Herbicide Injury Research Articles

Safety and efficacy of linuron with or without an adjuvant or S-metolachlor for POST control of Palmer amaranth (Amaranthus palmeri) in sweetpotato

AbstractField studies were conducted to evaluate linuron for POST control of Palmer amaranth in sweetpotato to minimize reliance on protoporphyrinogen oxidase (PPO)-inhibiting herbicides. Treatments were arranged in a two by four factorial in which the first factor consisted of two rates of linuron (420 and 700 g ai ha−1), and the second factor consisted of linuron applied alone or in combinations of linuron plus a nonionic surfactant (NIS; 0.5% vol/vol), linuron plus S-metolachlor (800 g ai ha−1), or linuron plus NIS plus S-metolachlor. In addition, S-metolachlor alone and nontreated weedy and weed-free checks were included for comparison. Treatments were applied to ‘Covington’ sweetpotato 8 d after transplanting (DAP). S-metolachlor alone provided poor Palmer amaranth control because emergence had occurred at applications. All treatments that included linuron resulted in at least 98% and 91% Palmer amaranth control 1 and 2 wk after treatment (WAT), respectively. Including NIS with linuron did not increase Palmer amaranth control compared to linuron alone, but it resulted in greater sweetpotato injury and subsequently decreased total sweetpotato yield by 25%. Including S-metolachlor with linuron resulted in the greatest Palmer amaranth control 4 WAT, but increased crop foliar injury to 36% 1 WAT compared to 17% foliar injury from linuron alone. Marketable and total sweetpotato yields were similar between linuron alone and linuron plus S-metolachlor or S-metolachlor plus NIS treatments, though all treatments resulted in at least 39% less total yield than the weed-free check resulting from herbicide injury and/or Palmer amaranth competition. Because of the excellent POST Palmer amaranth control from linuron 1 WAT, a system that includes linuron applied 7 DAP followed by S-metolachlor applied 14 DAP could help to extend residual Palmer amaranth control further into the critical period of weed control while minimizing sweetpotato injury.

Herbicide Tolerance of Sugarcane Genotypes to Post-emergence Application of Halosulfuron Methyl and Metribuzin: An Inadvertent Preliminary Assessment

Thirty-one sugarcane genotypes were planted in the experiment and post-emergence application of Halosulfuron Methyl 75% WG and Metribuzin 70% WP was carried out at the rate of 67.5 g and 1000 g a.i. per hectare on 42 days after planting (DAP). Lower leaves of some of the genotypes were found to show injuries on 5 days after spraying (DAS). Phytotoxicity was recorded in visual scoring scale of 0 to 10 at 7, 15, 21 and 30 DAS. Phytotoxicity rating of the 31 genotypes studied ranged between 0 and 4. Nine genotypes showed no visual injury and found tolerant, while eight genotypes showed moderate toxic effect (rating 4). All the genotypes (14 nos.) that showed phytotoxicity rating of 1 to 3 recovered visually (leaf injuries) except Co 06027 at 30 DAS, while all the genotypes that showed moderate phytotoxicity did not recover completely except Co 94008. The genotypes with Co 7201 and Co 775 as one of the parents showed phytotoxicity rating ranging from 1 to 4. The genotypes, Co 06030, Co 86032, Co 11015, Co 92005 and Co 09004 did not exhibit phytotoxicity symptoms, while their parent, CoC 671 exhibited phytotoxicity. Seven parental genotypes showed 100% probability of no herbicidal injury in their progenies and exhibited herbicidal tolerance from initial stage. Cane yield reduction (> 5%) was observed only in Co 8021, Co 94008 and Co 99006 with herbicide treatment over no herbicide application. The present study provides a preliminary information on the genetic variation among sugarcane genotypes for herbicide tolerance and their parental relationship, which could be utilized for the development of herbicide tolerant varieties for effective weed management in sugarcane agriculture.

