Joe E. Toler

Reduced sensitivity in Monilinia fructicola to propiconazole following prolonged exposure in peach orchards

The baseline sensitivity of Monilinia fructicola in a peach orchard not previously exposed to demethylation-inhibiting (DMI) fungicides was determined for propiconazole, using the concentration in an agar medium required to suppress radial growth of mycelium by 50% (EC50) The baseline sensitivity was found to be approximately 0.03 μg/ml. Prolonged, regular exposure of the natural population of M. fructicola to propiconazole in the test orchard over a 3-year period (29 total applications) resulted in a wider range of sensitivity (EC50 of 0.02 to 2.16μg/ml) among isolates than was observed in the initial population (EC50 of 0.02 to 0.15 μg/ml). Comparisons with isolates from commercial orchards where DMI fungicides were used regularly showed that sensitivities were comparable to, or less than, those of isolates from the population in the test orchard that had been exposed to propiconazole for the 3-year period. M. fructicola in South Carolina peach orchards might now be less sensitive to DMI fungicides than when those fungicides were first introduced for brown rot control, although effective disease control in the field has been maintained.

Measurement and modeling of the transpiration of a temperate red maple container nursery

This study was designed to estimate transpiration in a container nursery under both irrigated and water stressed conditions using a biologically based canopy model. The model, MAESTRA, was parameterized with a suite of physiological measurements and an explicit response function for soil moisture deficit was incorporated. The model was validated against transpiration measurements monitored by the stem heat balance method in both irrigated and non-irrigated plots. Distinct disconnects between estimated and measured values were found at high soil moisture deficits. The data justify the incorporation of a soil moisture component to simulate transpiration of plants with root zones in limited soil volumes. The agreement between measured and modelled canopy transpiration separated at a soil moisture deficit of 0.85 or greater, however, estimates of daily transpiration simulated by the model were in agreement with sap-flow measurements when water was not limiting. The data indicate that cuticular conductance at soil moisture deficits ≤0.85 may explain the separation in model estimates and actual plant water loss.

Spread and persistence of benomyl-resistant Monilinia fructicola in South Carolina peach orchards

The spread and persistence of benomyl-resistant Monilinia fructicola were studied in an experimental peach orchard, and results were compared with conditions in several commercial peach orchards in which resistance to benomyl had occurred. One fungus strain that was resistant to iprodione was also examined in the experimental orchard. Benomyl-resistant strains became established and spread in the experimental orchard, but the frequency of isolation of these strains relative to sensitive strains declined as the progressed unless the trees were sprayed with benomyl (...)

Rimsulfuron plus thifensulfuron-methyl combinations with selected postemergence broadleaf herbicides in corn (Zea mays).

Field studies were conducted in 1995 and 1996 to investigate postemergence (POST) applications of rimsulfuron (12 g ai/ha) plus thifensulfuron-methyl (6 g ai/ha) in tank-mixtures with various acetolactate synthase (ALS)- and non–ALS-inhibitor herbicides for weed control in corn. Rimsulfuron plus thifensulfuron-methyl controlled giant foxtail and common lambsquarters at least 95% but did not control common ragweed. Rimsulfuron plus thifensulfuron-methyl tank-mixed with 20 g ai/ha primisulfuron-methyl, 17 g ai/ha CGA-152005 plus 18 g ai/ha primisulfuron, 18 or 36 g ai/ha halosulfuron-methyl, 18 g ai/ha nicosulfuron, or 280 g ai/ha dicamba controlled giant foxtail at least 89%, common lambsquarters at least 96% and, with the exception of the nicosulfuron combination, controlled common ragweed at least 88%. Rimsulfuron plus thifensulfuron-methyl tank-mixed with flumetsulam (26 g ai/ha) plus clopyralid (69 g ai/ha) plus 2,4-D (140 g ai/ha), atrazine (560 g ai/ha), 2,4-D (280 g/ha), or dicamba (308 g/ha) plus atrazine (588 g/ha) reduced the control of giant foxtail to less than 78% 26 d after treatment (DAT). Corn injury was less than 12% from rimsulfuron plus thifensulfuron-methyl and from mixtures of rimsulfuron plus thifensulfuron-methyl with other herbicides except when rimsulfuron plus thifensulfuron-methyl was mixed with flumetsulam plus clopyralid plus 2,4-D. This combination injured corn 26%. In these studies the appropriate tank-mix partners for rimsulfuron plus thifensulfuron-methyl were primisulfuron, CGA-152005 plus primisulfuron, and halosufluron-methyl. Nomenclature: Atrazine; CGA-152005 (proposed name prosulfuron), 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)-phenylsulfonyl] urea; clopyralid; 2,4-D; dicamba; flumetsulam; halosulfuron-methyl; primisulfuron-methyl; rimsulfuron; thifensulfuron-methyl; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; corn, Zea mays L. ‘Pioneer 3394’. Additional index words: Herbicide interaction, weed management. Abbrevations: ALS, acetolactate synthase (EC 4.1.3.18); DAT, days after treatment; MSO, methylated seed oil; NIS, nonionic surfactant; POST, postemergence; UAN, urea ammonium nitrate.

