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K-State Turf and Landscape Blog

Category: Environment

Iris Leaf Spot: A Common Problem in Kansas

By Judy O’Mara

I was out working in the garden last weekend and I saw the first appearance of iris leaf spot (Didymellina macrospora). This is a very unattractive fungal disease. The iris planting puts out nice looking flowers each year but for the rest of the season everything looks rough, with heavy leaf spotting and leaf scorch. Iris leaf spot will show up in most years but will be severe in years that are wet.

Iris leaf spot is not an easy disease to clean up because it overwinters in the residue. So the first step for management is to clean up the flower bed in the fall after frost has killed the tops. This will help to reduce the amount of disease that is carried over. Unfortunately it won’t get rid of the disease. If the planting is old and crowded, digging them up and respacing them will improve air flow. This can help to reduce disease severity.

Start fungicide protection (chlorothalonil or mycloblutanil) when leaf spotting first shows up early in the spring. Four to six applications may be needed at 7-10 day intervals. Adding a spreader sticker will help coverage and effectiveness of the treatment.

For more information on iris leaf spot check out the following K-State Horticulture fact sheet. https://hnr.k-state.edu/extension/info-center/common-pest-problems/common-pest-problem-new/Iris%20Leaf%20Spot.pdf

Flowering Ornamentals and Crabgrass Emergence

By Jack Fry and Ward Upham

Efficacy of some preemergence herbicides is strongly dependent upon the timing of application relative to crabgrass emergence.  For example, application of a preemergence herbicide that has a relatively short residual, such as pendimethalin, closer to crabgrass emergence, will extend the period of time which the herbicide is effective.  Herbicides with longer residuals, such as prodiamine (Barricade), are often applied well before crabgrass emergence, and can even be effective if applied late in the previous autumn.

In our climate, calendar dates don’t always adequately identify crabgrass emergence or herbicide application.  Biological indicators, such as flowering ornamentals, may be useful for predicting crabgrass emergence and preemergence herbicide application.

From 1995 to 1997, K-State researchers worked with those at the Univ. of Nebraska to identify ornamentals at each location which best represented crabgrass emergence and preemergence herbicide application time.  Ornamentals evaluated were bridal wreath spirea, callery pear, daffodil, flowering quince, forsythia, iris, lilac, redbud, saucer magnolia, tulip, and vanhoutte spirea.  Obviously, there may be ornamental cultivar differences in blooms, so this was an average of those observed.  In addition, crabgrass can vary in rate of emergence, but getting an herbicide out before the first plants emerge is preferable.  For this article, we’ll focus on results in Kansas.

Crabgrass emergence in bare soil and thin turf was evaluated at the Rocky Ford Research Center in Manhattan. Over three years, the earliest date of crabgrass emergence in bare soil was April 15 1995, whereas the latest date was May 9, 1996.  In the thin turf (10% bare soil evident while standing), the earliest date of emergence was May 5, 1997 and the latest date was May 22, 1995.

Withering of blooms was a better indicator of crabgrass emergence, particularly in thin turf.  In this case, we looked at bloom wither and then compared it to a date 2 weeks prior to emergence.  This 2-week window would allow time for the herbicide to be applied. In Kansas, withering of most ornamentals was not useful for estimating emergence of crabgrass in bare soil, as emergence often occurred before blooms had withered. However, a date 2 weeks prior to  crabgrass emergence in bare soil could be estimated by adding 6 to 12 days to the date of daffodil wither.

Bloom wither of flower ornamentals was used as a date to determine time of application of short-residual preemergence herbicides (a date 2 weeks prior to crabgrass emergence)

 

Flower wither of all ornamentals could be used indicators of emergence (and herbicide application date) in thin turf in Kansas (see Table 1 below). For example, by adding 28 to 33 days to the date of forsythia bloom wither, you will estimate a date 2 weeks prior to crabgrass emergence in thin turf, which would allow time for preemergence herbicide application.  This timeline is quite different from the often used theory that herbicides must be put down at the time forsythia blooms.  Ultimately, biological indicators, along with soil temperatures, will be better indicators of for crabgrass emergence and application of short-residual preemergence herbicides than calendar dates.

Table 1.  Ornamentals and the number of days to be added to flower wither to estimate the date 2 weeks prior to crabgrass emergence in thin turf.  Data were based upon observation of ornamental blooms and crabgrass emergence for a 3-year period.

Ornamental Number of days to add to bloom wither to estimate the date 2 weeks before crabgrass emergence (range allows for standard error)
Bridal wreath spirea 4 to 13
Callery pear 32 to 41
Flowering quince 36 to 42
Forsythia 28 to 33
Iris 8 to 15
Lilac 17 to 22
Redbud 25 to 32
Saucer magnolia 28 to 32
Tulip 21 to 29

 

Note – This article is based upon:

Fry, J., S. Rodie, R. Gaussoin, S. Wiest, W. Upham, and A. Zuk.  2001.  Using flowering ornamentals to guide preemergence herbicide application in the Midwest U.S.  International Turfgrass Society Research Journal.  p. 1009-1012.

