Sudeep S. Sidhu

Nicosulfuron Absorption, Translocation, and Metabolism in Annual Bluegrass and Four Turfgrass Species

Abstract Nicosulfuron provides POST weed control in corn, pastures, and grassy roadsides, and has potential for use in fine turfgrass. The objective of this research was to evaluate tolerance, absorption, translocation, and metabolism of nicosulfuron in annual bluegrass and four turfgrass species. In greenhouse experiments, relative tolerance of grasses to nicosulfuron (35, 70, or 140 g ai ha−1) from high to low was bermudagrass  =  zoysiagrass > tall fescue > creeping bentgrass > annual bluegrass. In laboratory experiments, grasses had similar foliar and root absorption of 14C-nicosulfuon. Annual bluegrass and creeping bentgrass averaged 80% greater radioactivity per unit dry mass in shoots than bermudagrass following root uptake of 14C-nicosulfuron, but other species were similar to these grasses. At 72 h after treatment (HAT), annual bluegrass metabolized 36% of absorbed 14C-nicosulfuron, which was less than bermudagrass, tall fescue, and zoysiagrass that metabolized 47 to 58%. Creeping bentgrass metabolism of nicosulfuron was similar to annual bluegrass. Tall fescue had similar levels of metabolism to bermudagrass and zoysiagrass, averaging 67%, at 168 HAT but produced fewer metabolites. Overall, turfgrass tolerance to nicosulfuron is associated with relative herbicide concentrations in shoots and differential species metabolism. Nomenclature: Annual bluegrass (Poa annua L.); bermudagrass (Cynodon dactylon × transvaalensis Burtt-Davy) ‘Princess 77’; creeping bentgrass (Agrostis stolonifera L.) ‘Penn A-4’; tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbyshire] ‘Titan’; zoysiagrass (Zoysia japonica Steud.) ‘Zenith’.

Dithiopyr Behavior in Smooth Crabgrass (Digitaria ischaemum) as Influenced by Growth Stage and Temperature

Abstract Dithiopyr provides PRE and early POST control of smooth crabgrass, but POST efficacy is often inconsistent on tillered plants. Experiments were conducted to evaluate the interaction of temperature and growth stage on dithiopyr efficacy, absorption, translocation, and metabolism in smooth crabgrass. In greenhouse experiments, I50 (predicted rate to induce 50% injury) measured < 0.14, 0.14, and 0.15 kg ha−1 at low temperatures (average 23 C) for multi-leaf, one-tiller, and multi-tiller smooth crabgrass, respectively, while I50 measured < 0.14, 0.88, and > 2.24 kg ha−1 at high temperatures (average 32 C), respectively. Multi-tiller (three to five tillers) smooth crabgrass absorbed more root applied 14C-dithiopyr than multi-leaf (three to four leaves) and one-tiller plants, but specific radioactivity (Bq mg−1) was two to three times greater in multi-leaf plants compared to tillered plants. Smooth crabgrass treated at 15/10 C (day/night) had ≈ two times greater specific radioactivity following root applied 14C-dithiopyr than at 30/25 C. Radioactivity distribution to shoots from root applications measured 43, 30, and 20% of the total absorbed for multi-leaf, one-tiller, and multi-tiller plants, respectively. Smooth crabgrass had two times more foliar absorption of 14C-dithiopyr at 15/10 than 30/25 C while 14C losses were greater at 30/25 than 15/10 C. Smooth crabgrass metabolism of 14C-dithiopyr was ≈ two times greater at 30/25 than 15/10 C, and multi-leaf plants averaged 10 to 20% more metabolism than tillered plants at 7 d after treatment. Results suggest differential absorption, translocation, and metabolism may contribute to dithiopyr efficacy on smooth crabgrass at various growth stages, but use under high temperatures (30/25 C) could increase losses from volatilization, reduce foliar absorption, and increase metabolism compared to cooler temperatures (15/10 C). Nomenclature: Dithiopyr; smooth crabgrass, Digitaria ischaemum (Schreb.) Schreb. ex Muhl.

Target and Nontarget Resistance Mechanisms Induce Annual Bluegrass (Poa annua) Resistance to Atrazine, Amicarbazone, and Diuron

Annual bluegrass is a weed species in turfgrass environments known for exhibiting resistance to multiple herbicide modes of action, including photosystem II (PSII) inhibitors. To evaluate populations of annual bluegrass for susceptibility to PSII inhibitors of varied chemistries, populations were treated with herbicides from triazolinone, triazine, and substituted urea families: amicarbazone, atrazine, and diuron, respectively. Sequencing of the psbA gene confirmed the presence of a Ser264 to Gly amino acid substitution within populations that exhibited resistance to both atrazine and amicarbazone. A single biotype, DR3, which lacked any previously reported psbA gene point mutation, exhibited resistance to diuron, atrazine, and amicarbazone. DR3 had a significantly lower rate of absorption and translocation of atrazine and had enhanced atrazine metabolism when compared with both the Ser264 to Gly resistant mutant and susceptible biotypes. We thus report possible nontarget mechanisms of resistance to PSII-inhibiting herbicides in annual bluegrass. Nomenclature: Amicarbazone; atrazine; diuron; annual bluegrass, Poa annua L. Poa annua es una especie de maleza en ambientes de céspedes conocida por presentar resistencia a múltiples modos de acción de herbicidas, incluyendo inhibidores del fotosistema II (PSII). Para evaluar la susceptibilidad de poblaciones de P. annua a inhibidores PSII de diferentes características químicas, varias poblaciones fueron tratadas con herbicidas de las familias triazolinone, triazine, y urea sustituidas: amicarbazone, atrazine, y diuron, respectivamente. La secuenciación del gen psbA confirmó la presencia de una sustitución de amino ácidos de Ser264 a Gly en poblaciones que presentaron resistencia a atrazine y amicarbazone. Un solo biotipo, DR3, el cual carecía de cualquier reporte previo de mutaciones puntuales en el gen psbA, presentó resistencia a diuron, atrazine, y amicarbazone. DR3 tuvo una tasa de absorción y translocación significativamente menor de atrazine y un mayor metabolismo de atrazine cuando se comparó con biotipos resistentes con la mutación Ser264 a Gly y con biotipos susceptibles. De esta forma, reportamos posibles mecanismos de resistencia a herbicidas inhibidores de PSII en P. annua que no involucran el sitio activo.