Weed Management Systems for Cotton (Gossypium hirsutum) with Reduced Tillage

Abstract: Current environmental concerns demand intensive research on conservation tillage for cotton production. Studies were conducted in 1994 and 1995 at Florence, SC, to evaluate weed and cotton response to various weed management systems in cotton with reduced tillage. Broadcast application of pendimethalin at 1.1 kg ai/ha and fluometuron at 2.2 kg ai/ha preemergence (PRE) followed by pyrithiobac at 0.07 kg ai/ha early postemergence (EPOST) was more effective than was a 38-cm band of these herbicides in controlling naturally occurring populations of sicklepod, Palmer amaranth, goosegrass, and southern crabgrass and in providing cotton yields equal to yields under weed-free conditions. With the 38-cm band of PRE and EPOST herbicides, two supplemental weed treatments at 3 and 7 wk after planting using glyphosate applied at 0.84 kg ae/ha POST with a hooded sprayer or a no-till cultivator was required to achieve acceptable weed control, but cotton yields were less than yields for the broadcast treatment alone. Glyphosate- or cultivation-only systems were generally ineffective in reducing weed interference and precluding cotton yield reductions. Optimum cotton production with reduced tillage can be achieved with broadcast application of PRE and EPOST herbicides but alternative methods offer promise for reducing costs and environmental effects and deserve additional study. Nomenclature: Fluometuron; glyphosate; pendimethalin; pyrithiobac; goosegrass, Eleusine indica (L.) Gaertn. # ELEIN; Palmer amaranth, Amaranthus palmeri L. #3 AMAPA; sicklepod, Senna obtusifolia L. Irwin and Barneby # CASOB; southern crabgrass, Digitaria ciliaris L. # DIGSP; cotton, Gossypium hirsutum L. ‘KC 311’. Additional index words: Banded herbicide application, broadcast herbicide application, cultivation, fluometuron, pendimethalin, pyrithiobac. Abbreviations: EPOST, early postemergence; fb, followed by; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAP, weeks after planting.

Efficiency of Foliar Versus Granular Fertilization: A Field Study of Creeping Bentgrass Performance

ABSTRACT Limited information comparing foliar versus granular fertilization of turfgrasses is available. The objective of this research was to evaluate liquid and/or granular N fertilization on turfgrass quality, clipping yield, and root biomass of ‘L-93’ creeping bentgrass. Treatments consisted of two annual nitrogen (N) inputs, 127 and 190 kg ha−1, using 100% granular urea fertilizer, 50% granular urea + 50% liquid urea fertilizer, or 100% liquid urea fertilizer. These results suggest a rate of at least 190 kg N ha−1 yr−1 is needed to maintain acceptable bentgrass quality in the transition zone of the U.S. Combining both liquid and granular methods appear superior compared to relying on one method exclusively.

‘Tifway’ Bermudagrass Growth Regulation with the Use of Trinexapac-Ethyl and Flurprimidol1

Studies were conducted for 12 wk from June 16 to September 8, 2003 and July 10 to October 4, 2004 with the objective of evaluating growth regulation, lateral regrowth, and injury of Tifway bermudagrass [Cynodon dactylon (L.) × C. transvaalensis Burtt-Davy Tifway] in response to two GA-inhibiting plant growth regulators, trinexapac-ethyl and flurprimidol. Trinexapac-ethyl was applied alone at 0, 0.052, and 0.104 kg ai/ha and flurprimidol alone at 0, 0.14, and 0.28 kg ai/ ha, plus all combinations. Applications were made every 3 wk for the duration of the study. Tifway bermudagrass clipping yield was reduced 33% and 54% by trinexapac-ethyl at 0.104 kg/ha at 4 and 8 wk after initial treatment (WAIT), respectively. Flurprimidol at 0.28 kg/ha reduced clipping yield 49% 8 WAIT. Lateral regrowth was reduced 20% 2 WAIT by trinexapac-ethyl at 0.104 kg/ha, and 26% 2 WAIT by flurprimidol at 0.28 kg/ha. Lateral regrowth was reduced 13% 4 WAIT by trinexapac-ethyl at 0.104 kg/ha, and 15% 4 WAIT by flurprimidol at 0.28 kg/ha. Overall, acceptable injury (<30%) was observed with a trinexapac-ethyl and flurprimidol tank mixture; however, this evaluation did not indicate an advantage in growth regulation when using a tank mixture of these products, compared to using them alone. Nomenclature: Flurprimidol; trinexapac-ethyl; Tifway bermudagrass, Cynodon dactylon (L.) × C. transvaalensis Burtt-Davy Tifway. Additional index words: Plant growth regulator, fairways, injury, clipping reduction, percent lateral regrowth, turfgrass. Abbreviations: GA, gibberellic acid; PGRs, plant growth regulators.

