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  • Author or Editor: M.L. Elliott x
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The growth responses of 10 Rhizoctonia zeae isolates, obtained from turfgrasses in Florida and Ohio, to four temperatures (20, 25, 30, and 35 °C) and seven fungicides at four concentrations (0, 1, 10 and 100 μg·mL-1 a.i.) were compared. Greenhouse pathogenicity tests were conducted using hybrid bermudagrass [Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy]. Optimal temperature for growth for all isolates was 30 °C. Growth of R. zeae isolates from both geographic locations was severely limited (>75%) at 20 °C. All R. zeae isolates were insensitive to the benzimidazole fungicides, benomyl and thiophanate methyl. Their sensitivities to iprodione, mancozeb, and quinotzene fungicides were similar. The Florida isolates were more sensitive to chlorothalonil, and the Ohio isolates to thiram. All isolates were pathogenic to hybrid bermudagrass. Chemical names used: methyl 1-(butylcarbamoly)-2-benzimidazolecarbamate (benomyl); dimethyl 4,4′-O-phenylene bis(3-thioallophanate) (thiophanate methyl); pentachloronitrobenzene (quintozene); 3-(3,5-dichlorophenyl)-N-(1-methylethyl)-2,4-dioxo-1-imidazolidinecarboxamide (iprodione); tetrachloroisophtalonitrile (chlorothalonil); tetramethylthiuram disulfide (thiram); manganese ethylenebisdithiocarbamate (mancozeb).

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The rhizospheres of creeping bentgrass (Agrostis palustris Huds.) and hybrid bermudagrass (Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy) putting greens were sampled quarterly for 4 years. Six bacterial groups, including total aerobic bacteria, fluorescent pseudomonads, actinomycetes, Gram-negative bacteria, Gram-positive bacteria, and heat-tolerant bacteria, were enumerated. The putting greens were located in four geographic locations (bentgrass in Alabama and North Carolina; bermudagrass in Florida and South Carolina) and were maintained according to local maintenance practices. Significant effects were observed for sampling date, turfgrass species and location, with most variation due to either turfgrass species or location. Bentgrass roots had significantly greater numbers of fluorescent pseudomonads than bermudagrass roots, while bermudagrass roots had significantly greater numbers of Gram-positive bacteria, actinomycetes and heat-tolerant bacteria. The North Carolina or South Carolina locations always had the greatest number of bacteria in each bacterial group. For most sampling dates in all four locations and both turfgrass species, there was a minimum, per gram dry root, of 107 CFUs enumerated on the total aerobic bacterial medium and a minimum of 105 CFUs enumerated on the actinomycete bacterial medium. Thus, it appears that in the southeastern U.S. there are large numbers of culturable bacteria in putting green rhizospheres that are relatively stable over time and geographic location.

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A mosaic disease of wax myrtle (Myrica cerifera L.) occurring in Florida is described. Affected plants had small, distorted leaves that displayed a virus-like mosaic pattern characterized by pale green blistered areas interspersed with dark green, normal-colored tissues. Affected epidermal, palisade, and spongy mesophyll cells were disorganized, distorted, and frequently contained fewer definable chloroplasts than healthy leaves. Standard virus indexing techniques yielded no evidence of a viral etiology; however, a new species of eriophyid mite, Calepitrimerus ceriferaphagus Cromroy, was recovered from symptomatic tissue. Symptomatic plants produced symptomless new growth after treatment with the systemic acaricide oxamyl, suggesting an association of the mite with the mosaic disease. Chemical name used: methyl 2-(dimethyl-amino)-N-[[methylamino)carbonyl]oxy]-2-oxoethanimidothioate(oxamyl).

Open Access