Yellow Submarine Spring
Diagnostic Lab Update
At this time, turfgrass diagnostic services at MU remain suspended due to the COVID-19 pandemic until at least mid-June. This includes the MU Plant Diagnostic Clinic as a whole and turfgrass parasitic nematode submissions. We are working through several issues regarding reopening, including no support staff, restricted access to campus facilities, limited mail services and no online payment system. When we do open, anticipate limited hours, strict sample submission guidelines and no sample drop offs. Some of the diagnostic labs open at this time include University of Wisconsin, North Carolina State University, and Kansas State University. We appreciate your patience.
Here Comes Summer
- A cool May followed a cool April, with many areas 2-3 degrees below normal – MU Climate Center
- The first week of June looks to bring summer heat to much of central U.S. – NOAA
Despite a few near 90-degree high blips, May followed April's script and ended 2-4 degrees below average for much of the region. Considering the amount of rainfall for much of us, the cool temperatures were fortunate for cool-season turfgrasses, but a large patch kick-in-the-pants for zoysiagrass (see below). Looking to the air, we've also had quite a severe spring for tree disease outbreaks. Peach leaf curl and fire blight on apple and pear were prominent, but most striking and conspicuous was anthracnose on trees, particularly sycamore. Many of the sycamores and other trees have already started to releaf as air and soil temperatures get back to normal levels to begin summer. Speaking of which, summer is set to arrive in full force this week, with a heat wave set for the first week on into the middle of June. This will assuredly set off the disease activity, particularly brown patch on tall fescue lawns which as noted below is starting to produce its first symptoms.
Extremely high May rainfall totals (10-12") were recorded in Springfield, Branson, and much of SW Missouri and northern AR. May is normally Missouri's wettest month, but these totals double our statewide average of five inches. Corn and other crops are at risk of ponding or flood damage, and the Pythium threat on creeping bentgrass putting greens is magnified greatly. St Louis and Kansas City will end 1-2" above normal while on the flip side Columbia and mid Missouri will end 1-2" below normal. A dry down is expected along with hotter temperatures, meaning the root systems built this spring should get their first real test.
Wet May Along and South of I-44
- May 1-28 was fairly normal in the mid MO, but well above average in SW MO. – NOAA
- A welcome dry down accompanies the heat this first week of June. – NOAA
Big Spring for Large Patch
- Untreated areas are obvious in our trials.
- Even broadcast inoculation from last fall led to scattered symptom development.
- Large Patch – Quite a May for large patch outbreaks, with many fall-only fungicide applications falling flat by the end of the month. Our research plots have been hammered this year by the disease, and we are also seeing symptoms in our bermudagrass plots as well. This being stated, large patch thins out zoysiagrass and is a good conduit for common bermudagrass infestation. Again this year, we have noted better large patch control with fungicides applied early (April 1) than those applied in late April. Also consider making applications to your hot spots in at least 2 gallons water carrier/M or more if possible.
- Pythium Prevention on Putting Greens – May spells Pythium root disease prevention on putting greens in Missouri. On sites with a history of the disease, a half rate of Segway (0.45 fl oz/M) + a QoI fungicide like Insignia, Heritage or Fame should have been applied, and if not heavily considered early this week. With the heavy rains many experienced in May, early June could be a busy time for these diseases.
- Dollar Spot Season Launches – Since about mid-May, dollar spot potential eclipsed threshold levels according to the Smith-Kerns model (see here). At the MU Research Farm, we are observing infection centers on our most susceptible cultivars (Armor, Penncross) but have not observed wide-scale outbreaks yet.
Oddball Bermudagrass Smut
- Disease that causes conspicuous demise of the inflorescence, but little else.
- Bermudagrass smut is related to corn smut, which also targets the seedhead.
- Bermudagrass Smut – With all of the rain in SW Missouri, an oddball showed up in mid-May. Bermudagrass smut, caused by Ustilago cynodontis, was reported on common bermudagrass in a lawn near Joplin, MO. Unfortunately for many aiming towards the demise of common bermuda in lawns, this disease only attacks the inflorescence and doesn't cause any appreciable impairment of growth that we might prefer. The disease is closely related to corn smut, Ustilago maydis, which also targets the seedhead but is much more important. Most farmers want to avoid corn smut, but in Mexico it's considered a delicacy, termed cuitlacoche.
