Ted Whitwell

Phytotoxicity, uptake, and distribution of 14C-simazine in Acorus gramenius and Pontederia cordata

Abstract Phytoremediation depends on the ability of plants to tolerate and assimilate contaminants. We have been interested in the use of common ornamental plants to ameliorate the effects of pesticide waste on golf courses and ornamental plant nurseries. This research characterized the interaction between two ornamentals, Acorus gramenius and Pontederia cordata, and the herbicide simazine. Simazine tolerance levels for the ornamentals were determined by exposing plants to 0, 0.01, 0.03, 0.1, 0.3, 1.0, or 3.0 mg L−1 in aqueous nutrient media for 7 d. Response endpoints included fresh weight gains for both species after 7 d exposure and 7 d postexposure. Quantum efficiency of P. cordata was also measured using dark-adapted (Fv/Fm) and light-adapted (fluorescence yields) plants. Simazine uptake and distribution within each plant was determined by exposing plants to [14C]-simazine in nutrient media (0.24 mg L−1) for 1, 3, 5, or 7 d. Plant tissues were combusted and analyzed by liquid scintillation counting. Pontederia cordata fresh weight gains were reduced 76 and 70% by 1.0 and 3.0 mg L−1, respectively, after 7 d exposure. Acorus gramenius fresh weight gains were reduced 103, 124, and 144% at 0.3, 1.0, and 3.0 mg L−1 following 7 d exposure, respectively. Photosynthetic efficiency measured on dark-adapted P. cordata (Fv/Fm) was reduced 21, 47, and 71% by 0.3, 1.0, and 3.0 mg L−1, respectively, whereas photosynthetic efficiency measured on light-adapted plants (fluorescence yields) were reduced 9, 25, 59, 87, and 96%, respectively, by 0.03, 0.1, 0.3, 1, and 3 mg L−1. Simazine activity in solution was reduced 45 and 34% over 7 d with A. gramenius and P. cordata, respectively. By day 7, activity was distributed throughout the plants, but predominantly in the leaves. Uptake of simazine was correlated with water uptake throughout the 7 d. These results suggest that A. gramenius and P. cordata may be good candidates for incorporation in a phytoremediation scheme for simazine. Nomenclature: Simazine; Acorus gramenius L., sweet flag; Pontederia cordata L., pickerel weed.

Detecting Annual Bluegrass (Poa annua) Resistance to ALS-Inhibiting Herbicides Using a Rapid Diagnostic Assay

Abstract Annual bluegrass is the most problematic winter annual weed in managed turfgrass. Acetolactate synthase (ALS)-inhibiting herbicides are effective for annual bluegrass control, but reliance on this mode of action can select for herbicide-resistant biotypes. Two annual bluegrass biotypes not controlled with ALS-inhibiting herbicides were reported at golf courses in South Carolina and Georgia. Research was initiated at Clemson University to verify the level of resistance of these biotypes to ALS inhibitors. Two ALS-susceptible (S) and suspected resistant (SCr, GAr) annual bluegrass biotypes were established in a greenhouse. Dose-response experiments were conducted on mature annual bluegrass plants using trifloxysulfuron, foramsulfuron, and bispyribac-sodium, all ALS-inhibiting herbicides. Additionally, a rapid diagnostic ALS activity assay was optimized and conducted using the same herbicides. For dose-response experiments, the rate of herbicide that reduced shoot biomass 50% (I50) values for the S biotypes were 13.6 g ai ha−1 for trifloxysulfuron, 7.0 g ai ha−1 for foramsulfuron, and 38.3 g ai ha−1 for bispyribac-sodium. Fifty percent shoot biomass reduction was not observed in either the SCr or GAr biotypes at eight times the labeled field rate of all ALS-inhibiting herbicides tested. For in vivo tests of ALS activity, the SCr biotype yielded I50 (concentration of herbicide that reduced ALS activity 50%) values 3,650, 3,290, and 13 times the S biotypes following treatment with trifloxysulfuron, foramsulfuron, and bispyribac-sodium, respectively. Similarly, I50 values for the GAr biotype were 316, 140, and 64 times greater than the S biotypes following the same herbicide treatments. This research indicates high levels of annual bluegrass resistance to multiple ALS-inhibiting herbicides in South Carolina and Georgia. Future research should focus on the mechanisms of ALS resistance in these annual bluegrass biotypes as well as alternative options for control not targeting the ALS enzyme. Nomenclature: Bispyribac-sodium; foramsulfuron; trifloxysulfuron; annual bluegrass, Poa annua L.

