My Lawn Has Never Looked This Bad!
Tony Koski, Extension Turf Specialist

Winter desiccation (aka "freeze-drying); made worse because the thatch layer was a little
thick? Probably some rabbit activity, and maybe some cranberry girdler as well? That 
combination will kill grass in the best of lawns during a severe winter.

It seems like nearly every lawn up and down the Front Range has experienced some level of turf injury this spring – more than I can remember in my 30+ years at CSU. Many have been cared for by avowed lawn geeks (like Alison’s lawn, pictured here!). These folks are used to turf perfection, so are especially shocked, dismayed and embarrassed by the spots and patches that have appeared in their normally picture-perfect lawn. What has caused so many beautiful (in 2021, anyway) lawns to become so bad this spring that owners are reluctant to send me pictures of them? Pinning down the exact cause of the turf damage without visiting the lawn can be difficult, but if you are seeing dead patches in your lawn this spring it’s almost certainly one of the following problems. Lawns that were seeded or sodded in 2021 (especially later in the year) were more likely to be injured. If the lawn hasn’t greened up by this point in time – especially after the recent rain – then it’s almost certainly dead, with the solution being new sod or seeding (go here

for some videos on seeding and sodding lawns https://planttalk.colostate.edu/youtube-videos/lawn-videos/#reseed)

Winter Desiccation (freeze-drying)
This is probably the most common cause of lawn damage this spring, most likely to occur on areas of the lawn that were drought-stressed going into winter last fall.  Turf stressed by poor irrigation coverage in 2021 (broken/plugged/low/crooked heads, low pressure, bad spacing) was more susceptible to being damaged by the dry, cold, sunny, windy winter conditions we experienced this year. Lawns with thick layers of thatch also appear to be more likely to have been injured. Check spots that are dead now for irrigation coverage deficiencies – before re-seeding or sodding. You rarely can detect non-uniform water application by simply watching your sprinkler system (“It looks like water is going everywhere” you say…but it’s not going everywhere uniformly). Don’t blindly trust your “irrigation guy”/sprinkler company when they tell you that everything “looks fine”. To be certain about uniformity of water application, it has to be measured by a formal or informal irrigation audit (here’s a DIY method to help you identify dry spots in your lawn).

This turf died from winter desiccation. When you can see where the
irrigation heads are, you know there are irrigation coverage problems. The
dead areas in this lawn were drought-stressed LAST FALL - which resulted
in the turf succumbing to the severely dry and cold winter. The turf also 
survived around the young tree - because of winter watering of the tree.

Insect Feeding Damage

Feeding by cranberry girdler (https://csuhort.blogspot.com/2020/10/cranberry-

This lawn was weakened by cranberry girdler feeding
last fall (2021); the cold, dry, windy winter resulted in
the death of the stressed turf

girdler-rears-its-ugly-head.html) or white grubs (https://extension.colostate.edu/topic-areas/insects/billbugs-and-white-grubs-5-516/) last fall could have gone undetected and so weakened turf root systems that the turf more easily succumbed to winter desiccation. Dead turf that peels up easily from the soil surface was likely fed upon by these insects. If the lawn hasn’t greened up by now, it’s dead and the only alternatives are to seed or sod the affected areas.

Turfgrass mites damaged this lawn. Notice the
lack of mite injury in the neighboring lawn (top
of photo) which received winter watering.

Mite Feeding

Winter mite activity can kill large areas of turf, usually on lawns facing south or west. The damage caused by winter mites can look identical to winter desiccation injury: orange or brown grass (early death), changing to grey/silvery grass (dead for awhile). Mite-damaged turf will still be strongly rooted, distinguishing it from damage caused by root-feeding insects. Even when mites are actively feeding in lawns, they can be difficult to detect – so mite injury is often confused with other types of winter damage. The best control for mites is late winter/early spring irrigation, or a few good snowfalls or rainy spring weather. Since they aren’t insects, insecticides don’t provide great control of turfgrass mites.

Rabbit Injury

Look for rabbit pellets (aka "poop") in the brown spots
in your lawn as a sign of rabbit activity.

