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K-State Turf and Landscape Blog

Category: Diseases

Cut-and-burn those pine wilt infected trees

Posted on by kennelly

(Megan Kennelly)

Got pine wilt?

 

Get that tree outta there! Chop and burn or chip, making sure not to leave stumps. Get this done by April 1!

You know the drill. This disease has been killing our pines for decades. It is caused by a nematode that is spread by a beetle. The nematodes and beetles spend the winter in dead and dying trees. The beetles, loaded up with nematodes, start emerging in late April or early May and spread to new trees.

In the eastern 2/3 of the state, if you have a dead pine, there is a decent chance it has pine wilt. We have detected pine wilt a handful of times in western Kansas too.

Get those pine-wilt infected dead trees out of the landscape to help prevent spread to surrounding trees.

Pines have multiple problems though, and if you have any doubt you can work with your KSRE Extension agent to ship a sample up to KSU. For more information on pine diseases, check out our publication about Pine Diseases in Kansas

Iris leaf spot – spring cleaning to disrupt fungal life cycle

Posted on by kennelly

(Megan Kennelly, KSU Plant Pathology)

Irises are a popular plant, often grown in large groups. Iris leaf spot is a fungus that can cause mild spotting to severe dieback.The fungus spreads by spores that are dispersed in wet weather.

Red-brown spots with yellow halo:

A closer view – the black bumps are spore-producing structures:

 

Another close-up view of one spot:

Spots can coalesce to cover a large area

More significant dieback:

Where does that fungus spend the winter? In old infected leaves. Get those outta there to reduce your risk of infection in the new year. Clearing out old infected plant tissue breaks the life cycle.

More information about managing iris leaf spot is available in a recent article by Ward Upham in the KSU Horticulture News

 

Large patch goes trick or treating

Posted on by kennelly

Your zoysiagrass fairways and tees might have tried to dress up like a jack-o-lantern, turning itself orange for Halloween. The moderately cool, moist, foggy conditions are perfect for large patch development. We are seeing it in our inoculated plots at Rocky Ford but in lots of other places too. Normally zoysia is shutting down right now. Normally, one application in the fall usually does a great job. You can view a short podcast on large patch fungicide research at KSU. But when the disease is active into November? I’m not sure.

I’ve never seen zoysia this green in November. What a weird fall. Lots of strange things happening in plants. At home we are still harvesting peppers and tomatoes after dinner while comfortably wearing short sleeves, shorts, and sandals.

Anyway – what are you seeing out there? Did you treat in mid-September? If so, is it holding? If not, did you go back in? Let us know what is and isn’t working for you.

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Dollar spot keepin’ on keepin’ on

Posted on by kennelly

Dollar spot loves, dew, fog, and temperature 65-85 degrees and we have had those conditions lately.

As you think about your fungicide program, don’t forget about rotating among different mode-of-action groups. The Chemical Control of Turfgrass Diseases publication from Kentucky does a great job outlining those principles. Don’t forget to look at the active ingredient names and FRAC codes along with the trade name. You might think you are rotating, but you are not. You can read the general info on that page, and/or scroll to the info specific for dollar spot a few pages in.

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The Kentucky publication highlights some points about fungicide resistance. In a recent survey of isolates collected in Kansas, nearly all were fully resistant to thiophanate-methyl. That is, the fungus blew through it like it was not even there.

Rust activity in turfgrass

Posted on by kennelly

Over the past 1-2 weeks we’ve been seeing a lot of rust in lawn height turf. At Rocky Ford we are finding it in mainly perennial ryegrass but in little pockets in some newly-established zoysiagrass too.

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The rust spores need wet leaf surfaces to infect, and we have definitely had some moist, dewy days and even some very foggy mornings. Though the fungus itself spreads best during wet weather, plants that have been stressed by drought are more susceptible. Nutrient-deficient turf is also more susceptible.

We have some information about rust in our publication Rust Diseases in Turfgrass (pdf).

Large patch in zoysiagrass

Posted on by kennelly

 

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(Megan Kennelly, KSU Plant Pathology)

 

If you manage zoysiagrass and have a history of large patch, you are undoubtedly already thinking about this disease, and maybe you just put out an application or are getting ready to do it soon.

There is some great info about large patch control at this link, starting on page 14.

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

We’ve done quite a few trials at KSU over the years, and our results match pretty closely with the efficacy data shown at the above link. Regarding timing, we’ve had good control from most application timings in September.

Large patch tends to be in the same areas from one year to the next, so one option is to map out “hot spots” and focus on those.

Inoculation time!

