Herbicide Rates Research Articles

Electrostatic spraying of imazamox to control the floating aquatic plant Salvinia molesta and its effects on environmental indicators of water quality

This study aimed to assess, in a microcosm condition, the efficacy of electrostatic spraying of herbicide imazamox in the control of Salvinia molesta and the effects of decomposition of plant material on water quality. The herbicide rates used were 600, 700, 800, and 900 g ai ha−1 and spray volume of 50 L ha−1 in electrostatic application. Control effectiveness was assessed at 7, 15, 30, 45, and 60 days after application (DAA), expressed in percentage (0–100%) of visible injury symptoms in the plants, biochemical oxygen demand (BOD5), chemical oxygen demand (COD), chlorophyll a and pheophytin a contents at 0, 7, 15, 30, 45, and 60 DAA, and fresh and dry biomass at 60 DAA. Imazamox was effective in controlling 63% of S. molesta with 900 g ai ha−1 in 45 DAA and 30% with 800 g ai ha−1 in 30 DAA, and reduced 82.3% and 17.5% of fresh weight and 62.6% and 9.3% of dry weight of plant at 60 DAA, respectively. The imazamox spray reduced chlorophyll a with all doses applied and increased BOD5 in 45 DAA with 900 g ai ha−1 and COD in all assessment periods, but for temperature, dissolved oxygen, electrical conductivity, and pH, there was no significant effect after spraying. The herbicide imazamox reduced S. molesta plants with 900 g ai ha−1, without causing significant effects on environmental indicators of water quality. Electrostatic spraying of herbicide can be used in management strategies of aquatic plants to reduce plant density in water bodies and maintain the colonization of plants at a level not harmful to the aquatic biota.

ЗАБУР’ЯНЕНІСТЬ ПОСІВІВ ГОРОХУ ОЗИМОГО ЗА ДІЇ ГЕРБІЦИДУ, РЕГУЛЯТОРА РОСТУ РОСЛИН І МІКРОБНОГО ПРЕПАРАТУ

Weed infestation of agricultural crops in Ukraine is growing and is becoming a big threat to stable and high yields. Therefore, today, it is impossible to do without the development of science-based measures to control the level of weed infestation in crops, adaptation of herbicides to ecological farming methods and energy-optimized cultivation technologies. The analysis of the results of studies of weediness of winter pea crops at different rates of application of MaxiMox herbicide (0.8; 0.9; 1.0 and 1.1 l/ha) separately and in tank mixtures with plant growth regulator Agriflex Amino at the rate of 1.0 kg/ha on the background of seed treatment before sowing with the microbial preparation Optimize Pulse at the rate of 3.28 l/t, and without treatment is given. Spraying of vegetating plants with herbicide and their tank mixture with a plant growth regulator was carried out in the phase of 3-4 developed runners (BBCH 13–14) of the crop. Weed infestation of winter pea crops was counted on the thirtieth day after plant treatment with preparations. Weeds were counted by the quantitative weight method per 1 m2 according to the method of S. A. Tribel. Statistical processing of the data was carried out according to the generally accepted methods. It has been established that with the combined application of different rates of MaxiMox herbicide with plant growth regulator Agriflex Amino on the background of seed treatment before sowing with the microbial preparation Optimize Pulse, the technical efficiency of weed control increases, both in terms of quantity and weight. The greatest number and weight of destroyed weeds was noted in variants with the introduction of MaxiMox herbicide at the rates of 0.8; 0.9; 1.0 and 1.1 l/ha in combination with plant growth regulator Agriflex Amino at the rate of 1.0 kg/ha on the background of seed treatment with the microbial preparation Optimize Pulse at the rate of 3.28 l/t, where the percentage of destroyed weeds averaged 91–99 % quantitatively and 94–100 % in mass. The increase in the effectiveness of the studied preparations obviously occurred due to the improvement of biometric indices of winter pea plants under the direct action of the plant growth regulator and microbial preparation, which eventually increased the competitiveness of the crop to weeds.

