Oilseed Rape Yield Performance in the Clearfield® System under Varying Management Intensities

Oilseed rape production is under pressure due to a limited availability of herbicides. Therefore, the performance in terms of management intensity (MI) and herbicide strategy (HS) and the involved yield formation was evaluated in a two-year Clearfield® oilseed rape field experiment. Furthermore, weed density and weed composition were also investigated. The variants of MI were standard sowing density (StS; seed rate: 50 seeds m−2, primary tillage: plow, row width: 12 cm), reduced sowing density (RD; seed rate: 25 seeds m−2, primary tillage: plow, row width: 50 cm), and strip-till (ST; seed rate: 25 seeds m−2, primary tillage: strip tillage, row width: 50 cm). The variants of HS were preemergence strategy (PES; application of dimethachlor, napropamide, clomazone in preemergence and application of prapaquizafop in postemergence) and Clearfield® strategy (CLS; application of imazamox, quinmerac in preemergence, no postemergence herbicide application). In the first year of the trial, there were no interactions between the factors in terms of grain yield. Grain yield in StS was 3.85 t and 5.2% significantly lower than in ST, and the value of RD was not significantly different from StS and ST. Grain yield in CLS was 3.7 t and 2.7% lower than in PES. In the second year of the trial, the grain yield in ST CLS was significantly lower, and there were no significant differences between the other variants. Higher weed emergence was observed in CLS RD (2.7 to 4 times higher weed density compared to PES RD) and CLS ST (2.8 to 4.5 times higher weed density compared to PES ST). No significant differences existed between StS PES and StS CLS in both trial years. The Clearfield® system offers significant advantages in the control of cruciferous weeds. Although these did not occur on the trial fields, the Clearfield® system in this study showed to be an alternative to the more common pre-emergence system, especially with regard to the parameter grain yield.

Allelopathic Potential of Rice Straw Incorporation on Weed Emergence in Rice Cultivars

Laboratory experiment was conducted to evaluate the effect of in corporation of rice straw on the germination of different rice cultivars viz: ADT 36,ADT 38,ADT49,CO43.Further the allelopathic impact of crop residues on weed count and weed biomass was also registered. Different rates of incorporation was tried and higher the rate of incorporation, higher the inhibitions on rice and weed observations. Reduction in the performance of rice seed germination and growth parameters was observed with increased rice straw incorporation in all the four rice cultivars tried. Perhaps the rice straw incorporation had an influence on the biomass of rice cultivars too. Supporting research evidences also reveals that allelopathic effect of rice straw on rice and weed performance can stand as a remarkable achievement for recycling rice straw in rice producing countries.

Weed emergence and seedbank after three years of repetitive shallow cultivation in a muck soil field

Frequent cultivation is often used to control weeds in crops such as lettuce. The efficacy of this technique on weed populations has been evaluated, but the effect on weed emergence and seedbanks is less documented. Studies in mineral soil indicate that soil disturbance can increase both weed emergence and seed persistence depending on where seeds are redistributed in the soil profile. Evaluations done in muck soil are scarce. This study evaluated the effect of two and four repetitive shallow (3.4 to 7.1 cm deep) cultivations on weed emergence and the weed seedbank in muck soil. Cultivation treatments (0, 2 and 4 cultivations using a inter-row rototiller) were done in lettuce plots from 2017 to 2019. Weed density was evaluated by species before each cultivation date and after crop harvest. Viable seedbanks were evaluated by collecting soil samples before and after each growing season and placing them in greenhouse flats. Statistical analyses were based on mixed models. Results showed that shallow cultivation modified the emergence patterns of weeds but did not reduce total emergence during the subsequent years or viable seedbanks. After two seasons without seed inputs, total emergence was reduced by 46.6% and the seedbank was reduced by 31.7% regardless of the cultivation treatment. However, the seedbank of the very abundant common purslane (<i>Portulaca oleracea</i>) remained high.

