Revisiting the concept of the critical period of weed control

Weeds are a major biotic constraint to the production of crops. Studies on the critical period of weed control (CPWC) consider the yield loss due to the presence of all weeds present in the crop cycle. The CPWC is the time interval between the critical timing of weed removal (CTWR) and the critical weed-free period (CWFP), and the weed presence before and after the extremes of CTWR and CWFP may not significantly reduce crop yield. The crop yield is taken into consideration and weed density or biomass of individual weeds (annual or perennial) is not so important while calculating the CPWC. Only weed density or biomass is considered for calculating weed control efficiency of a particular management practice for which the weed seed bank is also a criterion. However, weed biomass is the outcome after competition experienced by each weed species with the fellow crop and the weeds. Consequently, the weed pressure in the subsequent season will be the cumulative effect of the preceding season too, which is unaccounted for in CPWC. It is argued that in organic farming or low-input farming systems, where herbicides are not used, the concept of CPWC can be misleading and should be avoided. It is concluded that CTWR is more meaningful than the CPWC.

Allelopathic Allelopathic impact of sorghum on weed management, yield and quality of maize under different seed rates

A field study was carried out to estimate the allelopathic potential of sorghum immature and mature plant extracts under various seed rates on weeds density and yield of maize cultivar Dadu Maize-I. The experiment contained of different weed control practices i.e., control (No weeding), various levels of sorghum immature and mature plant extracts, herbicides and hand weeding under various seed rates (20, 25, 30 & 35 kg per ha). The analysis of variance showed that various weed control practices demonstrated substantial decrease in weeds and caused increase in kernel yield over control. The application of sorghum immature extract @ 15 L per ha in combination with herbicide (Mesotrione Atrazine) @ 1.0 L per ha decreased effectively weed density (m-2) and dry biomass (g m-2) and resultantly produced superior growth and yield traits particularly kernel yield (t per ha) of maize. Sorghum mature plant extract @ 15 L per ha in integration with herbicide (Mesotrione Atrazine) @ 1.0 L per ha ranked 2nd in effectiveness of controlling weeds as well as increasing maize kernel yield (t per ha). As much as effect of seed rates is concerned, the least weed density (m-2) and greatest kernel yield (t per ha) were noticed in seed rate 35 kg per ha but optimal kernel yield (t per ha) was record in seed rate 30 kg per ha. Hence, the results suggested that combination of plant extracts and herbicide at reduced doses controlled weeds efficiently and optimum enhancement in kernel yield of maize was noticed at seed rate 30 kg per ha.

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.

Herbicide Efficacy of Spot Spraying Systems in Fallow and Postharvest in the Pacific Northwest Dryland Wheat Production Region

Real-time spot spraying technology has the potential to reduce herbicide costs and slow herbicide resistance. However, few studies exist on the efficacy of this technology in the Pacific Northwest (PNW). This research compared the herbicide efficacy (reduction in weed density and cover) of WEED-IT and WeedSeeker spot spraying systems to uniform spraying in fallow and postharvest in 2019 and 2020. Weed community types included naturally occurring weeds, natural + Russian thistle (Salsola tragus L.), or natural + kochia (Bassia scoparia (L.) A. J. Scott). Herbicides included glyphosate or the pre-mix bromoxynil + pyrasulfotole. Additionally, herbicide efficacy was studied with short stubble (~10 cm), tall stubble (~25 cm), and normal stubble (~20 cm) with chaff and straw removed. In fallow, herbicide efficacy was 1.5 times higher for uniform applications than for WEED-IT or WeedSeeker in 2019 and 2020. Herbicide efficacy was also 1.9 times higher for uniform applications in postharvest in 2019 but no differences were found in 2020. The weed community impacted herbicide efficacy but herbicide efficacy did not differ between residue management treatments. Finally, WEED-IT and WeedSeeker used 53% less herbicide volume in comparison to uniform applications. This research demonstrated that spot spraying technology can be efficacious and economical for growers in the PNW.

Evaluation of Alternative Pre-emergence Herbicides to Atrazine for Weed Control on Maize (Zea maysL.) plot in Ogbomoso, Southwest Nigeria

Field experiments were carried out at the Teaching and Research Farm of the LadokeAkintola University of Technology, (LAUTECH), Ogbomoso to evaluate the effectiveness and determine the optimum rate of applying alternative herbicides to atrazine on maize plots in view of the current criticism against the herbicide. Five herbicides, namely; 3-maize force, Xtra force, Pre-maize Guard force (solution and pellet) at two rates (100% and 50% recommended rates) were compared with atrazine at full dose and 3 hoe-weeding in a Randomized complete Block Experiment with 3 replications. Maize, Variety OBA Super, maturing in 75 days, was planted at two plants per stand at a spacing of 75 x 50cm in two-year trials and maintained following the standard procedures. The herbicides were applied using a knapsack sprayer calibrated to deliver at 200liters/ha. Results showed that there were no significant differences (p=0.05) among the treatment and between the treatments and control with respect to seed germination, plant survival and other growth parameters. The highest grain yield (6757.3kg/ha) obtained with atrazine was not significantly different from those of other treatments and control. The effectiveness of the herbicides, measured using weed density and biomass, showed comparable effectiveness across the herbicides and atrazine. Furthermore, at a dosage of 50%, the herbicide’s effectiveness was highly comparable to those of atrazine at 100%. The implications of these findings were discussed.

Effect of Crop Establishment Methods and Weed Management Practices on Weed Density and Productivity of Basmati Rice (Oryza sativa L.)