Rabbits feeding is often concentrated in small areas of the lawn. The persistent feeding and deposition of urine can kill small to large areas (depends on how many rabbits are in the yard) over the winter. Rabbits can be trapped and relocated (where legal; check with local animal control for the laws that apply where you live); applying the fertilizer Milorganite to your landscape (lawn and garden beds) can repel rabbits - if they have somewhere else to feed and live.

Rabbit activity can result in the death of large areas in the home lawn.

While it’s good to know what may have killed parts of your lawn – so that you can take measures to prevent the same thing from happening in the future – the “fix” is generally the same: repairing the dead areas by seeding or sodding (here and here, for how to do this).

Cranberry Girdler Rears its Ugly Head

 Posted by: Alison O'Connor, Larimer County Extension

Doesn’t it seem weird that we have a type of sod webworm called cranberry girdler that lives in lawns in Colorado? Because this insect is a pest of cranberry bogs, Douglas-fir, and true fir…along with cool season lawns. Weird.

Regardless of its preferred hosts, these guys can do damage. Quickly. And I’ve seen a number of lawns this fall with damage. For example, there was this lawn in Loveland, which was the worst damage I’ve seen. All of the brown areas are dead. This lawn was a mix of fine fescue, tall fescue, and Kentucky bluegrass.

As for the actual insect, it appears to be a western problem in states like Utah, Colorado, and Wyoming. There’s not a lot of information about it, nor much research. (Utah State University has the best publication.) It’s a sod webworm that does its feeding and damage in late summer into fall. The damage looks a bit like drought stress, until you tug on the grass. Then it peels up like a cheap toupee.

Cranberry girdler can kill lawns by chewing through the roots, resulting in browning and the resulting toupee. Identification of this pest can be hard because it looks like most other sod webworms—grayish, smallish, with an orange-brown head measuring about ¾” long at maturity. The adult is a small moth with three black dots at the base of the wings, a buff color, and measure about ½” wide.

Adult moths (which emerge from overwintered larvae) emerge in mid-June and actively mate for 6-8 weeks. Eggs are laid on turf blades and hatch 9-11 days later. The larvae burrow into thatch or grass crowns, where they feed for two months. And that’s when we start to see damage (August-September).

Larvae will burrow deeper into the soil when temperatures start to cool. I think that’s why we’re seeing damage so late this fall—we really haven’t had cooler daytime temps, so the larvae were still feeding near the surface and easy to spot in late September.  

Now, you will be hard pressed NOT to find some sod webworms in your lawn, but there is a threshold you should consider before treatment. First, how widespread is the damage? If it’s a significant percent of the overall lawn, then treatment could be considered. Do you have the ability to water in products? If so, then treatment can be considered. But just because you see little white moths flying about doesn’t justify treatment. Many lawns will do well with some sod webworms present—especially those that are properly maintained.

A couple of things about treatment. The first is that if you have damage this fall, you should consider a spring-applied treatment for control next year. A promising (and easily available) product for homeowners is acelepryn, which is found in Scotts GrubEx. Apply this in late May to early June, watering it in with at least ½” of water. This product will control sod webworms and all white grubs (here’s looking at you, Japanese beetle).

But this fall, acelepryn or other recommended insecticides (beta-cyfluthrin, carbaryl, and chlorpyrifos) will not work quickly enough to kill damaging larvae. One of the few options is trichlorfon (sold as Dylox) and can work as a “rescue” treatment. This should be applied by a lawn care professional. Prior to application, water the lawn well with at least ½” of water and after application, apply another ½” of water. While very effective, this insecticide only lasts a couple days, so timing is important. It will not work if the caterpillars have pupated deeper into the soil.

And what do you do with the damaged areas of the lawn? You’ll have to reseed or re-sod. Seeding now (in early October) will not likely be super successful, so waiting until spring would be a better option. You could sod into late fall, as long as you can water.

So chalk it up to another 2020 “kick-you-while-you’re-down” problem. Boo cranberry girdler. Boo.

Guttation – Just a Curious Plant Thing?

Tony Koski, Extension Turf Specialist

Plants don’t do meaningless, stupid things. Every process and reaction that occurs in plants has a

purpose – although the purpose or benefit might not be apparent to those of us who grow plants. A great example of a “why does the plant do that?” came up this week – the occurrence of “guttation”.

