Recipient Organization
CLEMSON UNIVERSITY
(N/A)
CLEMSON,SC 29634
Performing Department
Agricultural & Environmental Sciences
Non Technical Summary
This project aims to examine and provide solutions for some of the most recalcitrant pathology problems in golf course bermudagrass greens at this time. These problems include diseases such as spring dead spot, Rhizoctonia leaf and sheath spot or blight, and nematode infestations. The approach will be to determine with the best scientific methods, the causal agents responsible for the diseases, and utilize this knowledge to design and evaluate integrated control measures to limit the damage from these diseases. The approaches will yield new knowledge of the pathogens, their identification and diversity, and methods of management.
Animal Health Component
60%
Research Effort Categories
Basic
10%
Applied
60%
Developmental
30%
Goals / Objectives
A. Identification and characterization of causal agent(s) of leaf and sheath spot disease, spring dead spot, and plant parasitic nematodes in ultradwarf bermudagrasses.B. Development of disease management practices and programs for ultradwarf bermudagrasses.C. Development of integrated control practices for plant parasitic nematodes in bermudagrass putting greens.
Project Methods
Typical mycological techniques for isolation and culture of Rhizoctonia-like fungi will be utilized. Symptomatic tissues will be lightly surface sterilized using 70% ethanol, followed by sterile water rinses, and tissues plated onto water agar or 1/4xPDA with antibiotics to suppress bacteria. In some cases, amendments of benzimidazole fungicides such as thiophanate methyl at 10-50 ppm will be used to select forWaitea.These fungi will also be identified using molecular techniques. Pathogenicity tests will also be conducted . Greenhouse-grown bermudagrass will be grown in sand-peat soil mixes. Plants will be cultured from aerial stolons. Plants can be established in cone-tainers or small pots. Inoculum can be prepared on sterile oat seeds infested with the test fungi and placed near the soil surface. Inoculated plants can be incubated in growth chambers to determine pathogenicity and virulence of the tested fungi. Additionally an objective to further investigate these fungi as causal agents by field inoculations.For Spring Dead Spot (SDS) samples are not limiting. , Hierarchical sampling can be employed to study theditsribution of causal agents. Greens, tees or fairway samples can be obtained, and samples from coastal, mid-state and western SC can be obtained. A reasonable total sample size would be about 200 separate isolates. Isolation of SDS causal agents can be done in the spring . Plugs of symptomatic turf are collected, and the root system washed thoroughly to reveal roots with lesions. Roots are cut into section about 1 cm in length and surface sterilized with 20% chlorine bleach for up to 5 minutes. Roots are blotted dry and plated directly, onto 1/4x PDA amended with antibiotics. Incubation at root temperature usually reveals slow growing fungi from cut edges of the roots. These will be sub-cultured onto clean isolation plates as working cultures for PCR using hyphal mats cultured on full strength potato dextrose broth. Primers from Wetzel, et.al., 1999, will be used to identify O. korrae, O. herpotricha or O. narmariConcerning nematodesField trials will emphasize control of sting nematodes,the most damaging of any of the known turf parasitic nematodes. Trials will be conducted on infested golf courses. Power analyses to determine sample sizes for plant parameters are needed to determine chances of detecting differences if they exist. Experimental designs to account for heterogeneity of population, such as the use of covariate analysis, may be needed.Efficacy will be based on visual turf quality and improvement in root health. Power analyses will determine the compromise needed to determine field replications, and sub-sample number needed to increase accuracy and precision. Individual plot size will be of a size sufficient to detect visual plant health improvement. Nematode population densities will be determined by systematically sampling soil in the root zone (about 3-4 inches deep) using a standard 1-inch soil probe. Subsamples will be collected and bulked, stored in a cool environment and assayed quickly in the lab by standard techniques. Soil cores of 1-2 inch diameter can also be taken for rooting estimates at mid- and final evaluation dates. Cores will be frozen to stop root growth in storage, and washed of soil and organic matter, removed from stolons, and scanned as per WinRhizo protocols. After scanning, roots can be determined by ashing. Using these methods, the efficacy of nematode control and management products will be evaluated to provide data needed for product registrations or to determine if a product is truly efficacious, even if registered for use.For development of disease management programs, typically, these trials are conducted in small plots (1.5 m2), utilizing 4 replications in randomized complete block design. Materials are applied by water diluent sprays delivered through CO2-pressurized, shielded sprayers or applied as dry granular formulations to mimic industry methods of application. Timing of sequential applications or rotations of materials in disease control programs will vary depending on the specific objectives of each study. Plots may be infested with isolates of virulent pathogenic fungi from the principal investigators' culture collection. For example, dollar spot is easily induced in the field by culturing inocula on sterile grass seed, such as tall fescue, mixing with dry topdressing sand at a ratio of 1 part inoculum to 10 parts sand, and broadcast applying the mixture using a rotary fertilizer spreader. After inoculum is broadcast, plots are irrigated to hydrate the inoculum, and plots may be temporarily covered with open-weave fabrics to improve environmental conditions for infection. Plots are evaluated visually for percent of plot area affected by disease, numbers of infection centers per plot or by image analysis systems whereby digital photographs are enhanced to better denote diseased vs. healthy areas, and diseased areas digitally quantifiedFor plant parasitic nematodes in turfs, efficacy trials in the field and in the greenhouse will be conducted to determine the relative benefits these and other products may have for management of plant parasitic nematodes in turf. Greenhouse trials may utilize pure cultures of nematodes, such as sting, for directed efficacy studies. In this way, cultures of sting nematode will be maintained and increased on St. Augustinegrass. Pots or cone-tainers of varying size containing sand/peat mixtures that will support sting reproduction will be used and planted with nematode-free nodes from stolons of bermudagrasses until establishment. Varying numbers of nematodes depends on the particular experiments but, for example, 50 sting nematode individuals can be added per 100 cc of soil to provide an initial population capable of inhibiting rooting and plant health. Subsequent treatments may be imposed to examine rates, nematicide product movement in soil profiles, etc. Another approach is to use natural infestations from golf courses, sod farms or nurseries to provide intact soil cores of 2 inches in diameter, using sampling tubes with polybutyl liners that can be used intact as the experimental units. Replications will be increased to account for variations in nematode populations (typically 8 replications), and non-treated cores (units) can be collected adjacent to cores designated for treatments for use as covariates. Field experiments can be similarly conducted on green nurseries, in fairways, etc. where cooperators will allow untreated checks and allow root core collections for assay of rooting parameters such as dry weight and/or root length, width, surface area, etc. through analysis with WinRhizo scanning technology. In some cases, the relative efficacy of products is generally well known, and includes knowledge of timing of applications (McGroary et.a., 2013). Therefore it is proposed to begin to evaluate season-long 'programs' aimed at nematode management. These programs may include varying products, such as Nortica, MultiGuard Protect, Avid 0.15EC and the addition of fungicides such as azoxystrobin (Heritage) or other root active broad spectrum fungicides that may improve plant health. The influence of soil wetting agents, application and post-application water volume, and other factors can also be examined in directed studies and in season-long program approaches. Both directed studies and season long program evaluation experiments will be focused on root health, with measures of visual root improvement from soil cores removed after applications and varying intervals, as well as 'final' root health measures from large soil cores (2 inch diameter) with up to 3 sub-samples per plot and at least 6 replications in most experiments to provide sufficient sample sizes for determination of efficacy.. .. .