Use of high-resolution unmanned aerial systems imagery and machine learning to evaluate grain sorghum tolerance to mesotrione

Manual evaluation of crop injury to herbicides is time-consuming. Unmanned aerial systems (UAS) and high-resolution multispectral sensors and machine learning classification techniques have the potential to save time and improve precision in the evaluation of herbicide injury in crops, including grain sorghum (Sorghum bicolor L. Moench). The objectives of our research are to (1) evaluate three supervised classification algorithms [support vector machine (SVM), maximum likelihood, and random forest] for categorizing high-resolution UAS imagery to aid in data extraction and (2) evaluate the use of vegetative indices (VIs) collected from UAS imagery as an alternative to traditional methods of visible herbicide injury assessment in mesotrione-tolerant grain sorghum breeding trials. An experiment was conducted in a randomized complete block design using a factorial treatment arrangement of three genotypes by four mesotrione doses. Herbicide injury was rated visually on a scale of 0 (no injury) to 100 (complete plant mortality). The UAS flights were flown at 9, 15, 21, 27, and 35 days after treatment. Results show the SVM algorithm to be the most consistently accurate, and high correlations (r = − 0.83 to −0.94; p < 0.0001) were observed between the normalized difference VI and ground-measured herbicide injury. Therefore, we conclude that VIs collected with UAS coupled with machine learning image classification has the potential to be an effective method of evaluating mesotrione injury in grain sorghum.

Effectiveness of Herbicide to Control Rice Weeds in Diverse Saline Environments

To mitigate environmental pollution and food contamination caused by inappropriate and excessive herbicide usage, most potent herbicides should be screened to control rice weeds. A research trial was executed for assessing the comparative efficacy of different herbicides to control rice field weeds and to evaluate the toxicity on rice under normal (distilled water) as well as different salinity levels (4 and 8 dS m−1). The study was designed to select the most potent herbicide and its appropriate dose for weed control of rice crop in coastal areas. Fourteen herbicidal treatments were included weed free crop, Pretilachlor (0.25, 0.50, 0.375 and 0.75 kg a.i. ha−1), Propanil + Thiobencarb (0.6 + 1.2, 0.9 + 1.8, 1.2 + 2.4 and 1.8 + 3.6 kg a.i. ha−1), Bensulfuron + MCPA (0.03 + 0.05, 0.045 + 0.075, 0.06 + 0.1 and 0.09 + 0.15 kg a.i. ha−1) and weedy check (control). The results revealed that all tested herbicides in higher than recommended doses for non-saline rice fields were effective in controlling Cyperus iria, Echinochloa colona (salt-tolerant) and Jussiaea linifolia but showed in light injury in rice plants grown in non-saline soils. These higher doses of herbicides recorded severe crop injury under saline conditions indicating their differential efficacy from normal non-saline conditions. Treatments including Pretilachlor (0.375kg a.i. ha−1), Propanil + Thiobencarb (0.9 + 1.8 kg ai/ha), Bensulfuron + MCPA (0.06 + 0.1 kg a.i. ha−1) and Pretilachlor (0.50 kg a.i. ha−1) remained superior in terms of weed control and grain yield production under all salinitylevels at TanjungKarang, Malaysia. It is concluded that herbicides respond differently under saline conditions and optimization of their doses potentially prevent herbicidal injury in rice plants.

Effect of Imidacloprid and Acephate for Tobacco Thrips (Thysonaptera: Thripidae) Management on Flumioxazin Injured Peanut

ABSTRACT Experiments were conducted in 2016 and 2017 in Stoneville and Starkville Mississippi to determine the impact of different insecticide management options for thrips on herbicide injured peanut. Insecticide treatments included imidacloprid in-furrow at-planting, one or two foliar applications of acephate, and an untreated control with and without an application of flumioxazin. In Stoneville, herbicide applications were made immediately following planting, and in Starkville, applications were made as plants were emerging to maximize herbicide injury. The Stoneville experiment also had an additional factor in which plots were flooded or not flooded to simulate a heavy rainfall in order to maximize herbicide injury and also to give added stress from saturated soils. Thrips counts, thrips injury ratings, plant vigor ratings, plant biomass, width between plant canopies, and yield were recorded. Few interactions were observed, but temporary flooding, herbicide injury, and thrips injury affected peanut growth as measured by biomass and canopy. Imidacloprid was the most consistent insecticide treatment for reducing thrips numbers and injury, but acephate provided some protection. Temporary flooding during the seedling stage, flumioxazin injury, and thrips injury all reduced peanut pod yield. Based on these results, every attempt should be made to minimize early season stress in peanuts including the use of an effective in-furrow insecticide.

Soil‐residual herbicides: Is there a trade‐off between waterhemp control and soybean injury?

