Ascochyta Leaf Blight: Facts and Myths

Tony Koski, Extension Turf Specialist
Dept. of Horticulture and Landscape Architecture

The visible wheel tracks does NOT mean that mowing 

"tracked" the ALB fungus on to the lawn. Rather, the 
lawn was drought-/heat-stressed when it was mowed. 
The wilted grass leaves were killed by the weight of 
the mower - but the grass plant is still alive.

It's back, in full force, on Colorado's lawns. Cool, wet springs, like this year's, create perfect conditions for Ascochyta leaf blight (ALB) outbreaks. When the transition from spring to hot, dry summer conditions occurs as suddenly as how it happened this year, ALB becomes epidemic in lawns.

We've blogged about ALB a number of times, so there's no reason to repeat what you can read there (2013, 2015, 2016, 2017). Without re-hashing what was written in years past,  the most important takeaway: it's a problem of drought, heat stress, and lack of water (or a sign of an irrigation system problem); mowing the stressed turf often increases the injury. The good news is that the grass is NOT dead, but can be revived with sensible watering and by paying closer attention to future irrigation needs.

Some ALB facts:

• While it is a disease, ALB is really a problem of water - not enough, or not frequently enough. 
• ALB can affect bluegrass, fescue, and ryegrass lawns.
• Fungicide applications will NOT make it recover more quickly - so don't apply them (or don't pay for your lawn care company to apply them!)
• While an ALB outbreak looks terrible and the grass appears dead, this disease does NOT kill grass.
• An infected lawn will recover, though it may take 1-3 weeks for full recovery. Recovery rate depends on severity, species of grass, and how you water (not swampy, but consistent moisture).
• Light fertilization - if your lawns has not yet been fertilized this year - can help speed recovery.
• The ALB fungus does infect grass leaves through the mowed off tip of the leaf blade - but that doesn't mean you should stop mowing the lawn when disease is active (mowing doesn't spread the fungus, nor does it significantly increase the amount or severity of the disease). 

Some popular myths about ALB:

• Maybe you've read on the never-wrong internet that the ALB fungus is spread by mowers? Wrong! The wheel tracking often seen on ALB-affected lawns occurs because the lawn was mowed when it was drought- and/or heat-stressed. The weight of the mower crushes the wilted leaves under the wheels, leaving brown tracks a day or so later. Often there is no ALB disease IN the wheel tracks - but plenty of blighted turf between the wheel marks. 
• You will also find claims that lawn mowing equipment should be disinfected between lawns - or after you mow you own lawn. Wrong again! The fungal spores that can result in ALB are everywhere already. Disinfecting your mower with bleach solutions or Lysol will not prevent future ALB on your lawn, nor will it prevent its occurrence on lawns of other clients (if you own a lawn care or mowing business).
• You will also read on that you should throw grass clippings from lawns suffering an ALB outbreak into the trash, because leaving them on the lawn will make the problem worse - or will cause it to happen in the future. Again, there is no evidence to suggest this to be true. As before, the spores are EVERYWHERE already. Grass clippings can be safely composted or used as mulch in gardens (because the fungus causing the lawn disease doesn't affect vegetable or flower garden plants).

While people will always claim that "it can't be water", it ALWAYS is. When you can see where the sprinkler heads are in a lawn affected by ALB, that should be a sure indicator that it is a watering issue. Read the previous blogs listed above for suggestions on getting a lawn back to health after an ALB outbreak.

Ascochyta Leaf Blight on Lawns – 2017 Version

Mowing drought-stressed lawns can make
Ascochyta worse. Notice no disease at top
of photo - shadier and no drought stress here!

Tony Koski
Extension Turf Specialist

The appearance of Ascochyta Leaf Blight has become an annual springtime event on lawns in Colorado. We have written about Ascochyta before: see our 2013, 2015 and 2016 blogs on this lawn disease. For more detailed information on Ascochyta in lawns, read those blogs because I’m not going to repeat everything that we've already written about it.

What I do want to talk about is WHY the Ascochyta disease appeared so suddenly over the last week. We’ve been inundated with calls, emails and texts with a common theme: “My lawn was perfectly green, and now you should see it! What happened?”. The explanation of why – that the disease is incited by drought stress –  doesn’t make sense to people because it appeared after the very wet (2 plus inches of water) snowy/rainy storm that came on May 16-18. That abundance of moisture (here’s what people DON’T remember) was preceded by two WEEKS of above-normal temperatures and very dry weather (red flag weather, if you recall?). And while everyone who has seen this happen to their lawns claims they were watering, I saw a lot of drought-stressed turf in the week before the storm. All it takes to turn Ascochyta on is a day or two of drought stress and heat during the spring – which this graph clearly shows was probable in home lawns this May. Those who REALLY were watering their lawns (or have shady lawns, or north exposure lawns) are not seeing Ascochyta. 

Much of first half of May was warmer (red line) than average (green line).And there was almost no precipitation May 1-16. This is a perfect "recipe"for Ascochyta on lawns that aren't irrigated enough during warm springs.The disease cycle began BEFORE the wet storm, with the symptoms appearing immediately after the storm. The moisture came a couple of days too late!

Here are some pics of what we’ve seen the past week.

