ASCOCHYTA LEAF BLIGHT / DOLLAR SPOT LAWN FUNGUS

THE SUMMER LAWN FUNGUS CAUSED BY SHORT GRASS ROOTS


What is Ascochyta or Dollar Spot Lawn Fungus?

Ascochyta or Dollar Spot Fungus is a minor stress lawn fungus that can attack all cultivars of turfgrass worldwide, but is very common in the Boulder and Fort Collins Colorado area. This lawn fungus is most commonly found when the weather changes from cool wet weather to hot dry weather. This common lawn fungus is typically active when daytime temperatures are above 80 degrees Fahrenheit.

Ascochyta Leaf Blight or Dollar Spot Fungus problems occur in lawns with short grass roots. Short roots are caused by poor lawn watering practices and poor cultural practices.. A lawn with deep digging grass roots will not be able to develop ascochyta leaf blight.

Shallow grass roots are typically caused by shallow and frequent lawn watering. The ascochyta leaf blight fungus can become visible quickly when there is a fast change in climactic conditions, i.e. quick change from wet spring to hot summer. Typically, but not always Ascochyta is found where poor sprinkler coverage occurs or in areas where little or no water is being applied to a lawn.





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The Ascochyta lawn fungus is identifiable because the damage to the turf will begin in the middle of the foliage. Notice in this picture that the top and the bottom of the blade of grass are both green.


How to Identify Ascochyta Leaf Blight or Dollar Spot Lawn Fungus

A good way to properly identify Ascochyta leaf blight fungus is by examining newly infected leaf blades. To do this you will have to get on your hands and knees and go to the edge of the damaged area. Find a blade of the grass that is neither completely damaged nor completely healthy. You will notice the blade of grass will be collapsed (folded in half lengthwise) and the brown area of the blade will begin in the center and the top and the bottom of the blade of grass will be unaffected (brown center, top green, bottom green). This means that the grass' top will be green, the center will be brown, and the bottom will be green. The difference between Ascochyta Leaf Blight and Dollar Spot is that Ascochyta does not have a dark band above the brown middle section and the Dollar Spot fungus does have a dark band. Other than the band there is no real difference between the two common lawn diseases of Colorado.

Ascochyta leaf blight / Dollar Spot lawn fungus seldom causes severe damage because it doesn’t damage the crown of the blade of grass. To repair the lawn problem and avoid future fungus outbreaks, adjustments to the lawn's watering schedule will be necessary. Remember Ascochyta is a symptom of a problem and that problem is the lawn has very short grass roots. Short roots are typically caused by shallow frequent lawn watering, where the roots never have to dig deep for water. Short roots can also be caused by too much water, because the excessive water replaces air in the soil and the roots are staying shallow because they are searching for air.

Even though Ascochyta leaf blight / Dollar Spot fungus typically is found in areas of drought, the fungus can enter the grass through damaged or cut leaf tips. The lawn fungus often uses water as a transportation method to infect new blades of grass. This is the reason why we advise waiting 24 hours after mowing before watering the lawn. (See Step 5 Below)

Ascochyta/Dollar Spot is like a cold to a human. Everybody can get a cold; however, the healthier the person the less likely the person is to contract a cold. The same applies with turf grass. Lawns with deep digging roots and also have proper organic fertilization, aeration, deep and infrequent watering, proper lawn mowing, and strong “alive” soil conditions will almost never suffer from a minor lawn disease or a lawn fungus.

This lawn in Boulder Colorado is suffering from Ascochyta Leaf Blight, which is a fungus that only occurs in lawns with shallow digging roots.


How to cure Ascochyta or Dollar Spot fungus:

Scenario A – Short Roots Caused By Shallow Watering or Too Little Water (Recovery in 7-14 Days)

When the lawn watering is too shallow the lawn's roots never dig deep because there isn’t any moisture deep in the soil.

