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Ascochyta Leaf Blight Scorches Iowa Lawns

June 17, 2010

Dave Minner, ISU Extension Turfgrass Specialist

Fanny Iriarte, ISU Plant Diagnostic Clinic

If your lawn went from one of the best in the neighborhood to one that resembled a straw field seemingly overnight then we may have an answer for you. Ascochyta leaf blight causes a rapid straw to bleached appearance of the leaves primarily on Kentucky bluegrass and to a lesser extent on perennial ryegrass and tall fescue. Home owners want to know why this happened only to their lawn and not to the neighbors. This is the most wide spread outbreak of Ascochyta that I have seen in my 30 years of managing turf. The good news is that Ascochyta spp. primarily attack turfgrass leaves and lawns usually recover quickly. 

The damaged lawns started showing up around the first of June and 15 days later I have already started to see some regrowth from lower shoots. Some of the more severely damaged areas may require 3 or 4 weeks of good growing conditions to fully recover. More information about Ascochyta Leaf Blight can be found from these links to theColorado State University and University of Missouri fact sheets. Here are some answers to the questions you have been asking about this turf problem.

What caused the problem?

A fungus called Ascochyta leaf blight cause the rapid straw discoloration of turf leaves and it was instigated by dry hot and dry conditions.

Why did the problem seem to stop right on the property line and why is my lawn having the problem?

The problem started with the hot and windy conditions in the last week of May that caused heat and moisture stress on many lawns. Since lawns with less nitrogen and no previous irrigation are more tolerant of sudden drought and heat, these more hardy lawns (usually the lighter green and less attractive lawns) were less affected by Ascochyta leaf blight. 

Should I change my lawn management practices or lawn care company?

It is unsettling that the best looking lawns suddenly become the worst looking lawns, but I wouldn’t pin the blame necessarily on yourself or your lawn care company. We see Ascochyta leaf blight every year on a very small scale and it is normally an insignificant disease that simply recovers and goes away on its own. If you are fertilizing with 2 to 4 lbs N/1000 sq.ft. per year then you are not using excessive nitrogen. If you feel your lawn is receiving too much nitrogen then apply 0.5 to 1.0 lbs N/1000 sq.ft. less in a year to determine if you are content with the appearance at a lower level of nitrogen. A more important factor is how you water the lawn. 

It appeared to me that many lawns with automatic watering systems were damaged. Your goal should be to water about once a week to supply approximately one inch of water. Watering more often produces shallow rooting, lush plants, more disease spores, and an overall less drought tolerant plant. The problem is not having an automatic irrigation system; instead it is how you use it. Automatic systems are an efficient and simple way to water the lawn. It doesn’t mean that just because you invested in one that you need to run it often. Instead your goal should be to operate the system as infrequently as possible. Allow the lawn to dry between irrigations and show slight wilting in just a few spots before you initiate an irrigation cycle. This insures air in the rootzone and promotes deeper rooting and plant cells that are more tolerant of dry conditions and disease. 

The two most damaged lawns that I visited had been frequently watering with their automatic irrigation system and then suddenly stop using it for repairs when the hot and dry conditions hit in late May. The frequent watering may have produced excessive Ascochyta inoculum that only caused infection with the onset of heat and drought stress. 

Should I use a fungicide?

No, fungicides are not recommended. First it is impossible to predict when Ascochyta will damage turf. Ascochyta is almost always associated with heat or drought stress, but turf often recovers from both of these stresses when Ascochyta is not present. It would not be practical to treat preventatively for Ascochyta every time we have heat and drought stress. Applications of fungicide on lawns already damaged by Ascochyta are also not recommended because leaves already damaged by this foliar disease cannot be helped and the recovering green leaves are not infected. 

What should I expect from my damaged lawn and what should I do?

Really, you should do nothing drastic to the lawn. In most cases the lawn will recover in 3 to 4 weeks. Once the brown tips of the leaves have been pushed up and mowed off the new green leaves will make the lawn look more normal. The straw turf along with the thatch in some lawns created dead looking debris on the surface and many of you have asked about power raking, dethatching , and reseeding to remove the brown grass. It is a judgment call that you and your lawn care company can make based on the amount of actual damage in the lawn. 

Most of the lawns I am seeing will recover with at least 80% green turf and for that reason I would do nothing except irrigate only enough to avoid severe wilting. Since we are heading into the hottest and most stressful part of the summer I would not add more stress to the lawn by dethatching during the summer; save your coring and dethatching operation for the fall.