Extending the critical period for weed control model to better include weed succession using common sunflower as a mimic weed in high-yielding cotton

The critical period for weed control (CPWC) adds value to integrated weed management by identifying the period during which weeds need to be controlled to avoid yield losses exceeding a defined threshold. However, the traditional application of the CPWC does not identify the timing of control needed for weeds that emerge late in the critical period. In this study, CPWC models were developed from field data in high yielding cotton crops during three summer seasons from 2005 to 2008, using the mimic weed; common sunflower, at densities of 2 to 20 plants m−2. Common sunflower plants were introduced at up to 450 growing degree days (GDD) after crop planting and removed at successive 200 GDD intervals after introduction. The CPWC models were described using extended Gompertz and logistic functions that included weed density, time of weed introduction and time of weed removal (logistic function only) in the relationships. The resulting models defined the CPWC for late emerging weeds, identifying a period after weed emergence before weed control was required to prevent yield loss exceeding the yield-loss threshold. Where weeds emerged in sufficient numbers toward the end of the critical period, the model predicted that crop yield loss resulting from competition by these weeds would not exceed the yield-loss threshold until well after the end of the CPWC. These findings support the traditional practice of ensuring weeds are controlled before crop canopy closure, with later weed control inputs used as required.

Peanut Response to Flumioxazin and S-Metolachlor Under High Moisture Conditions

The United States produced $1.28 billion worth of peanuts in 2019 of which Georgia produced 51% of the total production (USDA-NASS 2021). Peanut is susceptible to weed competition due to slow canopy establishment, prostrate growth habit, and wide critical period for weed control from 3 to 8 weeks after planting (Burke et al. 2007; Everman et al. 2008). Georgia-06G is the dominant peanut cultivar planted in the southeast and in 2020, 87% of the acres grown for certified peanut seed available for sale to growers was Georgia-06G (Anonymous, 2020a). Peanut is commonly in rotation with cotton in the region and therefore, similar weed issues between these systems persist. This includes Palmer amaranth ( Amaranthus palmeri S. Watson) which has been documented to be resistant to multiple herbicide modes of action making its control difficult (Heap 2021). To minimize yield loss from weeds, preemergence (PRE) herbicides are frequently used in peanut to inhibit weed germination and provide residual weed control (Grichar et al. 2001). In response to resistance issues, producers have continued to integrate PRE herbicides into their herbicide programs to minimize weed emergence.

REVIEW OF THE INFLUENCE OF CROP ROTATION AND PRIMARY TILLAGE OPERATIONS ON WEED SEED BANK

In this study, we reviewed weed seed bank dynamic and main agriculture operations to come up with the weed seed management modeling designed to increase crop productivity by removing weed competition. Weed contributing with 10% loss of total global grain production. Weed seed bank regulate by five demographic processes seedling recruitment and survival, seed production, dispersal and seed survival in soil. The main agriculture operations that interference with weed seed bank are crop rotation and primary tillage. Tillage systems affect weed emergence, management, and seed production; therefore, changing tillage practices changes the composition, vertical distribution, and density of weed seed bank in agricultural soils. Weed species vary in their response to various crop rotations, due to the variability of weed-crop competition in their relative capacity to capture growth–limiting resources. Crop rotations affect weed emergence, management, composition, and density of weed seed bank. Finally, the study suggests elevating crop competitiveness against weeds, through a combination of crop rotation and reduce_ zero tillage, has strong potential to reduce weed-induced yield losses in crop.

Winter Weed Emergence during Carinata (Brassica carinata) Production

This publication provides information for predicting emergence timing of common winter weed species for carinata production. Written by Ruby Tiwari, Pratap Devkota, and Michael J. Mulvaney, and published by the UF/IFAS Agronomy Department, June 2021.

