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An Instant Classic, Kentucky Bluegrass decline, and a Big Storm

July 19, 2010

The Open Championship concluded over the weekend with first time major champion Louis Oosthuizen running away from the field for the victory. With three of the four majors completed the summer is off and rolling.

The Field Day Classic was held last week at Jewell Golf and Country Club. It was a great day despite the heat with temperatures reaching into the high 90’s and a heat index well over 100. The course was in great shape and the weather didn’t seem to hinder low scoring. Special thanks to Brian Abels and his entire staff for hosting and putting on a great event.


 

 

 

 

 

 

The hot temperatures have also been causing havoc to our cool-season turfgrasses as well. Soil temperatures are now reaching into the low 80’s causing root growth to stop. Research has shown that creeping bentgrass generally loses about three quarters of its root biomass from the end of May to the beginning of June. This natural root decline coupled with the extreme rainfall amounts during the month of June which caused roots to pull back has resulted in turf that is especially sensitive to environmental and fungal stresses.

I have seen Kentucky bluegrass beginning to decline over the last couple of weeks. The pictures below show a low-mow Kentucky bluegrass intermediate rough. After inspecting the area, the decline seemed to be the result of leaf spot/melting out disease. The disease activity was also more prevalent where the turf was under shade part of the day. Notice how the common type Kentucky bluegrass in the primary rough remains largely unaffected. Mowing height also appears to be playing a large role in the disease activity. Leaf spot can be controlled on a curative basis but applications are most effective in the early stages of the disease.

 

 

 

 

 

 

 

 

Diseases will continue to wreak havoc on our cool-season grasses the rest of the summer. For those of you with large acres of perennial ryegrass, the prime window for gray leaf spot is right around the corner.

On a side note, Ames and central Iowa had severe storms roll through Saturday night with winds reaching speeds of over 70 mph. While I kind of like severe weather I do not enjoy the cleanup. Waking up Sunday morning it looked like a bomb had went off in the neighborhood with plant debris and trees down everywhere. Luckily the picture below wasn’t from my house but wasn’t too far away. Hopefully the rest of you in central Iowa were able to avoid damage as well.


 

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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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SUMMER PATCH AT HORTICULTURE RESEARCH STATION

July 10, 2013

These are pictures of Summer Patch on Kentucky bluegrass at the Horticulture Research Station.  It is caused by the fungi Magnaporthe poae.  It typically shows up in early summer, particularly in years like this that are very wet early followed by a quick drying period and hot temperatures.  This showed up over the 4th of July (right on time).

The blighted areas with a green center that are surrounded by a circle of dead grass are known as “frog-eyes” and are typical of a number of patch diseases.  It is believed that the organism begins as a saprophyte (organism that feeds on dead plant material) in the middle and moves outward in a circle without damaging living grass.  It only attacks living grass if conditions are right and it reaches a certain level of virulence. The patches here are 10 to 12 inches in diameter, which is common for this disease.

There are several systemic fungicides labeled for this disease, but the trick is to get them down before the symptoms develop.  Contact fungicides will not work.  To treat now would do no good and the symptoms will like last through the summer.  This is a disease for which good records are a must.  On this area, I would need to apply a systemic fungicide in late June next year before symptoms develop.  Core aeration in the fall and irrigation during the stress period of early summer can also help prevent its development.

 

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RUST DISEASE SHOWING UP IN NORTH CENTRAL IOWA

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  (http://www.ntep.org/).  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.

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LEAF SPOT EVERYWHERE

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.

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