Beach vitex (Vitex rotundifolia): an invasive coastal species.

Abstract Beach vitex is a salt-tolerant, perennial, invasive shrub that has naturalized in coastal areas of the southeastern United States. Since its introduction in the 1980s, this Pacific Rim native has invaded many fragile beach-dune ecosystems along the Mid-Atlantic, Southern Atlantic, and Gulf of Mexico. Large-scale monocultures of beach vitex supplant native species through rapid vegetative reproduction and seed production. Fruits are capable of water-based dispersal, allowing for potential rapid range expansion in coastal areas. Ecosystem damage resulting from exclusion of native plant species by beach vitex and fears associated with potential negative effects on sea turtle nesting have served to promote the control and survey efforts presently underway in coastal areas of the Carolinas, Virginia, and Maryland. Nomenclature: Beach vitex, Vitex rotundifolia L. f

Nutrient allocation of 'TifEagle' bermudagrass as influenced by trinexapac-ethyl

ABSTRACT Inhibiting shoot growth of dwarf bermudagrass [Cynodon dactylon(L.) Pers. × C. transvaalensis Burtt-Davey] with a plant-growth retardant, trinexapac-ethyl (TE), may redirect nutrients and photosynthate away from leaf tissue to promote root growth and improve nutrient-use efficiency. Two greenhouse experiments evaluated three rates of TE, 0.025, 0.05, and 0.075 kg a.i. ha−1, applied every three weeks on ‘TifEagle’ bermudagrass for 12 weeks. Lysimeters constructed to United State Golf Association specifications were arranged in a randomized complete block design with four replications. Increased TE rates quadratically reduced clipping yield 38%–75%, improved turf quality 6%–13%, and enhanced chlorophyll concentrations 30%–70% over the untreated grass. Dry-root mass increased with TE rate 11%–37% after 12 weeks. Total clipping nutrients recovered from five sampling dates were reduced by approximately 50%, 85%, and 90% for turf receiving TE at 0.025, 0.05, and 0.075 kg ha−1 3 wk−1, respectively. Thatch (stolons and rhizomes) and roots had higher nitrogen (N) concentration and retention with increased TE rate, suggesting inhibited leaf growth increased N storage in belowground plant tissue. Overall, TE may effectively enhance turf quality, root growth, and nutrient-use efficiency of dwarf-type bermudagrasses. Chemical name used: trinexapac-ethyl, [4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethylester].

Mowing and Nitrogen Influence Green Kyllinga (Kyllinga brevifolia) Infestation in Tifway Bermudagrass (Cynodon dactylon × C. transvaalensis) Turf1

