ALL: How do you time large patch and spring dead spot preventive fungicide applications in the fall?

Sept 15 and Oct 15
When I see symptoms
70 F soil temperature threshold
First nighttime lows in the 50s
When Bermuda/zoysia growth starts to slow

Update (10/9/2019)

Working the Late Shift

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Temperature Finally Flips to Fall

  1. September 2019 temps was one for the record books. – Missouri Climate Center
  2. Cool Fall temperatures expected through mid October. – NOAA

September was one for the record books as several cities including Springfield, St. Louis, West Plains, and Columbia experienced their warmest September. The unofficial statewide temperature of 74.7 F ends up 6.4 degrees above average (largest departure from average for the year) and will presumably end up as the 2nd warmest September on record (since the warmest in 1931). September also had the highest dew point on record, and September had the highest departure from average for the year. All of this resulted in a September that felt much like the meat of July, and considerable physiological stress on cool season turfgrasses. This effect was particularly severe on bentgrass putting greens in the region, which did not appreciate a jolt of summer occurring after August. The first few days of October didn't offer much relief, but we've now settled into a fall pattern that may…

Turn quickly to winter. Forecasts into this weekend and into mid-October indicate a turn towards cold, perhaps even freezing weather as the jet stream plummets south. Northern parts of the region should experience their first frost of the season that may dip down even into St Louis and southwards. Hard to imagine snow, but our northern neighbors should be getting a good dose of it through the weekend.

Rainfall over the last two weeks has followed the same broken record, with significant rains occurring in the west and north, with the east receiving much less. Not coincidentally, putting green samples are still coming in from these regions where the spigot simply won't turn off. Forecasts do indicate a dry down into next week, which will undoubtedly be welcome in those regions.

October Dry Down?

  1. Extreme rains to the north and west over the last 14 days. – HPRCC
  2. For much of central U.S., a dry down is expected through mid October. – NOAA

Quick Hits

Frost/Freeze Guide: If you're curious about when the first fall frost traditionally occurs in Missouri visit The Missouri Frost/Freeze Guide here. This informative web application uses historical information to show the dates and probabilities for when a first freeze event should occur in your Missouri location. For example, using the "weather station map" tab, St. Charles should have a 10% probability of having a 32 F temperature before Oct. 7 and a 30% probability before Oct. 17. Another neat feature is the extreme date maps, which shows the earliest dates of temperatures at or above 32 F (or various other temps) in mid to late September for most of Missouri (none in the last 20+ years). The median date for the first fall frost at or below 32 F in Missouri is mid-October for middle portion of the state, so if it does occur later this week it'll be approximately 10 days early for most Missouri residents. This would indeed be right out of the fryer (90s on October 1-2) to the freezer in just over a week's span.

    Late September Fairy Ring Outbreak on Putting Greens

    1. Fairy ring activity on NTEP putting green trial.
    2. Green Type II rings evident on 'Penn A1' green.

  • Late Fairy Ring on Greens: Coinciding with the warmth in late September, we did note some late Type I and II fairy ring activity on our putting greens. We did not notice any activity in plots previously treated with preventive spring applications, but April – May treatments would presumably be hard pressed to last this far into an extended season. These fairy rings have fizzled out now with the cooler weather, but in Septembers that act like summer it may be advisable to keep some flutolanil and wetting agent on hand to beat back any late arrivers.

  • Bermuda vs. Zoysia NTEP Trial - Sept 27

    1. Bermuda after establishment by plugs or seed on July 2.
    2. Zoysia after establishment by plugs on July 2.

  • Bermuda vs. Zoysia: Our bermudagrass and zoysia NTEP sports turf/fairway height trials were established on July 2nd. Thirty-five varieties of zoysia (all plugged) and bermudagrass (22 plugged, 13 seeded) were planted in 5 x 10 ft plots with three replicates. Note disappointingly there are no seeded zoysia cultivars in the study. Also as shown above, the zoysiagrass establishment is well behind that of the more aggressive bermudagrass, demonstrating the zoysiagrass adage that the "first year it sleeps, the second year it creeps, and the third year it leaps". This also demonstrates the common homeowner frustration of attempting to plug in zoysia bought online or through mail order and expecting it to knit together in one season. Sodding or heavy sprigging earlier in the season would be a better course of action, as was done by many golf superintendents in late spring/early summer due to last year's winterkill. We will be covering this zoysiagrass this winter in an effort to increase survival.

