Browsing by Author "Goatley, James M."
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- Comparing Digital and Visual Evaluations for Accuracy and Precision in Estimating Tall Fescue Brown Patch SeveritySykes, Virginia R.; Horvath, Brandon J.; Warnke, Scott E.; Askew, Shawn D.; Baudoin, Antonius B.; Goatley, James M. (2017-11)Brown patch (Rhizoctonia solani Kuhn), a destructive disease of tall fescue (Festuca arundinacea Schreb.), is typically evaluated visually. The subjectivity of visual evaluations may be reduced using technology like digital image analysis (DIA). This study compared DIA and visual evaluations for accuracy and precision of brown patch ratings of glasshouse grown tall fescue plants. Across four experiments, 112 plants were inoculated with R. solani. Disease was rated visually and using DIA-WP (digital image analysis whole plant canopy). In two experiments, disease evaluations were replicated using three images and three visual evaluations per pot. Absolute error was calculated as the difference between actual disease severity [calculated using an individual leaf DIA method previously quantified as highly predictive of actual brown patch disease severity on tall fescue (r(2) = 0.99)] and DIA-WP and visual evaluations, respectively. Standard deviations within repeated measures were also calculated. A mixed-model ANOVA was used to determine differences (P < 0.05) in mean absolute error and mean standard deviation by method, disease range, and method by disease range. Disease ranged from 0 to 100%. Mean absolute error did not differ between methods but did by disease range, exhibiting a bell-shaped curve from 0% to 100% disease severity. Mean standard deviation exhibited significant method by disease range interaction. Mean standard deviation did not differ across the disease range within DIA-WP evaluations but did across the disease range within visual evaluations. The more consistent precision of DIA across the disease range could reduce variability in brown patch evaluations of tall fescue.
- Efficacy of Entomopathogenic Nematodes and Entomopathogenic Fungi against Masked Chafer White Grubs, Cyclocephala spp. (Coleoptera: Scarabaeidae)Wu, Shaohui (Virginia Tech, 2013-05-07)Entomopathogenic nematodes (EPN) (Heterorhabditis bacteriophora and H. megidis) and entomopathogenic fungi (EPF) (Metarhizium anisopliae and Beauveria bassiana) were evaluated for efficacy against masked chafer white grub, Cyclocephala spp., under laboratory and greenhouse conditions, as well as their efficacy against various grub stages in the field. Under both laboratory and greenhouse conditions, additive interactions were found between EPN and EPF in their combined application against Cyclocephala spp., except a few observations that showed antagonism or synergism. Significantly greater control occurred from the combination of a nematode and a fungus compared with a fungus alone, but not compared with a nematode alone. The combined effect did not differ significantly for nematode and fungi applied simultaneously or at different times. EPF had no significant impact on EPN infection and production of infective juveniles (IJs) in grub carcasses. Nematodes alone or in combination with fungi were comparable to the insecticide Merit 75 WP (imidacloprid) against 3rd instar Cyclocephala spp in the greenhouse. Efficacy of EPF and EPN varied dramatically between field sites and conditions; EPN and EPF applied alone or in combination were less effective than Merit 75 WP in >50% field trials, but some EPN + EPF treatments were more effective than the insecticide in reducing grub numbers. EPN and EPF showed better potential than insecticides for providing extended control of white grubs in the subsequent generation. In addition, the sub-lethal effects of EPF on southern masked chafer, C. lurida, were investigated. Neither M. anisopliae nor B. bassiana had a sub-lethal effect on grub weight gain, adult longevity, oviposition, pupation and eclosion. Finally, interaction between H. bacteriophora and M. anisopliae was examined to determine the potential of the nematode in improving fungal distribution in soil. H. bacteriophora enhanced fungal distribution in sandy loam soil without grass thatch, but not in sandy soil with thatch. In both soil types, soil depths significantly affected nematode and fungal distribution. In water profile, M. anisopliae conidia germinated hyphae that attached to sheath of H. bacteriophora IJs, which molted to detach from the fungus. IJs mortality and virulence were not affected by the presence of M. anisopliae.
- Evaluation of Seashore Paspalum in Southeastern VirginiaCrawford, Claudia (Virginia Tech, 2014-07-23)Seashore paspalum (Paspalum vaginatum Sw.) has been successfully grown in warm, humid environments in both the United States and southeastern Asia. In the U.S., seashore paspalum has been planted in parts of North Carolina south to Florida, Texas, California and Hawaii. Very tolerant of low mowing heights, this species has been used primarily for golf courses, but also has applicability as a turf for lawns. High salt tolerance makes it a promising turf for areas near the Chesapeake Bay and the Atlantic Ocean. Research and testing of seashore paspalum in the U.S. has been conducted primarily in Georgia and Florida. Virginia Tech has not conducted any research on this potential new turf species for Virginia. For this project, I have evaluated the adaptability of nine vegetative and three seeded cultivars of seashore paspalum in southeastern Virginia in comparison to Bermuda grass (Cynodon dactylon L.) as an industry standard for comparison. Evaluations of turf cover were made weekly during establishment and at time of spring green-up. Weed competition significantly reduced establishment, with only the vegetative cultivars ‘Sea Star’ and ‘Sea Isle Supreme’ seashore paspalum achieving greater than 65% cover during the first growing season. No cultivar planted by seed successfully established due to weed competition. All seashore paspalum cultivars planted vegetatively survived the winter; however, only Sea Isle Supreme and Sea Star had exceeded 75% turf cover by June 19, 2014, approximately 75 days after breaking dormancy. ‘Yukon’ Bermuda grass achieved an 85% turf cover in the same time frame.
- Screening Tall Fescue for Resistance to Rhizoctonia solani and Rhizoctonia zeae Using Digital Image AnalysisSykes, Virginia R.; Horvath, Brandon J.; McCall, David S.; Baudoin, Antonius B.; Askew, Shawn D.; Goatley, James M.; Warnke, Scott E. (2020-02)Brown patch, caused by Rhizoctonia solani, is a destructive disease on tall fescue. Compared with R. solani, Rhizoctonia zeae causes indistinguishable symptoms in the field but varies in geographic distribution. This may contribute to geographic variability observed in the resistance response of improved brown patch resistant cultivars. This study examined R. solani and R. zeae susceptibility of four cultivars, selected based on brown patch performance in the National Turfgrass Evaluation Program (NTEP), and nine plant introductions (PIs). Twenty genotypes per Pl/cultivar were evaluated by using four clonal replicates in a randomized complete block design. Plants were inoculated under controlled conditions with two repetitions per pathogen. Disease severity was assessed digitally in APS Assess, and analysis of variance and correlations were performed in SAS 9.3. Mean disease severity was higher for R. solani (65%) than for R. zeae (49%) (P = 0.0137). Interaction effects with pathogen were not significant for PI (P = 0.0562) but were for genotype (P < 0.001). Moderately to highly resistant NTEP cultivars compared with remaining PIs exhibited lower susceptibility to R. zeae (P < 0.0001) but did not differ in susceptibility to R. solani (P = 0.7458). Correlations between R. solani and R. zeae disease severity were not significant for either PI (R = 0.06, P = 0.8436) or genotype (R = 0.11, P = 0.09). Breeding for resistance to both pathogens could contribute to a more geographically stable resistance response. Genotypes were identified with improved resistance to R. solani (40), R. zeae (122), and both pathogens (26).