National Pesticide Safety Education Month

By: Frannie Miller

Did you know there are about 1 million certified pesticide applicators in the United States? There is somewhere between 11,000 to 15,000 pesticide products registered for use in each state. Common consumer products that contain pesticides include flea collars, weed and feed, and roach baits. Pesticides play an important role in improving the quality of food and feed yields. They also protect the public health, controlling pests in our homes, turf, forests, waterways, and right-of-way.

February is National Pesticide Safety Education Month, which is important in raising awareness and support for land-grant Pesticide Safety Education Programs (PSEP). Pesticide Safety Educations Programs like the one at Kansas State University deliver pesticide applicator trainings on safe use of pesticides in various settings, as well as deal with state-specific needs and laws.

Have you ever wondered how safe you are when using pesticides? You can take a self-assessment of personal pesticide safety practices to evaluate where you could do better:

Self-Assessment of Personal Pesticide Safety Practices

Ice, Ice Baby.

By Dr. Jack Fry

Ice can cause many problems for turf, in various forms.

Ice Inside the Plant

Ice routinely forms inside plants when temperatures drop below freezing. Where the ice forms is important – when it’s outside the plant cells, it’s usually not an issue. This is called extracellular freezing.  However, no plant cell will survive when ice forms inside it.

The most important part of the turfgrass plant regarding survival is the crown, or growing point. Again, ice forming outside cells inside the crown is common and usually not harmful. It can become an issue, primarily in warm-season grasses, like bermudagrass, when temperatures are very cold for extended periods of time. This forces water inside cells to exit toward the ice (a matter of physics), and too much water leaving the cells will cause dehydration, which can cause the crown to die.

Freezing injury on bermuda is caused by ice forming outside cells within the crown of the plant that causes dehydration.

Ice formation inside cells of the crown commonly causes the death of grasses in the northern U.S, and it’s called intracellular freezing or crown hydration injury.  Usually, grasses that succumb to this type of injury become well hydrated in early spring, often growing in low areas that don’t drain well. Hydrated crowns that are then subjected to extremely low temperatures often suffer from ice formation inside cells of the crown;  when this occurs, they don’t survive. This is common in the northern U.S. on annual bluegrass on golf greens. It could also occur here, but would be most likely on warm-season grasses lying in low areas.

Ice Covering the Plant

Fortunately, in the central U.S., we don’t deal with extended periods of ice cover on turf. Ice cover can result from sleet, freezing rain, or snow melting and refreezing. Turf managers in the northern U.S. begin to worry about ice cover when it remains in place for about 60 days. That’s usually the limit for annual bluegrass – being under ice cover more than that can cause issues with lack of oxygen and/or accumulation of toxic gases under the ice

Ice on the Leaf Surface – Frost!

In a humid environment, when the leaf surfaces cool to temperatures below freezing, ice will form as frost on the leaves. Leaves of cool-season grasses tolerate frost on leaves just fine. Leaves of warm-season grasses don’t like frost, and we often see them go dormant shortly after the first hard frost in the fall.

Frost on the leaf surface can damage when foot or vehicle traffic causes the crystals to puncture the leaf cells (photo courtesy of Dr. Hoyle).

Frost is primarily a problem for turf managers in spring and fall on cool-season grasses. Foot or vehicle traffic pushes the ice crystals through the leaf surface and punctures cells, causing them to collapse. The result is that there is often brown turf where traffic was present. Honestly, I don’t think we know enough about the physics of ice that comprises frost, and I suspect that frost differs a lot – some ice forming on leaves may be more damaging than other ice.

Following are a few articles related to frost on turf.

For golfers:

https://www.usga.org/content/usga/home-page/articles/2018/01/5-things-to-know–frost-delays.html

For superintendents managing golf courses:

https://www.golfcourseindustry.com/article/golf-frost-delay

Apparently, in Japan, golfers play year-round regardless of temperature.  Some courses ignore frost to sustain income and have had less damage than expected:

https://www.blog.asianturfgrass.com/2016/12/how-to-lose-120-million-yen-with-frost-delays.html

 

Natural needle drop, or plant disease?

(Megan Kennelly, KSU Plant Pathology)

Which of these is a disease, and which is natural needle drop?

If you guessed natural needle drop for the first and disease (Dothistroma needle blight) for the second, you are right!

If you were not sure, here are some resources to figure it out.