In addition to large patch management, it is also time for large patch inoculations for research. Yup, most of you want to get rid of large patch. Here at KSU, we want MORE! I’m working with PhD student Mingying Xiang and Dr. Jack Fry in collaboration with Texas A&M, Purdue, University of Arkansas, and other universities to screen zoysiagrass breeding lines for disease resistance and agronomic traits as part of a USGA-funded project. We recently inoculated plots with the fungus that causes large patch disease. We cultured the fungus in the lab, grew it out on sterilized oats in glass jars, and then hauled our tailgate-of-death-and-destruction out to the field. To inoculate, we put the colonized oats just below the thatch. We might see some symptoms this fall, otherwise we definitely should see patches by spring. We will measure disease severity using digital images and other methods. We are hoping to find some breeding lines with good resistance. As we all know, starting with a resistant variety is the foundation of integrated pest & disease management.

 

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“My knees are getting tired from all this crawling”

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No, that is not our snack. Those are jars of the fungus growing on oats. Yum!

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We dig just barely down into the soil and place the oats, then put the flap of grass back down.

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Even after one (rainy) night, there was already new mycelium growing off the oats.

Turf health problems, above and below ground. And why your putting green soil should not look like tiramisu.

Posted on by kennelly

(Megan Kennelly, KSU Plant Pathology)

The soggy weather continues, and diseases are in full swing. Dewy, wet mornings lead to mycelial growth of the pathogens that cause dollar spot or foliar Pythium. These are mainly golf course concerns, but the diseases can occur at other sites.

Here is a sample that came into the lab, loaded with foliar Pythium:

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It is from a golf course fairway at a site that has received a lot of rain and some foggy mornings where everything is wet-wet-wet.

For management info on foliar Pythium, you can check these links:

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

(scroll through to the Pythium part on p.17)

http://extension.missouri.edu/p/IPM1029-17#Pythiumfoliarblight

 

Root health continues to be a problem, especially on putting greens. We’ve posted a lot of information this year about wet soils leading to physiological decline and triggering Pythium root rot in some cases (see links at bottom of this post). Putting greens with poor drainage, less-than-ideal construction, or a build-up of organic matter are particularly susceptible. Here are some putting green rootzones with a lot of organic matter build-up, visible as dark layers:

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All those layers kind of look like tiramisu…mmm… yummy… getting distracted.

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Unlike delicate layers of a tiramisu, layering in a putting green rootzone is NOT a delectable delight. Another complication of poor drainage is that it can make the turf more prone to anthracnose. I received a couple of samples in recent days with crown rot anthracnose. Both also had layering problems and root decline.

There is some information about anthracnose here:

http://www.bookstore.ksre.ksu.edu/pubs/EP147.pdf

and here is an excellent list of best management practices:

http://turf.rutgers.edu/research/bmpsanthracnose2015.pdf

Many of the practices to reduce anthracnose also promote overall turf health. That is, when you implement agronomic practices to promote good rooting you also reduce the risk of anthracnose and other problems. You may not be able to do ALL of the beneficial agronomic practices you would like, due to budgetary limits or lack of equipment or golfers’/greens committee opinions, but the more you can fit in, the better.

We posted on these topics earlier this year. If you want to go back and review, here are some links:

https://blogs.k-state.edu/turf/season-long-agronomic-practices-to-reduce-anthracnose-risk-in-putting-greens/

https://blogs.k-state.edu/turf/root-decline-it-aint-benign/

https://blogs.k-state.edu/turf/best-management-practices-for-turfgrass-anthracnose/

https://blogs.k-state.edu/turf/your-turf-is-trying-to-bike-up-a-mountain/

https://blogs.k-state.edu/turf/bentgrass-declining-its-from-western-europe-you-live-in-kansas-by-dr-fry/

 

 

Gray leaf spot in perennial ryegrass

Posted on by kennelly

(Megan Kennelly, KSU Plant Pathology)

If you manage perennial ryegrass you are probably well aware of the risks of gray leaf spot.I have not seen it, but I just got my first question about it for the year.

In this region the most common time for GLS symptoms to first appear is early to late August. In some years, epidemics can be severe. In other years, there is little to no GLS. The fungus is picky, with 82-90 degrees as its favorite temperature range. The fungus needs wet conditions as well. The fungus requires certain durations of leaf wetness at different temperatures. At that prime window of 82-90 degrees the infection can occur quickly.

Damage in a rye fairway, a few years ago.

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GLS spores in the microscope, a few years back.

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For more details and photos you can check out this page for general information:

http://extension.missouri.edu/p/IPM1029-11#Grayleafspot

And, here is some detailed fungicide information (scroll to page 13):

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

 

 

Dutch Elm Disease

Posted on by kennelly

(Megan Kennelly, KSU Plant Pathology)

“Dutch elm disease -is that still out there?”

