Preemergence Treatments Research Articles

Dissipation dynamics of terbuthylazine in soil during the maize growing season.

Ever since terbuthylazine (TBA) replaced atrazine in herbicide crop treatment, its much greater persistence has raised considerable environmental concern. The aim of our field experiment was to establish the dissipation dynamics of TBA and its degradation product desethylterbuthylazine (DET) in soil over five months of maize growth. We applied TBA as part of pre-emergent treatment in the regular and double-the-regular amounts. Soil samples were collected periodically at the following depths: 0-10 cm, 10-20 cm, 20-30 cm, and 30-50 cm. For TBA and DET soil residue analysis we used microwave-assisted extraction with methanol, followed by HPLC-UV/DAD. Regardless of the application rate, more than 80 % of the applied TBA dissipated from the first 50 cm of soil in the two months after herbicide application and 120 mm of rainfall. Three months later (at maize harvest), less than 4 % of total TBA remained in the soil, mostly in the top 20 cm rich with organic carbon on which TBA is likelier to adsorb. The loss of TBA from soil coincided with the rise in DET, especially the top soil layers, during the periods of low rainfall and highest soil temperatures. This points to biodegradation as the main route of TBA dissipation in humic soils. The applied amount had no significant effect on TBA dissipation in the top (humic) layers, but in the layers with less than 1 % of organic carbon, it was higher when the doublethe- regular dose was applied.

Optimising Clearfield and ExpressSun sunflower technologies for Central European conditions

The efficacy and selectivity of herbicides and tank-mix combinations at different application terms in Clearfield and ExpressSun sunflowers were evaluated. Five-plot field trials (2011–2015) were carried out in Prague. The efficacy of tribenuron (TBM) was excellent and quite rapid on Chenopodium album. Its efficacy on other tested dicot weeds ranged around 90%, depending on weather conditions and growth stages of weeds. Echinochloa crus-galli was not controlled by TBM. The tank-mix combination of TBM + propaquizafop (PQF) caused sunflower injury when applied in a very cold growing period. Under dry conditions, PQF efficacy on E. crus-galli was strongly reduced. The split application of TBM, when PQF was used at the second application, was less negatively affected by herbicide antagonisms. Very good results were obtained on plots with pre-emergence treatment with dimethenamid and post-emergence with TBM. The efficacy of imazamox (IZM) on dicot weeds was strongly affected by growth stages of weed and weather conditions during application. Efficacy of IZM on E. crus-galli was increased by oil adjuvant, but this adjuvant reduced IZM selectivity. The best efficacy, selectivity, and Clearfield sunflower yield were on plots with the split application of IZM.

Best timing for glyphosate treatments and possible combinations with pre and post-emergence weed control practices in no-till maize

Use of reduced and no-tillage systems has increased in recent years due to concerns for ecological and economic sustainability of agricultural production. Effective weed control is a serious concern in reduced tillage production. This study was conducted to investigate weed control practices in reduced and no-till maize production. The most effective timing of glyphosate application, either before or after sowing, was investigated in combination with pre-emergence application of acetochlor (840 g a.i/L), post-emergence application of foramsulfuron (22.5 g a.i/L), and two hoeing treatments. The treatments were maintained on the same plots during 2011 and 2012 to evaluate the cumulative effects of the treatments. Main plot treatments consisted of four timings of glyphosate application: 20 or 10 days before sowing, day of sowing, 5 days after sowing, and an untreated control. Sub-plot treatments were: pre- plus post-emergence herbicides, pre-emergence herbicide plus rotary hoeing, post-emergence herbicide plus rotary hoeing, and post-emergence herbicide plus two hoeing treatments (rotary and lister hoe). In the main plots, the lowest weed biomass was produced in glyphosate treatments at sowing and 5 days after sowing; the highest biomass was produced in control plots and in the plots with glyphosate treatments 20 days before sowing. In the sub-plots, the greatest weed biomass was produced in plots with two hoeing treatments (rotary and lister hoe). Glyphosate treatments at sowing and post-emergence herbicide treatment combinations produced the best weed control. Economic analysis revealed that pre-sowing, non-selective herbicide treatments provided a slight increase in net profit. Mechanical hoeing decreased net income due to increased production costs. The highest income was obtained from the pre-emergence plus post-emergence herbicide treatment combinations with no glyphosate.

