Grady L. Miller

Factors affecting seed germination of tropical signalgrass (Urochloa subquadripara)

Abstract Tropical signalgrass is one of the dominant weeds in the Florida turfgrass industry and is potentially troublesome for the southeastern turfgrass industry. Tropical signalgrass is especially problematic for St. Augustinegrass sod producers because of lack of control options. The objectives of our research were to determine the effect of light, pH, temperature, water potential, and planting depth on tropical signalgrass germination and emergence. Tropical signalgrass germination does not require light and is optimum at pH 5 to 6, temperature 25 C, and water potentials greater than − 0.4 MPa. Tropical signalgrass shoots emerged from depths of 0 to 7 cm, with maximum germination when placed on the soil surface. Tropical signalgrass seedlings emerged in the field during the second week of March in Ft. Lonesome, FL. Weekly mean soil and ambient air temperatures at the time of emergence were 20 C. Tropical signalgrass emergence was first observed at 118 and 73 growing degree-days (GDD) (13 C base temperature), with a peak emergence period at 222 and 156 GDD for 2001 and 2002, respectively. Nomenclature:  Tropical signalgrass, Urochloa subquadripara (Trin.) R. D. Webster BRASU; St. Augustinegrass, Stenotaphrum secondatum (Wait.) Kuntz.

Analysis of Double-Ring Infiltration Techniques and Development of a Simple Automatic Water Delivery System

Double-ring infiltrometers are routinely used by turfgrass specialists, soil scientists, and other professionals to measure the infiltration rate of field sites. Measurement of infiltration rate is important in proper golf course design development and other scenarios that require estimates of runoff. This study compared several commonly performed double-ring infiltration methods as follows: 30- (inner) and 60-cm (outer) diameter rings with a constant water depth (head), 15- (inner) and 30-cm (outer) diameter rings with a constant head, and 15- (inner) and 30-cm (outer) diameter rings with a falling inner head. In addition, a Mariotte siphon device was fabricated to maintain a constant inner head for the 15-cm diameter rings. The 15- and 30-cm rings with the constant head resulted in significantly higher infiltration rates compared to 30- and 60-cm diameter rings with a constant head and 15- and 30-cm rings with a falling head. This was due to variation in the 30- and 60-cm test inner ring water level that had to be maintained manually and because of the non-constant water level in the 15- and 30-cm falling head test. Thus, we concluded that the constant head 15- and 30-cm double-ring test was adequate to represent the infiltration rate in the sandy soils tested. The Mariotte siphon device made it easy for one person to conduct a test while maintaining a constant inner head under infiltration rates ranging from 22 to 225 mm/h.

Tropical signalgrass (Urochloa subquadripara) control with preemergence- and postemergence-applied herbicides.

Tropical signalgrass is one of the most serious weed problems in the St. Augustinegrass sod production in Florida, and its presence increases production costs and lowers turfgrass quality. The objectives of our research were to: (1) evaluate herbicides preemergence and postemergence for control of tropical signalgrass and (2) compare control of tropical signalgrass and other problem weeds (torpedograss, blanket crabgrass, and India crabgrass) with postemergence herbicides. In preemergence herbicide field trials, only benefin + oryzalin, imazapic, imazapic + 2,4-D, and oryzalin provided ≥75% tropical signalgrass control 8 wk after application (WAA). By 11 WAA, only benefin + oryzalin and imazapic + 2,4-D provided ≥75% tropical signalgrass control. In greenhouse experiments, eight herbicide treatments were applied postemergence to tropical signalgrass seedlings at the two-, four-, six-, and eight-leaf stages. Asulam and CGA 362622 provided ≥89% tropical signalgrass control at all application timings. Imazaquin controlled tropical signalgrass ≥98% when applied before the eight-leaf stage. However, in field trials with mature tropical signalgrass (>20 cm stolons), none of the 20 herbicide treatments applied postemergence provided acceptable control. Nomenclature: Asulam; benefin; CGA 362622, N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-3-(2,2,2-trifluoroethoxy)-2-pyridinesulfonamide; 2,4-D; imazapic; imazaquin; oryzalin; blanket crabgrass, Digitaria serotina (Walt.) Michx. #3 DIGSO; India crabgrass, Digitaria longiflora (Retz.) Pers. # DIGLO; St. Augustinegrass, Stenotaphrum secondatum (Walt.) Kuntz; torpedograss, Panicum repens L. # PANRE; tropical signalgrass, Urochloa subquadripara (Trin.) R. D. Webster # BRASU. Additional index words: BRASU, DIGLO, DIGSO, PANRE. Abbreviation: WAA, weeks after application.