  • 1-2-3 of Late September Pythium

    1. Kentucky bluegrass plots seeded on September 19th.
    2. Trial area covered to prevent seed movement and irrigated.
    3. September heat, covered plot and heavy moisture = Pythium damping off on October 2.

  • Pythium Damping Off on Turf Seedlings –Fall Disease Prevention When Pythium damping off occurs in late September, the fall is surely odd. In this case, we seeded a trial to evaluate new Kentucky bluegrass cultivars and seeded the surrounds with tall fescue. To ensure the seed didn't move from one plot to another and to aid establishment, we covered the plots for two weeks and watered frequently. Low and behold significant Pythium damping off on the seedlings (mostly on the tall fescue) was rampant under the cover, demonstrating that hot, humid conditions under any circumstance, in any month, can drive a disease epidemic.

  • Dollar Spot Probability Crash: Note the potential for dollar spot activity has crashed below the threshold for much of the region since October 5th (to check your area of the state click here). If the potential does not go back up, perhaps we may be done with this disease for the season, or at most one more strong fungicide application can seal the 2019 dollar spot deal.

  • South Farm Showcase - Sept 28
    The turfgrass demo area included many kids activities, including planting seed.

  • South Farm Showcase – In the worst kept secret in Columbia, the MU turfgrass team hosted local families and kids at the research farm for fun in the form of flying kites, putting on the green, bubbles, soccer, bags, washers, etc along with education in answering lawn questions and planting seed. The official tally hasn't come in yet this year, but last year nearly 14,000 were estimated in attendance. Hopefully the seed will also sprout in the minds of the Showcase attendees that lawns, turfgrass, horticulture and agriculture are intertwined in their lives and important to research and develop. If you are planning a trip to Columbia next year, target this late September weekend for both the Showcase and the Roots–n–Blues festival.

Fall Disease Prevention

Large Patch & Spring Dead Spot Prevention Time

  1. Fall large patch outbreaks thus far have been light due to warm September temps.
  2. Spring dead spot needs to be controlled in the fall.

With the quick advent of fall, a late shift towards warm-season disease prevention also ensues. The first fall preventive fungicide application for both spring dead spot and large patch on areas with a history of the disease should be timed around the 70 degree 2-inch soil temperature threshold (5-day average). Except for Kansas City, this just occurred in the past five days for most of the region.

An often-asked question is if an earlier application in late August or early September was "wasted". In mid-September, some reports were received and observations of active large patch were made at the research farm in some of our typical areas. Many of these areas recovered along with the summer-like temperatures that persisted through the month. Another fall application on a 21 to 28-day interval should suffice for large patch prevention on high amenity zoysia, but remember this fall when next May and June come around. Scout intensely and be quick to make a curative application if necessary. If this cold weather sticks around and zoysia goes quickly into the winter good night, consider an early spring preventive rather than relying solely on fall applications, a strategy that has worked well in our previous studies.

Spring dead spot prevention, however, may be a tougher nut. Applications made earlier this September may indeed not do a good job at preventing the disease come next spring. Two applications on a 21 – 28 day interval will most likely be necessary this fall, but in reality might it need to be three? The table below shows the dates over the last nine years that the 70-degree soil temperature threshold has been reached. Obviously apparent are the last four years in which the threshold has been later than the previous six. Particularly in 2017, sub-par control from preventive spring dead spot applications was reported in several instances, and we also noticed this effect on our own plots. The ineffective applications in most cases were applied in mid-September and mid-October as per tradition. In reality, the 70 degree threshold occurred much later, which should've pushed the second application 21 – 28 days later into late October or even November. Serendipitously that year we did make later applications that ended up working much better than the earlier applied treatments.

Long story short, once again the summer ghoul has worked the graveyard shift well into our fall. This weather shift has already had ramifications on cool season turfgrass health. It also may translate into a required shift of our preventive strategies for warm season turfgrass disease management later towards Halloween then we've previously considered, or in the case of large patch, a slide towards next spring.

Lee Miller

Extension Turfgrass Pathologist
University of Missouri
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