Weed Response to Agronomic Practices and Herbicide Strategies in Grain Sorghum

Core Ideas High sorghum density and narrow row spacing reduce biomass of troublesome weeds. High spatial crop uniformity extends large crabgrass and sicklepod control over time. Optimized crop density and row width may limit the need for postemergence herbicide in sorghum. Sicklepod [Senna obtusifolia (L.) H.S. Irwin & Barneby] and large crabgrass (Digitaria sanguinalis L.) are ranked among the top 10 most common or troublesome weeds in grain sorghum [Sorghum bicolor (L.) Moench] in the southeastern United States. Field studies conducted in North Carolina from 2012 to 2014 investigated the effects of three row widths, four sorghum populations, and three herbicide programs on weed control, density, biomass, and grain yield. Results indicated that 19‐ and 38‐cm rows provided greater sicklepod control 7 and 10 wk after planting (WAP) compared to 76 cm but had no effect on crabgrass control. Under weed‐controlled conditions, sorghum population ≥297,000 plants ha−1 allowed to maintain higher late‐season sicklepod and crabgrass control as compared to lower crop densities. In the weedy control, row spacing had no effect on weed density and biomass, whereas crop population ≥297,000 plants ha−1 reduced sicklepod density and biomass by 38 and 65%, respectively, compared to 99,000 plants ha−1. Effect on crabgrass was less pronounced with density and biomass reduction by 18 and 45%, respectively, for 396,000 plants ha−1 compared to 99,000 plants ha−1. In the absence of water stress, the highest grain yields were obtained with high spatial uniformity, corresponding to 19‐cm rows and sorghum population ≥297,000 sorghum plants ha−1. Our results indicate that increased sorghum density associated with narrow rows may reduce the need for a postemergence (POST) herbicide but underscore the importance of a timely activated preemergence (PRE) treatment to efficiently control sicklepod and crabgrass.

Herbicide Programs for Annual Bluegrass (Poa annua L.) Control in Nebraska

Core Ideas Research done on annual bluegrass (ABG) control in other areas of the US are likely applicable to Nebraska. However, extreme weather can dramatically affect short‐term annual bluegrass cover and emphasize the need for long‐term control studies. Three fall POST applications of mesotrione plus prodiamine applied preemergence in August and/or November were effective for ABG control in Kentucky bluegrass fairways. Replacing mesotrione with ethofumesate was also effective when combined with prodiamine in August and November. June applications of bispyribac‐sodium at 4 oz/ac was highly effective for controlling ABG in creeping bentgrass fairways, and adding two more fall applications at the same rate improved control slightly, but there was no benefit to raising the rate to 6 oz/ac. Annual bluegrass (Poa annua L.) (ABG) is common in golf courses, and its control has been thoroughly researched in cool‐season turf east of the Mississippi River in the United States. However, ABG response to herbicides varies widely among environments and/or biotypes, and little ABG control research has been done in the northern Great Plains. Therefore, our objective was to validate ABG herbicide control systems in golf course fairways of Kentucky bluegrass (Poa pratensis L.) (KBG) or creeping bentgrass (Agrostis stolonifera L.) (CBG) in Nebraska. Preemergence (PRE) treatments of prodiamine or mesotrione were applied in late summer over 3 yr with or without fall postemergence (POST) treatments of mesotrione or ethofumesate for ABG control in a low‐mow KBG fairway. We also evaluated rate and frequency of bispyribac‐sodium applications with or without a late summer–applied PRE (dithiopyr) in early September for ABG control over 3 yr in a CBG fairway. Our research indicates that ABG control work done in other areas are likely applicable to Nebraska. Three fall POST applications of mesotrione plus prodiamine applied as a PRE in August and/or November was effective for ABG control in KBG fairways. Replacing mesotrione with ethofumesate was also effective when combined with prodiamine in August and November. June applications of bispyribac‐sodium at 4 oz/ac were highly effective for controlling ABG in CBG fairways, and adding two more fall applications at the same rate improved control slightly, but there was no benefit to raising the rate to 6 oz/ac. Lastly, extreme weather in one summer and one winter dramatically affected short‐term ABG cover and emphasized the need for long‐term control studies in areas with dramatic weather cycles.