АКТИВНІСТЬ РИЗОСФЕРНОЇ МІКРОБІОТИ ГОРОХУ ОЗИМОГО ЗА КОМБІНОВАНОЇ ДІЇ ГЕРБІЦИДУ І БІОЛОГІЧНИХ ПРЕПАРАТІВ

The article presents the results of studies the total number of bacteria, micromycetes and azotobacter in the rhizosphere of winter peas, depending on the use of different rates of herbicide MaxiMox (0,8; 0,9; 1,0 and 1,1 l / ha), separately and in tank mixes with plant growth regulator Agriflex Amino (1,0 kg/ha) on the background of bacterization seeds material with the microbial preparation Optimize Pulse (3,28 l/t) and without background. The obtained results showed the dependence of the functioning of the rhizosphere microbiota of winter peas on the application of different herbicide rates, but with the complex application of MaxiMox (0,8–1,0 l/ha) with the plant growth regulator Agriflex Amino (1,0 kg/ha) on the background of bacterization seeds material with the microbial preparation Optimize Pulse (3,28 l/t) was observed to reduce the negative impact of xenobiotics on the soil microbiota, which was manifested in an increase the total number of bacteria by an average of 3-21%, micromycetes - 42-73% and azotobacter - 2-9%

ВМІСТ ПІГМЕНТІВ У ЛИСТКАХ СОРГО ЗЕРНОВОГО ЗА ДІЇ ГЕРБІЦИДУ ЦИТАДЕЛЬ 25 OD, РЕГУЛЯТОРА РОСТУ РОСЛИН ЕНДОФІТ L1 І БІОПРЕПАРАТУ БІОАРСЕНАЛ

Content of the chlorophylls and carotenoids in a pigment complex is one of the most important factors that determine the productivity of crops of cereals. Although it is well known that herbicides and plant growth regulators may cause changes in the amount of pigments, there is lack of researches about their separate and integrated influence on the pigment complex of grain sorghum (Sorghum bicolor (L.) Moench). Therefore, we aimed our research to investigate the response of grain sorghum’s pigment complex to the impact of the herbicide in different combinations with the plant growth regulator and biopreparation. In result, it was found that the content of the pigments was decreasing simultaneously with increasement of the herbicide rate. However, the obtained data indicates that the complex usage of the herbicide and plant growth regulator had an auspicious influence on the pigments content, compared to the variants where only herbicide was applied. The similar auspicious effect appeared, when the herbicide was applied on the background of pre-sowing seeds treatment by the biopreparation Bioarsenal. It is noticeable that in this case the increasement of pigments content was higher than in the variants of compatible application of the herbicide and plant growth regulator. The highest indicators of the pigments content formed when the herbicide was applied compatible with the plant growth regulator on the background of pre-sowing seeds treatment. The content excess of the chlorophylls a, b, a+b and carotenoids, relatively to the control, amounted 7,4 – 9,1%, 16,0 – 18,3%, 9,4 – 11,2% and 35,5 – 40,2% respectively. It is evident that usage of the herbicide Citadel 25 OD compatibly with the plant growth regulator Endofit L1 on the background of pre-sowing seeds treatment by the biopreparation Bioarsenal is an effective measure, which allows to reduce the harmful impact of the xenobiotic on the pigment complex of grain sorghum

Effects of low-dose applications of 2,4-D and dicamba on cucumber and cantaloupe

AbstractAgronomic crops engineered with resistance to 2,4-D or dicamba have been commercialized and widely adopted throughout the United States. Because of this, increased use of these herbicides in time and space has increased damage to sensitive crops. From 2014 to 2016, cucumber and cantaloupe studies were conducted in Tifton, GA, to demonstrate how auxinic herbicides (namely, 2,4-D or dicamba), herbicide rate (1/75 or 1/250 field use), and application timing (26, 16, and 7 d before harvest [DBH] of cucumber; 54, 31, and 18 DBH of cantaloupe) influenced crop injury, growth, yield, and herbicide residue accumulation in marketable fruit. Greater visual injury, reductions in vine growth, and yield loss were observed at higher rates when herbicides were applied during early-season vegetative growth compared with late-season with fruit development. Dicamba was more injurious in cucumber, whereas cantaloupe responded similarly to both herbicides. For cucumber, total fruit number and relative weights were reduced (16% to 19%) when either herbicide was applied at the 1/75 rate 26 DBH. Cantaloupe fruit weight was also reduced 21% and 10% when either herbicide was applied at the 1/75 rate 54 or 31 DBH, respectively. Residue analysis noted applications made closer to harvest were more likely to be detectable in fruit than earlier applications. In cucumber, dicamba was detected at both rates when applied 7 DBH, whereas in cantaloupe, it was detected at both rates when applied 18 or 31 DBH in 2016 and at the 1/75 rate applied 18 or 31 DBH in 2014. Detectable amounts of 2,4-D were not observed in cucumber but were detected in cantaloupe when applied at either rate 18 or 31 DBH. Although early-season injury will more likely reduce cucumber or cantaloupe yields, the quantity of herbicide residue detected will be most influenced by the time interval between the off-target incident and sampling.

