Features Agronomy
Learn the signs, symptoms of lawn problems

When turfgrass experiences a problem, it typically turns a shade of yellow, tan or brown, no matter if the culprit is a disease or insect, making it difficult to accurately diagnose. Lawn care professionals must therefore gather as much information as possible to determine the exact cause of the problem, former turfgrass extension specialist Pam Charbonneau said.

Speaking in August at a Nutrite-sponsored customer appreciation day for lawn care professionals at Guelph’s Springfield Golf Course, she said the professional needs to know everything possible to get to the bottom of the lawn problem, including asking pertinent questions of the homeowner.

Two types of injury can be attributed to home lawn problems: abiotic and biotic. Charbonneau, who now consults for DCS & Associates after retiring from the Ontario Ministry of Agriculture, Food and Rural Affairs in 2015, said it is important to be able to distinguish between the two.

Abiotic causes of turfgrass problems can include watering too much or too little, mowing at improper heights, excessive drought, ample shade, too much thatch or excessive compaction. Biotic causes include disease, weeds, moss, algae and those brought on by insects.

Improper mowing, especially scalping, is one of the most common abiotic causes of problems on lawns. A scalped lawn opens up the canopy to let more light in, allowing crabgrass and other weeds to move in.

“You’re really just asking for trouble,” Charbonneau said. “It’s hard to train all homeowners to learn to mow properly.”

By the same token, waiting too long between mowing events will result in a “hayfield” with large clumps of clippings laying on the surface. Once the excessive clippings begin to decompose, the grass can smother and lead to problems with the turf.

Homeowners can also be blamed for not knowing how to properly spread fertilizer if nutrition is not part of their lawn care program.

“You need the right amount of fertilizer to get a good response from turf.”

Many turf problems are related to inadequate moisture or an overabundance of it. If a lawn is irrigated, there may be poor overlap or coverage. A drought year will allow deficiencies in an irrigation system easy to ascertain. An over-irrigated lawn can pave the way for annual bluegrass to enter the stand. It isn’t the most desired species of lawn cover due to its susceptibility to winter injury, disease and drying out.

Excessive shade will result in thin stands of turf, allowing moss and algae to move in.

Compacted soils inhibit air and water movement. Additionally, soils compacted beyond 250 pounds per square inch make it impossible for roots to grow.

“The good thing about compaction is that you can actually measure it.”

The presence of weeds on a lawn “tells a story,” Charbonneau said.

“If you have low fertility, if you’re mowing too short and you’ve got excessive moisture, you’ll get an invasion of annual bluegrass.”

There are many things that can cause damage in turf that have nothing to do with living organisms, she added.

Typical lawn diseases include pink snow mould, grey snow mould, red thread, leaf spot, dollar spot, necrotic ring spot, powdery mildew and rust. Insects to be concerned about include European chafer, Japanese beetle, crane fly, billbugs, chinch bugs and sod webworm.

Signs and symptoms of disease
“Each of those causes very distinct damage,” Charbonneau said, adding the signs and symptoms of a disease are two different things.

“With insects we often have evidence of the insect. That’s when you see something other than the insect itself. In that case we’re usually talking about what the insect leaves behind when it feeds (frass or excrement).”

Insects are also larger than disease spores and can usually be seen by the naked eye, allowing visual confirmation of the symptoms and damage they have caused.

In distinguishing between the sign and symptom of a disease, Charbonneau said rust pustules would be the sign of a disease while yellowing turf would be the symptom. For an insect-related problem, the sign would be frass while the symptom would be dead turf.

Before a disease can occur, a pathogen is needed as well as a susceptible host.

“Not every disease attacks every species of grass. If you don’t have a susceptible host but you have the pathogen, then you’re not going to see the disease.”

A disease must also have a favourable environment in which to thrive.

“Diseases usually start within a single infection site. A spore will land and start growing within a single site. Then it will usually colonize a bit and it can either form a spot, it can form a ring or it can form a patch. Sometimes diseases can coalesce. It starts as one spot and then another and, as both spots grow, they grow together and look less regular looking.”

Signs of the disease can be seen at different points in their lifecycle, she said.

“So you may see mycelium, you may see lesions or you may see pustules.”

Lesions, for example, are irregularities on leaf blades, often seen as an hourglass shape with two borders, as in dollar spot on Kentucky bluegrass, or a black margin with a water-soaked centre, as in leaf spot on Kentucky bluegrass.

Many of these diseases can be cured through good nutrition, Charbonneau said.

