevent the spread of the fungus in the spring. Aspen leaf spot is usually not severe enough to warrant the use of fungicide, but if the symptoms occur year after year, apply a product such as Daconil 2787 in the spring when leaves are emerging from the bud. It's too late to apply fungicide once the symptoms are evident. Read and follow label directions carefully. Aspens are very sensitive to many pesticides. If applied incorrectly, pesticides can cause the leaves to turn black.

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Bill Bugs
Billbugs are a type of weevil or "snout beetle". Adult weevils can be seen crossing sidewalks and driveways during late summer or spring. In spring and summer, adults cause minor injuries to grasses as the females cut small holes in the sterns of plants and insert their eggs.
The young billbug "grubs" are the primary damaging stage. Billbug grubs are legless, generally white or cream, with a brown head. They may reach 1/3 to 1/2 inch long when full-grown. Young grubs feed within the crown area of the plant and kill it. The stems of infested plants are easily detached at the soil surface. The ends appear sawed-off often with a sawdust-like material present. Older billbug larvae feed in the lower crown and plant root zone. Small piles of light sawdust-like material are produced during feeding.

Billbug injury is most common on new lawns, particularly those established with sod. Within lawns, most damage occurs near evergreen shrubbery or other protective sites. Billbug injury appears as wilting and occasional death of grass, often in small scattered patches. Extensive areas of a lawn may be killed during severe infestations.

Billbug Control

Different varieties of bluegrass exhibit a range in resisitance to bluegrass billbug. The common varieties tend to be more resistant. Billbug resistance also occurs in many perennial ryegrass cultivars, particularly those that contain endophytic fungi.

Biological controls include predation by birds and hunting wasps, fungal diseases and parasites. Also, insect parasitic nematodes (Steineernema species, Heterorhabditis species) are effective against both larvae and adult stages and may be used as a biological control. The nematodes are available from many mail order suppliers and several nurseries.

Controlling billbugs with insecticides is difficult when they are in the larval (grub) stage. Young larvae are protected within the plant. Older larvae occur in the root zone where insecticides fail to penetrate.

Best control for the bluegrass billbug occurs when sprays are applied in early May to kill adult insects prior to egg laying. Current information on the Denver billbug indicates that a slightly later timing, in early June is more appropriate. Apply adult sprays so insecticide residues remain as long as possible on foliage and in the crown area of the plant. This may be achieved better with liquid sprays than with granular formulations.

If lawn areas are damaged by white grubs or billbugs, give extra attention to the grass to help it grow back. Provide additional water to help the plants tolerate root loss and apply fertilizers (not high nitrogen) to promote root regrowth. Adjust mower heights to 2 1/2 to 3 inches to encourage root growth. After grubs move into the soil in fall, bluegrass often will repair much of the earlier damage. The most important means to limit white grub injury is to grow a healthy lawn.

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Sod Web Worm
Birds feeding in a lawn usually indicate the presence of insects. Some insects are not harmful to a lawn, but some can damage the lawn grass.

The sod webworm is one of the most common grass pests in the Rocky Mountain region. Adult webworms are small moths which flit about the lawn during mowing, but do not feed on the lawn.

Young webworms are caterpillars, measuring about one-quarter to one inch in length. They are brown or gray and with rows of dark spots on their backs. During the day, young webworms live in silk-lined tunnels in thatch and the surface of the soil. At night, they feed on grass leaves.

A heavily infested lawn may not grow very much, the grass may become thin and some dead patches may develop. Most lawns are healthy enough to withstand substantial webworm populations without dead spots or thinning grass.
Similar small dead patches occurring in July and August may be caused by billbugs. To identify billbug damage, pull on the dead-looking grass stems. If the stems break off at the soil line and sawdust-like material is on the broken ends of the grass, the damage was caused by billbugs.

If insects are causing brown spots, an insecticide such as Bifenthrin, Cyfluthrin, Imidacloprid, Permethrin or Sevin (Carbaryl) may be required and should be carefully applied according to the label instructions. If there are no brown spots, let the birds do their job. It's Mother Nature's way of controlling insects.

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Ants
Ants are common throughout Colorado and Wyoming, and large numbers occur in the average landscape. Most ants are beneficial in controlling pest insects, destroying weed seeds and improving soil with their nesting habits. However, ants can cause problems when they nest in the lawn, garden or children's playground area.

Ant nests are produced underground, and colonies can contain thousands of workers. Carpenter ants are large black ants that usually construct their nests in decaying wood. Ants forage constantly during the summer months, and will chew through plant roots if their nest area is located adjacent to plants. Ants are highly adaptable in their nesting habits. You can usually find their nests by watching the movement of the ants. Although some ants build conspicuous mounds, others don't, so watching the pathway of the workers will direct you to the nest.

Ants that damage plants in the garden are sometimes associated with aphids that are feeding on the roots. Ants feed on the sweet excretion of the aphids, which protects the aphids and creates feeding tunnels in and around plant roots. Ants found climbing trees are either interested in the aphids feeding on the foliage, or the sap flowing from the tree as a result of natural causes, disease or injury. Ants are also attracted to peonies because of the sap the flower buds secrete. It's a myth that ants are necessary to permit peonies to bloom.

Ants are really hard to control and it usually takes several applications to rid them.

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