Herbicide safener increases weed-management tools for control of annual grasses in wheat

AbstractAnnual grass weeds reduce profits of wheat farmers in the Pacific Northwest. The very-long-chain fatty acid elongase (VLCFA)-inhibiting herbicides S-metolachlor and dimethenamid-P could expand options for control of annual grasses but are not registered in wheat, because of crop injury. We evaluated a safener, fluxofenim, applied to wheat seed for protection of 19 soft white winter wheat varieties from S-metolachlor, dimethenamid-P, and pyroxasulfone herbicides; investigated the response of six varieties (UI Sparrow, LWW 15-72223, UI Magic CL+, Brundage 96, UI Castle CL+, and UI Palouse CL+) to incremental doses of fluxofenim; established the fluxofenim dose required to optimally protect the varieties from VLCFA-inhibiting herbicides; and assessed the impact of fluxofenim dose on glutathione S-transferase (GST) activity in three wheat varieties (UI Sparrow, Brundage 96, and UI Castle CL+). Fluxofenim increased the biomass of four varieties treated with S-metolachlor or dimethenamid-P herbicides and one variety treated with pyroxasulfone. Three varieties showed tolerance to the herbicides regardless of the fluxofenim treatment. Estimated fluxofenim doses resulting in 10% biomass reduction of wheat ranged from 0.55 to 1.23 g ai kg−1 seed. Fluxofenim doses resulting in 90% increased biomass after treatment with S-metolachlor, dimethenamid-P, and pyroxasulfone ranged from 0.07 to 0.55, 0.09 to 0.73, and 0.30 to 1.03 g ai kg−1 seed, respectively. Fluxofenim at 0.36 g ai kg−1 seed increased GST activity in UI Castle CL+, UI Sparrow, and Brundage 96 by 58%, 30%, and 38%, respectively. These results suggest fluxofenim would not damage wheat seedlings up to three times the rate labeled for sorghum, and fluxofenim protects soft white winter wheat varieties from S-metolachlor, dimethenamid-P, or pyroxasulfone injury at the herbicide rates evaluated.

Bean cultivar mixture allows reduced herbicide dose while maintaining high yield: A step towards more eco-friendly weed management

Integrated weed control methods are increasingly demanded to maintain high yield while alleviating negative environmental side effects of control measures. Five field experiments were conducted during 2015–2017 at three locations in Iran to determine the advantage of exploiting enhanced competitive ability of bean (Phaseolus vulgaris L.) via cultivar mixture to reduce herbicide dose. For all experiments, the experimental design was split-plot in randomized complete block with four replications. Main plots were assigned to the factor "herbicide dose" with 5 levels between 0 and 100 % of recommended dose and subplots comprised monoculture of a stand growth type cultivar (STAND), monoculture of a climbing growth type cultivar (CLIMB) and the substitutive (50 % STAND/50 % CLIMB) cultivar mixture (MIXCR). Without herbicide application, the yield of STAND, CLIMB and MIXCR was estimated at 588, 1026, and 1637 kg ha−1, and the corresponding weed biomass (W0) at 388, 215, and 239 g m-2, respectively. The herbicide dose to decrease W0 by 50 % (ed50) was estimated as 69 % of the recommended dose for STAND, while it was 53 and 45 % for CLIMB and MIXCR, respectively. Herbicide application at full rate increased the average yield of STAND by 2610 kg ha−1, but 1115 and 1532 kg ha-1 for CLIMB and MIXCR, respectively. Potential yield of CLIMB at full herbicide rate application was 2141 kg ha−1, while STAND and MIXCR showed statistically the same potential of producing 3198 and 3169 kg h−1 bean yield. However, MIXCR could achieve its potential yield at half of the recommended dose. Relative yield total (RYT) was lower than or equal to one at 75 % and 100 % of the recommended dose, but with decreasing herbicide dose to 50 or 25 % RYT raised to 1.2. Careful selection of cultivars for growing in mixture that combines strong competitor with high yield cultivars is crucial to achieve potential yield with less dependence on herbicides. As we could show for bean, this will help to overcome conflicting management objectives to reach both environmental and economic goals in weed control and crop production.