Here are a few pictures from the 20 lawns I visited in Des Moines, Ankeny, and Ames.​


 

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More Ascochyta Disease Across the State

August 17, 2011

Dave Minner, ISU Extension Turfgrass Specialist
Mark Gleason, ISU Extension Plant Pathologist
Erika Saalau, ISU Plant Diagnostic Clinic

For the second year in a row Ascochyta has hit lawns, athletic fields, and golf course turf. Ascochyta leaf blight is a grass fungus that causes a rapid straw to bleached appearance of the leaves primarily on Kentucky bluegrass and to a lesser extent on perennial ryegrass and tall fescue. The damaged lawns started showing up around the first of June and out breaks have been occurring all summer long. Some of the more severely damaged areas may require 3 or 4 weeks of good growing conditions to fully recover.

The damaged areas seem to occur very quickly; one day the grass appears fine and the next there is bleached tan grass everywhere and most noticeably where the mower tires track. In fact, to those unfamiliar with this problem they think that someone has damaged the lawn with a pesticide or fertilizer application. The Ascochyta related problems I am seeing have nothing to do with product applications. The fungus likes to grow during wet conditions favored by lots of rain or over irrigation. Infectious spores are everywhere throughout the lawn and with a sudden increase in hot temperatures they rapidly infect the stressed grass.

Tire tracks show up because the tires spread the spores and also cause just enough abrasion stress for the fungus to enter the plan tissue. Look for bleached leaf tips that are collapsed. It looks devastating because the top part of the plant is severely damaged but the crowns and lower stems are seldom killed. The attacks are so haphazard that it is impossible to give a good recommendation as to when to avoid mowing but in general raising the mowing height and mowing less frequently will reduce your chance of experiencing a mowing track incidence. It is interesting to note that Ascochyta blight in home lawns only occurs in full sun areas and it stops where the shaded lawn has less heat stress.

The damage at first appears very dramatic but the good news is to simply be patient because most of the damage is on the leaves while the crowns and roots of the plant are not damaged. As the plants continue to grow and after about a month of normal mowing the damaged leaf tips will be removed and the lawn will return to normal.
Normally we don’t recommend a preventative fungicide because it occurs too haphazardly and a curative fungicide doesn’t help after the leaf tissue is blighted. However, if you have experienced this in the same lawns and athletic fields for two years in a row you may want to consider a single preventative application of a fungicide next year from mid May to mid June.

Much of the turf I have sampled this summer has been confirmed to be Ascochyta by laboratory identification of spores. Like most of you old timers over the years I have observed tire tracking that we have assumed to be related to hot or dry conditions. Laboratory identification of the pathogen is the best way to determine if it was related to Ascochyta. Next year we will be conducting research with fungicides, moisture conditions, and wheel pressure to determine what is causing the tire tracking; is it Ascochyta or is it simply high temperature or low moisture stress. I think most of the blighting and wheel tracking we observed in June and July were associated with Ascochyta. To a lesser degree we may have also observed some wheel tracking from high temperature/drought stress.

Areas that have been severely injured can be recovered by dethatching, hollow tine aerification, and reseeding in September.

Here are some of the Ascochyta injured lawns that we have observed in Iowa during the summer of 2011.
 

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Ascochyta in mower streaks on athletic field in Iowa City, IA.  Picture taken 7/15/11.

 

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Close up of Ascochyta symptoms on Kentucky bluegrass.  Note the bleached leaf tips and banding of leaf blades.  These symptoms are different from dollar spot that has leaf lesions with bleached centers and brown boarders.

 

 

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Obvious tire tracks from mower associated with Ascochyta in Ankeny, IA.  Picture taken 5/20/11.

 

 

 

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Picture in Ames, IA showing wheel and deck tracks associated with Ascochyta.  Picture taken 6/16/11.

 

 

 

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Ascochyta can also injure lawns without leaving the mowing tracks.  Picture taken in Ames, IA 6/16/11.

 

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Wheel track lawn injury from Ascochyta but notice that the tracks are not present in the shaded areas where the grass has less heat stress.  The Ascochyta spores may be present everywhere but it usually requires a period of sudden heat or drought before symptoms appear.  Picture taken 6/1711 Ames, IA.

 

 

 

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More Ascochyta mower tracks from Parkersburg, IA.

 

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Darker green lawn (bottom) with higher nitrogen fertility shows more Ascochyta injury than lower fertility lawn (top).  Nitrogen applied at 2 to 4 lbs N/1000sqft/yr is suggested to maintain healthy lawn growth.

