St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is host to the southern chinch bug (SCB) (Blissus insularis Barber). This study evaluated and compared field and laboratory resistance of St. Augustinegrass germplasm to the SCB. Turf field plots of 20 St. Augustinegrass genotypes were monitored monthly for 2 years for damage by the SCB. After each occurrence of damage, plots were treated individually with an insecticide and allowed to become damaged again. Genotypes differed in frequency of damage, which varied from 1.02 occurrences per year for FX-22 and FX-338 to zero occurrences per year for `Floratam'. During the next 2 years when no insecticide was applied, the portion of dead canopy varied from 86% for FX-313 to 0% for `Floratam'. In a second field experiment, SCB damage was evaluated in 10 polyploid St. Augustinegrass genotypes. Damage varied from 90% for `Bitterblue' to 0% for `FX-10'. Oviposition rate was determined from SCB confined in the laboratory on genotypes from both field experiments. Oviposition rate differed among genotypes and predicted (P < 0.01; r2 = 0.67 to 0.79) field damage. To my knowledge, this paper is the first to report field resistance to the SCB in St. Augustinegrass, validating the use of laboratory bioassays.
St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] has low freezing tolerance and suffers winter injury in the southeastern United States. Laboratory methods have determined that the lethal cold temperature of St. Augustinegrass stolons and buds is between -4.5 °C and -7.7 °C. The field survival of St. Augustinegrass to winter freezing is poorly known because most field reports have been based on a single location experiencing a single winter minimum air temperature. The objective of the study was to assess the winter survival of St. Augustinegrass cultivars across a range of winter minimum air temperatures occurring in experimental plantings at 24 Florida counties, following a severe Arctic cold front that moved through Florida beginning 21 Dec. 1989. Except for two counties, the limit for St. Augustinegrass winter survival was a minimum air temperature between -6 °C and -9 °C. Based on a nonlinear estimate using a 3-parameter sigmoidal model (r2 = 0.70, P < 0.0001), 50% survival of St. Augustinegrass would be predicted at -7.9 °C. Time since planting had no relationship with survival. Differences among St. Augustinegrass cultivars were observed at only two counties.
St. Augustinegrass [Stenotaphrum secundatum (Walt.) Kuntze] is less drought-resistant than other C4 grasses and frequently requires irrigation in lawns. The objectives of this study were to search for St. Augustinegrass germplasm having little wilting and to determine if minimal wilting under drought is associated with reduced canopy loss. St. Augustinegrass cultivars and breeding lines, representing polyploids (2n = 27 to 32) and diploids (2n = 18), were grown in sand soil and exposed to irrigation suspensions during seasonal droughts in three experiments. In the first experiment, during brief (3 to 14 day) irrigation suspensions, wilted area over 3 years was significantly less for polyploids (6% of canopy) than for diploids (23%). In the second experiment, during a permanent irrigation suspension, frequency of wilt was highest for diploids (57%), least for African polyploids (27%), and intermediate (53%) for other polyploids. When rain resumed after 41 days of drought, allowing refoliation, canopy loss was 51%, 4%, and 47% for diploids, African polyploids, and other polyploids, respectively. In the third experiment, during a permanent irrigation suspension, wilted area was 33% for `Jade,' a diploid, which was more (P ≤ 0.05) than for the polyploid `FX-10,' with a wilted area of 20%. `Floratam' and `Bitterblue' were intermediate in wilted area, 28% and 25%, respectively. When rain resumed after 18 days of drought, canopy loss was 58% and 56% for `Jade' and `Bitterblue,' respectively, which was more than for `Floratam' and `FX-10,' 11% and 6%. Following permanent irrigation suspensions, canopy loss was closely associated with wilting, r2 = 0.88 and 0.94 by the Gompertz nonlinear model. Because the sand soil had low water-holding capacity, the wet subsoil and shallow (1.35 m deep) water table may have been a source of water. Wilt-avoidant St. Augustinegrass may help reduce turfgrass water use.