Integrated Effect of Chlorusulfuron, Nitrogen Fertilizer and Varieties on Striga Management in Sorghum in Western, Tigray, Ethiopia

A field experiment was conducted during the cropping seasons of 2017/2018 to evaluate the effect of levels of herbicide and N fertilizer and sorghum varieties on striga management in the Western Tigray. Split-split plot design was used to conduct the experiment using three replicate. The experiment comprised of four levels of N fertilizer in the main plot (control (0 kg/ha, 23, 46 and 69 kgha-1) and herbicide applications in sub-plot (0, 10, 15 and 20 gha-1) and three sorghum varieties (Birhan, Deber and Wediaker) in sub-sub plot under naturally S. hermonthica infested area. Striga counts and striga growth parameters were recorded. Results showed that days to first flowering, striga count per sorghum plant, stand counts of striga at 45 DAP, 65 DAP and 85 DAP per m-2, branch number per plant, plant height and biomass of striga were significantly (P<0.01) affected with the application of N fertilizer, herbicide rates and varieties. Generally, an integrated approach was found to be the best method to control striga.

Rehabilitation of Soil Properties by Using Direct Seeding Technology

The application of direct seeding technology on typical and ordinary chernozems in the European territory for four years has resulted in a significant increase in the content of soil organic matter in regions with sufficient moisture supply and some tendency of its in regions with insufficient moisture supply (Stavropol region). A tendency for an increase in the available phosphorus and exchangeable potassium contents has also been observed. The yield of crops and profitability of production in the course of long-term (> 7 yr) application of direct seeding are approximately 30% higher than in the case of traditional technologies. Application rates of glyphosate-containing herbicides to control weeds can be significantly reduced in the case of using cover crops, modern biochemical methods, and strict compliance with the technology of herbicide application. Taken together, these measures ensure an increase in the number and species diversity of microorganisms that can suppress pathogenic microflora significantly reducing the damage to plants from diseases and pests.

Recurrent Selection with Glufosinate at Low Rates Reduces the Susceptibility of a Lolium perenne ssp. multiflorum Population to Glufosinate

Repeated applications of herbicides at the labelled rates have often resulted in the selection and evolution of herbicide-resistant weeds capable of surviving the labelled and higher rates in subsequent generations. However, the evolutionary outcomes of recurrent herbicide selection at low rates are far less understood. In this study of a herbicide-susceptible population of Lolium perenne ssp. multiflorum, we assessed the potential for low glufosinate rates to select for reduced susceptibility to the herbicide, and cross-resistance to herbicides with other modes of action. Reduced susceptibility to glufosinate was detected in progeny in comparison with the parental population following three rounds of selection at low glufosinate rates. Differences were mainly observed at the 0.5X, 0.75X, and 1X rates. Comparing the parental susceptible population and progeny from the second and third selection cycle, the percentage of surviving plants increased to values of LD50 (1.31 and 1.16, respectively) and LD90 (1.36 and 1.26, respectively). When treated with three alternative herbicides (glyphosate, paraquat, and sethoxydim), no plants of either the parental or successive progeny populations survived treatment with 0.75X or higher rates of these herbicides. The results of this study provide clear evidence that reduced susceptibility to glufosinate can evolve in weed populations following repeated applications of glufosinate at low herbicide rates. However, the magnitude of increases in resistance levels over three generations of recurrent low-rate glufosinate selection observed is relatively low compared with higher levels of resistance observed in response to low-rate selection with other herbicides (three fold and more).