Disease symptoms can differ, depending on the turf species. On higher cut grass, pink snow mould doesn’t have as much of a distinct patch as it does on lower cut grass. When observing the leaf blades, grey snow mould has sclerotia not found on pink snow mould.

“If you apply a lot of nitrogen in the fall, you’ll get more snow mould. If you get lots of snow cover, you’ll get more snow mould. Where you see it really badly is where you pile your snow up when you’re shoveling your driveway.”

She said a home lawn with abundant creeping bentgrass in it is more susceptible to snow mould than one that is mostly Kentucky bluegrass. Snow mould may be seen in patches of creeping bentgrass while the surrounding Kentucky bluegrass remains unaffected.

Having the right species of turfgrass with the right type and amount of fertilizer is helpful, Charbonneau said. A little bit of nitrogen fertility will help with red thread which is purely a superficial disease that affects only the grass blades without killing the plant.

Leaf spot and melting out appears as yellowing grass in clumps and can be confused with chinch bug damage or a variety of other things, she said. Upon closer examination, however, lesions are readily visible. Melting out occurs when the lesions usually found on the leaf blades form on the stem and crown of the grass plant. They will eat through the crown, resulting in some death to the grass. Leaf spot and melting out usually occurs during the transition period from spring to summer or from cool and wet conditions to hot and dry settings.

If a lawn is grown to Kentucky bluegrass, it will have the ability to outgrow that by putting out rhizomes and repairing itself, Charbonneau said.

A high shot of readily available nitrogen in the spring will render a lawn more susceptible to leaf spot and melting out, she said, but added it’s less of a problem with the controlled-release fertilizers most lawn care professionals use.

Dollar spot is a prevalent disease on golf course putting greens, but can also occur on home lawns in Kentucky bluegrass. Charbonneau said dollar spot looks different in a golf setting than it does on a lawn, and “a shot of nitrogen” will help its prevention.

Acidifying fertilizers will usually help control necrotic ring spot in addition to watering deeply and infrequently and overseeding with perennial ryegrass.

Powdery mildew is a problem associated with shade. The sign is a powdery mycelium that grows on the surface of leaf blades. Kentucky bluegrass is susceptible if excessive shade is present. One way around powdery mildew, Charbonneau said, is to plant shaded areas with more shade-tolerant grasses such as fine fescue.

A yellow tinge throughout the turf is a sign of rust pustules on Kentucky bluegrass and perennial ryegrass. Rust, which will cover shoes when walked upon, can be dealt with through fertility.

“A well fertilized stand of grass will have much less rust than a poorly fertilized stand.”

Although both are susceptible to rust, perennial ryegrass is more prone than Kentucky bluegrass.

Charbonneau advised lawn care professionals to take a closer look to detect the signs of a disease to know specifically what is being diagnosed, adding the symptoms of many diseases are similar. Understanding the time of year associated with various diseases will also help in the diagnosis.

Insect damage
Leatherjackets, or the larvae of crane flies, are detected each year at about Mother’s Day when homeowners are raking their yards for the first time or digging in their gardens.

“They (leatherjackets) do a fairly good job of chomping the grass blades down to almost nothing when there’s a heavy population of them.”

Leatherjackets like low-lying wet areas. Adult crane flies, which resemble large mosquitoes, lay their eggs around the middle two weeks of September. The eggs hatch by mid to late October. Nematodes are an ideal mechanism for the biological control of grubs, but Charbonneau said she has had bad luck with that approach with leatherjackets. Nematodes kill grubs from the inside by getting into their bodies through the mouth, anus and other orifices, but leatherjackets have no openings other than the mouth and anus.

Crane fly leatherjackets feed occasionally at the surface, leaving bare soil, and at night tend to feed on roots, producing dead patches of grass. They are a favourite food source for birds, particularly when they are in large populations.

“If you see excessive bird feeding on a lawn, definitely get up and investigate that because there’s likely extra protein on the lawn that the birds are after.”

Moving further along into the season, the next insect pest to be encountered is the bluegrass billbug. Members of the weevil family, their damage is done from mid-July to mid-August. The evidence of billbug presence is a sawdust-like frass left behind by the larvae. The larvae are small and legless with a brown head capsule and white body, about a half-centimetre in length.

The billbug larvae tend to feed in the thatch at the crown and will attack individual plants one at a time.

“If you see a clump of dead grass and you pull it and it comes right up – we call that the tug test – you probably have billbug damage.”

Charbonneau said that by digging a little closer, the larvae or telltale frass may be found.