Residential Irrigation Uniformity and Efficiency in Florida

Residential water use is increasing in central Florida. Irrigation accounts for 50% or more of typical residential use volume. The goal of this project is to document irrigation water use and system uniformity in the Central Florida Ridge region. Three types of irrigation/landscape combinations are being installed: T1, typical irrigation and landscape; T2, well designed irrigation system and typical landscape; T3, well designed irrigation system and a landscape designed to minimize water use. To date, seven T1’s and three T3’s exist. Initial results indicate that 80% of water use is irrigation. Measured distribution uniformities (DUlq) are lower than Mobile Irrigation Lab reports and may be classified as “good” (n=1), fair (n=3), “poor” (n=3), and “fail” (n=1) on the homes tested. Over irrigation was common among home sites.

Uniformity Comparison of Common Residential Irrigation Sprinkler Heads

Due to droughts, irrigation has become a necessity for residential homeowners desiring high quality landscapes in Florida. In an efficient system a number of components must be considered; design, scheduling, and equipment. Catch-can tests of the system are an accepted method of determining the uniformity of the irrigation distribution, which can be related to efficiency. The DUlq values of the spray and rotor zones of residential irrigation tests in Central Florida were 0.40 and 0.48 respectively. Brand and pressure effects on uniformity of spray and rotor heads were found to be significant. From uniformity tests performed on spray and rotor heads under ideal conditions, the rotor heads had the most uniform distributions, 0.55, regardless of pressure variation. The spray heads had the better uniformity when fixed quarter circle nozzles were used as opposed to adjustable nozzles, with average DUlq values of 0.52 and 0.44 respectively.

Temperature Increase on Synthetic Turf Grass

Artificial turfgrass is a synthetic material made to resemble real grass. A new generation of synthetic turfgrass is made of plastics with different composite materials, and is supported by a sand and/or rubber infill material and subsurface base layer. Synthetic turfgrass is being increasingly used on many athletic fields, such as soccer, football and rugby, as well as in urban landscapes. It is superior to natural grass in aspects, such as lower maintenance, no irrigation required, and surface uniformity. However, high temperatures on synthetic turfgrass surface during hot weather may be dangerous and could result in heat related health problems, such as heat stroke. The objective of this study was to evaluate the temperature increase among different synthetic turfgrass types and to predict temperature increase on the synthetic turfgrass surfaces. In this study, four types of synthetic turfgrasses (1 – 4) with four infill materials and base layers (A – D) were installed in central Florida, surrounded by large irrigated natural grass fields. Temperature measurements were taken at 23.5 cm above the ground and 5 cm below the ground. The results indicated that there were no differences in air temperatures above the ground between the synthetic turfgrass and the natural turfgrass, due to the small size of the plots and the high wind speed during the daytime. The temperature below the surface (base temperature) for the synthetic turfgrass was always higher than the natural surfaces at noon time. The base temperature differences between the two surfaces were higher in July and August and lower in November. Overall, the infill temperature difference increased with an increase of the depth of the base layer and the color of synthetic turfgrass. Base temperature increase on synthetic turfgrass (Tsyn) was linearly related to the incoming solar radiation (Rs). Relationships based on solar radiation and temperature on natural surfaces (Tnat) (both natural grass and bare soil surface) were developed for all units (Tsyn – Tnat = a Rs + b) so that the temperature increase on synthetic turfgrass could be predicted.

St. Augustinegrass root growth response following plant growth retardant application

St. Augustinegrass [(Stenotaphrum secundatum (Walt.) Kuntz.] is the preferred warm season turfgrass for Florida’s commercial and residential landscapes with an estimated 0.7 million hectares under growth and management. Previous plant growth retardant (PGR) research has demonstrated excellent responses in fine warm season turfgrasses such as bermudagrass [Cynodon dactylon (L.) Pers.] and centipedegrass [Eremochloa ophiruroides (Munro) Hack]. However, limited information is available regarding St. Augustinegrass response to currently labeled or potentially registered PGRs. This two-year study was designed to evaluate St. Augustinegrass root length density (RLD) following PGR application. Treatments included flurprimidol and paclobutrazol at 1.1 kg ha-1, trinexapac-ethyl and mefluidide at 0.28 kg ha-1, and imazapic (formerly AC 263,222) at 0.028 kg ha-1. Root growth was traced at two, four, and six weeks following PGR application on acetate paper attached to the front surface of 15.0 x 50.0 cm clear Plexiglas tubes placed on greenhouse benches at 20° to the vertical. Newman’s random line intersect technique, at an accurate viewing depth of 0.2 cm, was used to quantify RLD. With the exception of imazapic, all PGRs provided RLD values equal to the untreated turfgrass at each of the three biweekly tracing periods during both years. Imazapic inhibited root growth ≈68% for four weeks. However, RLD values for imazapic exceeded the untreated turfgrass at least 50% by week six during both years. Although not significant, paclobutrazol and flurprimidol provided ≈ 11 % and ≈20% higher RLD values at week four in 1994 and 1995, respectively, while trinexapacethyl provided 9% and 43% higher RLD values in 1995 at weeks four and six, respectively. Mefluidide RLD values were similar to the untreated control for the entire rating period of both years.