Effects of Chlorsulfuron 75% WDG Herbicide and Varieties on Striga Control and Sorghum Yield in Tigray, Ethiopia

Sorghum [Sorghum bicolor (L.)Moench] is widely cultivated but the productivity is very low due to different factors such as Striga hermonthica. Field trails were carried out at Humera location to determine the management of striga to different rates of herbicide application to increase sorghum yield during 2017 cropping season. The trail consisted of eight treatments; 0 (control), 10, 15 and 20gha-1 rates of Chlorsulfron. The herbicide rates were assigned to the main plot while sorghum varieties were assigned to subplots, replicated three times in a split plot design. The data of days to 50%emergence, 50%flowering, plant height at maturity, Panicle length, panicle weight (g), yield per panicle (g), 1000 seed weight (g), grain yield (kg ha-1), above ground dry biomass (kg ha-1) and striga data days to first striga emergence, days to first flowering, number of striga count, branch number per striga plant, striga count per sorghum plant, striga height and biomass (kg/m2 respectively. Partial budget analysis was computed to assess the economic visibility of herbicide application where recorded. Result showed that application of herbicide rates and varieties increased plant height, panicle length, number of heads harvested per plot, panicle weight, yield per panicle, 1000 seed weight and grain yield over the control. Maximum grain yield (3725kg ha-1) was obtained from application of 15 g ha-1 Chlorsulfron with variety Deber. Days to first flowering, striga count per sorghum plant, stand counts of striga at 45DAP, 65 DAP and 85DAP M-2, branch number per plant, plant height and biomass of striga were significantly (P<0.01) affected with the application of herbicide rates and varieties. The partial budget showed that an investing of 1.0 birr on application of herbicide with varieties earn 2.34 birr. Generally, application of Chlorsulfuron75% WDG and use local variety with high yielder could be an advantage to obtain highest yield and profit for the farmers in striga infestation areas.

Antioxidant enzymes activity in grain sorghum plants under the action of herbicide, a plant growth regulator and a biopreparation

Herbicides, being substances with a high physiological activity, can affect not only weeds but also cultural plants. At the same time, there are many evidences that usage of plant growth regulators and pre-sowing seeds treatment by biological preparations can reduce the potential harmful impact of herbicides. Antioxidant systems are one of the first plant systems which react to the permeation of exogenous physiologically active substances. Therefore, one of the effective ways to estimate the influence of different preparations on plants condition is estimation of the antioxidant enzymes activity, particularly — catalase, peroxidase and polyphenoloxidase. To estimate enzymes activity in leaves of grain sorghum, a field experiment has been laid. It was conducted in crop rotation of the biology department of Uman national university of horticulture during 2019–2020. In the experiments were used: grain sorghum (Sorghum bicolor (L.) Moench) of the Milo W hybrid, herbicide Cytadel 25 OD in rates of 0,6; 0,8 and 1,0 l/ha, plant growth regulator Endofit L1 (30 ml/ha) and biopreparation Bioarsenal (800 g/100 kg). Enzymes activity was estimated in phases of tillering and throwing panicles. It was established that the enzymes activity of grain sorghum depended on the herbicide rate and raised simultaneously with its increasement. However, application of the herbicide in conjunction with the plant growth regulator Endofit L1 caused more significant increasement of the investigated enzymes compared to the variants where only herbicide was applied. The similar effect established in variants where the herbicide was applied on the background of pre-sowing seeds treatment by the biopreparation Bioarsenal. The highest activity of the antioxidant enzymes established in the variants where the herbicide Citadel 25 OD in rates of 0,6; 0,8 and 1,0 l/ha was applied in conjunction with the plant growth regulator Endofit L1 on the background of pre-sowing seeds treatment by the biopreparation Bioarsenal. It indicates increasement of the plant’s antioxidant status in case of using this combination of preparates.

Spray solution pH and soybean injury as influenced by synthetic auxin formulation and spray additives

AbstractUse of synthetic auxin herbicides has increased across the midwestern United States after adoption of synthetic auxin-resistant soybean traits, in addition to extensive use of these herbicides in corn. Off-target movement of synthetic auxin herbicides such as dicamba can lead to severe injury to sensitive plants nearby. Previous research has documented effects of glyphosate on spray-solution pH and volatility of several dicamba formulations, but our understanding of the relationships between glyphosate and dicamba formulations commonly used in corn and for 2,4-D remains limited. The objectives of this research were to (1) investigate the roles of synthetic auxin herbicide formulation, glyphosate, and spray additives on spray solution pH; (2) assess the impact of synthetic auxin herbicide rate on solution pH; and (3) assess the influence of glyphosate and application time of year on dicamba and 2,4-D volatility using soybean as bioindicators in low-tunnel field volatility experiments. Addition of glyphosate to a synthetic auxin herbicide decreased solution pH below 5.0 for four of the seven herbicides tested (range of initial pH of water source, 7.45–7.70). Solution pH of most treatments was lower at a higher application rate (4× the labeled POST rate) than the 1× rate. Among all treatment factors, inclusion of glyphosate was the most important affecting spray solution pH; however, the addition of glyphosate did not influence area under the injury over distance stairs (P = 0.366) in low-tunnel field volatility experiments. Greater soybean injury in field experiments was associated with high air temperatures (maximum, >29 C) and low wind speeds (mean, 0.3–1.5 m s−1) during the 48 h after treatment application. The two dicamba formulations (diglycolamine with VaporGrip® and sodium salts) resulted in similar levels of soybean injury for applications that occurred later in the growing season. Greater soybean injury was observed after dicamba than after 2,4-D treatments.