Halosulfuron and 2,4-D Mixtures' Effects on Common Lambsquarters (Chenopodium album)1

Greenhouse and laboratory experiments were conducted to investigate the response of common lambsquarters to POST applications of halosulfuron–methyl plus 2,4-D admixtures and to investigate the effects of 2,4-D on the absorption, translocation, and metabolism of halosulfuron. In the greenhouse, halosulfuron at 0, 4.5, 9, 18, and 36 g ai/ha was applied alone and mixed with 2,4-D at 0, 17, 35, and 70 g ai/ha POST to 7.5- to 9-cm seedlings, and plant fresh weights were determined 4 wk after treatment (WAT). Halosulfuron alone did not control this weed, while fresh weights of common lambsquarters treated with 2,4-D declined hyperbolically as rates increased. A synergistic response for mixtures of these herbicides occurred, as observed fresh weights for all combinations were less than expected based on independent action and the calibrated marginal responses. In the laboratory, 7.5- to 9-cm seedlings were treated POST with commercially formulated halosulfuron at 9 and 18 g/ha and 2,4-D at 0, 70, and 140 g/ha, respectively, followed by foliar-applied 14C-halosulfuron. Absorption of 14C-halosulfuron increased with time, and absorption and translocation were not influenced by the addition of 2,4-D. Results from these studies inferred that halosulfuron and 2,4-D were generally synergistic on common lambsquarters and that mechanisms other than absorption, translocation, and metabolism may explain this response. Nomenclature: 2,4-D; halosulfuron; common lambsquarters, Chenopodium album L.#3 CHEAL. Additional Index Words: Absorption, synergism, translocation, metabolism, herbicide mixtures, acetolactate synthase. Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); CDE, combined dosage equivalency; HAT, hours after treatment; LSS, liquid scintillation spectroscopy; NIS, nonionic surfactant; TLC, thin-layer chromatography.

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].

Combinations of Sethoxydim with Postemergence Broadleaf Herbicides in Sethoxydim-Resistant Corn (Zea mays)"

Field studies were conducted in 1995 and 1996 to investigate postemergence tank mixtures of sethoxydim with various acetolactate synthase (ALS)- and non–ALS-inhibitor herbicides for weed control in sethoxydim-resistant (SR) corn. Giant foxtail control with sethoxydim was 96% and was equal to control with tank mixtures of sethoxydim plus bentazon, dicamba, dicamba plus atrazine, bromoxynil, and nicosulfuron plus bromoxynil. Giant foxtail control with sethoxydim plus atrazine, sethoxydim plus bentazon plus atrazine, and sethoxydim plus ALS-inhibiting herbicides plus 2,4-D was reduced to 60 to 89%. Common ragweed control was equal to or above 91% for tank mixtures that included bentazon plus atrazine, dicamba, dicamba plus atrazine, halosulfuron plus 2,4-D, and CGA 152005 plus primisulfuron plus 2,4-D, and the tank mixture of nicosulfuron plus bromoxynil. Common lambsquarters control was equal to or above 91% from all broadleaf herbicide treatments except bentazon and the tank mixture of halosulfuron plus 2,4-D. In these studies, only tank mixtures of sethoxydim plus dicamba or dicamba plus atrazine controlled giant foxtail, common ragweed, and common lambsquarters equal to or greater than 91% in SR corn. Nomenclature: Atrazine; bentazon; bromoxynil; CGA 152005 (proposed name prosulfuron), 1-(4-methyl-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl)-phenylsulfonyl] urea; dicamba; 2,4-D; halosulfuron; nicosulfuron; primisulfuron; sethoxydim; common lambsquarters, Chenopodium album L. #3 CHEAL; common ragweed, Ambrosia artemisiifolia L. # AMBEL; giant foxtail, Setaria faberi Herrm. # SETFA; corn, Zea mays L. ‘Dekalb 592SR’. Additional index words: Herbicide-resistant corn, herbicide tank mixtures, sethoxydim-resistant corn. Abbreviations: ACCase, acetylcoenzyme-A carboxylase; ALS, acetolactate synthase (EC 4.1.3.18); COC, crop oil concentrate; DAT, days after treatment; MCB, multiple comparisons with the best; NIS, nonionic surfactant; POST, postemergence; SR, sethoxydim resistant.