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K-State Turfgrass

Category: Diseases

Large Patch Evaluation Study Update

By: Manoj Chhetri

With temperatures cooling down and days being shorter, we are already starting to see warm-season grasses, including zoysiagrass, going to sleep. At the Rocky Ford Turfgrass Research Center, located in Manhattan, KS, we have shut down the irrigation in warm-season plots.

Our zoysiagrass in the large-patch tolerant breeding plot is not cooperating with us as much as we wanted. We inoculated the field in mid-September with fresh Rhizoctonia pathogen and kept the field pretty wet to encourage fungi to flourish. However, to our dismay, we did not see much of the disease activity, except in a few poor drainage spots. With disease research, it is the type of research where we want disease pathogens to have no mercy on us. We are impatiently waiting for spring, which in fact is a more favorable time of the year for large patch activity.

We are hopeful that we have at least one or two new zoysiagrass progeny that possess greater large patch tolerance. Again, it is hard to make comparison and evaluate when we don’t have disease pressure. So far, we have narrowed down to 10 best progeny out of 60. On the positive note, we have seen more disease pressure on our non-selected progeny than in our top-ten selected progeny. This tells us that we did a good job on choosing those ten-best progeny.

This project is aiming to develop a large patch tolerant zoysiagrass that can significantly reduce cost on fungicides and protect the environment. It is a collaborative project between Texas A & M and K-State University.

Pictured Above: Zoysiagrass progeny evaluated in large patch disease environment.

Pictured Above: One of the zoysiagrass progeny showing large patch in one inoculated half (right side) and fungicide treated cleaner side on other half (left side).

Temperature fluctuations and turf diseases

(Megan Kennelly, KSU Plant Pathology)

As I write this on Thursday we are looking into a weekend with forecast lows deep down into the 30’s. This comes after a September with multiple days in the 90’s and even more in the upper 80’s. Depending on how the weather shakes out after this weekend our warm-season turf may start showing signs of dormancy. Right now it is all still quite green.

In our cool season turf I’ve not seen much dollar spot lately, and it should be simmering down. I have heard a few reports of rust,

and my first suggestion in those cases is to review the fertility regime and make sure it’s not too low on N.

We are seeing and hearing reports of large patch across the region. Here is one example from today at our research facility in Manhattan:

Spring dead spot happens in … spring. But fall is a time to think about it. I’ll point you to an excellent summary of fall disease info from Dr. Miller next door in Missouri, with details about large patch, spring dead spot and other diseases:

https://turfpath.missouri.edu/reports/2019/10_09_19/

 

Zoysia breeding line evaluation work continues

(Megan Kennelly, KSU Plant Pathology)

KSU continues its work with the turf breeding team at Texas A&M and colleagues at Purdue. We recently inoculated some breeding lines with the large patch pathogen. We grow the fungus on sterilized oats then bury it just under the thatch layer. Sometimes we see symptoms in fall, but often we do not see them until spring. Scientific research takes a lot of patience :). In the meantime, we are keeping the plots moist to foster fungal growth.

In the meantime, large patch is active especially in wet areas:

Take note of these areas. It’s too late to fertilize zoysia now, but when spring comes around a bump of slow-release N may prompt recovery. In the meantime there may be actions you can take to improve drainage.

Breaking disease life cycles with good sanitation

(Megan Kennelly, KSU Plant Pathology)

Many plant pathogens like to survive the winter in infected crop debris. One example is iris leaf spot.

 

Here is a zoom – the black spots are structures where the fungus produces spores:

Here are some other flower diseases that carry over on debris:

Rose black spot lesions, close-up of lesions, and microscopic view showing abundant spores:

Cercospora leaf spot on hosta:

For many of these common flower-garden leaf spots, removing diseases and dead leaves can help reduce the amount of the fungi lurking over winter to cause disease next year. If composting, don’t put the compost back in the spot where you took the leaves.

Keep an eye out for powdery mildew in your landscape…

By Christian Webb

As summer starts winding down, you may begin to notice some of your bedding plants developing a white powdery coat on the upper surface of their leaves. No, this is not your plants putting on a winter coat for the cool autumn nights. It’s actually caused by the infection of a fungus on the surface of your plants leaves called powdery mildew.

Powdery mildew can be commonly found developing on many types of landscape plants during the late summer. On most plants, this disease will develop on the lower leaves and move up through the canopy. The typically symptoms of the infection will appear as a white to grey dusty growth on the upper surface of the leaves. In severe cases, leave may appear distorted and the cause defoliation.

Pictured to the left: Powdery mildew on Ox-eye Daisy (Heliopsis helianthoides)

To develop, the fungus requires high relative humidity and temperatures around 70⁰F. Many woody and herbaceous ornamentals may be affected by powdery mildew. As a general rule, the powdery mildew on one host will only affect hosts in that genus. For example, the fungi that you will find on oaks trees will only affect oaks and the powdery mildew on grapes will only affect grapes.