In a recent article in Horticulture News, Ward Upham mentioned some recent reports about natural needle drop on evergreens. You can read more about it here:

http://www.ksuhortnewsletter.org/newsletters/natural-needle-drop-on-spruce-arborvitae-and-pines

In addition, this publication talks about pine diseases and at the end there is a section about natural needle drop:

https://www.bookstore.ksre.ksu.edu/pubs/l722.pdf

If you see yellowing, browning, or dropping of needles and you still are not sure you can reach out to your local K-State Research and Extension office or contact the KSU Plant Disease Diagnostic Lab:

Plant Disease Diagnostic Lab

1712 Claflin Road
4032 Throckmorton PSC
Manhattan, Kansas 66506
(785) 532-5810
Fax: (785) 532 5692
clinic@ksu.edu

 

Preparing for the Cold Season Ahead

By: Brooke Garcia

It seems as through Kansas only knows how to jump, skip, or hop into a new season. We had a small taste of Fall weather, and it is now feeling a lot more like winter. The landscape has most likely dramatically changed in the last few weeks. If you overseeded your lawn, you’re hopefully enjoying the green color of the freshly germinated seed. Several garden weeds are dying back. Mums are flowering and showing off their color. Maples, as well as other fall foliage, are showing off their beautiful fall color as well. Visit the Horticulture e-Newsletter for more information on some of the reasons these trees have color.

While some of our favorite landscape items are full of life and color, there are a handful of plants in the landscape that have entered dormancy or have died back. Not only have they lost their leaves or blooms, they may be ready for cutbacks. If you had annuals planted in the landscape, they may have recently died back from the recent freezing temperatures we experienced throughout Kansas. They will need to be removed from the landscape. Fall is an important time to perform a garden clean-up. For more specific information on perennial cutbacks, visit the Horticulture e-Newsletter for their recent post.

Want to know what to do with all of those leaves? Here is a previous blog post about Mow-mulching fall leaves.

It is also not too late to plant Spring-Flowering Bulbs. As long as the soil
temperatures >40 degrees Fahrenheit, the spring bulbs should continue to develop. For more information, read the article “There is Still Time to Plant Spring Flowering Bulbs” on the Horticulture e-Newsletter blog.

After you’ve completed cutbacks and bulb planting, mulching is an important task to be completed in the Fall. Not only does it “freshen” up landscape beds, it helps to retain soil moisture and protect the roots of plantings for the winter months ahead.

In addition to all of these Fall tasks, it is also important to consider general clean-up tasks that include:

  • Power-washing exterior of buildings and/or structures, as well as driveways or sidewalks
  • Container/planter re-fresh: Remove dead plantings from containers or planters. Empty used soil out of containers and store containers in a warmer/dry place. This can reduce cracking and general wear/tear.
  • Remove dead weeds from landscape
  • Remove fallen leaves/debris within landscape, and add to compost bin
  • Unscrew hose, and place hose-bib covers over hose bibs in preparation for freezing temperatures
  • Cover or store exterior furniture. Store cushions, umbrellas, etc.

This may seem like a lot of fall tasks to consider, but they are all important tasks to keep your landscape(s) looking beautiful during the fall and winter seasons. Hopefully this helps you develop your Fall clean-up program or builds onto an existing clean-up program for your landscape and garden.

Don’t forget to follow our Turfgrass Facebook Page for blog updates and other timely information.

Sharp drop in temperature may be a cause for concern in trees

Western Kansas experienced an extremely sharp drop in temperature recently. Temperatures in some areas of northwest Kansas were near 80 on Wednesday and dropped to near 20 or lower Friday morning. Unfortunately, trees were not hardened off before this happened. In other words, they were not ready for these cold temperatures.

What does this mean? You can read the whole article here in the Horticulture News. Go to this page and scroll down partway:

http://www.ksuhortnewsletter.org/

Cooler weather brings the return of the Mesonet Freeze Monitor

(Chip Redmond, Mary Knapp and Dan Regier; Weather Data Library/Mesonet)

Cold weather is making its appearance with frost advisories issued this last weekend and freeze warnings this week. The average freeze date in northwest Kansas is as early as the last week in September. However, southeast Kansas does not usually see freezing temperatures until the end of October. Average dates for the first occurrence of 24-degree F temperatures are even later.

For more information check out the KSU Agronomy eUpdate.

https://webapp.agron.ksu.edu/agr_social/m_eu_article.throck?article_id=2358

Fall Fertilization and Turf Tips

(By Jared Hoyle, KSU Turfgrass Research and Extension)

Dr. Bill Kreuser, Assistant Professor and Extension Turfgrass Specialist, at the University of Nebraska – Lincoln posted some great information on fall turfgrass fertility and some other fall turfgrass tips.

