Search results


June 10, 2013

Conditions have been very wet in the Midwest this spring, which has resulted in a very fast growth rate of turf.  Most of us are having a hard time keeping up with mowing.  These wet conditions in spring are often followed by a leaf spot breakout in turf.  The picture below is from the Chicago area.  It shows the typical leaf spot symptoms on fairway bent.

Symptoms generally include blighting from the tip down on bent, rather than the standard leaf spot lesions seen on other species.  The turf on the area may also look like it is dry, even if the soil is wet.  The grass also takes on a brown "haze" when you look at it from a distance.

The fungi that causes this is usually attributed to Bipolaris or Dreschslera (formerly Helminthosporium), depending on the author.  I will let the pathologist sort that one out.

Chlorthalonil (Daconil and other commercial names) is the standard answer for this problem, although there are several fungicides labeled for this disease.

This disease can also hit greens, but most golf courses are treating greens and it is not as common as it once was.  Because of the cost, fewer superintendents are treating fairways and that is where we are seeing most of the problem this spring.



October 2, 2012

On September 4, I put up a post warning that Gray Leaf Spot might show up in Iowa because of the unusually warm conditions around labor day.

On the 4th I wrote the following:
"This disease is caused by the fungi Pyricularia grisea. It seems to selectively hit perennial ryegrass on intensely managed areas such as golf course fairways and sports fields. Under the right conditions, it can be more devastating than Pythium blight. When it hits, it can wipe out large areas of turf overnight.  Fungicides, such as Banner/Daconil will control it, but they must be applied before the outbreak.  Once the disease begins, it is too late to apply.  The reason I bring this up is that we are in the same weather pattern again this year.  The disease does not always occur when its hot around Labor Day, but it did last year and I would watch for it this year".

What I didn't know at the time was that it would be me that would get hit with the gray leaf spot.  When I went out to take data on the perennial ryegrass trial at the research station in mid September I found that the ryegrasses in the trial appeared to have collapsed.  They looked terrible.  I then looked at two other areas of perennial ryegrass on the site and saw that it looked the same.  Andrew Hoiberg, who recently graduated with his Ph.D. was at the station at the time and commented that it looked like gray leaf spot.  On closer inspection, that is what it appears to be.  It was right on time, shortly after Labor Day during an unusually warm spell.

This trial is part of the national turfgrass evaluation trials (NTEP) and we purposefully do not treat it with fungicides.  The damaged cultivars are beginning to show some recovery as of the beginning of October, but they are still showing signs of the damage.  Under normal conditions, we would simply reseed into the ryegrass and we would have it back in a couple of weeks.  We are unable to do that here because of all the different varieties that are involved.  We will have to wait for recovery.

By the way, is it Gray Leaf Spot or Grey Leaf spot?  You will see many examples of each if you search the internet.  I'm using Houston Couch's book as my source and going with Gray.

The pictures below are of the site in mid September when the damage was most severe.  The first three are of the NTEP perennial ryegrass trial.  The last four are closeups of the damage.





September 24, 2012

Here are some pictures of rust disease on Kentucky bluegrass submitted by Damian Richardson, Landscape and Conservation Specialist from Alden, IA.  Rust is caused by fungi in the genus Puccinea.  It is common on Kentucky bluegrass and other grass species in Iowa, but there has not been a lot of it so far this year.  It usually begins to show up about the first of August.  This is the first report of it that I have received this year.  This one was on September 20.  These are some good closeups of the rust pustules on the individual blades of grass.  Thanks for submitting them Damian.

While there are several fungicides that will control rust, I usually do not recommend chemical treatment unless it is on a critical area.  It is usually a sign of relatively low nitrogen.  Just add a little nitrogen and mow regularly and the problem should run its course and disappear.  Some cultivars of Kentucky bluegrass are more susceptible that others.  If it is a continuous problem each year, you may want to kill the existing cultivars with Roundup and replace them with more tolerant varieties.  For information on which varieties show tolerance of rust, see the National Turfgrass Evaluation (NTEP) web site at  (  They have data over several years on rust infestation of many cultivars of Kentucky bluegrass.