If you are looking to control powdery mildew in your landscape, there are a few ways to protect your plants. For annuals, increasing the spacing between plants will increase airflow through the canopy create more unfavorable conditions for powdery mildew develop. Along with altering the plant canopy, consider planting resistant hosts. Replanting the same susceptible hosts will likely result in a reinfection.

Pictured above on left: Powdery mildew on Zinnia (Zinnia elegans). Right: A microscopic image of the powdery mildew spores on the surface of a Zinnia leaf.

There are labeled fungicides for the control of powdery mildew. But you consider apply any product, be sure that your infection is caused by powdery mildew. Downy mildews looks similar to powdery mildew, but are caused by a different type of organism and may not be controlled by products labeled for powdery mildew. Powdery mildew is typically found on the upper surface of the leaf, while downy mildew is associated with the underside of the leaf. For recommended products for the control of powdery mildew, please consult the following factsheet: Link.

For further assistant in identifying powdery mildew, contact your local extension office.

To find your local extension office, the list of Kansas extension offices can be found here.

Further discussion of powdery mildew on woody ornamentals can be found at this Link on pgs. 48-50

Reference:

https://www.fs.fed.us/rm/pubs/rmrs_gtr335.pdf

https://hnr.k-state.edu/extension/info-center/common-pest-problems/common-pest-problem-new/Peony%20Powdery%20Mildew.pdf

Powdery Mildew Resistant Peony Varieties

By Kenneth Dodson

Powdery Mildew is a common fungal disease that can appear on a wide range of plants. This year has seen a high level of powdery mildew on peonies, leaving bushes looking snow-covered or dusty. The best way to avoid dusty looking peony bushes is to use resistant plants. A look through the peony demonstration planting at the K-State Gardens showed a wide range of disease susceptibility to powdery mildew.

Pictured above: Powdery mildew on Peony (Paeonia spp.) 

Here are a few peony varieties that showed good resistance to powdery mildew. In terms of Herbaceous Peonies: Red Charm, Lillian Wild, and Pink Luau were the best options, followed by Madame de Verneville, and Pink Hawaiian Coral. If you’re looking for Tree Peony varieties, there are several that show strong resistance to powdery mildew: Rockii, Joseph Rock, Kamata Nishiki, Shima Daijin, Hakuo Jishi, Kinkaku, and Kokamon all looked good. Lastly, the Itoh or intersectional peonies Pea Green, Yellow Charm, and Morning Lilac exhibited good disease control against powdery mildew.

Just fyi, the major distinction between the three growing types is the in the way they overwinter. Tree peonies will have a woody stem that stays above ground, while herbaceous peony stems will die back to

the ground every year. Itoh varieties have herbaceous stems as well, and will die above ground, but Itoh peonies typically have the same flowering types as tree peonies.

Ash Leaf Spot on Green Ash Trees in Kansas

By: Christian Webb

You may notice brown spots beginning to develop on the lower foliage of green ash trees. Symptoms of Ash leaf spot include irregularly shaped brown spots on the leaf that merge to form large patches of brown spots. In severe cases, the tree may defoliate four to six weeks earlier than normal causing the tree to appear bare long before other trees lose their leaves.

Pictured above on the left: A branch of lower leaves on an Ash tree affected by leaf spot. Right: Brown leaf spots with white speckling on the surface of the upper leaf caused by Ash leaf spot

The fungi that cause Ash leaf spot (Mycosphaerella spp.) survive in the leaf litter underneath the ash tree. In the early summer, the fungi in the leaf litter will begin producing spores capable of infecting leaves. Initial infections will appear on the lower leaves, and then quickly spread throughout the tree. By late fall, the fungus will produce structures able to survive the harsh conditions of winter and be ready to infect new leaves during the following summer.

The severity of the disease will depend on the conditions present during the period of leaf infection. Typically, the disease will become apparent in the late summer and early fall, which may not cause significant cosmetic damage. But in summers with abnormally wet conditions, the disease may develop earlier than normal and cause premature defoliation. Multiple years of these conditions may lead to weak trees with reduced vigor prone to branch dieback.

Pictured above: A microscopic image of fungal structure emerging from the surface of the leaf.

There are few recommended methods to protect ash plantings from Ash leaf spot. Since the disease will survive in the residue around the trees, raking up fallen leaves will reduce the amount of disease carried over to the next growing season. No ash trees resistant to leaf spot have been reported although they may vary in susceptibility.

Reference:

More information on Ash leaf spot may be found at the following Link on page 46-47. https://www.fs.fed.us/rm/pubs/rmrs_gtr335.pdf

Turf disease update

(Megan Kennelly, KSU Plant Pathology)

Around this time every year we all look forward to early September. Often Labor Day weekend marks the end of “summer diseases” and the beginning of fall repair and renovation to our cool-season grasses.