To know whether leatherjackets or billbug larvae are present in turf, a simple test can be conducted. She said to take a plug of turf and place it in a salt solution by supersaturating water with salt. If the insects are present, they will float to the top.

Chinch bug damage occurs about the same time as that of billbugs. Chinch bug damage is similar with patches of tan-brown grass. Unlike diseases, they are not distinct spots. Damage from chinch bugs are associated with wider areas and produce less of a pattern.

Where they have overwintered is where the damage can be seen. Individual grass blades are sunken as the result of chinch bugs’ handiwork. The insects suck the juices out of each individual grass blade. Devoid of water, the grass collapses, leading to sunken patches.

Employing the same salt solution test used to detect the presence of leatherjackets and billbugs will fail with chinch bugs. They are feeding on only the blades and not the roots or crowns, leaving the dead grass still firmly rooted.

Taking a closer look
Charbonneau suggested that if a visual approach is preferred by a lawn care professional willing to get down on his hands and knees, the insects likely won’t be found within the dead patch because they will already have moved on. An area surrounding the patches is the better place to look.

She said a means to monitor chinch bugs is to take a plug and place it in plain water. The insects will float to the top.

If other insect damage is noticed about mid-September, a close-up look should be made for a green, soft, pellet-like frass produced by sod webworm feeding, Charbonneau suggested. Adults are seen flitting about all summer at dusk and webworm damage will occur by about mid-September. She said it will resemble typical grub damage and the frass and caterpillars will be visible, but what makes it distinctive is that feeding occurs in the thatch that peels away right in the middle. If it were grub damage, it would peel away at the soil-root interface. It can still be pulled up like a carpet, but in the thatch layer and not in the soil.

Unlike leatherjackets, sod webworms can effectively be controlled by nematodes, Charbonneau said.

An effective means of monitoring for webworms, she said, is to use a soap flush to bring the pests to the surface. Mixing two to four tablespoons of dishwashing liquid into a four-litre container of water and pouring the contents onto the turf will bring any webworms and cutworms present to the surface. Although it’s primarily only a monitoring technique, she said birds tend to swoop in and make a meal out of the flushed up worms.

European chafer adults fly about from mid-June to mid-July, peaking around Canada Day, and lay their eggs in the turf. Tiny grubs will then feed until “the snow flies.” Damage is visible by the end of September or beginning of October, appearing as the result of drought or damage by other insects. Once the damage has reached advanced stages, the dead turf can be pulled up like a carpet, separating at the thatch-soil level. At this stage, skunks and raccoons forage for the grubs,
compounding the damage to greater levels.

The Japanese beetle can still be found in early August and is readily visible in its adult stage, feeding on various ornamental species. It is characterized by its bronze colouring with white tufts of hair on either side of its abdomen. Unlike the European chafer that comes out at dusk, the Japanese beetle is present during the daytime. Turf damage is visible about the end of September or beginning of October. Grubs feed throughout the fall and again in the spring.

Nematodes are effective with both European chafer and Japanese beetle grubs, Charbonneau said, adding an ideal window for their introduction is the end of August or beginning of September. Nematodes travel in the soil moisture stream, making it easier for them to migrate in a wetter-than-normal year than a dry year.

When attempting to correctly identify a lawn problem, it’s best to learn what species is being attacked, she said. Many diseases will attack only certain species of grasses. If the problem is seen in only one species, it’s likely a disease whereas if it affects various species on a lawn, the culprit is probably an insect, she added.

Abiotic problems are not confined to one species, either.

Charbonneau said lawn care professionals must make note of a number of things when trying to get to the bottom of a lawn problem. They must identify the part of the plant that is affected, whether or not the problem is above or below the surface (diseases are often just above ground with the exception of necrotic ring spot), whether the problem is in the open or a predominantly shaded area, the amount of thatch present and anything unusual about the soil.

Homeowners must also be asked about their frequency of mowing, the amounts and timing of their fertilizer applications, and how often and in what amounts the lawn is irrigated. She said it is also important to note what the weather was like before the problem first occurred and whether or not weather conditions are hindering or helping a problem.

Sometimes a problem might be the result of a chemical spill or a fertilizer contaminated by a pesticide or other agent. If a lawn care professional thinks the problem might be caused by something other than a disease or insect, a sample should be taken from an infected area as well as another from a non-infected area nearby and sent in for analysis, Charbonneau advised. She suggested if the suspected problem is a disease in dead grass that a sample should be taken from the affected area as well as another from healthy grass near the edge.