The white spots on the leaves of this
hydrangea occur when guttation evaporates,
leaving behind salts and sugars that
were dissolved in the guttation fluid.

So why write about guttation in January? Well, a couple of days ago fellow blogger Alison received a cool photo from her brother Jeffrey, head grower/propagator for Bailey Nurseries in Oregon (you can read more about what Jeff does at Bailey Nurseries in this blog by Alison). The leaves on one of the many hydrangeas he is growing had an interesting pattern of white deposits on the leaf margins. What are they… where did they come from… and are these a problem?

Turns out that these spots are residue left behind after droplets of guttation fluid had evaporated from the hydrangea leaves. Guttation is water that is forced out of pores called hydathodes that are present in the leaves of some plant species. Different than stomata (structures on leaf surfaces that open and close to regulate air and water exchange), hydathodes are always open and are connected to the xylem of the plant (those tube-like structures in stems and leaves that move water and nutrients from the roots to the leaves).

Guttation on grass leaves (often occurs along with dew) can
encourage the occurrence of some diseases - so early morning
irrigation can wash it off and help reduce disease incidence.

Under nighttime conditions of high soil/media moisture levels, warm soil temperatures (think summer…or a warm greenhouse), high relative humidity, and cool air temperature (cooler than the soil or media in the container), roots will absorb water that travels upward in the plant to the leaves. Since stomata are mostly closed at night – which prevents water loss from the leaves – this water being forced upward into the leaves needs someplace to go. The hydathodes allow the water to exit the leaf, acting as a sort of pressure relief system. The result is that droplets of water form on the margins and tips of leaves during the early morning hours. After a few hours of sunlight, the water evaporates - sometimes leaving a whitish residue on the leaf.

Tomatoes (and many other vegetables) can form guttation. It is 

thought that bacteria and viruses can be "sucked" inside the

plant leaf when guttation dries - providing a opportunity for 

infection.

The white deposits occur because guttation droplets contain some amount of mineral salts, sugars, and amino acids. The saltiness of this residue can occasionally cause a slight burn on leaf edges, but it's usually harmless to the plant. Because it's often sweet from the sugars, it may attract ants, foraging bees, and other pollinators. In the case of turfgrasses, it is considered important to remove guttation early in the morning by watering or mowing – the goal being to reduce the occurrence and severity of some diseases (fungi may use the sugars in guttation as a food source).

Guttation doesn’t occur with all plants. Because of physics (we won’t go there!), guttation occurs in shorter plants (less than about 3 feet tall). Guttation has not been observed with conifers, but is very common in grasses (like your lawn!). It is also common on some houseplants (including many succulents) – especially if you water your plants just before dark.

The residue left behind when guttation evaporates is often
mistaken for disease or an insect infestation. Look
closely to be sure before you attempt control of a
non-existent problem!

So is guttation a problem for plants? Aside from the minor leaf edge burn that might occur from salt deposition, guttation is generally a harmless occurrence in most cases (so Jeff’s hydrangeas should be just fine). However, there is good evidence to suggest that the organism responsible for bacterial canker on tomatoes and botrytis gray mold can be present in the guttation of infected plants – and can be easily spread to healthy plants by gardeners tending their plants early in the morning before the guttation has dried. Similarly, viruses like tobacco mosaic virus have been found in the guttation of infected plants, which can then be spread healthy plants on mornings when plants are wet from guttation and dew. This suggests the importance of adequate plant spacing and careful removal of obviously diseased plants (tomatoes, cucumbers) from among the healthy population. Finally, less observant gardeners may mistake the white guttation residue for scale insects, mealybugs, or powdery mildew – leading to unnecessary and ineffective treatments for a non-existent problem. So carefully and closely check those white spots on your jade plant for guttation residue. 

Be Careful with Crabgrass Pre-Emergent Herbicides

Tony Koski, Extension Turf Specialist

Pre-emergent herbicide injury on a Kentucky bluegrass
home lawn. The herbicide was on a fertilizer carrier, thus
the darker appearance where a higher-than-recommended
rate was applied.