In these 2 photos, there is less/no Ascochyta in parts of the lawn that are shaded or receiving a little more water from gutter downspouts. Ascochyta is turned on by heat and drought stress in the spring

Some quick bullets on the disease (go here for more details):

• As bad as it looks, it isn’t dead!

• Affected turf will take 1-3 weeks to recover, depending on severity and turf species.

• It is NOT spread by mowing equipment – so there is no need to sanitize your mower.

• Fungicides are NOT EFFECTIVE for preventing or curing the disease – so don’t apply them!

• Adjust watering (and fix sprinkler coverage issues) to maintain consistent soil moisture, but not so that it is swampy (which will slow down recovery).

• This appears to be a disease that occurs when cool weather turns into hot weather (hence a spring disease), so it will pretty much disappear as we become consistently warm in the summer.

Ascochyta doesn't kill the grass plant. You will see new growth
under the dead leaves almost immediately following an outbreak
of this disease. Recovery can take 1-3 weeks, depending on
severity and grass species.

While you can see mowing patterns with Ascochyta, mowing and the mower
doesn't spread the fungus. The mowing is an additional stress when turf is
heat and drought-stressed - so the Ascochyta and mower stress combine to
cause the browning of the turf.

Turf Rant: Believe me, it IS an irrigation problem!

Tony Koski, Extension Turf Specialist

The home owner insisted they were "watering enough". Clearly

they are not!

In case you missed my last blog on brown spots in the lawn and Ascochyta a few weeks ago, well, it’s still a problem. If you are seeing these symptoms in your lawn: it’s an irrigation problem. Yes, it’s water! Even if you don’t believe me – and most people (professional turf managers and home owners alike) don’t – trust me, it really, REALLY is an irrigation problem. Repeat after me...

There is an irrigation head in the middle of
that green spot - which is in the middle of that
huge brown spot. Hmmmm...could this be
an irrigation problem?

There is the head...way down in the turf.

Poor head-to-head coverage, heads that aren’t level, heads that are too deep, heads that aren’t turning or are plugged, “shadows” created by trees, shrubs, perennials and other obstructing plants in your landscape. There are so many potential causes of poor water distribution, problems that are magnified when we have hot weather and it doesn’t rain for 1-2 weeks. We have seen every conceivable cause of poor irrigation coverage in the past month, after being reassured by the client that “it can’t be water… it has to be something else”. Well, we were correct and they were wrong. Yes, this is turning into a bit of a rant…intentionally!

Yes, it kinda sorta still works. Water comes out,
but not nearly enough to reach adjacent heads.

Just because "this has never happened until this year" (though it probably did)….or you are watering “enough” or “more than I used to” (maybe, maybe not)…. or “it looks like water is going everywhere” (yes, but not evenly)… or “it’s a new irrigation system” (sorry, no guarantees of anything there)… or yada yada yada…. Well, hopefully you get the gist? If you are seeing spots like this in your lawn (especially if there is a bright green spot in the middle of it, or next to it), it’s a water problem.

Conduct your own informal irrigation audit
by placing containers in your lawn (on the
brown and green spots); collect water for an
entire run time and compare depths.

If you still don’t believe me, place identical containers (Tupperware, pint Mason jars, empty yogurt containers or cat food cans, drinking cups that won’t tip over) on the healthy, green areas of your lawn AND on the not-so-good brown areas the evening before your system is set to irrigate the lawn. In the morning, measure the depth of water in the containers. The depth of water on the brown areas will be less than on the green, healthy turf (that’s a promise). It might only be a difference of 0.1 or 0.2 inches, but that difference in water adds up quickly under summer growing conditions. Those parts of the lawn receiving less water become drought- and heat-stressed sooner and more severely than the adequately watered parts of the lawn. The stressed areas are more susceptible to Ascochyta leaf blight, which turns the grass brown (but doesn’t kill it) – or the grass might just begin going dormant (= brown!).

Your job is then to figure out WHY the coverage is lacking on the stressed areas (station run time, sprinkler spacing, pressure, heads that are broken or plugged or obstructed or too deep, etc.) and remedy the problem. If you can’t figure it out or don’t have the expertise, hire someone who understands irrigation systems to help you. Once fixed, the grass can recover remarkably quickly – but that will depend on how long you have waited to do something about it.

Ascochyta outbreak on 9 June 2016 in Windsor

Turf can recover relatively quickly after the irrigation problem is resolved. This photo taken 2 weeks later (23 June 2016)

Looks even better after another week of recovery! (29 June 2016)

Avoid the temptation to turn your lawn into a rice paddy to speed recovery of the brown areas. Soggy conditions can actually slow down recovery. Simply maintain adequate – but not soggy, mushy, swampy – soil moisture. And hope that the monsoon rains begin soon - though predictions aren’t favorable for a good monsoon season at this point (CAUTION: for weather geeks only).

If you are living in a county that offers the CSU Lawncheck service and would like an on-site consultation (we diagnose the problem, but don't repair irrigation systems!), go here: http://www.extension.colostate.edu/lawncheck/book.shtml

There is a fee for this service in those participating counties.

Also, many water suppliers offer irrigation audits (generally free of charge) to homeowners and HOAs. Check with your water supplier to see if it is offered and you qualify.