Aim: Present experiment was conducted to study the effect of crop establishment methods and weed management options on weed dynamics and performance of Basmati rice. Study Design: Split plot design. Place and Duration of Study: Iinvestigation was conducted during the kharif-season of 2019 and 2020 at Crop Research Center, S.V.P.University of Agriculture &Technology, Meerut (U.P.), India. Methodology: Mainfactors consist of the crop establishment methodsviz.(1) Conventional Puddled Transplanting, (2) Unpuddled Flat and (3) Furrow Irrigated Raised Beds, the sub factors consist of five weed management options viz., (1) Pretilachlor @ 0.75 Kg ha-1 PE fb Bispyribac sodium @ 20 g a.i. ha-1 POE at 20 DAT, (2) Almix 4 g a.i. ha-1 + Bispyribac sodium @ 20 g a.i. ha-1 POE at 20 DAT, (3) Bispyribac sodium @ 25 g a.i. ha-1 POE at 20 DAT, (4) Two hand weedings and (5) Weedy check. Results: Minimum total weed density was recorded under CPT (E1) followed by FIRB(E3) while itwas maximum under UPF(E2). Two hand-weedings effectively reduced total weed density. In herbicides, application of pretilachlor @ 0.75 Kg ha-1fb Bispyribac sodium @ 20 g a.i. ha-1 (W1) was found most effective in reducingtotal weed density.Higher yield and yield attributes were found under CPT which was significantly higher than the UPF and at par with FIRB. Amongweed management practices highest yield and yield attributes were obtained with pretilachlor @ 0.75 Kg ha-1fb Bispyribac sodium @ 20 g a.i. ha-1.Lowest yield and yield attributes were obtained in weedy check. Conclusion: Puddled transplantation in rice might be the best option to get higher yield and for weed control, application of Pretilachlor @ 0.75 Kg ha-1 PE fb Bispyribac sodium @ 20 g a.i. ha-1 POE at 20 DAT may be done to get higher yield.

EVALUATION OF BIO EFFICACY AND PHYTO TOXICITY EVALUATION OF INDAZIFLAM 500 SC IN ACID LIME

Field experiments were conducted to evaluate the bio efficacy and phyto toxicity of Indaziflam 500 SC in acid lime at Central Block, Horticultural College and Research Institute, Periyakulam during kharif and rabi seasons of the years 2017 and 2018. Experiments were carried out in Randomized Block Design with ten treatments and replicated thrice. Indaziflam 500 SC was sprayed as pre emergence as well as combination with post emergence herbicides in acid lime before the onset of South West Monsoon and North East Monsoon at kharif and rabi seasons respectively. Indaziflam 500 SC either alone or in combination with post emergence herbicide was completely dissolved while making stock solutions. There were no phyto toxicity symptoms on acid lime at higher doses of pre emergence application and combination with post emergence application of Indaziflam 500 SC. Pre emergence application of Indaziflam 500 SC @ 62.5 g a.i./ha recorded significantly lower no. of weed density on 30, 60, 90 and 120 DAA during both the seasons. Increased weed density was observed in untreated control at all stages of crop growth during both the seasons. Pre emergence application of Indaziflam 500 SC @ 62.5 g a.i./ha recorded significantly lower weed DMP at 90 DAA during both the seasons of the study followed by pre emergence application of Indaziflam 500 SC @ 50 g a.i./ha and resulted in higher weed control efficiency at all stages of observation. Significantly higher acid lime fruit yield of 12.45 and 13.85 t/ha was recorded with hand weeding during kharif and rabi respectively due to weed free condition maintained during entire growth stage of the crop and it was followed by pre emergence application of Indaziflam 500 SC @ 62.5 g a.i./ha.

Особенности статуса борщевика сосновского в Украине и характеристика ликвидации опасного вида сорняка в Черновицкой области

The pest risk analysis (PRA) was carried out for Sosnowsky’s hogweed to determine the ability of the species to be a quarantine object by analyzing the available scientific data. According to the results of the PRA, Sosnowsky’s hogweed can be classified as a regulated weed and socially dangerous to human and animal health, highly aggressive in spread, and extremely difficult to eradicate in many areas, where it is widespread in small numbers. It allows to apply measures to it as for any quarantine plant: to control its appearance and completely eradicate it’s entry source. The results of developed method have been proposed using the example of town Chernivtsi. Weed density have decreased from 47,8 and 43,5 plants to 4,8 and 1,2 plants on 1 m2 in a number of hotbeds. These measures allowed to decrease the quantity of Sosnovsky’s hogweed in some hotbeds by more than 25 times.

Response of Cowpea [Vigna unguiculata (L.) Walp.] as Succeeding Crop to Residual Effect of Extreme Levels of Atrazine Administered in Preceding Maize (Zea mays L.)

Background: Globally, grain legumes are the paramount family of agricultural crops following cereals. Generally, sequence cropping has manifested effectual in increasing farm productivity and profitability. However, sometimes herbicides administered in previous crop may be associated with phytotoxic effects that can later cause damage to the succeeding crops. The present study aimed to understand the residual effect of extreme levels of atrazine on succeeding cowpea under maize-cowpea cropping system. Methods: Field experiments were conducted during Kharif and rabi season of 2019-20 and 2020-21 in a randomized block design with eleven treatments, replicated thrice. Result: Residual effect of pre-emergence atrazine at 0.50 kg a.i. ha-1 followed by tembotrione at 120g a.i. ha-1 as post-emergence at 25 DAS recorded the lowest total weed density (4.41), total weed dry weight (9.81 g m-2) and highest weed control efficiency (39.25%) during rabi 2019-20 while during rabi 2020-21 lowest total weed density (5.03), total weed dry weight (10.68 g m-2) and highest weed control efficiency (39.65%) were noticed in pre-emergence atrazine 50% WP at 2.00 kg a.i. ha-1. Highest seed yield (788.67 and 842.33 kg ha-1) was obtained in weed free treatment.