The Effect of Different Doses of Tank-mixed Herbicides on Antioxidant Enzymes Activity of Soybean

Background: Herbicide plays the main role in guaranteeing the quantity and quality of food. Soybean reactive oxygen species scavenging system eliminates the herbicides’ side effects on the plant by activating antioxidant enzymes, which affects the yield. So, we investigated this procedure to reveal the effect of herbicides on food production. Methods: Experiments were carried out in two locations of Alborz province in 2014 during the growing seasons. Seven different tank-mixed herbicides were produced by mixing one triple mixture of imazethapyr+bentazon+sethoxydim active ingredient, three double mixture of imazethapyr+bentazon, imazethapyr+sethoxydim, and bentazon+sethoxydim, as well as single usage of imazethapyr, bentazon, and sethoxydim. Reduced herbicide rates were 100, 60, and 30% of the recommended dosage inducing soybean plots through leaf expanding phase. Results: Both herbicides and their reduced rates changed soybean yields through antioxidant enzymes’ activity. Maximum soybean yield was registered at tank-mixed imazethapyr+bentazom+ sethoxydim which were induced at 33, 320, and 125 g active ingredient/hectare, respectively. The minimum activity of enzymes (superoxide dismutase 3.9 international unit) was also demonstrated in this research. Our data showed that when the herbicide rate was reduced from 100% to 30%, as a result, the label recommended soybean yield was reduced by just 17%, while superoxide dismutase activity was reduced too. The minimum yield was 1.2 ton/hectare of sethoxydim with 225 g active ingredient/hectare. Conclusion: Antioxidant enzymes were promoted to maximum activity by increasing the herbicide rate for scavenging the herbicide side effects. Tank-mixed herbicides, with reduced herbicide rates can eliminate poison residue in the environment and food chain while increasing weed control.

How Do Intensification Practices Affect Weed Management and Yield in Quinoa (Chenopodium quinoa Willd) Crop?

Quinoa cultivation is well-adapted to sustainable cropping systems, even if seed yield could be severely limited due to several constraints, such as weeds. Field trials were performed in Gorgan (Iran) to quantify the effects of agro-ecological service crops (rye, CCr; winter vetch, CCw; and no cover, CC0), tillage regimes (conventional tillage, CT; and no-tillage, ZT), and herbicide rates (100% rate, H100; 75% rate, H75; and without herbicide, H0). Weed characteristics and quinoa yield were measured. Quinoa seed yield was the highest in CCw-ZT-H100. Seed yield in H100 and H75 were higher compared with H0 (2.30 vs. 1.58 t ha−1, respectively). Under conventional tillage, 46% of weed seeds were observed in the 0–10 cm soil layer and 54% in 10–20 cm soil layers, respectively, while, under no-tillage, about 63% of weed seeds were located up to 10 cm of soil. Amaranthus retroflexus L. was the most abundant species. The total weed density was the lowest in CCr-ZT-H100 and tended to be higher in CC0 (30.9 plant m−2) and under CT (29.0 plant m−2). These findings indicate that cover crops have potential for managing weeds in quinoa; however, their inclusion should be supported by chemical means to maintain high seed.