AbstractThe perceived risk of pre‐emergence (PRE) herbicide injury negatively affecting soybean [Glycine max (L.) Merr.] grain yield may cause growers to select herbicides and/or rates that, consequently, reduce waterhemp (Amaranthus tuberculatus (Moq.) J.D. Sauer] control. Research was conducted over 3 years with flumioxazin and sulfentrazone to evaluate the influence of herbicide rate and mixture on waterhemp control and soybean injury, density, development, and grain yield. In a year with limited rainfall, waterhemp control was &gt;90% up to 9 weeks after planting (WAP) and soybean injury never exceeded 7% from all treatments. In years with more adequate moisture, reduced rates of either flumioxazin or sulfentrazone applied with any mixture herbicide provided similar waterhemp control (&gt;95%) to a full‐labeled rate of flumioxazin or sulfentrazone applied alone at 3 WAP. A full‐labeled rate of flumioxazin or sulfentrazone in mixture with fomesafen + S‐metolachlor provided the greatest and most uniform waterhemp control (&gt;90%) at 9 WAP. When applied at full‐labeled (1x) rates, soybean injury at 3 WAP from flumioxazin‐ and sulfentrazone‐based treatments ranged from 8 to 18% and 2 to 6%, respectively. Similar trends among treatments were observed for soybean density. Despite early‐season injury, treatments applied at a 1x rate did not reduce grain yield. However, applicators should be cognizant of spray boom overlap as 2x rates increased the extent of yield loss by up to 10 bu acre–1. Soybean injury at 9 WAP was a more accurate predictor of grain yield loss (R2 = .51) than injury at 3 WAP (R2 = .14).

Diagnosing Herbicide Injury in Cotton

This publication describes the behavior and injury symptoms of various kinds of herbicides in cotton.

New Lead Discovery of Herbicide Safener for Metolachlor Based on a Scaffold-Hopping Strategy.

The use of herbicide safeners can significantly alleviate herbicide injury to protect crop plants and expand the application scope of the existing herbicides in the field. Sanshools, which are well known as spices, are N-alkyl substituted compounds extracted from the Zanthoxylum species and have several essential physiological and pharmacological functions. Sanshools display excellent safener activity for the herbicide metolachlor in rice seedlings. However, the high cost of sanshools extraction and difficulties in the synthesis of their complicated chemical structures limit their utilization in agricultural fields. Thus, the present study designed and synthesized various N-alkyl amide derivatives via the scaffold-hopping strategy to solve the challenge of complicated structures and find novel potential safeners for the herbicide metolachlor. In total, 33 N-alkyl amide derivatives (2a–k, 3a–k, and 4a–k) were synthesized using amines and saturated and unsaturated fatty acids as starting materials through acylation and condensation. The identity of all the target compounds was well confirmed by 1H-NMR, 13C-NMR, and high-resolution mass spectrometry (HRMS). The primary evaluation of safener activities for the compounds by the agar method indicated that most of the target compounds could protect rice seedlings from injury caused by metolachlor. Notably, compounds 2k and 4k displayed excellent herbicide safener activities on plant height and demonstrated relatively similar activities to the commercialized compound dichlormid. Moreover, we showed that compounds 2k and 4k had higher glutathione S-transferase (GST), superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and polyphenol oxidase (PPO) activities in rice seedlings, compared to the metolachlor treatment. In particular, 2k and 4k are safer for aquatic organisms than dichlormid. Results from the current work exhibit that compounds 2k and 4k have excellent crop safener activities toward rice and can, thus, be promising candidates for further structural optimization in rice protection.

Diagnosing Herbicide Injury in Peanut

This 9-page publication aims to provide information on peanut injury symptoms related to various herbicide modes of action and help in identifying general injury symptoms associated with certain herbicide mode of action groups. Written by S. Morichetti, J. Ferrell, and P. Devkota, and published by the UF/IFAS Agronomy Department, revised April 2020.&#x0D; Original Publication:&#x0D; Morichetti, S., and Jason Ferrell. 2010. “Diagnosing Herbicide Injury in Peanut”. EDIS 2010 (4). https://journals.flvc.org/edis/article/view/118669.