Among the mostly widely used lawn weed control products, pre-emergent herbicides (aka “crabgrass preventers") are generally very safe to use on most turf species. Safe, that is, if applied at the correct rate. Using a spreader without adjusting its setting to apply the correct rate, applying the product with a spreader that isn’t operating properly (plugged, skipping, etc.), applying with excessive overlap, or thinking that “more is better” can cause unintended damage to the desirable turf. In the past few weeks we've seen a greater than normal number of pre-emergent herbicide "oops" on home lawns.

New root growth suppressed by a 

misapplication of a pre-emergent herbicide,

displaying the symptomatic root clubbing.

Pre-emergent herbicides “prevent” annual weeds like crabgrass and foxtail from becoming a problem by killing very young, germinating seeds and seedlings; they don’t sterilize the soil, and they don’t kill seeds in the soil. These herbicides kill the young crabgrass, foxtail, and barnyardgrass seedling by stopping root formation – so the tiny plant can’t take up water and dies from drought stress. The crabgrass preventers used most often on home lawns (by lawn care companies, as well as in do-it-yourself products sold to the homeowner) include pendimethalin (Scotts crabgrass prevention products), prodiamine (sold as Barricade; also in Ferti-Lome, Monterey, Bonide, and Pennington home lawn care products), and dithiopyr (sold as Dimension; also in some Ferti-Lome, Hi-Yield, Bonide, and Pennington homeowner products).

Note the root clubbing (red arrows)
on shallower roots: deeper
roots (green oval) are more normal
in appearance because they are
growing beneath the pre-emergent
herbicide layer.

Misapplication due to poor technique (excessive overlap), using a faulty spreader, and intentional or unintentional application at excessive rates can damage desirable turf by stopping or stunting root production in the spring – when these products are typically applied AND when the grass plant is forming its root system. Damaged roots can’t take up water effectively, resulting in turf that is very drought sensitive. Severely damaged plants die – often in spots in the lawn where there was excessive overlap (as in the photos) – leaving brown strips or spots.

Diagnosing this injury can be tricky. Plants on the border of the dead turf will often display stunted root systems – with roots showing little or no branching and a distinctive “clubbing” at the end of the stunted roots. Because pre-emergent herbicides aren’t very water soluble and tend to remain near the surface of the lawn, deeper roots (maybe only an inch or so deeper; see photo) may grow more normally and not display the clubbing seen on roots growing near the surface. Above-ground, the turf may appear dead or severely thinned in stripes that follow application/overlap patterns. As the turf thins, new leaves formed by the surviving grass plants will be wider/more coarse due to the lack of crowding by adjacent plants (the more dense a turf is, the finer the leaf blades will be). The herbicide-stressed turf may also be more susceptible to diseases like leaf spot and dollar spot.

More subtle above-ground symptoms of
pre-emergent herbicide injury on a Kentucky
bluegrass lawn.

Pre-emergent herbicides can last a long time in the soil (4-6 months) – a good thing for providing season-long weed control. That long residual is a bad thing, however, when a pre-emergent causes turf death from over-application – and the residual effect can be even longer because of the very high rates of application that have killed the grass. This makes it difficult to repair areas by overseeding into them – because the herbicide will kill the young seedlings as they germinate. Creeping grasses (bluegrass, the more rhizomatous tall fescue cultivars, bermudagrass) will grow into the killed areas slowly over the summer. Repair by overseeding may have to wait until fall, when the herbicide has been degraded by soil microbes and other degradation forces in the soil. Worth trying, however, is core cultivation/aeration of the affected areas, followed by overseeding with perennial ryegrass. The seed will germinate below the herbicide “layer” on the surface and has a good chance of surviving and masking the damaged turf.

The take-home message? All herbicides have the potential to harm non-target turf, so always follow the label instructions and apply the product using good technique and well-maintained, properly-calibrated equipment.

Winter Water or Re-Sod, Your Choice

Posted by: Curtis Utley, Jefferson County Extension

Unless you have been living under a rock you will have noticed that

 we have been experiencing abnormally warm and dry weather

 this fall, and the long-range forecast looks to promise more

 of the same. In fact, NOAA reported: 

 
Native rocks which one could be proud to live under

...NOVEMBER 2017...DRIER AND MUCH WARMER THAN NORMAL...

