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  • Author or Editor: Philip Busey x
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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, r 2 = 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.

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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; r 2 = 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.

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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 (r 2 = 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.

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Abstract

Bermudagrass (Cynodon spp.) turf in subtropical Florida normally requires higher levels of N than other grasses and frequently requires pesticide applications. Three sequential 2-year cycles of clonal selection were performed in replicated field plots to recognize bermudagrass germplasm adapted to suboptimal fertilization and natural pest infestation. Low fertility, 19 to 25 g N·m−2, was applied yearly, including the establishment phase. No nematicides, fungicides, or insecticides were applied. Severely damaging mole cricket (Scapteriscus sp.) populations were left uncontrolled. Among 95 clones, 4 experimentals (FB-109, PI-291586, T-72-54, and FL-2400) survived repeated cycles with relatively high turfgrass coverage and quality. Among cultivars, only ‘Tifgreen-II’ and ‘Ormond’ performed well. African introductions and artificially-induced mutants of hybrid cultivars were the best sources of adapted germplasm. Although the mechanism of this adaptation is unknown, field tests were an effective prescreening method for clonal selection.

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Abstract

Visual evaluations of a 5-year-old replicated planting of 63 zoysiagrass (Zoysia spp.) genotypes in southern Florida showed highly significant (P < 1%) differences in overall vigor and survival, flight selections and 2 commercial cultivars (‘Emerald’ and ‘Meyer’) were sodded at 2 distant sites. Selected genotypes (FZ-28, FZ-80, FZ-26, and FL-1753) were significantly better adapted, had significantly less weed encroachment and greater vigor and ground coverage, than Emerald or Meyer. The latter commercial cultivars were unacceptable in most evaluations. Furthermore, FZ-28 and FZ-80 had low sting nematode (Belonolaimus longicaudatus Rau) counts and FZ-28 had few eggs of Banks grass mite (Oligonychus pratensis [Banks]). Sod webworm (Crambus spp.) infestation appeared to be another variable closely associated with adaptive differences among genotypes and explained serious establishment problems at some sites. Zoysiagrass was successfully established as a turf only on one site involving fumigated soil and generally proved poorly suited for this subtropical region.

Open Access

Phenoxy and related herbicides used in turfgrass have the potential for volatilization and movement from treated areas. Three studies assessed potential injury to subtropical landscape plants caused by volatile turf herbicides in polyethylene enclosures. Phenoxy herbicide mixtures were emphasized. There were significant differences among the seven landscape species tested. The most sensitive species were african marigold (Tagetes erecta), joseph's coat (Alternanthera ficoidea), and tomato (Lycopersicon esculentum). Severe injury was caused by exposure to herbicides containing 2,4-D isooctyl ester and MCPA isooctyl ester. Exposure to individual active ingredients 2,4-D dimethylamine, dicamba acid, atrazine, and metsulfuron resulted in no injury to the species tested.

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