Sensitivity of Hydrangea paniculata Plants to Residual Herbicides in Recycled Irrigation Varies with Plant Growth Stage

Recycling irrigation return flow is a viable option to achieve sustainability in horticultural production systems, but residual herbicides present in recycled water may be phytotoxic. The sensitivity of plants to residual herbicides may vary depending on the growth stage of the plant. If sensitive growth stages are avoided, the risk associated with using recycled water can be reduced. Here, we quantified the effect of residual oryzalin and oxyfluorfen exposure at various growth stages of Hydrangea paniculata. Exposure to both herbicides reduced plant growth, leaf visual rating, soil plant analysis development (SPAD) chlorophyll index, net photosynthesis, and light-adapted fluorescence of H. paniculata. Herbicide injury was greater for plants exposed to herbicides at early growth stages, however, the recovery rate of those plants was also rapid. For oxyfluorfen, plants produced healthy new growth immediately after the end of exposure, but for oryzalin, even newly formed leaves developed herbicide injury after the end of exposure, therefore leaf damage continued to progress before recovering. However, damage caused by residual herbicide exposure at all growth stages recovered over time. Physiological measurements such as the SPAD index, net photosynthesis, and light-adapted fluorescence responded quickly to herbicides exposure hence provided an early indicator of herbicide damage and recovery.

Response of tomato transplants to varying soil residual levels of preplant herbicides

ABSTRACT Processing-tomato (Lycopersicon esculentum L.) cultivation in California has transitioned to the use of transplants, subsurface drip irrigation (SDI), and shallow tillage from direct-seeded, flood-irrigated, deep-tillage systems. Observation of stunted tomato plants in fields treated with preplant herbicides suggests that the herbicides may not be disintegrating as rapidly in the newer system. Greenhouse studies were conducted to assess plant response to trifluralin, S-metolachlor, and pendimethalin at soil-residue levels of 0, 0.03, 0.06, 0.12, 0.25, and 0.5 ppm (0, 0.03, 0.06, 0.12, 0.25, and 0.5 mg l-1, respectively; 1 ppm = 1 mg l-1). Plants grown for 45 days after transplanting showed that all three herbicides at levels as low as 0.03 ppm (0.03 mg l-1) reduced shoot and root growth. Therefore, appropriate methods need to be developed to reduce soil carryover effects of these herbicides in tomatoes grown with SDI system. All herbicides resulted in some reduction in shoot and root biomass of the tomato plants at the higher doses (>0.12 ppm) compared to the non-treated plants. Both S-metolachlor and trifluralin caused significant reductions in shoot and root biomass at 0.5 ppm and the potential of the plants to recover from herbicide injury is unknown. Pendimethalin had a lower potential to cause injury than the other two herbicides. Although the effect of shoot and root biomass reduction on fruit yield and quality was not recorded, this study suggests that preplanting soil tests and appropriate management to reduce soil carryover of these herbicides may be necessary in processing tomatoes grown with SDI.

The Effect of Salicylic Acid and 20 Substituted Molecules on Alleviating Metolachlor Herbicide Injury in Rice (Oryza sativa)

Salicylic acid (SA) is an endogenous plant hormone that has a wide range of pharmacological effects. Studies have indicated that SA has herbicide safening activity. In this study, the herbicide safening activity of SA and 20 substituted molecules were tested on agar-cultured rice. Biological assay results indicated that SA and substituted SA had a low inhibitory effect on the growth of rice seedlings (Oryza sativa), and partially alleviated the effects of metolachlor toxicity. Moreover, at 0.25 mg L−1, the safening effect of compounds l and u lessened the effects of metolachlor phytotoxicity on plant height and fresh weight when compared to the effects of the control, fenclorim. The effects of metolachlor toxicity were reduced on root length due to the safening effects of compounds l, n, and u; these effects were greater than those of fenclorim. These compounds could facilitate the development of novel herbicide safeners.

