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Volatile loss rates of pesticides from turfgrass were measured using the Backward-Time Lagrangian Stochastic Dispersion model (Flesch et al., 1995). Solar radiation, ambient temperature, surface temperature, relative humidity, wind direction, and wind speed were monitored continuously. Growth regulator was applied to the turf plot several days before pesticide application to maintain a constant grass height and aerodynamic roughness length during the experiment. No irrigation occurred following application. Pesticides were applied as mixtures to allow direct comparison of evaporative loss. Mixtures studied were chlorpyrifos + triadimefon + ethofumesate and triclopyr (acetic acid) + propiconazole + cyfluthurin. Airborne flux estimates correlated with temperature, solar radiation, wind speed, time, and vapor pressure of the active ingredient. A log vapor pressure vs. 1/Temperature (K) relationship was observed between flux and surface temperature over a single day for most pesticides. An exponential attenuation of flux was observed over a period of several days and correlated with attenuation of dislodgeable surface residues for two of the pesticides. A fugacity-based model for predicting initial evaporative loss rates from turf grass is presented. Input parameters include pesticide vapor pressure, molecular diffusion coefficient, surface temperature, wind speed profile, atmospheric stability, surface roughness, and average upwind fetch. The GC retention method (Jensen, 1966) was used to estimate pesticide vapor pressures over an environmentally relevant temperature range. The model predicts fluxes that are an order of magnitude greater than measured values. This bias may be due, in part, to deviation from the assumption of pesticide saturated vapor density at the foliar surface. In addition, sensitivity analysis suggests improved estimates of leaf surface temperature and pesticide vapor pressures have the greatest potential to improve model performance. / Graduation date: 2003

The status of Curvularia lunata as a primary pathogen of creeping bentgrass (Agrostis palustris) has been debated in the literature for many years. The most recent and most complete evidence indicates that this fungus is a weak pathogen, colonizing only senescing tissues. In the present study, four groups of experiments were conducted: 1) The effects of five herbicides on the growth of C. lunata in vitro were determined. 2) Acute high temperature stress was evaluated as a predisposing factor in the susceptibility of creeping bentgrass to C. lunata. 3) The effects of acute high temperature stress and exposure to five different herbicides on creeping bentgrass were evaluated together and separately. 4) The potential of chronic, moderately high temperature stress and exposure to five herbicides when occurring separately and together to serve as predisposing factors on the susceptibility of creeping bentgrass to C. lunata were evaluated. It was found that effects of the herbicides on the growth of C. lunata depend on both the specific herbicide and the concentration. High temperature stress and herbicide exposure increase the colonization of creeping bentgrass by C. lunata only to the extent that these treatments produce moribund plant tissue. / Master of Science

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Sclerotinia homoeocarpa F.T. Bennett, causal agent of dollar spot on creeping bentgrass (Agrostis palustris Huds.); and Rhizoctonia solani Kihn, causal agent of brown patch on tall fescue (Festuca arundinacea Schreb.), are important pathogens of turfgrass. This research evaluated the ability of twenty bacterial strains of the genus Pseudomonas as potential biological agents for the control of these diseases. Year 1 dollar spot field trials resulted in the identification of five strains performing statistically as well as the recommended fungicide, chlorothalonil. Year 2 trials, using the top strains from Year 1, employed different application schedules and inclusion of a commercial spray adjuvant, Agri-Dex™, Results from Year 2 dollar spot trials indicated that eight strains performed statistically better than the non-treated control. Results from Year 1 and Year 2 of brown patch field trials provided three strains that performed statistically better than the nontreated control during Year 1, but only one strain during Year 2. Laboratory tests performed with all strains and both pathogens showed that demonstration of agar-based inhibition is more difficult to obtain with R. solani. Six strains evaluated using AgriDex™ and S. homoeocarpa in laboratory and greenhouse tests, determined that application with Agri-Dex™ can be more effective than with bacteria alone. Supporting greenhouse tests using the top strains from the S. homoeocarpa field trials to evaluate application timing in controlling dollar spot, indicated less disease with earlier and more frequent applications. With further research, several strains have the potential for disease control on turf, particularly dollar spot, and may reduce the reliance on chemical fungicides. / Master of Science