Influence of sugarcane straw on weed germination control

This research studied the effectiveness of herbicide treatments in weed control and during different periods of emergence, when applied to varying amounts of straw. The experiment was conducted in a greenhouse with pre-emergent herbicides: amicarbazone, metribuzin, indaziflam, isoxaflutole, amicarbazone + indaziflam, metribuzin + indaziflam, and isoxaflutole + indaziflam, against three species (Sorghum halepense, Rottboellia exaltata, and Mucuna aterrima). The experimental design was completely randomized in a 5x4 factorial scheme, with five amounts of straw (0, 1, 2, 3, and 5 t/ha) and four periods of weed emergence (0, 30, 60, and 90 days after treatments). The residual control of indaziflam was influenced by the amount of straw. Metribuzin presented a low residual control, while isoxaflutole was not affected by the amount of straw. Amicarbazone offered residual control for Mucuna aterrima. The association between indaziflam + isoxaflutole displayed a suitable residual control against Sorghum halepense and Rottboellia exaltata. The association of indaziflam + metribuzin adequately controlled Mucuna aterrima and Sorghum halepense. herbicide physical-chemical characteristics can influence their performance, and the association of products may increase residual and weed spectrum control. Highlights This partial or total removal of remaining sugarcane straw from the soil surface alters weeds dynamics in sugarcane fields. In this situation we have monocot and dicot weeds infesting the sugarcane crops. Among these species, some plants are even more difficult to control, such as Sorghum halepense, Rottboellia exaltata, and Mucuna aterrima Indaziflam herbicide presented a better performance in controlling monocotyledonous plants than eudicot plants. The herbicides amicarbazone and metribuzin presented adequate control of Mucuna aterrima despite having lower residual control. The association of indaziflam + metribuzin, resulted in satisfactory results for Mucuna aterrima, Sorghum halepense, and Rottboellia exaltata.

Establishing white clover (Trifolium repens) as a living mulch: weed control and herbicide tolerance

With the increasing focus on herbicide-resistant weeds and the lack of introduction of new modes of action, many producers have turned to annual cover crops as a tool for reducing weed populations. Recent studies have suggested that perennial cover crops such as white clover could be used as living mulch. However, white clover is slow to establish and is susceptible to competition from winter weeds. Therefore, the objective of this study was to determine clover tolerance and weed control in established stands of white clover to several herbicides. Studies were conducted in the fall and winter of 2018 to 2019 and 2019 to 2020 at the J. Phil Campbell Research and Education Center in Watkinsville, GA, and the Southeast Georgia Research and Education Center in Midville, GA. POST applications of imazethapyr, bentazon, or flumetsulam at low and high rates, or in combination with 2,4-D and 2,4-DB, were applied when clover reached 2 to 3 trifoliate stage. Six weeks after the initial POST application, a sequential application of bentazon and flumetsulam individually, and combinations of 2,4-D, 2,4-DB, and flumetsulam were applied over designated plots. Clover biomass was similar across all treatments except where it was reduced by sequential applications of 2,4-D + 2,4-DB + flumetsulam in the 2019 to 2020 season indicating that most treatments were safe for use on establishing living mulch clover. A single application of flumetsulam at the low rate or a single application of 2,4-D + 2,4-DB provided the greatest control of all weed species while minimizing clover injury when compared to the non-treated check. These herbicide options allow for control of problematic winter weeds during clover establishment, maximizing clover biomass and limiting canopy gaps that would allow for summer weed emergence.

Emergence Patterns of Winter and Summer Annual Weeds in Ethiopian mustard (Brassica carinata) Cropping System

Ethiopian mustard (Brassica carinata A. Braun) is a biofuel crop that was recently introduced in the southeastern United States. In order for this crop to be successful, there is a need to develop integrated weed management strategies that complement its rotation with summer cash crops. The objectives of this research were to evaluate the effect of previous season summer crops on winter weed emergence patterns during Ethiopian mustard growing season and to assess the impact of planting Ethiopian mustard on the emergence patterns of summer weed species. Gompertz models were fit to winter and summer weed emergence patterns. All models represented more than 80% of the variation with RMSE values less than 0.20. The emergence pattern for winter weed species was best described using Growing Degree Days (GDD) accumulation, and this model can be utilized for implementing weed control strategies at the critical Ethiopian mustard growth stages. The results also showed that summer weeds can emerge during the winter in northern Florida but do not survive frost damage, which might create off-season seed bank reductions before the summer crop growing season.