Evaluation of Seed Treatment, Herbicide, and Nematicide on Tobacco Thrips (Thysanoptera: Thripdae) and Reniform Nematode (Tylenchida: Hoplolaimidae) Control

Numerous pests infest cotton early in the season. Some economically important are Palmer amaranth, Amaranthus palmeri (S. Wats); tobacco thrips, Frankliniella fusca (Hinds); and reniform nematode, Rotylenchulus reniformis (Linford and Oliveira). Thrips and weed management are essential to prevent delayed maturity and reduced crop yield. A field study was conducted during 2015 and 2016 to evaluate the influence of insecticide seed treatment, herbicide, and nematicide on tobacco thrips and reniform nematode control, as well as the impact on cotton growth, development, and yield. Treatments consisted of insecticide seed treatment (insecticide seed treatment and fungicide only), herbicide application (S-metolachlor, glufosinate, S-metolachlor plus glufosinate, and no herbicide), and nematicide application (1, 3-dichloropropene and no nematicide). There were no significant interactions between insecticide seed treatment, herbicide, and nematicide for any parameter. Nor were there any interactions in respect to nematode densities, thrips densities, thrips injury, herbicide injury, or plant biomass. Nematode densities were reduced with the use of 1,3-dichloropropene when sampled at first square and post-harvest. Thrips densities and injury were reduced at the 1- to 2-leaf stage sample timing with an insecticide seed treatment, but not at the 3- to 4-leaf stage sample timing. Herbicide injury was the greatest following S-metolachlor plus glufosinate applications (&lt; 12%). A significant interaction between nematicide and insecticide seed treatment was observed for cotton yield, where the use of 1,3-dichloropropene and the insecticide seed treatment resulted in greater yields than all other treatments.

Proximal sensing estimation of glyphosate injury on weeds in central Brazil

Herbicide injury on weeds is quantified through responses such as mortality, biomass, and visual scores, which are time consuming and/or subjective, making it hard to evaluate injury in experiments and making the site-specific management impracticable in major crops. The objective of our work was to build prediction models of glyphosate injury on weed species of economic importance in the Brazilian Cerrado (savana) through multispectral digital images. Two weed species with different levels of susceptibility to glyphosate, Eleusine indica (L.) Pers. and Brachiaria decumbens L., were cultivated in pots and subjected to increasing doses of glyphosate, simulating a gradient of injury. Visual scores were given by three trained evaluators during three weeks after the application. Images of the pots were acquired with a digital multispectral camera in the following bands of the electromagnetic spectrum: blue (450 nm), green (560 nm), red (660 nm), and near-infrared (850 nm), with a digital camera at 0.9-m height from the ground. Images were first segmented to separate plant from soil using the hue–saturation–value color space. Vegetation indices were calculated and used as explanatory variables for phytotoxicity in regression models. A field experiment was conducted in order to validate predictions. The injury pattern of glyphosate on E. inidica and B. decumbens was best modeled by an exponential function of the median of hue for plant pixels, which could be reproduced at field scale with prediction errors below 8%. Differences in sensitivity to glyphosate between the two species were detected with the kernel density of hue for plant pixels, with absolute correlation with phytotoxicity above 0.8.

Protective Responses Induced by Chiral 3-Dichloroacetyl Oxazolidine Safeners in Maize (Zea mays L.) and the Detoxification Mechanism.

Herbicide safeners selectively protect crops from herbicide injury while maintaining the herbicidal effect on the target weed. To some extent, the detoxification of herbicides is related to the effect of herbicide safeners on the level and activity of herbicide target enzymes. In this work, the expression of the detoxifying enzyme glutathione S-transferase (GST) and antioxidant enzyme activities in maize seedlings were studied in the presence of three potential herbicide safeners: 3-dichloroacetyl oxazolidine and its two optical isomers. Further, the protective effect of chiral herbicide safeners on detoxifying chlorsulfuron in maize was evaluated. All safeners increased the expression levels of herbicide detoxifying enzymes, including GST, catalase (CAT), and peroxidase (POD) to reduce sulfonylurea herbicide phytotoxicity in maize seedlings. Our results indicate that the R-isomer of 3-(dichloroacetyl)-2,2,5-trimethyl-1,3-oxazolidine can induce glutathione (GSH) production, GST activity, and the ability of GST to react with the substrate 1-chloro-2,4-dinitrobenzene (CDNB) in maize, meaning that the R-isomer can protect maize from damage by chlorsulfuron. Information about antioxidative enzyme activity was obtained to determine the role of chiral safeners in overcoming the oxidative stress in maize attributed to herbicides. The interaction of safeners and active target sites of acetolactate synthase (ALS) was demonstrated by molecular docking modeling, which indicated that both isomers could form a good interaction with ALS. Our findings suggest that the detoxification mechanism of chiral safeners might involve the induction of the activity of herbicide detoxifying enzymes as well as the completion of the target active site between the safener and chlorsulfuron.