Public tendency, of late, is to reduce liberal use of harmful synthesized chemicals for promoting plant health. Today, biological control is becoming a commonly cited disease control option. Biological control agents (BCAs) not only control disease , but also promote plant growth. Application of biological control is based largely on knowledge of control mechanisms employed by antagonists, as well as the means of application that will ensure that an antagonistic population is established. Knowing the advantages is not the only factor that should be considered before application commences as, the disadvantages must be clearly outlined and explored further before a constructive decision as on implementation of biological control. A literature review was undertaken to provide the necessary technical information about biological control, its potential uses, methods of application, mechanisms of action employed, advantages and disadvantages associated with biological control application, public perceptions and the potential future of biological control. Diseases encountered within the KwaZulu-Natal Midlands on pasture and turf grasses were determined by a once-off survey conducted over 1999/2000. The aim of the survey was to determine broadly the management practices of farmers and groundsmen in KwaZulu-Natal and the potential impact of these on the occurrence of weeds, insects and diseases. The survey also addressed the level of existing knowledge about biological control and willingness to apply such measures. In the pasture survey, farmers were questioned about: soil type, grass species common used, irrigation , fertilization and liming, grazing programs and weed, insect and disease occurrences and control measures implemented. The same aspects were addressed in a survey to a representative sample of groundsmen (turfgrass production) , including also: topdressing, greens base used, drainage systems, mowing practices and decompaction principles. The survey showed correlation between pest incidence and management practices implemented. In terms of pest control, both farmers and groundsmen indicated a stronger preference to the use of herbicides , insecticides and fungicides. Use of fungicides for disease control by farmers is considered an often unfeasible expense, rather more emphasis was placed on implementing cultural control methods. At present farmers do not apply biological control strategies, but they did indicate much interest in the topic. Alternatives to current, or lack of current, disease management strategies are important considerations, with two new diseases identified in the KwaZulu-Natal Midlands just within the period of this thesis. Biological control strategies are implemented by 8% of the groundsmen surveyed, with emphasis being placed on augmenting the already present natural predators rather than the introduction of microbial antagonists. Although often mis-diagnosed by farmers Helminthosporium leaf spot is a common disease in the KwaZulu-Natal Midlands on Pennisetum clandestinum (kikuyu), This disease reduces pasture quality and detracts from the aesthetic appearance and wearability of turfgrasses. Helminthosporium leaf spot is incited by a complex of causal agents , Bipolaris was confirmed as the casual agent of Helminthosporium leaf spot on kikuyu at Cedara. Disease control by two BCAs, Bacillus (B. subtilis Ehrenberg & Cohn.) and Trichoderma (T. harzianum Rifai), as commercial formulations was tested against the fungicide, PUNCH EXTRA®. In vitro, Trichoderma was shown to be aggressive in controlling Bipolaris sp. In vivo, disease control achieved with Trichoderma kd was comparative with PUNCH XTRA® but not statistically different (P>=0.05). Trichoderma and Bacillus provided better disease control in comparison to an untreated control. Improved growth of Lolium sp. was determined in vitro, with Trichoderma kd and Bacillus B69 treatments. The microbe-based treatments accounted for growth stimulation, with significant (P<=O.05) growth differences noted. A microbial activator, MICROBOOST®was added to the treatments to improve microbial efficiency. Improved plant growth with MICROBOOST® applications was shown. Improved growth associated with microbial treatments, Trichoderma harzianum kd; Bacillus subtilis B69 and Gliocladium virens Miller, Gibens, Foster and con Arx. ,was also determined in vivo at Cedara, on L.perenne L., Festuca rubra L. and Agrostis stolonifera L. Establishment of a suppressive soil with antagonistic microbes resulted in significant (P<=O.05) effects on final grass coverage (except G. virens), as well increased root and shoot lengths (P<=O.05). Increased germination rates, as expressed in vitro, were not shown in vivo. Microbial activity with the application of MICROBOOST® showed little effect on germination but increased root and shoot lengths significantly (P<=O.05). Increased weed growth associated with the treatments (except G. virens) was considered a drawback of the microbial-treatments. Microbial treatments were also applied to pasture grasses. An in vitro grazing trial was established at Cedara, using L. multiflorum L. to evaluate the microbe-based treatments Trichoderma kd, Bacillus B69 and G. virens for improved pasture establishment and for increased grazing preference by Dohne Merino sheep. Trichoderma kd was associated with increased dry and wet biomass , but lower dry matter yields in comparison to the control. Only G. virens accounted for a higher dry matter percentage than the control. However, differences between the control and the microbial treatments was very small and not significant (P>=0.05). Of the three grazing observations made, sheep showed no grazing preference to plots with or without microbial treatments In general, the body of this research has shown that microbial treatments have the potential for increased disease control and growth stimulation of grasses. However, lack of significant differences between microbial treatments and controls has raised the question as to effect of external factors on microbial activity and survival, especially in vivo. This raises the question as to the validity of the use of microbial treatments where growth conditions cannot be controlled , remembering that the cost of establishment must be covered by the economic returns from utilization. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.