If anyone else is seeing a lot of rust, let me know.



September 4, 2012

A year ago, on August 31, 2011, I put up a post warning about Gray Leaf Spot on perennial ryegrass.  This disease shows up rather infrequently in Iowa, but it does occur around Labor Day on years when temperatures are unusually high.  Last year's Labor Day temperatures were in the 90's and if you check the post from September 19, 2011, you will see that it did occur on several golf courses with perennial ryegrass fairways.

This disease is caused by the fungi Pyricularia grisea. It seems to selectively hit perennial ryegrass on intensely managed areas such as golf course fairways and sports fields. Under the right conditions, it can be more devastating than Pythium blight. When it hits, it can wipe out large areas of turf overnight.  Fungicides, such as Banner/Daconil will control it, but they must be applied before the outbreak.  Once the disease begins, it is too late to apply.

The reason I bring this up is that we are in the same weather pattern again this year.  The disease does not always occur when its hot around Labor Day, but it did last year and I would watch for it this year.

The pictures below were taken in 1998 on Willow Creek Golf Course in Des Moines and last year on Cedar Poine golf course in Boone. The dead grass is perennial rye and living grass is Kentucky bluegrass.

If anyone has an outbreak of Gray Leaf Sport this year, let me know and send some pictures. 



July 29, 2011

This is a follow up to my post of July 26 on leaf spot damage. By the way, I added a picture of my own lawn at the end of that post. Those of you with leaf spot in turf are not alone.

Yesterday, the 28th, I was asked to look at some lawns in the Polk City and West Des Moines area. What I saw was a lot more leaf sport damage.

On the lawns below, the entire subdivision had been irrigated during the early summer. Just before the heat, the irrigation system went down for a few days. We are just coming off of nearly two weeks above 90F. Some days reached 99 and 100. This is ideal conditions for leaf spot to develop. Even lawns that had irrigation in surrounding areas showed a lot of damage.

At this site, there was a clear pattern. It was the areas exposed to the sun, particularly south facing slopes that showed the greatest damage. This is very severe damage, but it will recover. Typical of leaf spot, the older leaves have died, but the new growth appears to be healthy. I recommended that they fertilize about the 15th of August and I predict that most of it will recover by October.

This is a south facing slope, and it shows some of the worst damage.

This is a very interesting picture. The foreground is a south facing slope. The background, which is on the same irrigation system and received the same treatments and mowing as the lawn in the foreground shows very little damage. The difference is that the background is a north facing slope that was protected from afternoon sun by the houses and by the slope.

Should you apply fungicides at this time? Damage is already done and recovery is beginning to take place. I don't think that fungicides would be worth the cost at this point.

This was a convergence of just the right conditions for this disease to occur. Hopefully we will not see damage this bad again for a few years.



July 26, 2011

Yesterday, July 25, I began to notice a lot of damaged grass around campus and around Ames. This was not unexpected because of the extreme weather that we have had lately. We are nearing records for days over 90 F, followed by 70+ F nights with sufficient moisture to keep the turf green. This is ideal conditions for several diseases.

The problem appears to be Leaf Spot caused by the fungal organism (Drechslera poae). The old genus name for this organism was Helmintosporium, a name that still in use by much of the industry. This disease is common at this time of year, particularly when the spring has been wet.

So, if you have this problem, what should you do. There are a number of fungicides labeled for this disease, but usually we let it run its course. The area should recover later in the season and through the fall. Notice in the last picture that the new leaves are emerging in a healthy condition. I am expecting full recovery by September.

The first three pictures below shows leaf spot on central campus at Iowa State. It has now gone into the crown and root stage and the damage is quite apparent.

Damage just outside of Horticulture Building.

Beardshear hall just off of central campus.

Individual leaf showing lesions.