AFTER AN OCTOBER WHICH EXPERIENCED A WIDE TEMPERATURE RANGE WITHIN

THE MONTH, NOVEMBER 2017 RECORDED A FAIRLY NARROW RANGE IN

TEMPERATURE DUE TO LACK OF EXTREME COLD. TWO DAILY HIGH TEMPERATURE

RECORDS WERE SET IN NOVEMBER. THE HIGH ON THE 26TH REACHED A RECORD

SETTING 74 DEGREES WITH 81 DEGREES REACHED ON THE 27TH. THE HIGH OF

81 DEGREES ON THE 27TH ALSO ESTABLISHED AN ALL TIME MONTHLY HIGH

TEMPERATURE RECORD FOR NOVEMBER. THE HIGH OF 81 DEGREES ON THE 27TH

EXCEED THE PREVIOUS MONTHLY HIGH TEMPERATURE OF 80 SET ON BOTH THE

6TH OF THE MONTH IN 2006 AND THE 16TH OF THE MONTH IN 2016.

AS FOR PRECIPITATION, NOVEMBER 2017 LANDED SHORT OF THE MONTHLY

AVERAGE AS PREDOMINANT STRONG WEST TO NORTHWESTERLY FLOW ALOFT

PROVIDED FOR FREQUENT BOUTS OF DRY DOWNSLOPE FLOW ALONG THE NORTHERN

FRONT RANGE. A FEW WEAK COLD FRONTS PUSHED THEIR WAY INTO NORTHEAST

COLORADO DURING THE MONTH, HOWEVER WITH LIMITED MOISTURE ASSOCIATED

WITH EACH ONE, ONLY LIGHT PRECIPITATION AMOUNTS WERE RECORDED. A

STRONG AND FAST-MOVING DISTURBANCE, WHICH PASSED ACROSS SOUTHERN

WYOMING AND NORTHERN COLORADO LATE IN THE DAY OF THE 17TH, PUSHED

RAIN SHOWERS ONTO THE LOWER ELEVATIONS AND GAVE DENVER THE HIGHEST

PRECIPITATION FOR THE MONTH WITH 0.23 ON THE 17TH.

AS THE THANKSGIVING HOLIDAY APPROACHED, A LARGE RIDGE OF STABLE HIGH

PRESSURE BEGAN TO DEVELOP OVER THE SOUTHWEST UNITED STATES ON THE

21ST. THIS STABLE RIDGE PERSISTED ACROSS THANKSGIVING AND INTO THE

NEXT WEEK WHILE KEEPING THE REGION AND DRY WITH WELL ABOVE AVERAGE

AND EVEN RECORD SETTING TEMPERATURES.

TEMPERATURES:

THE AVERAGE TEMPERATURE AT DENVER INTERNATIONAL AIRPORT FOR THE

MONTH WAS 45.3 DEGREES F, WHICH IS 7.0 DEGREES ABOVE NORMAL. THIS

NOW RANKS AS 10TH WARMEST NOVEMBER`S SINCE TEMPERATURES RECORDS

BEGAN IN 2017 1872. THE WARMEST NOVEMBER ON RECORD OCCURRED IN 1949

WITH AN AVERAGE MONTHLY TEMPERATURE OF 50.9 DEGREES F. THE COLDEST

NOVEMBER ON RECORD WAS OCCURRED IN 1880 WITH A MONTHLY AVERGAE OF

22.0 DEGREES.

TEN WARMEST NOVEMBER`S IN DENVER WEATHER HISTORY SINCE 1872:

50.9 1950

47.2 1999

46.2 1933, 1914

45.9 1981, 1927

45.6 1910, 1917

45.5 1917

45.3 2017

TEN COLDEST NOVEMBER`S IN DENVER WEATHER HISTORY SINCE 1872:

22.0 1880

28.9 2000

29.7 1985

31.5 1929

32.3 1952

32.5 1889

32.8 1972

33.0 1886

33.1 1872

33.3 1979

PRECIPITATION:

PRECIPITATION FOR THE MONTH OF NOVEMBER AT DENVER INTERNATIONAL

AIRPORT WAS 0.29 INCHES, WHICH IS 0.32 INCHES BELOW THE NORMAL OF

0.61 INCHES. THERE WERE 3 DAYS WITH MEASURABLE PRECIPITATION DURING

THE MONTH. 0.23 INCHES OF PRECIPITATION FELL ON THE 17TH, WHICH IS

THE GREATEST DAILY AMOUNT FOR THE MONTH.