Effect of elevated carbon dioxide concentration on growth, productivity and glyphosate response of parthenium weed (Parthenium hysterophorus L.).

The rise in atmospheric CO2 has huge impacts on the biology and management of invasive weed species such as Parthenium hysterophorus. This study evaluated the effect of ambient (400 ppm) and elevated (700 ppm) CO2 concentrations on P. hysterophorus growth, reproductive output and response to glyphosate applied at several doses including the recommended dose (800 g a.e.ha-1 ). The plants in control treatment (no herbicide) grew taller (41%), produced a larger number of leaves (13%) and flowers (39%), and higher dry biomass (34%) at elevated CO2 as compared to the ambient CO2 . Glyphosate caused significant reduction in chlorophyll content of P. hysterophorus plants grown at both CO2 concentrations in a dose-dependent manner. The percentage herbicide injury was relatively less at elevated CO2 as compared to the ambient CO2 at 7 and 14 days after glyphosate application but it was almost similar at 21 days after application. This shows that elevated CO2 might have slowed the translocation of glyphosate initially, but most plants were killed eventually close to 21 days after application. The survival rate was higher under elevated as compared to the ambient CO2 at recommended and lower doses of glyphosate. There was a negligible difference between the two CO2 concentrations for the plant dry biomass reduction over the control treatment. P. hysterophorus growth and reproductive potential (indicated by number of flowers) improved significantly by CO2 enrichment but there was little effect on the overall efficacy of glyphosate applied to control this species. © 2019 Society of Chemical Industry.

Tolerance of flax (Linum usitatissimum) to fluthiacet-methyl, pyroxasulfone, and topramezone

AbstractFlax yield can be severely reduced by weeds. The combination of limited herbicide options and the spread of herbicide-resistant weeds across the prairies has resulted in a need for more weed control options for flax producers. The objective of this research was to evaluate the tolerance of flax to topramezone, pyroxasulfone, flumioxazin, and fluthiacet-methyl applied alone as well as in a mix with currently registered herbicides. These herbicides were applied alone and in mixtures at the 1X and 2X rates and compared with three industry standards and one nontreated control. This experiment was conducted at Carman, MB, and Saskatoon, SK, as a randomized complete block with four replications. Data were collected for crop population, crop height, yield, and thousand-seed weight. Ratings for crop damage (phytotoxicity) were also taken at three separate time intervals: 7 to 14, 21 to 28, and 56+ d after treatment. Crop tolerance to these herbicides varied between site-years. This was largely attributed to differences in spring moisture conditions and the differences in soil characteristics between sites. Herbicide injury was transient. Hence, no herbicide or combination of herbicides significantly impacted crop yield consistently. Flumioxazin was the least promising herbicide evaluated, as it caused severe crop damage (&amp;gt;90%) when conditions were conducive. Overall, flax had excellent tolerance to fluthiacet-methyl, pyroxasulfone, and topramezone. Flax had excellent crop safety to the combination of pyroxasulfone + sulfentrazone. However, mixing fluthiacet-methyl and topramezone with MCPA and bromoxynil, respectively, increased crop damage and would not be recommended.

Transcriptome Profiling and Genome-Wide Association Studies Reveal GSTs and Other Defense Genes Involved in Multiple Signaling Pathways Induced by Herbicide Safener in Grain Sorghum.

Herbicide safeners protect cereal crops from herbicide injury by inducing genes and proteins involved in detoxification reactions, such as glutathione S-transferases (GSTs) and cytochrome P450s (P450s). Only a few studies have characterized gene or protein expression profiles for investigating plant responses to safener treatment in cereal crops, and most transcriptome analyses in response to safener treatments have been conducted in dicot model species that are not protected by safener from herbicide injury. In this study, three different approaches were utilized in grain sorghum (Sorghum bicolor (L.) Moench) to investigate mechanisms involved in safener-regulated signaling pathways. An initial transcriptome analysis was performed to examine global gene expression in etiolated shoot tissues of hybrid grain sorghum following treatment with the sorghum safener, fluxofenim. Most upregulated transcripts encoded detoxification enzymes, including P450s, GSTs, and UDP-dependent glucosyltransferases (UGTs). Interestingly, several of these upregulated transcripts are similar to genes involved with the biosynthesis and recycling/catabolism of dhurrin, an important chemical defense compound, in these seedling tissues. Secondly, 761 diverse sorghum inbred lines were evaluated in a genome-wide association study (GWAS) to determine key molecular-genetic factors governing safener-mediated signaling mechanisms and/or herbicide detoxification. GWAS revealed a significant single nucleotide polymorphism (SNP) associated with safener-induced response on chromosome 9, located within a phi-class SbGST gene and about 15-kb from a different phi-class SbGST. Lastly, the expression of these two candidate SbGSTs was quantified in etiolated shoot tissues of sorghum inbred BTx623 in response to fluxofenim treatment. SbGSTF1 and SbGSTF2 transcripts increased within 12-hr after fluxofenim treatment but the level of safener-induced expression differed between the two genes. In addition to identifying specific GSTs potentially involved in the safener-mediated detoxification pathway, this research elucidates a new direction for studying both constitutive and inducible mechanisms for chemical defense in cereal crop seedlings.

