Lawn Diseases & Insects

The following is a list of common pests and diseases which can be found throughout Alberta lawns.  It’s important to emphasize that a neglected lawn will be a haven for generations of problems that cannot be cured overnight.


Fairy Rings

Are circles or semi-circles of dead or dark grass in turf.  During wet periods throughout the season tan coloured mushrooms will often appear on the outer edges of the affected areas. These mushrooms should not be confused with the clusters of mushrooms which often appear in newly installed sod or established lawns after heavy rains. Non-fairy ring mushrooms will not harm the lawn and are easily removed by picking.  If mushrooms reappear in the same spot, they may be growing on decaying organic matter such as a tree stump buried under the grass. 

The soil beneath the ring is infested with masses of white threads of fungus.  Fairy rings can take a few years to become visible and enlarge as they age.  The area infected with the fungus forms a thin ring in the thatch under the turf.

Fairy rings are found in all kinds of turf areas - residential, parks, golf courses and pastures.  This fungus is common in all lawns but most noticeable in dry, unfertilized lawns.  The fungus feeds on the old thatch just above the soil surface.  The mycelium (threads of fungus) forms an impenetrable barrier to water so water cannot penetrate into the root zone of the turf which results in the dead ring of grass.  Fairy rings are spread by contaminated soil, contaminated shoes, tools, lawn maintenance equipment.

There is no effective chemical control for fairy rings.  However you can hide the rings with fertilizer applications or by aerating the ring and watering heavily and frequently.  To completely rid your lawn of fairy rings you have to dig up the ring and infested soil up 30cm out from the edge of the ring and to a depth of 15cm.  Then replace it with new soil.

Leaf Spot / Melting Out

Spots on the leave develop purplish-red to purplish-brown borders and brown to tan centers.  The spots may extend the width of the leaf and are somewhat longer then wide.  Melting out begins as spots on the grass blades then rapidly moves down the leaf sheath and into the crown and roots.  These diseases are caused by excess thatch, heavy nitrogen fertilization, excess shade, mowing too close, and broadleaf herbicides promote these diseases. 

The best control for these diseases is to avoid excess use of high nitrogen fertilizers, remove excess thatch, and keep grass well watered.  Control outbreaks by applying a fungicide when the spots appear, then repeat application 10-14 days later.

Dollar Spot

Straw coloured circular patches of dead grass.  In the morning you might see a faint cobwebby growth on the leaves of affected plants.  In early stages of this disease leaves develop tan-coloured spots and bands with a reddish-brown border.  Dollar spot develops with high humidity and low soil moisture and in lawns that are unfertilized or under stress.  Control by keeping lawns adequately fertilized and watered.  Use a fungicide when necessary.

Brown Patch

Circular or crescent shaped patches. In the morning the outer edge of the patch may have a dark grey to dark purple ring.  This fungus is most active is warm temperatures when grass blades stay wet for prolonged periods of time and is most severe when high nitrogen fertilizers have been used.
To reduce the chances of an outbreak avoid the use of excess nitrogen fertilizer before hot weather and avoid excessive thatch buildup.  When the weather creates ideal conditions for this fungus to develop use a fungicide to treat it.

Powdery Mildew

Grey or white powdery coating on the leaf blades.  Blades may turn yellow, orange or brown; most severe infestations are in the fall.  Mildew is most common in shaded areas or in lawns that to much or not enough nitrogen. To prevent outbreaks utilize shade tolerant grasses for heavily shaded areas, raise mowing height and do not apply excessive nitrogen.  With severe infestations a fungicide can be used.

Slime Mold

Creamy-white slimy substance coats the leaf blade; later this slimy coating turns powdery white, gray or blue-grey. The patches in the lawn look like spilled oil.  Damage is minimal as the mold grows on the surface of the grass and doesn’t attack it.  If the grass blade stays coated for a prolonged period the exclusion of light can weaken and yellow the blades.  The best method to prevent that is to brush off the grass.

Snow Molds

As the snow melts in the spring circular to irregular patches of dead grass covered with grey, white or pink mold appear. To prevent infestations reduce fertilizing and irrigation in late summer to allow turf to harden-off.  Rake up fallen leaves; break up piles of snow to speed the melting process in spring. In severe cases you can use a fungicide.


Dew Worms

In most instances earthworms are highly beneficial and desirable in the soil of home gardens and lawns.  However, there can be a limit to everything and in some cases and over abundance of worms can be a definite nuisance.  Too many worms in a lawn can cause the surface to become very uneven and bumpy.  The large dew worms throw up mounds of soil casting and if the soil has a clay base, these mounds become sun baked into hard lumps, making the lawn very uneven and uncomfortable, especially when mowing.


Small black to red insects that may make small mounds of dirt, especially in sandy soil.  They usually appear during the heat of summer.  They are not particularly harmful to turf but can make mowing difficult and in large numbers can be a nuisance. Apply an insecticide for control.

White Grubs

White grubs are actually the larval form of several insect species including June beetle, European chafer and Japanese beetle.  Lifting a section of turf may reveal the C-shaped grub.  If small irregular patches of grass gradually go brown and easily pull away in your hand, white grubs are probably present.  Spray with an insecticide in early-mid July just after the adults lay their eggs.

Chinch Bugs

In either nymph or adult form, it sucks juices from grass stems.  The nymphs, which are bright red when they hatch and then turn grey as they grow and begin to feed in early May.  You might not notice their effects, sunken patches that might contain more weeds than the rest of the lawn - until July or August when heat and drought lower your lawns defenses.  Lush, heavily fertilized turf is particularly vulnerable; a thick thatch layer is the bug’s favoured hiding place.  A handy way to detect them is to remove both ends of a coffee can, sink it part way into the turf and fill it with water.  After a few minutes the insects will float to the surface (adults are about 4mm long with a distinct white band across their abdomen). The best treatment is prevention; spray with an insecticide in July.

Sod Webworm

Also called lawn moths, they skeletonize grass blades or remove them completely.  You’ll notice irregular brown patches, or in heavy infestations, small buff colour moths in the lawn.  Spray affected area with an insecticide as soon as you identify the problem.

Turf Grass Scale

The adult has an oval, yellowish-brown body about 3-4mm long.  Found mostly in sodded lawns, it sucks plant juices at the base of the stems but causes no serious damage to the lawn.  Control young “crawlers”, which hatch in late June and early July with an insecticide.


Dogs can be very hard on a lawn!  Damage from dog urine appears as dead circular patches. Urine, mainly uric acid, contains a large amount of nitrogen and salt.  The soluble salts (nitrogen compounds) in urine are responsible for killing the grass. Essentially water is pulled away from the grass blades causing dehydration which in turn kills plant tissue.  Damage from dogs is worsened in hot, dry weather because there is an increase in dehydration which increases the degree of burn.

To repair damage you will need to flood the spot with a large amount of water to leach urine salts from the root zone. Then remove the dead grass and loosen up the soil. You can sprinkle the affected area lightly with dolomitic lime to help decrease the acidity of the soil.   Then you can reseed or resod the area, ensuring to keep moist until the seeds germinate or the sod takes.