The recommendations to treat Ascochyta/Dollar Spot when the short roots are caused by poor sprinkler coverage or shallow and frequent watering are as follows:

  1. Adjust the watering schedule of the lawn to properly water the lawn deeply and infrequently. Ascochyta leaf blight / Dollar Spot fungus is a symptom of shallow grass roots. If the lawn was suffering from shallow and frequent lawn watering, the first step is to fix the broken sprinkler head and / or make adjustments to the watering schedule.
  2. To bring the lawn out of the stressed environment we recommend watering the lawn deeply for 3 consecutive days. After the 3 deep soakings, go back to a proper lawn watering schedule. Also, it is important to water early in the morning instead of late at night or even worse in the daytime.
  3. Perform 2 aerations. One in the spring and one in the fall, to alleviate soil compaction.
  4. Apply Humate Soil Conditioner at any time of the year or at any time that the disease is active. Humate will increase the beneficial bacteria populations in the soil.
  5. Never apply synthetic pesticides (weed controls and lawn fungicides) to the infected area. Pesticides can hinder microbial activity, and microbial activity is essential to proper treatment of Ascochyta/Dollar Spot.
  6. Never mow the grass if it is wet, and always wait 24 hours after a mowing to water the grass. After a mowing the grass blades have been damaged. It takes 24 hours for a grass to repair the abrasion. If water is added to the lawn before the lesion has time to heal, the fungus can use the water as a transportation mechanism and infect new and otherwise healthy blades of grass.

Until the lawn fungus is eliminated, bag the grass in the infected area, increase the mowing height to 3” or 3.5”, and increase the mowing frequency so no more than 1/3 of the blade of grass is removed per mow.

This lawn in Fort Collins Colorado is suffering from Ascochyta Leaf Blight fungus, which is a mild stress fungus that can be easily fixed with a few adjustments to the sprinkler system.


Scenario B – Short Roots Caused By Too Much Water (Recovery in 14-28 days)

If the lawn has short grass roots because it has been over watered, the grass roots are short because the water has replaced all the air in the soil. Since there is no air in the soil the roots will stay shallow because they are starved for oxygen.

The recommendations to treat Ascochyta / Dollar Spot when the short grass roots are caused by severe over watering of a lawn:

  1. Adjust the watering schedule of the lawn to properly water the lawn deeply and infrequently. Ascochyta leaf blight / Dollar Spot lawn fungus is a symptom of shallow roots. If the lawn is suffering from too much water, the soil will be starved of oxygen and therefore the roots will stay at the surface looking for air. After fixing the watering it will take time and the lawn will need time to dry out so the roots to grow deeper.
  2. Perform 2 aerations, one in the spring and one in the fall, to alleviate soil compaction.
  3. Apply Humate Soil Conditioner at any time of the year or at any time that the disease is active. Humate will increase the beneficial bacteria because it is a healthy food source full of beneficial organic matter.
  4. Avoid applying synthetic pesticides (chemical weed controls and lawn fungicides) to the area. Pesticides can hinder microbial activity, and microbial activity is essential to proper treatment of Ascochyta/Dollar Spot.
  5. Never mow the grass if it is wet and always wait 24 hours after a mowing to water the grass. After a mowing the grass blades have been damaged. It takes 24 hours for a grass to repair the abrasion. If water is added to the lawn before the lesion has time to heal, the fungus can use the water as a transportation mechanism and infect new and otherwise healthy blades of grass.

Until the lawn fungus is eliminated, bag the grass in the infected area, increase the mowing height to 3” or 3.5”, and increase the mowing frequency so no more than 1/3 of the blade of grass is removed per mow.


Organo-Lawn is your local lawn care expert and we specialize in the treatment and cure of lawn care problems like Ascochyta Leaf Blight Fungus and Dollar Spot Fungus. These lawn fungus problems are common in the Boulder and Fort Collins Colorado areas, especially during the months of June, July and August. If you want to cure your lawn so these lawn fungus problems never occur again contact Organo-Lawn of Boulder (303) 499-2000 or Fort Collins (970) 225-9425.

This Ascochyta Leaf Blight in a tall fescue lawn in Arvada Colorado and you can see Ascochyta in a fescue lawn looks vastly different compared to a bluegrass lawn.

Ascochyta Leaf Blight fungus in a lawn in Boulder Colorado.