Characterization of rice cultivar response to florpyrauxifen-benzyl

AbstractMany factors such as environment, herbicide rate, growth stage at application, and days between sequential applications can influence the response of a crop to herbicides. Florpyrauxifen-benzyl is a new broad-spectrum, POST herbicide that was commercialized for use in U.S. rice production in 2018. Field experiments were conducted in 2018 at the Pine Tree Research Station (PTRS) near Colt, AR, and the Rice Research and Extension Center (RREC), near Stuttgart, AR, to evaluate crop injury and yield response of three rice cultivars to sequential applications of florpyrauxifen-benzyl. Greenhouse and growth chamber experiments were conducted at the Altheimer Laboratory in Fayetteville, AR, to evaluate cultivar responses when florpyrauxifen-benzyl was applied at 30 or 60 g ae ha−1 to rice exposed to different temperature regimes or at various growth stages. Three rice cultivars were used in all experiments: long-grain variety ‘CL111’, medium-grain variety ‘CL272’, and long-grain hybrid cultivar ‘CLXL745’. CL111 exhibited sufficient tolerance to florpyrauxifen-benzyl with only 10% visible injury and no effect on yield. CL272 showed 15% injury 3 wk after the second application in the field experiment when applications were made 14 d apart. Additionally, 12% injury was observed in greenhouse studies when florpyrauxifen-benzyl was applied at 30 g ae ha−1, averaged over various growth stages at application. Florpyrauxifen-benzyl did not reduce the yield of CL272 in field experiments, indicating that CL272 can recover from florpyrauxifen-benzyl injury. As much as 64% injury was observed for CLXL745 at 3 wk after application (WAA) when sequential herbicide applications were made 4 d apart. High levels of injury occurred in the growth chamber and greenhouse studies for this cultivar as well. Sequential applications of florpyrauxifen-benzyl reduced yields of CLXL745 in nearly all treatments. Data from these experiments suggest that CL272 and CLXL745 are sensitive to sequential applications of florpyrauxifen-benzyl. Growers must follow the prescribed guidelines for using florpyrauxifen-benzyl in these cultivars and others like it.

Role of nitrogen and herbicides in integrated management of mugwort (Artemisia vulgaris) in cool-season forage grasses

AbstractMugwort (Artemisia vulgaris L.) is becoming increasingly problematic in cool-season pastures and grasslands. A 3-yr field experiment evaluated different rates of nitrogen and herbicides for A. vulgaris management in a permanent grassland. The main plot had three nitrogen rates, 0, 62, and 124 kg N ha−1; the subplot had three herbicides, aminopyralid, clopyralid, and glyphosate; and the sub-subplot had three herbicide rates, aminopyralid (61, 122, and 244 g ae ha−1), clopyralid (140, 280, and 560 g ae ha−1), and glyphosate (552, 1,104, and 2,208 g ae ha−1). Results revealed that nitrogen had no effect on A. vulgaris control, rhizome biomass, and stem density. However, cool-season grass biomass was the highest (7,126 kg ha−1) in the plots that received 124 kg N ha−1 and 244 g ae ha−1 of aminopyralid. Only glyphosate caused grass injury, which varied from 65% to 100% depending upon application rate. By 9 mo after initial herbicide treatment (MAIT), A. vulgaris was controlled 60% to 98% with aminopyralid at ≥61 g ae ha−1 or glyphosate at ≥552 g ae ha−1. By 21 MAIT, aminopyralid at ≥122 g ae ha−1 or glyphosate at ≥1,104 g ae ha−1 resulted in >95% reduction in A. vulgaris stem density and rhizome biomass and provided ≥98% visual control. By 33 MAIT, complete control of A. vulgaris was confirmed in plots treated with aminopyralid at ≥122 g ae ha−1 or glyphosate at ≥1,104 g ae ha−1. Clopyralid was not effective; A. vulgaris control was <40% even after three annual applications at 560 g ae ha−1. Results indicate that integration of nitrogen fertilization with aminopyralid did not improve A. vulgaris control, but was advantageous in enhancing cool-season grass productivity.