Moisture and humidity continue to trigger turf diseases. Here are a few recent photos:

Brown patch

Brown patch in tall fescue, with mycelium present on a wet, humid morning. The first photo shows the characteristic lesions. As I write this on Friday Aug 16 there is a stretch of hot days and very warm nights ahead, so this disease may continue. But September is not far away…

 

Dollar spot

Dollar spot in an untreated bentgrass area:

The photo above is a worse-case scenario, with a susceptible cultivar untreated. If you are having breakthroughs, review your fungicide regime and maybe your N regime, as low N can make this one worse (but too much is a problem, too!). Check your calibration and coverage. If you’ve never read it, read the dollar spot section starting on page 14 here:

http://www2.ca.uky.edu/agcomm/pubs/ppa/ppa1/ppa1.pdf

Unlike brown patch, dollar spot loves the more moderate temps  of September, so this one does not fade away after Labor Day. So don’t let your guard down yet.

Continued root and crown woes

Another issue I’ve been seeing lately is continued problems with saturated roots, and there were more heavy rains this week. The wet soils deprive the roots of oxygen plus they hold heat, so turf does not have any “chill out time” overnight. Organic matter in the profile makes it worse. On top of the physiological issues, those wet soils can trigger Pythium root rot and sometimes anthracnose crown rot comes in on top of that.

For more details, you can check out the report this week from our great neighbor Dr. Miller here:

https://turfpath.missouri.edu/reports/2019/08_15_19/

Or here:

https://blogs.k-state.edu/turf/anthracnose-crown-rot-in-putting-greens-and-the-turf-stress-behind-it/

 

Localized dry spot

Finally, another issue I’d like to mention is hydrophobic soils. Despite all the rain, hydrophobic soils/localized dry spot can still occur.

Here is what localized dry spot can look like, and it can come on fast.

Keep an eye on your soil profile so you can stop this damage before it starts. When you get damage to the extent shown in those two photos above it is a long road to recovery.

To check for localized dry spot, pull up some cores and use the “droplet test” by putting drops of water on the plug. If the drops just sit there, not wicking in, you have a problem. The soil is water-repellent.

Sometimes there is a defined hydrophobic layer with normal soil above and/or below, so check at different depths, all the way down the rootzone:

You might also notice water beading up on the surface and not wicking in.

You don’t want this to sneak up on you. Keep an eye on your soil profile, especially locations with a history of problems. Aerification and use of wetting agents can help get moisture where it needs to go.

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

A little bit of everything in the landscape.

By: Judy O’Mara

If you drive around town you will notice that most ornamental pear trees have orange leaf spots. It can look pretty dramatic. This is a fungal disease called pear rust (Gymnosporangium globosum). It is part of the complicated group of cedar rust diseases that are common in Kansas which cycle back and forth between cedar trees and their alternate host (in this case pear trees). By the time you see the symptoms it is too late to manage the disease. Preventive fungicides can be applied in the spring during the months of April and May.

A nice fact sheet on this disease can be found at: https://hnr.k-state.edu/extension/info-center/common-pest-problems/common-pest-problem-new/Pear%20Rust.pdf

I look forward to the annual exploding London plane trees (and sycamore) on the K-State campus. Sometime during early to mid-July the outer bark slips off the tree…explosively. Bark pieces can wind up 20 feet away. The first time I saw this interesting event (30 yrs ago), I was worried that the tree was going to die. I’ve since learned that this is just a normal growth habit of the tree.

My colleague and I were walking through a landscape this week and she saw this long, tan linear symptom on some hosta leaves. We both knew immediately what it was caused by…Hosta Foliar Nematodes. The nematodes in the tan narrow lesions are limited by the veins, so symptoms are long and blocky. This disease requires really wet conditions to thrive and spread.

Here are some interesting facts about foliar nematodes. They are microscopic roundworms and can survive on leaf tissue or in the soil. They can complete their life cycle in 2-4 weeks. The nematode has the ability to survive in a dormant state as a fourth stage juvenile for up to two years. Spread of foliar nematodes is by infected leaves touching other wet leaves. The disease is unattractive but rarely kills the plant. Sanitation of infected plants will help to clean up the problem

Missouri has a nice article on Hosta Foliar Nematodes: www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/nematodes/hosta-leaf-nematodes.aspx

Rust on Turfgrass

(By Jared Hoyle, KSU Turfgrass Research and Extension)

Last week I came home after the KSU Turfgrass Annual Field Day that was held in Olathe, KS at the Olathe Horticulture Research and Extension Center and before I even made it into the house I knew I had rust in our back yard.  The shoes in the garage were a dead give away. The shoes that my wife were wearing in the back yard were orange. This disease can occur just about anywhere, when the leaves of turf are wet and when plants are stressed they are more susceptible.  We see it on perennial ryegrass but can occur on other species.

Don’t worry too much as the turf typically can grow out of it.

For more information on rust check out the KSU publication below, some past blog posts from Dr. Megan Kennelly and myself, as well as some information from Richard Jauron at Iowa State University.

https://www.bookstore.ksre.ksu.edu/pubs/EP163.pdf

https://blogs.k-state.edu/turf/tag/rust/

https://blogs.k-state.edu/turf/rust-activity-in-turfgrass/

https://hortnews.extension.iastate.edu/2019/07/rust-turfgrass?fbclid=IwAR2MhIyvUjMSn0BLsHXvpFrtmaQrlcau-h6MH-R1gwWmag2qJ5DfF7jWlhA