Q & A WITH DR . GRADY MILLER

I have never experienced our bermudagrass fields so slow to grow in the spring . We are seeing more exaggerated wear from normal use since the fields just do not seem to want to grow . Why so slow ?

– North Carolina

The last several years , turfgrass has performed poorly in the spring because it has been either excessively wet or excessively dry . This year , precipitation has been good , and it was complemented by warmer-thanaverage temperatures the first two-and-a-half months of the year . We had some early greening in March , which was concerning since our “ winter damage ” to warm-season grasses is usually due to warm early springs followed by several nights in the low 20s that can hammer tender warm-season grasses .

We dropped down into the upper 20s ( in Raleigh ) on consecutive late-March nights , but I did not think it would cause any lasting problems since we were back in the upper 40s the next night and a daytime high of 81 the following day . It seemed promising that we would have healthy turfgrass growth early this year . But as the cool night temperatures lingered into April and May , reports like yours started to fly into my inbox . This winter / spring did not result in widespread winterkill for the Carolinas , but it has been one of the worst springs for growing bermudagrass we have seen in several years .

The problem seems to be largely centered on cool temperatures . Old-timers like me often tell people that that bermudagrass needs nighttime temperatures consistently in the 60s before it will start to grow laterally . I know some wise people have also explained that the daytime high plus the nighttime low must equal at least 150 for bermudagrass regrowth in the spring . And that no amount of fertilizer , water or PGR will change this fact .

To test these two rules of thumb , non-scientifically , I made a quick comparison of Raleigh temperatures in 2023 versus 2022 . Greenup of bermudagrass was much less problematic in North Carolina in 2022 compared to 2023 . May 12 was the first day in 2023 that we had multiple consecutive nights in the 60s . In 2022 , it was April 12 — a full month earlier . May 2022 provided 22 nights in the 60s , whereas May 2023 had 12 . Checking the temperature sums

with 2023 data , there were two days that summed to 150 in April and four days in May . In 2022 , there was one day in April and 11 days in May that met that threshold . These data suggest that May 2022 had much more agreeable temperatures for growing bermudagrass than April or May in 2023 , which corresponds with what we have experienced .

The next step is to see if this is consistent with research . A study published in the Journal of the Mississippi Academy of Sciences ( McCurdy et al ., 2020 ) determined that Tifway bermudagrass growth begins at the base temperature of 55 degrees and that growth is optimized at 88 degrees . Latitude 36 needed slightly higher temperatures , with a base temperature of 57 and optimized growth at 90 degrees . Assuming worst-case nighttime lows and an idealized daytime temperature , a minimum sum for good growth would be 143 and 147 for these two grasses , which is pretty darn close to the sum to 150 rule . I am not sure one can easily compare the base temperatures from research to requiring consistent 60-degree night temperatures . But if the minimum for growth is in the mid- to low-50s , it seems reasonable to assume consistent nights of 60 degrees would ensure good growth .

The take-home message is that temperature has a strong influence on bermudagrass growth and until some minimum temperature is reached , the turfgrass will not grow very well . SFM

Reference : McCurdy , James D ., Ethan T . Flournoy , Barry R . Stewart , H . Wayne Philey , K . Raja Reddy , William C . Kreuser , Eric Reasor , and Christian M . Baldwin . “ Estimates of Turf-Type Hybrid Bermudagrass Base and Optimal Growth Temperatures .” Journal of the Mississippi Academy of Sciences 65 , no . 3 ( 2020 ): 258-267

Grady Miller , Ph . D . Professor and Extension Turf Specialist North Carolina State University

Questions ? Send them to Grady Miller at North Carolina State University , Box 7620 , Raleigh , NC 27695-7620 , or e-mail grady _ miller @ ncsu . edu

Or , send your question to Pamela Sherratt at 202 Kottman Hall , 2001 Coffey Road , Columbus , OH 43210 or sherratt . 1 @ osu . edu

50 SportsField Management | July 2023 sportsfieldmanagementonline . com