Activated charcoal reduces pasture herbicide injury in vegetable crops

Vegetable producers are often concerned about potential herbicide carryover and injury to vegetables following the application of livestock manure/compost from animals fed with treated hay. A greenhouse study was conducted to evaluate the effect of activated charcoal on soil residual activity of the herbicides aminopyralid, aminocyclopyrachlor, and picloram, applied at recommended field rates of 120 g ae, 70 g ai, and 303 g ai ha−1 respectively, on tomato, okra, and cantaloupe. A commercial source of activated charcoal was used at four rates [0, 0.5X, 1X, and 2X (1X = 336 kg ha−1)]. When no activated charcoal was applied, aminopyralid caused the greatest injury to tomato and okra, leading to plant death at 4 weeks after emergence/transplanting (WAE/T). At the highest rate (2X) of activated charcoal, crop injuries due to aminopyralid were reduced by 72 and 78% for okra and cantaloupe, respectively at 4 WAE, while tomato did not respond to the 2X rate of activated charcoal. For aminocyclopyrachlor, even a much lower rate (0.5X) of activated charcoal was sufficient to reduce about 70% of the injury caused on cantaloupe and okra. For picloram, activated charcoal application at the 2X rate reduced injury by 78–94% across the three vegetable species investigated. Under low herbicide residue levels that usually occur under carryover situations, a much lower rate of activated charcoal (<100 kg ha−1) may be sufficient and practically feasible. Overall, activated charcoal application shows promise for remediating soil contaminated with herbicide residues, but crop response can be variable and requires optimization for specific herbicide, species, and use scenarios.

Effect of postemergence fomesafen application on common milkweed (Asclepias syriaca) growth and utilization by monarchs (Danaus plexippus)

Field experiments were conducted to investigate impacts of herbicide injury to common milkweed (Asclepias syriaca L.) on oviposition preference of monarch butterflies (Danaus plexippus Linnaeus). Common milkweed seedlings were transplanted in patches containing five plants spaced 25 cm apart in a no-till soybean field shortly after soybean planting in 2016. Herbicide treatments included an untreated control and 0.14 kg ha−1 fomesafen plus 0.5% crop oil concentrate applied postemergence. The experiment was repeated in the same area in 2017 by planting soybean no-till prior to common milkweed emergence. Common milkweed leaves displayed chlorosis and necrotic lesions five days after fomesafen application during both years. Two weeks following application many leaves damaged by fomesafen dehisced, and plants averaged an injury rating of 3.4 (visual scale of 1 = healthy and 5 = dead). Leaves emerging from the apical meristem following fomesafen application appeared normal, and four weeks after application injury ratings decreased to an average of 2.6. Dry weight of common milkweed ten weeks after application was not affected by fomesafen in either year. Common milkweed plants were examined for monarch eggs and larval instars weekly from May to August. In 2016, patches averaged 0.8 eggs, whereas in 2017 patches averaged 45.2 eggs. Fomesafen did not affect oviposition preference by monarch butterflies in either year. Larval instars on the milkweed patches were recorded throughout 2017. Presence and survival of instars were not affected by fomesafen, with patches averaging 7.5 and 0.1 first and fifth instars, respectively. In greenhouse experiments, common milkweed survived fomesafen rates up to 0.28 kg ha−1, twice the rate typically used in soybean, and plants showed signs of recovery within two weeks of application.