May Follows 2020 Form
May temperatures, and all of spring for that matter, were eerily similar to those experienced in Missouri last year. A warm March was followed by two below average months of April and May in both years. This year, a preliminary estimate for the state is approximately two degrees below average with some regions up to three to four degrees below average.
May = Frequent Rain & Not Much Sun
May is typically Missouri's rainiest month (4.66" average), and over the last three years it has not disappointed. May 2019 was notorious with historic flooding, but both this year and 2020 also had above average precipitation in Missouri (6.1" in 2020 and 5.37" this year). Here in Columbia, we received 19 days in May with measurable precipitation. Along with that rainfall, cloudy conditions resulted in a significant decrease in solar radiation, with May 2021 having the least amount of sunlight since 1995. To demonstrate again how eerily similar this spring is to the last, last year's disease report on June 1 bemoaned this exact fact. This broken record has resulted in again chlorotic tall fescue, and not yet out of the gate zoysiagrass and bermudagrass - conditions which invite disease occurrence.
Summer on the Way
June is upon us and whether we realize it or not, summer is as well. June temperatures limped out of the gate today and yesterday, but should begin to ramp up over the weekend and into next week. Hotter, muggy conditions should begin to prevail, meaning the advent of more significant disease conditions for cool season turfgrasses.
Disease Activity Rises: Over the last few weeks at the turf farm, disease activity has reached a fever pitch. Dollar spot continued its severe progression and red leaf spot on creeping bentgrass started to join it in untreated research plots. Both of these diseases are normally well controlled in a preventive program. Large patch on zoysiagrass was extremely prevalent this spring, and we expect symptoms to last well into early summer. Bermudagrass growers in southern MO and AR have had enough trouble getting through terrible growing conditions, and growing out of spring dead spot, which has been impressive this year, will be especially difficult. The heat, and hopeful return of sunlight, will be welcome to those struggling with both of these diseases.
Dispersing clippings a key component to keeping tall fescue healthy.
Clippings Can Cause Chlorosis: Numerous observations of yellowing tall fescue lawns have come in over the last two weeks, not surprisingly just like last year (see 6/1/20 report here). While brown patch reared its ugly head last week in our plots (and my backyard), additional factors may also be at play. The wet, cool May may have led to anoxic conditions in poorly drained soils, but in most cases perfect growth conditions were present for tall fescue. Homeowners and turfgrass managers were forced to mow when the clouds allowed it, resulting in less frequent mowing, scalping and more clippings. Even at slow speeds with the best mulching decks clippings were smashed down, soaking and smothering live leaf blades beneath. If not dispersed or removed with a blower or rake, these areas turn yellow and chlorotic as shown in the above photo. Shaded lawns can be especially affected by clippings, and decline reapidly. Take a look after done with mowing, and determine if clippings need to be dealt with. Also, look at the older leaf blades for chlorosis, which can indicate a nitrogen deficiency (more on that below).
Low Nitrogen Diseases Prevail
Two diseases have been especially prevalent in the past week, and both indicate a low nitrogen environment. Red thread caused by Laetisaria fuciformis is often seen in a tank-mix with pink patch caused by Limonomyces roseipellis. This combo has been reported widely throughout the state, and whereas in most years we observe it on fine fescues, perennial ryegrass and Kentucky bluegrass, this spring we have also seen severe infections on tall fescue. While several fungicides can aid in good curative recovery, a solid shot of nitrogen (0.5 lb N or more) can also turn the red/pink color back to green… except for the colorblind.
Last week, we also observed our first case of anthracnose on an 'A4' creeping bentgrass putting green. Fortunately, the disease was still in its relatively less severe foliar phase, and the pathogen hadn't sunk its teeth down into its base of the plant. This being said, the finding served as an eye opener for both the superintendent and I, and that prevention should be on the menu. Interestingly and not surprisingly, the affected greens had less nitrogen applied than a few other greens on the course that were supplemented with an extra ¼ lb N a few weeks before.
Tall fescue lawns that have experienced heavy rainfall may also be deficient in nitrogen, which may be resulting in the widely reported chlorosis along with disease and clipping accumulation. Zoysia fairways and lawns that haven't been fertilized this spring may be yearning for nitrogen that is long gone from 2020. Remember that nitrogen doesn't result in more severe large patch, and recent research indicates applying nitrogen at 0.5 lb N/1000 sq ft or less per month does not increase brown patch.
Last, remember that turfgrass is starving because we mow it. Nitrogen is mobile in the plant and moves to the growing leaf tip - the reason that N deficiency shows up in the older leaf blades farther down in the canopy. No one harvests nitrogen like turfgrass managers do, and whether the cause is excessive rainfall and cold weather to inhibit microbial degradation of organic N, or a sand-based soil that can't quite hold on to it, it's likely that a supplement this early summer is necessary.