It is typical of this disease to damage older tissue first. Notice that the newly emerging leaves are health.

Here is an additional picture that I took yesterday afternoon on my own lawn.
In the area where afternoon shade cools the Kentucky bluegrass, there is very little leaf spot. In the area that gets the stress from the afternoon sun, there is considerable damage from leaf spot.



December 15, 2010

In the next few weeks, I'm going to upload a series of posts from ISU students who have been working on research projects and from those who were on internships last summer. They submit written reports on their experience and many of these are excellent.

The post below is from an undergraduate named Steve Johnson. He worked for Mark Gleason in pathology this summer and established some trials at the research station. This is the second of three posts from him. The first was on Sept. 27. This is the second one and the third one will come in a few days.

Steve Johnson, Soph. Summer Intern Blog #2

In continuation from my first blog I will go over the methods I used to carry out the experiment. However, while the idea of improving disease ratings by using multiple raters to average the results was the primary purpose, useful information on the effectiveness of specific fungicides to combat dollar spot was also gained through the experiment. The overall idea was to rate and evaluate the effectiveness of 19 fungicide treatments against a selected fungus disease, dollar spot, at two locations and in the process improve the disease ratings by using two raters to average the results.

The first plot was located at the ISU Horticulture Farm near Gilbert, Iowa, and the second at an old golf green located just north of Roy J. Carver Co-Lab on the northwest edge of the Iowa State campus. This location was called the WOI green, since the former WOI-TV building is also located nearby. Turf cultivars were ‘Emerald’ at the Hort farm and ‘Washington’ at WOI. Four sub-plots were needed for each of the 19 treatments making 76 plots. Four more plots were added as a control and not sprayed, totaling 80 sub-plots per location.

The first step to setting up the experiment was creating the sub-plots. By using Pythagoras’ theorem, accurate plot dimensions were insured for both site locations. A method that uses nails and a ball of white string, which is represented by the pictures, was utilized so that the corners of every 5-ft x 4-ft subplot could be seen temporarily. Orange spray paint was then used to mark the corners of each subplot so that the string could be removed and the subplots could still be located. Re-spraying the subplot corners for both locations was necessary every few weeks, especially following a heavy rain. Assignment of the spray treatments to specific sub-plots at both locations was randomized and then marked on maps for both the Hort Farm and WOI.

After the individual plots were marked the Hort Farm plot was ready to be inoculated with dollar spot. The WOI plot was not inoculated. Rye grain seeds were infested with Sclerotinia homoeocarpa, the fungus that causes dollar spot, which were then spread evenly across the surface of the 80 sub-plots. The green was kept moist but not water- logged for five days without mowing to incite fungal growth.

Following the inoculation a spray calendar was made based on the experiment’s protocol. The first spray began on 7 June, except for treatments 18 and 19 which began 24 May, and ended on 17 August. Re-application of the fungicides depended on the protocol, which had varying spray intervals. Backpack sprayers were used to apply the fungicides at 30 psi and a dilution rate of 5 gal per 1000 sq ft.

The day before a spray was to be made, the fungicide treatments were weighed out at the ISU Curtiss Farm plant pathology lab south of the ISU campus. The treatments were put into 2- liter bottles. Only about ½ inch of water was added to make a slurry. The rest of the water would not be added until right before the sprays, so that the chemical reaction would occur during the spray and not the day before, when measuring took place. On spraying days the weighed samples, in a slurry form, were transported to both spray locations and filled with the appropriate amount of water. After the bottles were filled with 1.5 liters water, the treatments were immediately driven to the plots and then sprayed.

Marked stakes were placed at every sub-plot according to a map that indicated the location of every spray treatment. These stakes would be placed in the middle of every sub-plot and then pulled out after the spraying had finished.

Tyvek suits and dual-cartridge, full-face respirator masks, with the appropriate filter necessary for pesticides, were worn for protection during sprays. During a spray date all walking took place on the borders of the sub-plots. This prevented fungicide treatments spreading to sub-plots with different treatments which, if it had occurred, would have made the data unreliable.