Design, synthesis and evaluation of novel cis-p-menthane type Schiff base compounds as effective herbicides

p-Menthane type monoterpene derivatives were identified as bio-based compounds with high herbicidal activities. In order to search novel p-menthane type monoterpene derivatives in good performance, a series of novel cis-p-menthane type Schiff base derivatives were designed and synthesized. All target products were easily available novel compounds and characterized by FT-IR, 1H NMR, 13C NMR and ESI+-MS. Their pre-emergence herbicidal activities against annual ryegrass were evaluated. The bioassays indicated that most of the target compounds displayed excellent herbicidal activities in pre-emergence treatment.

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Field experiments were conducted in two seasons at the farm of Sokoine University of Agriculture in Morogoro, Tanzania (6.85°S; 37.64°E and 568 m.a.s.l.) during the short rain (November 2014 to January 2015) and the long rain (March to June 2015). The experiment was a split plot in randomized complete block design (RCBD) with 4 replicates. Weed management practices (herbicides, hoe weeding (3x) and weedy) were the main plot treatments; four rice genotypes (NERICA-1, NERICA-4, NERICA-7 and Mwangaza) were the subplots. Significant differences (P<0.05) were recorded on weed counts. Dominant weed groups as determined by Summed Dominance Ratio (SDR) in both experiments were broadleaf species (50.8%), sedges (25.2%) and grasses (24.0%). Post-emergence (8.6%) and hoe weeding (12.3%) significantly reduced weed dry biomass as compared to pre-emergence (17.8%) and weedy (61.3%) treatments in both experiments, respectively. Significant differences (P<0.05) were recorded among the rice variables. Data showed that Mwangaza and NERICA-1 had the tallest and shortest plant height (129.8 and 39.1 cm), respectively in both experiments. The highest and lowest tiller (35.3 and 7.5 m2) count was recorded for both these genotypes, respectively. The lowest and highest LAI (2.5 and 4.5) were recorded on Mwangaza and NERICA-7 respectively; and NERICA-7 had the highest and lowest straw biomass (1603 and 305.1 g/m2) in both experiments. The highest rice grain yield were recorded for NERICA-1 on hoe weeded plots and plots applied with post-emergence herbicide (2187.5 and 1562.5; 4176.1 and 4630.6 kg/ha) as compared to plots applied pre-emergence herbicide and weedy plots (965.9 and 0.0; 3323.8 and 0.78 kg/ha) in 2014/2015 and 2015 experiments, respectively. The highest return on investment, 3 352 846 Tanzanian shillings (Tshs) was obtained on NERICA-1 in post-emergence herbicide plots, and this was also similar (P<0.05) to hoe weeded plots. Post-emergence herbicide was also effective in weed control and had significant effect on profit analysis. This treatment/practice should be used in combination with hoe weeding under integrated weed management for better weed control. Key words: Weeds, management, upland rice, yields, growth, profitability.

Synthesis and herbicidal activity of N-(2,2-dimethyl-7-alkoxy-2,3-dihydrobenzofuran-5-yl)-2-(4-arylxoyphenoxy)propionamides

In order to find novel herbicidal active compounds, a series of N-(2,2-dimethyl-7-alkoxy-2,3-dihydro-benzofuran-5-yl)-2-(4-arylxoyphenoxy)propionamides was designed, prepared and evaluated for their herbicidal activity. Bioassay results showed that most of the title compounds had excellent and selective herbicidal activity against the monocotyledonous grasses. In particular, compounds 1g and 1m showed 100% inhibition against the growth of three monocotyledonous grasses under both postemergence and preemergence treatments at the dose of 2250 g/hm2 (1 hm2=104 m2), and could be used as lead compounds for further development of novel potential herbicidal agents.

