Effects of Various Environmental Conditions on the Growth of Amaranthus patulus Bertol. and Changes of Herbicide Efficacy Caused by Increasing Temperatures

Understanding the effects of climate change on weed growth and herbicide activity is important for optimizing herbicide applications for effective weed control in the future. Therefore, this study examined how climate change affects the growth of Amaranthus patulus and the efficacy of soil and foliar herbicides at different temperatures. Although the control values for A. patulus differed between herbicides and temperature, the control values increased with increasing time after the herbicide treatments. Under growth conditions in which the temperature remained constant, the efficacy of soil-applied herbicides, ethalfluralin, metolachlor, linuron, and alachlor, on A. patulus was highest when the weeds were grown at high temperature. In particular, 100% control values of A. patulus were achieved in response to metolachlor treatments at the total recommended dosage in growth chambers at 35 °C. The efficacy of foliar herbicides, glufosinate-ammonium, bentazone, and mecoprop, on A. patulus was also highest when the plant was grown at high temperature, except for glyphosate isopropylamine, which had similar efficacy rates regardless of the temperature. A. patulus was 100% controlled in response to glufosinate-ammonium, bentazone, and mecoprop at the recommended dosages in growth chambers at 30 and 35 °C. Under growth conditions in which the temperature changed from day to night, the efficacy of soil-applied herbicides, alachlor and linuron, on A. patulus was highest when the weeds were grown at high temperature. On the other hand, the efficacy of the soil-applied herbicides metolachlor and linuron on A. patulus was similar regardless of the temperature. The efficacy of foliar herbicides, glyphosate isopropylamine, glufosinate-ammonium, bentazone, and mecoprop, on A. patulus was highest when the weeds were grown at high temperature. Although herbicide efficacy varied depending on whether the weeds were grown at constant or alternating temperatures, herbicide efficacy was generally highest when the temperature was high.

Synthesis and Identification of Epoxy Derivatives of 5-Methylhexahydroisoindole-1,3-dione and Biological Evaluation

Cyclic imides belong to a well-known class of organic compounds with various biological activities, promoting a great interest in compounds with this functional group. Due to the structural complexity of some molecules and their spectra, it is necessary to use several spectrometric methods associated with auxiliary tools, such as the theoretical calculation for the structural elucidation of complex structures. In this work, the synthesis of epoxy derivatives of 5-methylhexahydroisoindole-1,3-diones was carried out in five steps. Diels–Alder reaction of isoprene and maleic anhydride followed by reaction with m-anisidine afforded the amide (2). Esterification of amide (2) with methanol in the presence of sulfuric acid provided the ester (3) that cyclized in situ to give imides 4 and 4-ent. Epoxidation of 4 and 4-ent with meta-chloroperbenzoic acid (MCPBA) afforded 5a and 5b. The diastereomers were separated by silica gel flash column chromatography, and their structures were determined by analyses of the spectrometric methods. Their structures were confirmed by matching the calculated 1H and 13C NMR chemical shifts of (5a and 5b) with the experimental data of the diastereomers using MAE, CP3, and DP4 statistical analyses. Biological assays were carried out to evaluate the potential herbicide activity of the imides. Compounds 5a and 5b inhibited root growth of the weed Bidens pilosa by more than 70% at all the concentrations evaluated.

High Activity and Easily Hydrolyzable Sulfonylurea Inhibitor Design Based on Density Functional Theory Calculations

To find new sulfonylurea inhibitors with high efficacy and fast hydrolysis degradation rate, a few compounds were first designed based on the commercial product Chlorimuron-Ethyl (CE) by estimating the binding interaction between the inhibitor and the Acetohydroxyacid Synthase (AHAS) using the quantum mechanical approach. Meanwhile, the activation energy barriers of hydrolysis for the sulfonylurea inhibitors with the amino and nitro groups onto para position of the benzene ring were calculated. Based on the calculated binding interaction energy and hydrolysis energy barrier, six new sulfonylurea inhibitors I1–I6 were designed and synthesized. By measuring the half-lives through hydrolysis degradation assay, it was indicated that the compounds I1–I3 with the introduction of an amino group at the fourth position of benzene ring show much faster degradation rate than those compounds with nitro groups, which is in a good agreement with the calculated results for hydrolysis barrier. The herbicide activity tests show that the compounds I1 and I2 remained excellent herbicidal activity on both broadleaf weeds with soil treatment at a concentration about 150[Formula: see text]mg/l. Due to their short half-lives of chemical hydrolysis and high herbicidal activities, compounds I1 and I2 could be potential herbicidal candidates in the future, which are helpful for the sustainable development of the environment and ecology.