TEN WETTEST NOVEMBER`S IN DENVER WEATHER HISTORY SINCE 1872:

3.21 INCHES 1946

2.67 INCHES 1991

2.63 INCHES 1983

2.13 INCHES 2015

1.95 INCHES 1922

1.93 INCHES 1886

1.88 INCHES 1975

1.74 INCHES 1908

1.69 INCHES 1972

1.68 INCHES 1881

TEN DRIEST NOVEMBER`S IN DENVER WEATHER HISTORY SINCE 1872:

TRACE 1949, 1901, 1889

0.01 INCHES 1939

0.03 INCHES 1917

0.04 INCHES 1905, 1904

0.05 INCHES 2003

0.07 INCHES 1903

0.08 INCHES 1920, 1874

NO THUNDER WAS OBSERVED AT DENVER INTERNATIONAL AIRPORT AND

4 DAYS WITH DENSE FOG WITH A VISIBILITY AT OR BELOW 1/4 MILE DURING

THE MONTH. THE PEAK WIND GUST OF 52 MPH FROM THE NORTHWEST OCCURRED

ON THE 1ST.

While attending the Rocky Mountain Regional Turfgrass Association Conference and Trade Show last week my colleague, Carol O’Meara and I were lamenting the fact that landscapes along the Front Range are going to suffer if the dry warm weather continues through the winter. Both of us planned on watering our landscapes a little, over the weekend, to prevent winter-kill from desiccation.

I also received a few calls last week from landscape maintenance companies concerned about protecting customer’s lawns from turfgrass mites which can kill drought-stressed turf in the winter months. This morning I decided to inspect the turfgrass outside of my office for mite activity and sure enough, I found clover mites actively feeding on the turf close to a south-facing retaining wall. Without natural winter precipitation or winter watering it is likely the clover mite population will explode and cause enough feeding damage to the quasi dormant turf to kill it out right.

Southwest facing retaining wall

Active Clover mites

Clover mites and Bank’s grass mites are cool-season pests of turfgrass along the Front Range and have caused economic damage to landscapes in the past and will kill turf this year too unless susceptible aspects of lawns receive irrigation or natural precipitation. To learn more about turf mites, check out the factsheet http://extension.colostate.edu/docs/pubs/insect/05505.pdf   

What does that mean? Damage caused by these cool-season mites is always most severe on south or west facing slopes (aspects) or on the South or West sides of evergreen trees, shrubs, buildings, walls, and fences, so focus your winter watering efforts on those areas of your lawn specifically. To learn more about winter watering, check out the factsheet  http://extension.colostate.edu/docs/pubs/garden/07211.pdf

South facing slope with mite damage

South facing side of a blue spruce

West facing slope with mite damage

Check for mite activity in your lawn by swiping a white sheet of paper over the lawn. Turn the paper over and examine it for small red streaks; the streaks represent crushed mites. If found, know that your lawn at that specific location is in peril and you should water. If the paper has lots of streaks, consider spraying that aspect with an insecticidal soap to knock back the population of mites then begin watering. To learn how to check for mites, watch this video

Next spring, if you notice the south and west aspects of your lawn are not greening-up with the rest of your lawn, check the margins of the damage with a clean sheet of white paper. If you find streaks, begin watering.The areas of turf that have not greened up by April are probably dead and should be re--sodded, reseeded or, consider mulching those areas and planting western natives in those locations. To learn more, check out this factsheet http://extension.colostate.edu/docs/pubs/garden/07241.pdf  or this Plantalk script http://planttalk.colostate.edu/topics/lawns/1517-sodding-lawn/ . A little water now may save you the cost of replanting, and a lot of water next spring to re-establish your turf.

Small red streaks are crushed mite bodies and indicate activity