Palmer Amaranth (Amaranthus palmeri) Control with Preplant Herbicide Programs Containing Dicamba, Isoxaflutole, and 2,4‐D

Glyphosate‐resistant (GR) Palmer amaranth (Amaranthus palmeri S. Wats.) prevalence in Midwest soybean [Glycine max (L.) Merr.] production has increased in recent years. New soybean herbicide‐resistant traits will be important management tools for herbicide‐resistant weeds. The objectives of this research were to evaluate preemergence (PRE) herbicide treatments that contain dicamba, isoxaflutole, metribuzin, S‐metolachlor, and 2,4‐D for GR Palmer amaranth control. Herbicide programs that contained isoxaflutole provided 58 to 95% control compared with 41 to 85% control by 2,4‐D or dicamba. Control of GR Palmer amaranth with mixtures containing dicamba ranged from 71 to 85% compared with 41 to 53% control with mixtures of 2,4‐D. Treatments containing one herbicide mode of action (MOA) failed to provide more than 57 and 50% GR Palmer amaranth control at 21 and 42 days after the preemergence treatment (DAPT), respectively. A mixture that contained three herbicide MOA (metribuzin plus S‐metolachlor mixed with dicamba, isoxaflutole, or 2,4‐D) controlled GR Palmer amaranth 83 to 86% compared with a treatment with a single MOA that provided 31 to 50% control. Coapplication of metribuzin with dicamba, isoxaflutole, or 2,4‐D resulted in 67 to 72% control, while mixtures of S‐metolachlor with dicamba, isoxaflutole, or 2,4‐D provided 63 to 91% GR Palmer amaranth control. In most instances mixtures with two MOA resulted in GR Palmer amaranth control that was similar to mixtures with three MOA at 42 DAPT.

Strip Tillage and Early-Season Broadleaf Weed Control in Seeded Onion (Allium cepa)

Field experiments were conducted in 2007 and 2008 near Oakes, North Dakota (ND), USA, to evaluate if strip tillage could be incorporated into a production system of seeded onion (Allium cepa) to eliminate the standard use of a barley (Hordeum vulgare) companion crop with conventional, full width tillage, yet support common early-season weed control programs. A split-factor design was used with tillage (conventional and strip tillage) as the main plot and herbicide treatments (bromoxynil, DCPA, oxyfluorfen, and pendimethalin) as sub-plots. Neither tillage nor herbicide treatments affected onion stand counts. Common lambsquarters (Chenopodium album) densities were lower in strip tillage compared to conventional tillage up to three weeks after the post-emergence applied herbicides. In general, micro-rate post-emergence herbicide treatments provided greater early-season broadleaf weed control than pre-emergence herbicide treatments. Onion yield and grade did not differ among herbicide treatments because the mid-season herbicide application provided sufficient control/suppression of the early-season weed escapes that these initial weed escapes did not impact onion yield or bulb diameter. In 2007, onion in the strip tillage treatment were larger in diameter resulting in greater total and marketable yields compared to conventional tillage. Marketable onion yield was 82.1 Mg ha−1 in strip tillage and 64.9 Mg ha−1 in conventional tillage. Results indicate that strip tillage use in direct-seeded onion production was beneficial, especially when growing conditions were conducive to higher yields and that the use of strip tillage in onion may provide an alternative to using a companion crop as it did not interfere with either early-season weed management system.

Synthesis and herbicidal activity evaluation of novel α-amino phosphonate derivatives containing a uracil moiety.

