Turfgrass Physiology and Pathology 101

Sometimes I wonder if I am the only one that freaks out about grass.  Don't laugh, because it happens more often than you think.  Although I initially thought the course had come out of winter in great shape, things deteriorated quickly as the weather warmed and the course began to green up.  While most of the course showed great signs of life, the exact opposite could be said about the Poa Annua populations.

The poa initially looked fine coming out of snow cover, then slowly started to turn from brown, to tan, to white....while the rest of the turf was going from brown, to light green, to dark green.  What made matters even more confusing, was the patterns of damage I saw in the Poa.  Very distinctly round, circular patches of dead leaf tissue.  Even more concerning, was the presence of black sclerotia (part of the survival structure of a fungus) on the dead leaf tissue.  To me, and to almost everyone I showed these pictures to, it appeared that we must have a horrible breakthrough of grey snow mold or snow scald.

Very distinct patchy, disease appearance of dead Poa Annua

Black sclerotia on dead leaf tissue

However, a very good deal of evidence did not point toward any type of snow molds.  First and foremost, I made a very precise fungicide spray application last fall intentionally to combat snow mold.  Even a small amount of disease development this spring would have been a surprise, much less any wide spread development like this.  Furthermore, the damage was not present when the snow melted, it wasn't for a good two weeks until I noticed these symptoms.  Lastly, ONLY the Poa was affected, none of the bentgrass or kentucky bluegrass was even touched by this.  Snow mold generally does not discriminate on what it infects.

Regardless, I had to know what exactly we were seeing here in order to know how to properly search for a solution.  On wednesday of last week, I overnighted 3 samples to a turfgrass disease diagnostic lab in Missouri for analysis.  With in 24 hours, I had the answer:  all 3 samples tested completely clean of any form of snow mold.  Case closed.

Not quite.  The turf pathologist called back on Friday to inform me that an incredible amount of a soil borne, root infecting pythium fungus had been detected in the roots of the Poa plants.  This was absolutely mind boggling to me.  Pythium is absolutely not something we should even be talking about in early April in North Dakota.

Whereas a lot of things in life may have a very definitive answer, dealing with an organism as dynamic as a stand of turfgrass rarely presents any specific answers.  Now that the infection had been pin pointed, a new question arose.  Was the pythium infection the cause of the turf damage, or more a result of the turf damage?  I spoke with a wide array of turf professionals in the last week who have been very gracious to offer me some of their insight.  Most tend to agree however, that a root infecting pythium, at this time of year in this part of the country, is a very weak pathogen.  Moreover, it would not discriminate if it was going to attack Poa, bentgrass, bluegrass, ryegrass....etc.  The fact that we saw the damage only on the Poa was telling of another story.

The issue here more than likely goes all the way back to last fall.  From the point when we blew out the irrigation system, October 29th, until Christmas Day, nearly two full months, we saw only .14" of precipitation.  Essentially nothing.  The turf on the golf course was drought stressed to begin the winter with.  Furthermore, although the ground began to freeze in late November, we continued to experience some warm days above freezing through December.  Although the turf plant is dormant at this point in the year, the plant still respires moisture on warm days.  However, when the ground is frozen, the plant is unable to uptake water from the soil.  This process, known as dessication, was further enhanced by the lack of moisture in the plant in the first place from the dry fall. 

Another factor in this scenario was the lack of snowcover.  Many of you who may have read this blog probably heard me complain in December about our open winter.  Snowcover protects the turf from the dry winter air and winds (preventing dessication) as well as protects the turf from direct low temperatures.  Although temperatures in December were above average, we still saw some nights dip down around -4 or -5.  Without snowcover as insulation, the turf takes those temperature directly, which is not ideal.

The combination of these two events more than likely were very stressful to the turfgrass.  The last piece of this puzzle however is the physiology of the turfgrass stands on our golf course.  Both creeping bentgrass and kentucky bluegrass are very hardy, cold tolerant perennial grasses.  However Poa Annua (which is latin for Annual Bluegrass) is just that, annual.  What most people don't realize is that Poa is a plant whose natural lifecycle is to die every year!  Remember those white seed heads we used to see on the greens and fairways?  That is the Poa plant producing seed, its offspring, because it is preparing to die later in the fall.  Unfortunately, when it creeps into a turfgrass stand on a golf course, we end up treating it with such delicacy (irrigation, fertilizer, fungicides, growth regulators) that it manages to survive year after year.  However, the fact of the matter is that Poa is generally a very weak plant species because its sole purpose is to grow, produce seed, and die.

What we are seeing on the course this spring is the story of how different grasses respond to different conditions.  The bentgrass and the bluegrass experienced the exact same conditions this winter as the Poa.  The Poa however was too weak to take the stresses, and basically kicked the bucket.  The pythium infection likely originated with the EXTREMELY warm temperatures we had in March, and just took advantage of a very easily infected host in the already mostly dead Poa.  Again, the bentgrass and bluegrass also experienced the pythium in the soil, but was able to defend its self against a weak pathogen....

The morale of this story is a few things.  This fall, let's hope for some timely rains in October and November.  Furthermore, let's hope for a good blanket of snow (but not too much snow!) to cover the course by Thanksgiving.  Lastly, my vote is to tear up the fairways and greens, sterilize the soil to kill all remaining Poa Annua seeds, and reseed the entire golf course with some desirable grasses this fall!  Whose with me....?

This picture sums it all up.  On the right, is a stand of almost entirely
kentucky bluegrass.  This area used to be rough (Poa likes to grow
in short mowed areas).  We widened the fairway here last year, however
the old rough that we mowed down was still pure kentucky bluegrass. 
The left half of this picture is old fairway, with a lot of Poa in it. 
Pretty telling sign of what happened over the winter....

Fortunately, or unfortunately, all of the dead Poa areas will quickly refill themselves with more Poa.  Although it obviously isn't a desireable grass, it is still a grass that we can manage into a great golf course.  It just makes for a lot more headaches.  6 and 11 fairways have the highest Poa concentration, and definitely took the worst damage.  We will probably try to reseed in some kentucky bluegrass/perennial ryegrass seed that we have that was left over from the flood last year into these areas to see if we can increase the population of some stronger grasses. 

I fully expect with some warmer temperatures and a little extra fertilizer that the rest of the damaged areas will take care of themselves just fine.