The treatments were evenly coated at a consistent rate of application speed, moving up and down each sub-plot. The person spraying would spray one sub-plot at a time by going north and south, and then going in an east-west direction, so the spray occurred from two directions, thus fully and evenly coating a sub-plot.

In my next and final blog I will discuss the results of the experiment as well as the impact of natural events that plagued the experiment over the course of the summer.

Nails are placed appropriately on the outside perimeter of the total plot. The nails held the string tightly in place so that the corners in the inside not measured out or marked held by nails can be seen and marked with spray paint. A single continual piece of string was used to mark out the entire plot

One of the last of the inside corners, not supported by nails but now visible because of the string, is being sprayed.

Filling the backpack sprayer with a fungicide treatment that had been weighed out the day before in our Curtiss laboratory and then transported (dry) to the location in a 2 liter bottle and then filled with 1.5 liters water right before the spray.

Applying the fungicide treatment by backpack sprayer on previously marked out 5-ft x 4-ft plots at the WOI green.


Improving Accuracy of Disease Rating for Dollar Spot on Turf

September 27, 2010

The following is a post from a student named Steve Johnson. He is an undergraduate who was working for Dr. Mark Gleason on a pathology research project this summer. He is doing this as part of the requirement for his Hort 391 special studies course. Hopefully, this will start a trend and we will have several other posts like it this fall.

Steve Johnson, Soph. Summer Intern Blog #1

Many turfgrasses are susceptible to fungal diseases and this leads to many maintenance issues for turf practitioners.  In response to the detrimental effects of turf diseases caused by a wide assortment of fungi, a precise reading of the amount of turf infected by a disease is needed to determine the proper course of action.

In evaluating alternatives for suppressing turf diseases, its important to have a method to separate the effective treatments and the from the less effective ones.  This often requires replicated field trials, often at multiple sites, comparing each alternative in the same turfgrass stand.  But how, exactly, does one measure disease severity.

Disease severity is usually measured by some sort of visual estimation method.  In other words, you look at the turf that was treated with each respective fungicide treatment and try to visually estimate a number a represents how severe the disease symptoms appear.  This is not always accurate and may not be consistent from one rating to the next or from person to person.

As an example of this, lets consider the turf disease dollar spot, caused by the fungus Sclerotinia homeocarpa. Dollar spot is a relentless disease that is recognized by it distinctive lesions that are often the size of the a silver dollar and the lesions can grow together in severe cases.  Dollar spot is the most expensive disease to control on golf courses across much of the Midwest and Eastern United States.

In comparing dollar spot fungicide treatments to each other, how can we measure disease severity?  One way is to estimate the percentage of the plot that has turned brown due to the disease.  But one person rating the percentage of dollar spot may come up with a different number than someone else.  Others have two people rate the same plot independently of each other.  So how can we be sure that the disease ratings are consistent and reliable? 

Evaluating a way to accurately estimate dollar spot severity on greens-height creeping bentgrass was the objective of this study.  We wanted to find out how different two people would rate the same turf plots, and then average the ratings to reduce bias from individual ratings.  A trial was conducted during the summer of 2010 at the ISU Horticulture Research Station to evaluate dollar spot severity on creeping bentgrass.

The results of this study are mean to be relevant for disease severity ratings of many diseases and grasses, not just bentgrass and dollar spot.  


Examples of turf from the Hort farm plots infected with dollar spot.

1 and 2.

ISU Horticulture Farm turf plot marked out for the experiment. The white string was used to show where the corners of each were.  We then spray-painted the corners in order to visually locate where each plot was without the strings.  The strings were removed after all the corners had been painted so regular maintenance could continue.

WOI green located just north of Roy J. Carver Co-Lab on the northwest edge of the ISU campus.  It was marked out and prepared for the experiment in the exact same manner as the plots at the Research Station.