Abstract: A field study evaluated the effects of green kyllinga establishment method (seed vs. stolon), two mowing heights (2.5 and 5.0 cm), and three nitrogen (N) rates (0, 24, and 49 kg/ha/mo) on green kyllinga infestation in ‘Tifway’ bermudagrass turf. The study was initiated in vigorous and newly established or “weak” bermudagrass turf in May 1997 and continued until December 1998. The green kyllinga area was measured periodically each year and plant dry weight (g/500 cm2) was calculated in December 1997 and 1998. In 1997, stolon established green kyllinga plots were twice as large as seeded plots in vigorous turf and four times larger in weak turf. Method of establishment, however, was less important in 1998 as seedling populations became more established. In weak turf, increasing N rate to 49 kg/ha/mo decreased green kyllinga spread by 50% in 1997 and by 40% in 1998 compared to no N. In vigorous turf, mowing height influenced green kyllinga infestation more than N. Low mowing height (2.5 cm) increased green kyllinga infestations nearly twofold in vigorous turf in 1997 and more than fivefold in 1998. Golf course fairways are often maintained at clipping heights shorter than 2.5 cm, and green kyllinga is a prevalent weed at these sites. Green kyllinga may gain a competitive advantage in bermudagrass turf at lower mowing heights. Nomenclature: Green kyllinga, Kyllinga brevifolia Rottb.; bermudagrass, Cynodon dactylon Burtt-Davey × C. transvaalensis L. Pers. Tifway. Additional index words: Turfgrass cultural practices, weed competition, weed ecology. Abbreviations: N, nitrogen.

Formulation effects on isoxaben and trifluralin in runoff water from container plant nurseries

Abstract Sprayable and granular formulations of isoxaben and trifluralin were applied to container plant nursery beds to determine formulation effects on herbicide runoff and weed control. In 1998 herbicide application was followed by 0.8 cm of irrigation delivered in 60 min, and runoff water samples were collected on the day of application (DOA). The highest concentrations of isoxaben and trifluralin detected in runoff water were 0.50 and 0.15 μg ml−1, respectively. Total isoxaben in runoff water was greater from the granular than from the sprayable formulation, but no differences attributable to formulation were detected for trifluralin. In 1999 herbicide application was followed by irrigation applied in three pulse cycles of 30 min each (0.8 cm per cycle). Runoff water samples were collected daily through 2 d after herbicide application (DAA). The highest herbicide concentrations were found in the first runoff sample on the DOA. Isoxaben was detected at 1.6 μg ml−1 from both formulations, and trifluralin concentrations were 0.8 and 0.2 μg ml−1 from the sprayable and granular formulations, respectively. Isoxaben concentrations were similar between formulations on the DOA, higher from the granular formulation 1 DAA, and higher in five of the nine runoff samples 2 DAA. Trifluralin concentrations were higher from the sprayable formulation for the first pulse cycle on the DOA and higher from the granular formulation in three of the nine samples 1 DAA and in four samples 2 DAA. The total amount of isoxaben recovered was 9.1% of applied from the granular formulation and 7.3% of applied from the spray formulation. The total amounts of trifluralin found were similar among formulations (0.5% of applied). Weed control was effective for both formulations in both years. Nomenclature: Isoxaben; trifluralin.

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.

Beach Dune Sand Hydrophobicity Due to the Presence of Beach Vitex (Vitex rotundifolia L. f.)

Conservation and preservation concerns have led to efforts to understand mechanisms of invasiveness and the effects these mechanisms have on the environment. Vitex rotundifolia L. f. [beach vitex (BV)] was introduced as a salt-tolerant woody ground cover, but it has since become invasive on primary and secondary dunes in coastal areas of the southeastern United States. Much of its invasive potential may be the result of intense substrate hydrophobicity underneath established stands, which is believed to prohibit seedling establishment by other plants including native plant species. This research was conducted to better understand BV-induced sand hydrophobicity by carrying out dune surveys of BV-infested areas of the South Carolina coast, identifying the compounds responsible for this activity via chemical analysis, and quantifying hydrophobicity persistence by resampling sites following removal of above-ground BV. The findings indicated that sand under BV cover was significantly hydrophobic, that cuticular alkanes from leaves and fruits were responsible for this hydrophobicity, and that extreme substrate hydrophobicity persisted for >3 years following BV removal.