 

 

 

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Low maintenance (no fertilizer and no irrigation) Kentucky bluegrass along roadside showing mower tracks with Ascochyta injury.  Even though high nitrogen can cause lush growth that increases infection in this case turf was injured in a low nitrogen situation.

 

 

 

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Mowing tracks on golf course fairway.  Injury occurred during a period when turf was not wilted or under low moisture stress.  Grass died in lower wet areas but recovered on sloped areas.  Also notice that the tracks stop at higher cut rough in front of sand trap.  We will be conducting research next summer to discern what is Ascochyta related and what may be related to high temperature or drought stress wheel tracking.  Picture taken 7-20-11 Waverly, IA.

 

 

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Ascochyta Wheel Tracking Syndrome

June 11, 2012

Dave Minner, Iowa State University
Craig Longnecker, Perficut Lawn & Landscape

Summer wheeling tracking by mowers has once again been sighted in Iowa. The picture sent to me by Kreg Longnecker from Perficut on 25 May shows wheel track injury to an irrigated lawn in Des Moines. A week of extremely dry and windy conditions caused some pockets of turf wilting to occur and preceded the turf injury symptoms. There is no way of predicting the type of year we will have but late May through June is the time we usually see this disorder. The wheel tracking associated with Ascochyta or drought/heat stress is unrelated to product application by lawn care companies. Follow the links at the end of this article for previous updates and pictures related to this problem in both 2010 and 2011. We have been able to isolate the fungus Ascochyta from lawns showing symptoms of tan/bleached leaves in both wheel tracked areas and injured lawns without wheel tracks. This is important information but we are still not sure how the fungus, dry stress conditions, and tire tracking all fits together in terms of making recommendations to reduce turf injury.

What we know

  • The symptoms have been reported late May through June in 2010, 2011, and 2012. 
  • Depending on the severity of injury and post injury growing conditions, damaged areas will take from 2 to 4 weeks to recover. Recovered lawns can be reinjured throughout the summer if conditions favorable for injury reoccur. 
  • Symptoms can occur without prior wilt but usually moderate wilt precedes injury, especially wheel tracking symptoms. 
  • Symptoms are bleached tan to white upper leaves with some leaf tips collapsed (see links below for several descriptive pictures of the problem). 
  • The problem is more frequently observed in newer subdivisions where lawns are less than 10 years old. Lawns in older mature landscapes, especially with large shade trees, seldom show this problem. 
  • The problem seems to be more problematic on Kentucky bluegrass, moderate on perennial ryegrass, and seldom occurs on tall fescue. 
  • The symptoms of wheel tire streaking associated with Ascochyta or drought/heat stress should not be confused with fertilizer burn or pesticide phytotoxicity.  

What we don’t know

  • There is a lot we don’t know about this disorder. Here are some of my observations and internal questions that I still struggle with. You can help me by sending pictures, information and opinions describing this problem. My phone and email contact is at the end of the article. 

 

  • In most cases the best looking lawns in the neighborhood seem to express the most severe injury. Lawns with automatic irrigation and higher fertility may express more injury. 
  • Iowa sod produces produce excellent quality sod, however many lawns in new subdivisions have been sodded on very poor quality subsoil using newer varieties of Kentucky bluegrass. Your comments related to the role that sod, age of lawn, soil quality, and grass variety play is needed. 
  • While we have isolated Ascochyta from injured plants we are still trying to determine if the problem is more related to the fungus or more associated to a direct injury caused by wheel stress on wilted turf. You can help by sending samples to the ISU Plant and Insect Diagnostic Clinic to confirm presence or absence of Ascochyta when these symptoms are observed. The cost for disease identification is $20. 

Plant and Insect Diagnostic Clinic
327 Bessey Hall
Iowa State University
Ames, IA 50011-3140 USA
Phone 515-294-0581

Recommendations at this time

  • The recommendations are a work in progress since research information is lacking on Ascochyta and wheel tracking. 

 

  • Mow taller to reduce wilt stress and less frequent to reduce the number of events when injury could occur.
  • Fungicides are not recommended at this time because of the uncertain role that Ascochyta plays in the disorder and the unpredictability of disease occurrence. We are however making preventative fungicide applications from late May through June 2012 in areas where the problem repeatedly occurs to help us determine the role that Ascochyta plays in wheel tracking. 

David D. Minner, Professor
Extension Turfgrass Specialist
Horticulture Department
Ames, IA 50011
(o) 515.294.5726
(c) 515.231.1741
(f) 515.294.0730

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