Nostoc (aka "witches butter")
Gooey mess of cyanobacteria left over from frequent SW MO rains.
- Nostoc in SW Missouri – The persistent rains in SW MO also brought the blue-green algae to the party. While golf superintendents are familiar with blue-green algae as a producer of toxins and causal agent of yellow spot, several homeowners are also getting a taste of this treat in home lawns with infestations of witches butter. More properly known as Nostoc, this blue-green algae produces a snot-like mat of slime on open soils, particularly those treated with glyphosate or other non-selective herbicide. Since it's not a plant, most herbicides don't work well for this problem with the exception being Scythe (pelargonic acid) and potassium salts of fatty acids. Joe Boggs from The Ohio State University wrote a fantastic article describing Nostoc and chronicling the history of blue-green algae in Earth's timeline (click here to view article).
Yellow Submarine Spring = Chlorotic TTF
Yellow Tall Fescue
- A leatherjacket of a cranefly larvae (circled), and a mechanical pencil.
- Leaf spots and net blotch hitting older leaves in mid May.
Several reports and complaints in the last two weeks have been levied against yellowing or spotty tall fescue. In the previous report, net blotch was reported as a potential culprit for these diseases, but upon further review perhaps there are a few other environmental players contributing to this game.
- Rain/cloudy conditions – As mentioned several times, rain was persistent over much of the region, but the cloud cover was not mentioned. Even when it wasn't raining, cloud cover was also all too common. In Columbia, the average total solar radiation per day in May averages 19.37 MJ/sq meter. This past May was 16.57 MJ/sq meter, lowest since 2013. Columbia also averages 8 cloudy days in May (≤14 MJ/sq meter), and 12 occurred in 2020. Missouri felt like London for much of May. All plants, (even cool-season turfgrass), soaking in cold water with no sunlight like a submarine would be susceptible to some yellowing of older leaves. Some turfgrass etiolation was also reported last week - a plant growth response which follows this environmental pattern.
- Cranefly Larvae (aka leather jackets) – I have observed quite a few crane flies in my lawn and at the turfgrass research farm (see above pic of a "leather jacket"). Most healthy lawns should be able to compensate for quite a few of these, and this doesn't seem to be the European crane fly that is causing turf damage in the Pacific NW and NE U.S. So don't go spraying insecticides everywhere… just monitor and be aware.
- Nitrogen deficiency – Cool conditions in spring + frequent rainfall + frequent mowing = high growth potential of tall fescue and Kentucky bluegrass and potential quick use of and therefore lack of nitrogen. Exhibit A is Photo B above. Notice how the net blotch/chlorosis is affecting the older leaf and not the growing leaf tip? Nitrogen is mobile in the plant and moves to the tip, so nitrogen deficiency and any resulting susceptibility to a pathogen would impact the older, lower leaves first. This is also the reason that turfgrass needs nitrogen so often, because when mowing harvests that plant nitrogen off. Exhibit B is Photo B below. Many home lawns are built on subsoil not topsoil. In the photo below, this approximately $300-400k home will simply have the clayey subsoil mess graded and sodded or seeded. Therefore, the soil microbiology, and accompanying nitrogen cycle, must be built by the organic matter provided by the lawn. In all other systems where plants are grown in true topsoil, it's the other way around where the soil builds the plant. No wonder older lawns require less nitrogen… they've done all the work!
In the end this means that after a spring with cool temperatures, ample water and no heat stress that the lawn most likely needs a cheeseburger. I'm not saying go all Juicy Lucy here, but a good quarter pounder (or half pounder) with cheese (Royale with cheese across the pond) would serve nicely… 0.25-0.5 lb N/1000 sq ft suggestion.
Yellow Tall Fescue
- The first leaf symptoms of brown patch on tall fescue were observed this week.
- Nice house, but substandard housing for a lawn.
- Brown patch on tall fescue – This disease has not been impacting tall fescue throughout much of May to any appreciable level. However, late last week we did start seeing our first lesions both at the turf farm and on my home lawn. If the lawn is starving and hungry, restricting nitrogen will not help limit brown patch severity. Recent research indicates applying nitrogen at 0.5 lb N/1000 sq ft or less to stimulate growth on a monthly basis did not increase brown patch (see the research here). If the lawn hasn't been fertilized since April, then it probably needs it, so don't hold back on brown patch's account.
Extension Turfgrass Pathologist
University of Missouri
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