Dr. Kreuser quoted, “Fall is arguably the most import season for turfgrass managers. While we’re busy preparing for a new growing season in spring and trying to survive stressful conditions in the summer, fall is the time to recover from summer, renovate, and prepare for winter. It’s a season of seeding, cultivation, weed control, and fertilization. While fall is still widely considered the most important time to fertilize turfgrass, the fertilization recommendations have evolved over the past decade.”

I couldn’t agree with him more.  There has been lots of recommendations evolve over the years and just because “this” is way it has always been done doesn’t mean it is right.  See what Dr. Kreuser has to say and check out the links below.

 

  1. Rethinking Fall Fertilization
  2. Mid-Fall Turf Tips 

 

Declining Oaks

By Judy O’Mara

Declining Oaks...are not that easy to sort out. There is an assumption that if an oak tree is dying it must be due to a disease. That is usually NOT the case. Most of the poor growth that we see on oak trees in Kansas is generally due to a combination of site factors and environmental extremes. 2018 and 2019 provide back to back examples of weather extremes. Add in site factors like tree planting depth (too deep), construction damage, heavy soils or compacted soils that drain poorly, sandy soils that don’t hold on to water very well, and trees can develop root systems that are not as vigorous as they should be.  The result is a situation where trees are prone to declining under weather extremes – and Kansas is all about extreme weather.

A look at some weather data for Johnson County (Olathe, KS) provided by the K-State Weather Mesonet shows that the 20yr average annual precipitation is 40.04” for that location. At a glance it is easy to see that some years run wetter than average and some years are drier than average. I picked the Johnson County, KS location to highlight because we frequently get oak tree samples in the K-State Plant Disease Diagnostic Lab from the Kansas City area with questions about disease.

2018 was a dry year due to a winter drought and we saw trees decline across the state, including quite a few oaks from the Kansas City area. There was below average precipitation between November 2017 and September 2018. This weather snapshot also shows extreme weather during 2019, particularly during April and May. Saturated soils resulting in root damage and tree decline has been a common problem this year. Young trees and shrubs are particularly at risk due to smaller root systems. In many cases, damage wasn’t immediately apparent until June or July when higher temperatures put a greater demand on the root system. So bottom line, extreme weather patterns frequently play a role in the health of our landscapes.

That said (most oak problems are not due to disease), we have picked up two different oak diseases in the Kansas City area this summer that have the potential to cause tree decline, Hypoxylon canker and oak wilt.

Hypoxylon canker, also known as Biscogniauxia canker (Biscogniauxia atropunctata; B. mediterranea) is a disease common on oak trees throughout Kansas. It is considered to be a stress disease, usually associated with drought stress. Trees showing symptoms in 2019 were likely triggered by the dry growing conditions of 2018.

The initial symptoms of Hypoxylon canker are a tan or silver fungal mat on the trunk of the tree. This light colored surface layer quickly wears off and exposes a black crusty mass that looks like asphalt. Leaves turn yellow and shed and infected trees generally die within the first year. By the second year the dead oaks slough off the remainder of their bark. The best protection against Hypoxylon canker is to avoid stress. This starts with planting into well-drained sites and providing deep, regular watering during prolonged periods of dry weather. Also take care to avoid damage due to construction activities.

Oak wilt (Bretziella fagacearum) has been picked up in a couple of red oak trees in the Kansas city area (Johnson County, KS) this summer. It is an occasional problem on red oaks and pin oaks in northeast Kansas and in counties along the Missouri state line.

Oak wilt causes a partial leaf scorch (brown at the leaf tip and green at the base). Beneath the bark tissue, the disease produces dark brown streaks in the sapwood (see photos). Oak wilt on red oaks tends to start on a major limb or in a section of a tree and then progress until the tree dies, usually within a season.

 

The disease can be spread by sap feeding insects so it is important to avoid pruning oaks between April-June. Oak wilt can also spread to nearby red oak trees through roots that have fused.

There is no cure for the disease. Infected trees should be removed and destroyed. The wood should not be kept for firewood. If there are red oaks nearby, the root grafts between the trees should be severed.  Healthy red oaks nearby may benefit from a fungicide injection.

The best time to test for oak wilt is when trees are freshly wilted, generally in the spring.

More information on oak wilt can be found at the K-State Horticulture Information Center. Link is listed below:

https://hnr.k-state.edu/extension/info-center/common-pest-problems/common-pest-problem-new/oak-wilt.pdf

Common Oak Diseases in KS

  • Hypoxylon Canker
  • Bot Canker

Less common oak diseases in KS

  • Tubakia leaf spot
  • Bur oak blight
  • Oak wilt

Odd but interesting oak problems in KS

  • Oak galls
  • Obscure scale, Lecanium scale
  • Oak tatters