Flucarbazone-Sodium Absorption, Translocation, and Metabolism in Bermudagrass, Kentucky Bluegrass, and Perennial Ryegrass

Abstract Perennial ryegrass is overseeded in bermudagrass and Kentucky bluegrass to improve turf quality, but selective control may be warranted for transition back to monostand turfgrass. Flucarbazone–sodium controls perennial ryegrass in bermudagrass and Kentucky bluegrass, but the physiological basis of selectivity has received limited investigation. Greenhouse and laboratory experiments were conducted to evaluate efficacy, absorption, translocation, and metabolism of flucarbazone–sodium in these grasses. Flucarbazone–sodium reduced perennial ryegrass shoot mass from the nontreated an average ≈ 22 times and 3 times more than bermudagrass and Kentucky bluegrass at 4 wk after treatment, respectively. In laboratory experiments, foliar and root absorption of 14C–flucarbazone–sodium were similar among species. Bermudagrass distributed ≈ 25% more foliar-absorbed 14C to nontreated shoots than Kentucky bluegrass and perennial ryegrass. From root applications, all grasses averaged 84% distribution of 14C to shoots. Bermudagrass and Kentucky bluegrass metabolized 100% and 74% of 14C–flucarbazone–sodium at 1 d after treatment (DAT), whereas perennial ryegrass metabolism measured 44, 58, and 65% at 1, 3, and 7 DAT, respectively. Bermudagrass, Kentucky bluegrass, and perennial ryegrass had 4, 4, and 2 metabolites after 7 d, respectively. Results suggest differential metabolism of flucarbazone–sodium is attributed to selectivity for controlling perennial ryegrass in bermudagrass and Kentucky bluegrass. Nomenclature: Flucarbazone–sodium; bermudagrass [Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy] ‘Princess-77’; Kentucky bluegrass (Poa pratensis L.) ‘Midnight’; perennial ryegrass (Lolium perenne L.) ‘Manhattan V’.

Dithiopyr Controls Common Lespedeza (Kummerowia striata) in Bermudagrass

Abstract Common lespedeza is a problematic summer annual weed in bermudagrass lawns, with limited PRE herbicides available for control. Dithiopyr is a pyridine herbicide primarily used for PRE grassy weed control but has shown potential efficacy for controlling annual legumes. The objectives of this research were to evaluate efficacy and behavior of dithiopyr in common lespedeza. In a 3-yr field experiment, sequential dithiopyr applications at 0.42 or 0.56 kg ai ha−1 beginning in late winter and single applications of dithiopyr at 0.56 kg ai ha−1 in spring controlled common lespedeza ≥ 88%. Single and sequential applications of indaziflam at 0.035 and 0.053 kg ai ha−1 provided poor control (< 70%) of common lespedeza by late summer. In laboratory experiments, bermudagrass and common lespedeza had similar foliar absorption of 14C-dithiopyr, averaging 10% of the 14C applied, and both species retained > 80% of 14C in the treated leaf at 72 h after treatment (HAT). Common lespedeza translocated 6 times more root-absorbed 14C to shoots than bermudagrass and had 2.8 times greater absorption (Bq mg−1) at 72 HAT. In metabolism experiments, parent herbicide levels measured ≥ 84% of extracted 14C in both species at 1, 3, and 7 d after treatment. Overall, dithiopyr effectively controls common lespedeza in bermudagrass as a PRE treatment in spring. Susceptibility of common lespedeza to dithiopyr is associated with acropetal translocation and greater herbicide concentrations compared with a tolerant species, bermudagrass. Nomenclature: Common lespedeza (Kummerowia striata (Thunb.) Schindl.) ‘Kobe’; bermudagrass (Cynodon dactylon × C. transvaalensis Burtt-Davy) ‘Princess 77’.

Removal of sulfadimethoxine in soil mediated by extracellular oxidoreductases

Sulfadimethoxine (SDM) is an antibiotic commonly used in concentrated animal feeding operations and released into the environment via manure application on agricultural lands. Transformation of antibiotics in soil impacts the likelihood of their entry to water bodies, uptake by plants, and thus their effect on terrestrial and aquatic organisms. We conducted experiments to incubate SDM in a sandy loam soil in the presence of humification enzymes commonly found in natural soil, laccase, horseradish peroxidase, and lignin peroxidase. Incubation with the enzymes led to significant reduction in the fraction of SDM extractable from soil, indicating the formation of bound residues. Such transformation was enhanced when the organic matter content in soil is increased or when certain chemical mediators were used along with laccase. The study provided a basis for understanding the environmental fate of sulfonamides and help with the development of remediation methods to mitigate the release of sulfonamides from soil to water.