S. Bruce Martin

Biology of Turfgrass Diseases Incited by Rhizoctonia Species

Turfgrasses are those members of the family Poaceae (Gramineae) characterized by a dense foliar canopy and tolerance to mowing. Approximately 40 species in 18 genera represent two physiological groups commonly referred to as cool-season and warm-season grasses. Cool-season grasses are adapted to subarctic and temperate regions, with optimal growth occurring at 15–25°C. These species, known as C3 grasses, undergo photosynthetic carbon fixation through the Calvin cycle. In contrast, warm-season grasses are known as C4 grasses because they fix carbon via the Hatch-Slack pathway. These grasses are adapted to tropical and subtropical regions, with optimal growth occurring at 25–35°C (Smiley et al., 1992).

Yellow Nutsedge (Cyperus esculentus) Management and Tuber Reduction in Bermudagrass (Cynodon dactylon × C. transvaalensis) Turf with Selected Herbicide Programs1

Abstract: A 4-yr field study was conducted to evaluate yellow nutsedge suppression in ‘Tifway’ bermudagrass. Herbicide programs included preemergence (PRE) applications of metolachlor (3.4 kg ai/ha) and postemergence (POST) applications of imazaquin (0.28 kg ai/ha) plus MSMA (2.2 kg ai/ha) or halosulfuron (0.07 kg ai/ha) plus MSMA (2.2 kg/ha). Herbicides were applied to the same plots each year. Yellow nutsedge shoot suppression and tuber numbers were determined each year. Suppression of yellow nutsedge shoots increased over the 4-yr period from <74% in 1993 to >83% by 1996 with two annual applications of imazaquin plus MSMA or halosulfuron plus MSMA. PRE metolachlor applications did not suppress shoot production in any year; nor did they enhance suppression from POST treatments. Sequential applications of halosulfuron plus MSMA and imazaquin plus MSMA increased shoot suppression by 17 to 24% at 3 mo after initial treatment (MAIT) compared to single applications. All treatments reduced tuber numbers (>60%) after 4 years compared to untreated plots. Nomenclature: Halosulfuron, methyl 5-{[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl-aminosulfonyl}-3-chloro-1-methyl-1-H-pyrazole-4-carboxylate; imazaquin, 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid; metolachlor, [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide]; MSMA, monosodium salt of methylarsonic acid; yellow nutsedge, Cyperus esculentus L. #3 CYPES; bermudagrass, Cynodon dactylon Burtt-Davey X C. transvaalensis L. Pers. ‘Tifway’. Abbreviations: MAIT, months after initial treatment; POST, postemergence; PRE, preemergence; WAIT, weeks after initial treatment.

18S rRNA and COI haplotype diversity of Trichodorus obtusus from turfgrass in South Carolina

The stubby-root nematode, Trichodorus obtusus , was recently identified on zoysiagrass in South Carolina, USA. In Florida, T. obtusus causes more damage than other stubby-root nematodes encountered in turfgrass. The objective of this study was to use morphological analysis, mitochondrial DNA (COI: cytochrome oxidase 1) and nuclear (18S rRNA) sequence data to study the genetic structure and haplotype diversity of populations recovered from turfgrasses in South Carolina. Numerous morphological differences were observed among populations. Three 18S haplotypes were shared among South Carolina and Florida populations, and six mitochondrial haplotypes were identified in South Carolina samples. Of the six COI haplotypes, four haplotypes were restricted to one population from St Augustinegrass. The lowest haplotype diversity was found in samples from zoysiagrass. Sequences of the COI mtDNA gene of T. obtusus were published in GenBank and represent the first mtDNA sequences for the genus Trichodorus .

Effects of Trichodorus obtususon zoysiagrass and bermudagrass root weight and turfgrass quality

Trichodorus obtususis a damaging stubby-root nematode encountered on turf. Few reports exist about the effects of T. obtususfeeding on turfgrass in field settings. A 2-year field trial was conducted to evaluate the effects of T. obtususon turf quality and root weight of Tifway bermudagrass and Empire zoysiagrass. Core samples and turf quality ratings were taken on multiple sampling dates, from plots at multiple locations in South Carolina, USA. Nematode population densities, root weights and turf quality were used to describe the linear and non-linear relationships between them. Zoysiagrass root weights increased, but turf quality decreased with nematode population density. Bermudagrass root weights and quality decreased in response to increased nematode population densities. Our results show that T. obtususcan cause significant reductions in turfgrass quality, and zoysiagrass and bermudagrass were able to tolerate low nematode population densities before turf quality reductions were detectable.

Phylogenetic analysis of Gaeumannomyces graminis varieties based on sequence insertions in the small subunit rDNA

Gaeumanoumyces graminis (Gg) varieties (tritici, avenae and graminis) were found to possess sequence insertions in the middle region of the small subunit ribosomal DNA. The sequence insertions were used to distinguish Gg isolates from North America obtained from wheat, creeping bentgrass and St. Augustinegrass and to resolve their phylogenetic relationship. Based on the alignment of sequence insertions, Gg isolates were divided into two sets: set I contained all isolates of Ggt; Gga; and Ggg isolates WF 9124, WF 9238, and WF 9463; while set II contained the other Ggg isolates that possessed insertion sequences with different lengths. Phylogenetic analysis of sequence insertions from set I shows that Ggt are more closely related to Gga that is supported by bootstrap 85%. Ggg isolates did not form a distinct group and appeared mixed between the well supported Ggt and Gga groups. Parsimony analysis of Ggg set II insertions revealed a distinct clade consisting of three monophyletic groups.