Impact of reduced rates of 2,4-D and glyphosate on sweetpotato growth and yield

AbstractCommercialization of 2,4-D–tolerant crops is a major concern for sweetpotato producers because of potential 2,4-D drift that can cause severe crop injury and yield reduction. A field study was initiated in 2014 and repeated in 2015 to assess impacts of reduced rates of 2,4-D, glyphosate, or a combination of 2,4-D with glyphosate on sweetpotato. In one study, 2,4-D and glyphosate were applied alone and in combination at 1/10, 1/100, 1/250, 1/500, 1/750, and 1/1,000 of anticipated field use rates (1.05 kg ha−1 for 2,4-D and 1.12 kg ha−1 for glyphosate) to ‘Beauregard’ sweetpotato at storage root formation (10 days after transplanting [DAP]). In a separate study, all these treatments were applied to ‘Beauregard’ sweetpotato at storage root development (30 DAP). Injury with 2,4-D alone or in combination with glyphosate was generally equal or greater than with glyphosate applied alone at equivalent herbicide rates, indicating that injury is attributable mostly to 2,4-D in the combination. There was a quadratic increase in crop injury and quadratic decrease in crop yield (with respect to most yield grades) with increased rate of 2,4-D applied alone or in combination with glyphosate applied at storage root development. However, neither the results of this relationship nor of the significance of herbicide rate were observed on crop injury or sweetpotato yield when herbicide application occurred at storage root formation, with a few exceptions. In general, crop injury and yield reduction were greatest at the highest rate (1/10×) of 2,4-D applied alone or in combination with glyphosate, although injury observed at lower rates was also a concern after initial observation by sweetpotato producers. However, in some cases, yield reduction of U.S. no.1 and marketable grades was also observed after application of 1/250×, 1/100×, or 1/10× rates of 2,4-D alone or with glyphosate when applied at storage root development.

Dose response of yellow and white popcorn hybrids to glyphosate, a premix of 2,4‐D choline and glyphosate, or dicamba

AbstractPopcorn (Zea mays L. var. everta) is difficult to distinguish from field corn (Zea mays L. var. indentata) and is produced adjacent or in close proximity to field corn and soybean [Glycine max (L.) Merr.]. This creates a potential for misapplication or drift of herbicides used in nearby corn and soybean. Field experiments were conducted near Clay Center, Nebraska in 2017 and 2018 to determine the effect of glyphosate, 2,4‐D choline/glyphosate (premix), or dicamba on the growth and yield of popcorn. Treatments included nontreated control and four rates of glyphosate, 2,4‐D choline/glyphosate, or dicamba applied post‐emergence (POST) at five‐ or eight‐leaf (V5 and V8, respectively) popcorn growth stages to white and yellow popcorn hybrids. A three‐parameter log‐logistic model was fitted to treatment combination with varying herbicide rates. Glyphosate and 2,4‐D choline/glyphosate applied at V5 had greater injury, biomass reduction, height reduction, and yield loss than at V8. The two hybrids responded similarly to herbicides at most measurements. At the V8 application, 2,4‐D choline/glyphosate resulted in greater injury in the white hybrid; however, no hybrid differences in glyphosate sensitivity were observed at the V8 growth stage. Glyphosate and 2,4‐D choline/glyphosate at 0.25× rates resulted in complete plant death in both hybrids, whereas the highest dicamba dose (2×) caused 11% injury and no biomass reduction, plant height reduction, or yield loss. These results demonstrate the sensitivity of popcorn to glyphosate, 2,4‐D choline/glyphosate, or dicamba and can be of immediate educational use and practical implementation for popcorn producers, herbicide applicators, and agronomists.

Dissipation and phytotoxicity of imazethapyr and imazamox in soils amended with β-cyclodextrin-chitosan biocomposite

Use of imazethapyr and imazamox has been an environmental concern due to their high persistence, water solubility, residue build up and potential to injure the succeeding crops. Hence, it is necessary to develop effective decontamination technology. In present study, effect of β-cyclodextrin-chitosan biocomposite (LCD) amendment in soil on dissipation of imazethapyr and imazamox and their phytotoxicity on succeeding crop was evaluated. The influence of different experimental variables viz. extractant solution and its concentration, liquid to soil ratio, amount of soil and soil type on dissipation of imazethapyr and imazamox was assessed through chemical assays. Irrespective of herbicide formulation and application rate, amendment of soils with LCD increased the dissipation rate of herbicide and the residues were below the detection limit (<0.005 μg g−1) within 5 to 15 days in aridisol, entisol, inceptisol A, inceptisol B, inceptisol C and 7 to 21 days in alfisol and vertisol. Amendment of soils with LCD significantly reduced the growth inhibition of Brassica juncea (L.) Czern and improved the soil biological activity as evident from increase in dehydrogenase activity and soil bacterial count. Amendment of soils with LCD could be a promising, economically feasible and environmentally benign soil decontamination strategy for imazethapyr and imazamox contaminated soils.