Differential response of horseweed (Conyza canadensis) to halauxifen-methyl, 2,4-D, and dicamba

Halauxifen-methyl is an auxin herbicide for broadleaf weed control in preplant applications to corn and soybean. Our objective for this research was to characterize the phytotoxicity of halauxifen-methyl on horseweed, relative to 2,4-D and dicamba, in terms of weed height, the response to an auxin synergist, and root activity. The 50% reduction in plant growth (GR50) value for halauxifen-methyl on rosette-sized plants was 0.05 g ae ha−1, 100 times less than the labeled use rate of 5 g ae ha−1, compared with 36 and 31 g ha−1 for 2,4-D and dicamba, respectively. In a whole-plant bioassay, 240 g ae ha−1 of 2,4-D was calculated as the GR50 value on horseweed 20-cm tall, whereas applications of only 53 and 0.40 g ae ha−1 were necessary for dicamba and halauxifen-methyl, respectively, to achieve the same response. As weed size decreased, there was a concomitant reduction in the estimated herbicide dose for the GR50 with similar differences observed between halauxifen-methyl and the other two auxin herbicides. The addition of diflufenzopyr, an auxin synergist, to 2,4-D and dicamba resulted in a synergistic response on horseweed. However, the addition of diflufenzopyr to halauxifen-methyl resulted in an additive or antagonistic effect, depending on rate of diflufenzopyr, demonstrating a distinctive physiological pathway for halauxifen-methyl compared with 2,4-D and dicamba. In the agar-based bioassays, GR50 values for horseweed root length for 2,4-D and dicamba were 0.16 and 0.19 µM, respectively, whereas only 0.004 µM halauxifen-methyl was required for a comparable root response. These results indicate that horseweed exhibits a high level of sensitivity to halauxifen-methyl and suggest the activity of halauxifen-methyl is different from that of 2,4-D and dicamba. These differences in herbicide activity may reflect differential absorption, translocation, metabolism, or targeting of auxin receptors found in horseweed.

Spray deposition, adjuvants, and physiochemical properties affect benzobicyclon efficacy

Benzobicyclon is a new pro-herbicide being evaluated in the Midsouth United States as a post-flood weed control option in rice. Applications of benzobicyclon to flooded rice are necessary for efficacious herbicide activity, but why this is so remains unknown. Two greenhouse experiments were conducted to explore how herbicide placement (foliage only, flood water only, foliage and flood water simultaneously) and adjuvants (nonionic surfactant, crop oil concentrate, and methylated seed oil [MSO]) affect herbicide activity. The first experiment focused on importance of herbicide placement. Little to no herbicidal activity (<18% visual control) was observed on two- to four-leaf barnyardgrass, Amazon sprangletop, and benzobicyclon-susceptible weedy rice with benzobicyclon treatments applied to weed foliage only. In contrast, applications made only to the flood water accounted for >82% of the weed control and biomass reduction achieved when benzobicyclon was applied to flood water and foliage simultaneously. The second experiment concentrated on adjuvant type and benzobicyclon efficacy when applied to foliage and flood water simultaneously. At 28 days after treatment, benzobicyclon alone at 371 g ai ha−1 provided 29% and 67% control of three- to five-leaf barnyardgrass and Amazon sprangletop, respectively. The inclusion of any adjuvant significantly increased control, with MSO providing near-complete control of barnyardgrass and Amazon sprangletop. Furthermore, we used the physiochemical properties of benzobicyclon and benzobicyclon hydrolysate to derive theories to explain the complex activity of benzobicyclon observed in our study and in field trials. Benzobicyclon applications should contain an oil-based adjuvant and must be applied to flooded rice fields for optimal activity.

Carolina Redroot (Lachnanthes caroliniana) in Cranberry: Assessment of Shoot and Rhizome Control with POST Herbicides

Carolina redroot is a common weed of New Jersey cranberry beds that competes with crops for nutritional resources but also serves as a food source for waterfowl. Greenhouse studies were conducted in 2017 in Chatsworth, NJ, to determine control of Carolina redroot aboveground vegetation and rhizome production with 10 herbicide active ingredients. Herbicides were applied as a single application on 10- to 15-cm-tall plants. Diquat at 560 g ai ha−1and mesotrione at 280 or 560 g ai ha−1controlled more than 90% of emerged shoots at 63 d after treatment (DAT). Aboveground vegetation control at 63 DAT reached 87% with 2,4-D and flumioxazin but was limited with glyphosate, not exceeding 40%. Mesotrione at 560 g ai ha−1provided 98% control of roots and rhizomes (root/rhizome) at 63 DAT, a 10% increase compared with 280 g ai ha−1; and 2,4-D (90%), glyphosate (87%), diquat (86%), and flumioxazin (85%) also showed excellent root/rhizome control. The greatest reduction of plant biomass compared with the nontreated check (UNT) was noted with 2,4-D, mesotrione at 280 g ai ha−1and 560 g ai ha−1, and diquat, with decreases from 73% to 80% for shoots and from 82% to 88% for roots/rhizomes. Glyphosate had less impact on shoot biomass reduction (−56%) but similar effect on root/rhizome dry weight (−79%) compared with 2,4-D, mesotrione, and diquat. Flumioxazin and fomesafen significantly reduced root/rhizome biomass by 78% and 72%, respectively. Concurrently, 2,4-D, flumioxazin, fomesafen, and diquat reduced the number of secondary shoots 70% to 90% compared with the UNT, whereas glyphosate and mesotrione completely inhibited emergence of new shoots. These data suggest that mesotrione applied POST provides excellent control of Carolina redroot. Future research should evaluate field applications of mesotrione in early summer when Carolina redroot regrowth occurs following the dissipation of PRE herbicide activity.