Precipitation and heat are major limitations to the adaptation of tall fescue west of I-35. Tall fescue is a cool-season perennial forage that generally needs a minimum of 32-36 inches of annual rainfall for production and persistence. The long, hot and dry summers that are common to parts of Oklahoma and Texas can cause stand loss of tall fescue if it is not managed properly.
Some species of tall fescue have developed a mechanism to avoid these conditions by invoking summer dormancy, thus avoiding summer heat and drought. Tall fescues of this type are referred to as "Mediterranean," originating from the Mediterranean Basin of southern Europe and northern Africa. Currently there are two cultivars of summer-dormant tall fescue on the market: Grasslands Flecha, containing the AR542 novel endophyte, and Prosper, an endophyte-free cultivar.
Tall fescues that actively grow or are semi-dormant during summer are referred to as "Continental" tall fescue and make up the majority of tall fescue acreage in the United States. Common Continental cultivars include Kentucky 31 (Ky 31+), Jesup MaxQ, AU Triumph, Johnstone and others.
The summer dormancy trait will help persistence of tall fescue in warm, dry climates. But does this trait also reduce the forage yield of summer-dormant tall fescues compared to summer-active tall fescues? To answer this question, a three-year study was established in the fall of 2007 to evaluate fall through spring production of Ky 31+ (summer-active with wild-type endophyte), Jesup MaxQ and PDF AR584 (both summer-active with novel endophyte), Flecha AR542 (summer-dormant with novel endophyte) and NFOG101 (endophyte-free, summer-dormant orchardgrass). Four nitrogen (N) treatments (0, 60, 120, 180 lbs/ac) were applied to the grasses in September 2008, and growth was measured monthly from November to May. There was no difference in average forage yield between months from November to March (fall/winter) or April to May (spring). Results from these periods are summarized in Table 1 and Table 2.
In Table 1, adding 60 lbs/ac N increased yields over the 0 lb/ac N check in tall fescues, but not orchardgrass. Adding 120 lbs/ac N produced a response only in PDF AR584 and Ky 31+. In the overall average column, Flecha AR542 yield was equal to Jesup MaxQ and greater than Ky 31+. In Table 2, N did not affect yield due to volatility loss of N from urea used as the nitrogen source. However, looking at overall average yield, Flecha AR542 was equal in yield to PDF AR584 and higher than Jesup MaxQ or Ky 31+.
This is only one year's data, so one should be cautious in using these results to make management decisions. It does, however, look promising that Flecha AR542 will yield equally well with some of the summer-active tall fescue types.