Temps Soar in June
Although the state totals aren't in, if Columbia is a true barometer for state temperatures it certainly was another one for the record books. June 2018 ranked as the fourth warmest on record in Columbia since record keeping began in 1889, and was the warmest since 1953. This followed on the heels of the warmest May on record, and plants have noticed. More than 52% of the state ranks short/very short of topsoil moisture, 14% of corn and 35% of pastures are rated in poor to very poor condition (NASS stats - July 2, 2018). As indicated in the last update, ET rates soared well above rainfall supplies in June turning many lawns and nonirrigated areas dormant. NOAA predicts above average temperatures to remain in Missouri and throughout much of the U.S. through mid-July, so the heat stress on cool season turfgrasses looks to keep on, keeping on.
Fortunately at the end of June, a solid precipitation event dumped a few inches of rain along a swath right through the middle of the state. Three to three and a half inches were dumped out of rain gauges in Columbia, whereas southeast MO perhaps saw a bit too much with ~ four inches occurring in that region. This event has greened up inadequately irrigated turfgrass considerably in the middle portion of the state. The moisture release from soil should moderate air temperatures somewhat, but expect humidity to remain high. As for rainfall prediction by NOAA, Missouri is in the middle of a predicted dry upper and west central U.S. and above average rainfall in the southeast, Kentucky and Tennessee Valley.
Until Recently, June was Dry
Lance Nematodes Detected in High Numbers
Pythium Root Rot Impacting Golf Greens
Disease Taking Advantage of Stress
May let the fuse and June blasted cool season turfgrass stress into the clouds this year, meaning fireworks on the ground as well as the sky this 4th of July. Tall fescue/Kentucky bluegrass lawns, Kentucky bluegrass sports fields, and especially creeping bentgrass putting greens have felt the brunt of this hot summer. Environmental stress limiting growth is normally a predisposing factor required for disease development, so paying attention to management inputs is crucial for keeping turfgrass alive in this difficult season. Everyone's time is limited, so below a single word and concept is given for each turfgrass sector that may help to focus on during the summer strife.
Lawn Care: Patience - Human nature lends itself to the freak out emotion at the first sign of brown. As stated above, rainfall and presumably even supplemental irrigation was unable to keep up with the high ET rates in May and June. Many lawns went brown simply due to drought dormancy, a defense mechanism that tall fescue is extremely adept at provided it has an established root system. When drought occurs, examine for tell-tale lesions of brown patch, but without evidence don't apply fungicide, and in no case try to grow out of it high fertilizer rates. If the lawn can't be irrigated effectively by the homeowner don't do it. Last but not least (and definitely not popular), don't mow. Remember September is coming, and overseeding to rebuild density is a powerful tool.
Sports Fields: Moderation - In reality, this applies to all sectors. Mowing heights, particularly on sports fields under the big lights, are often on or just below the limit of healthy turfgrass. This provides a much lower limit for error than lawns and commercial areas. Consider raising mowing heights just a tick or skipping an extra day or mow a week under high heat conditions. If possible at larger facilities, moderate traffic by spreading out play and monitoring wear and density on fields. Also fertilize in moderation. Be careful with high rate granular applications, and consider lower nitrogen containing and slower releasing organics, or spoonfeeding with sprayable formulations.
Golf: Water - If sports fields are on the limit, then bentgrass putting greens have many toes over the ledge. In many cases, nothing out of a sprayer will counsel it back onto firm ground. Raising mowing heights and alternating rolling/mowing is wise but maintaining soil moisture on the dry side is key to getting through the 90+ days. Bentgrass roots grow until 86 F, but at 88 F cease growth and start declining. As shown by this post from PACE Turf, as soil volumetric water content increases so does soil temperature. At night, when air temperatures cool (not enough when still at 80 F), the water filling the sand pores retains heat much more than air would. Soil temperatures therefore don't correspondingly cool at night, and there's no time for root recovery. If the soil is wet during the heat of the day, boiled root soup occurs. Fans lower soil temperatures, increase root length density, and presumably allow for increased plant transpiration by moving water and humidity off the leaf surface (Guertal, van Santen, and Han, 2005). Greens need to be vented on a regular basis to allow air in to replace other gasses and dry out stubbornly wet organic matter. Last, consider using a TDR tool to measure soil volumetric water content, and get to your number first thing in the morning. This morning water may last the day and help limit syringing in the hot afternoon.
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Extension Turfgrass Pathologist
University of Missouri