Response of ‘TifEagle’ Bermudagrass (Cynodon dactylon × Cynodon transvaalensis) to Ethephon and Trinexapac-ethyl1

Turf managers combine ethephon with trinexapac-ethyl (TE) on bentgrass greens to suppress annual bluegrass, inhibit turf growth, and enhance turf quality; however, effects of this growth regulator combination have not been reported on bermudagrass greens. Two experiments were conducted at the Clemson University Greenhouse Complex to investigate the response of ‘TifEagle’ bermudagrass to ethephon and TE. TifEagle bermudagrass plugs were placed in pots with 23-cm depths, 324-cm2 total surface areas, and a soil medium of an 85:15 (v/v) sand and peat moss mix. Ethephon was applied at 0, 3.8 (EP1), and 7.6 (EP2) kg ai/ha/3 wk with TE at 0 and 0.04 kg ai/ha/ 3 wk over a 9-wk period. Initial responses of bermudagrass to ethephon included chlorotic leaves and severe thinning. Bermudagrass treated with ethephon had quality reduced as much as 33% from nontreated turf. TE enhanced turf quality 4 to 22% from 4 to 9 wk after initial treatment. TE helped mask ethephon-induced quality decline after the third application. In the presence of TE, bermudagrass clipping yield was reduced from nontreated turf by 57, 70, and 72% when ethephon was applied at 0, 3.8, and 7.6 kg/ha/3 wk. Ethephon linearly reduced root mass after 9 wk from nontreated turf by 20 and 33% at 3.8 and 7.6 kg/ha/3 wk, respectively. Compared with respective ethephon rates alone, bermudagrass treated with TE and ethephon at 0, 3.8, and 7.6 kg/ha/3 wk, averaged 28, 8, and 15% more root mass. Ethephon at 3.8 and 7.6 kg/ha/3 wk without TE reduced TifEagle bermudagrass root length 14 and 16%, respectively, compared with untreated turf. Bermudagrass treated with ethephon at 0, 3.8, and 7.6 kg/ha/3 wk with TE averaged 3, 11, and 17% higher root length compared with respective ethephon rates after 9 wk. Overall, ethephon may have negative effects on TifEagle root mass, root length, and turf quality. However, combining ethephon with TE may help reduce these deleterious effects. Nomenclature: Ethephon, (2-chloroethyl)phosphonic acid; trinexapac-ethyl, 4-(cyclopropyl-[α]-hydroxymethylene)-3,5-dioxo-cyclohexane carboxylic acid ethyl ester; annual bluegrass, Poa annua L.; TifEagle bermudagrass, Cynodon dactylon × C. transvaalensis. Additional index words: Dwarf bermudagrass, plant growth regulator, turf injury. Abbreviations: GA, gibberellic acid; PGR, plant growth regulator; TE, trinexapac-ethyl; WAIT, weeks after initial treatment.

Reestablishment Potential of Beach Vitex (Vitex rotundifolia) after Removal and Control Efforts

Abstract Beach vitex is an invasive plant of coastal areas of the southeastern United States from Maryland to Georgia. Many resources have been dedicated to the control of established beach vitex stands. Successful eradication will require knowledge of this plants ability to reestablish from seed after control efforts. To understand seed-based regenerative potential, studies were conducted to characterize the fruits and seeds, document the existence and size of seed banks, determine stratification requirements for germination, and ascertain seed dormancy mechanisms. Studies of fruit lots from three consecutive years (2003 to 2005) found that the average fruit contained 1.39 seeds, and more than 76% of fruits contained at least one viable seed. A positive correlation existed between seed number and both fruit mass and fruit diameter. A substantial soil seed bank was discovered that contained viable seeds 4 yr after vegetation removal. Stratification was required for seed germination. All stratification treatments induced germination, with highest rates realized when stratification was performed at 10 C for 8 or 12 wk. Germination rates were modestly increased (from 0 to 17%) through mild scarification in the absence of stratification. Results indicate that beach vitex has physical (fruit coat) and physiological (seed) dormancy mechanisms that are capable of delaying germination for multiple seasons, allowing development of a soil seed bank. Beach vitex can reestablish from seed after vegetation removal. Nomenclature: Beach vitex, Vitex rotundifolia L. f