“Elm trees – are there any of those still out there?”

Those are two questions, flip sides of the same coin, that I hear every year. The answer to both is YES.

Judy O’Mara, Director of our Diagnostic Clinic, handles most of the tree samples and she has picked up DED in several samples this summer, like we do every summer. Sanitation (removing and destroying infected trees) is essential to DED management. If infected trees are near other elms, root grafts need to be disrupted first. For nitty-gritty details on DED you can visit this page – click HERE.

Here is a photo of the DED spore-producing structures in the dissecting microscope.

DED-synnemata

 

Dutch elm disease is caused by this fungus (actually two related fungi) which is spread by elm bark beetles. In the photo above, we see the black stalks and a creamy, gooey ball of spores at the top. The beetles pick up the spores and move them around from tree to tree. The fungus can also spread tree-to-tree in neighboring trees by root grafts.

Initial symptoms are “flagging” of individual branches, especially when the disease was introduced by the beetles. The disease spreads over weeks or months through the rest of the crown.

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(Photo courtesy Ray Ladd, K-State Research and Extension)

Branches wilt, but leaves remain on the tree. Disease can develop more quickly when triggered by root graft method of spread. Discoloration in the vascular tissue can be seen by stripping off the bark of recently-wilted branches:

DED-streaking-branches

 

For high value elms, preventative fungicide injections (appropriately-labeled products of propiconazole or thiabendazole) are an option to reduce the risk of Dutch Elm Disease (though it is not a 100% guarantee). This can be one piece of the DED management system. Remember, sanitation is a key piece of reducing the risk of DED (See the link above). Here is a photo of the big elm at the K-State Garden.Garden-ELM

This tree is on a 3-year injection cycle. We thank Matt Giese from Syngenta for providing some Arbotect fungicide to inject this tree, and we thank Randy James, Consulting Arborist from Tree Biologics, for generously donating his time to inject the tree a few weeks ago. We use our injection days to educate students, Extension Master Gardeners, and others about DED.

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Pythium foliar blight

Posted on by kennelly

This yucky summer weather just keeps going. The past few days have been the most humid I have experienced in a while. Hot and humid = Pythium weather. We’ve mentioned foliar Pythium a few other times during this stressful summer of 2016. (As a reminder, foliar Pythium is distinct from root Pythium… which we’ve also discussed a few times!)

In the past we days we received a couple of samples of Pythium foliar blight (also called Pythium cottony blight). One was from a perennial ryegrass golf course fairway.

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In the photo above you can see the greasy, matted down appearance of the turf. With a handlens, or even just with the naked eye if you looked closely, mycelium was present. In the microscope it was clearly Pythium (see the tall fescue pics below).

Here are some shots of the ryegrass in the field:

rye-2016-fr-supers rye-2016-from super rye-2016-from-superintendent rye-2016-from-supers

 

The second sample was from a tall fescue home lawn. Usually we think about Pythium on ryegrass or creeping bentgrass, but it can attack other cool-season turfgrasses. Tall fescue has more potential to recover than perennial rye or bentgrass. In 11 years, I have seen it on tall fescue only 1 or 2 two times before.

Below is a photo of the greasy, matted-down tall fescue turf. After incubating overnight in a plastic box with wet paper towel the mycelium was present.

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In the microscope, the pathogen was clearly distinguishable as Pythium.

Pythium-structures-tall-fescue

Just as a comparison, check out the strong crosswalls that are found in the brown patch pathogen, Rhizoctonia solani:

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Here is a shot of the site, where it looks like the Pythium was tracked along with a mower:

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The pattern is different from brown patch, and brown patch lesions were not present. I have seen weird tracking patterns with fertilizer burn or other chemical injuries, too. It can be challenging to know what is what. If you have any doubt, send in a sample, and email some photos.

Pythium thrives in wet conditions, so avoid overwatering. Water deeply and infrequently, and avoid watering in the evening. Improve drainage and try to increase airflow and sunlight. Avoid overfertilizing – Pythium loves an overly lush lawn. As a bonus, those practices will also reduce the risk of brown patch.

Pythium is not a true fungus, it is an oomycete. The most effective fungicides for Pythium are the ones specifically for oomycetes. There is a comprehensive list here, from the Chemical Control of Turfgrass Diseases publication from University of Kentucky (click the photo to zoom in):

Kentucky-turf-fungicides-2015-ppa1_Page_17

 

There is some more excellent information, photos, and management tips here:

http://extension.missouri.edu/p/IPM1029-17#Pythiumfoliarblight

 

Brown patch is still active out there (it’s a little faint in the pic, but it’s there):

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And dollar spot is active, too (mixed in with more brown patch):

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