A series of novel α-amino phosphonate derivatives containing a uracil moiety 3a-3l were designed and synthesized by a Lewis acid (magnesium perchlorate) catalyzed the Kabachnik-Fields reaction. The bioassays {in vitro, in vivo [Glass House 1 (GH1) and Glass House 2 (GH2)]} showed that most of compounds 3 exhibited excellent and selective herbicidal activities; for example, in GH1 test, compounds 3b, 3d, 3f, 3h and 3j showed excellent and wide spectrum herbicidal activities at the dose of 1000 g/ha, and compounds 3b and 3j exhibited 100% inhibition activities against the four plants in both post- and pre-emergence treatments. Moreover, most of compounds 3 showed higher inhibition against Amaranthus retroflexus and Digitaria sanguinalis than Glyphosate did in pre-emergence treatment. In GH2 test, the four compounds (3b, 3d, 3h and 3j) exhibited 100% inhibition against Solanum nigrum, Amaranthus retroflexus and Ipomoea hederacea in post-emergence treatment and displayed 100% inhibition against Solanum nigrum, Amaranthus retroflexus in pre-emergence treatment at the rate of 250 g/ha, and compound 3b showed the best and broad spectrum herbicidal activities against the six test plants. However, the four compounds displayed weaker herbicidal activities against Lolium perenne and Echinochloa crus-galli than the other four plants at the rate of 250 g/ha in both pre- and post-emergence treatments. So, compounds 3 can be used as a lead compound for further structure optimization for developing potential selective herbicidal agent. Their preliminary structure-activity relationships were also investigated.

Invasion of Different Weeds on Gladiolus and their Control by Herbicides

Weeds are defined as plants growing where they are not desired. Presence of weeds highly effects the growth and development of desirable plants. Present study was carried out at Floriculture Research Area, University of Agriculture Faisalabad. The experiment was laid out in randomized complete block design with three replications. Five herbicide treatments were applied in three replications to the gladiolus variety “white prosperity”. By comparing results of pre and post emergence herbicide applications, it was observed that pre emergence treatments gave better results regarding weed control due to reduced competition between weed plants and crop plants. Pendimethalin applied at 12ml/litre was found to be the most effective treatment and controlled all weeds except Cyperus rotundus . Average number of plants and weed inhibition percentage of Cyperus rotundus in one foot square area were, 15.22 (39%), Convolvulus arvensis , 0.89 (77%), Coronopus didymus , 0.33 (91%), Chenopodium album , 0.22 (98%), Anagallis arvensis , 0.22 (98%), Conyza stricta , 0.89 (85%), Stellaria media , 0.22 (98%), Poa annua , 0.0 (100%), Melilotus indica , 0.22 (98%). Study revealed that Cyperus rotundus was efficiently controlled by S metolachlore than Pendimethalin where only average (2.22) numbers of plants were found in one square foot area and best weed inhibition percentage was upto (91%) for Cyperus rotundus.

THE EFFECT OF DICAMBA ON PEANUT WHEN APPLIED DURING VEGETATIVE GROWTH STAGES

Abstract The development of dicamba-resistant cotton and soybean cultivars has created great concern about the potential off-target movement of dicamba onto sensitive broadleaf crops. Peanut is often grown in close proximity to cotton and soybean. Therefore, field studies were conducted during 2012 and 2013 at Plains, Ty Ty, and Attapulgus, GA to evaluate peanut response to dicamba rates 35, 70, 140, 280, and 560 g ae ha-1 applied at preemergence (PRE), 10, 20, or 30 d after planting (DAP) corresponding to PRE, V2, V3, and V5 peanut growth stages, respectively. Nontreated controls were included for comparison. Location by rate (P < 0.0002) and location by treatment timing (P < 0.004) interactions were significant. As dicamba rate increased peanut injury and yield loss increased. There was variation in peanut response by location after PRE treatments. Plains peanut was injured less among locations, possibly due to the Greenville soil there having higher organic matter and clay contents at 3.8 and 30%, resp...

FIELD BINDWEED MANAGEMENT IN DRIP IRRIGATED PROCESSING TOMATOES

Subsurface drip irrigation in processing tomatoes (Solanum lycopersicum) has been rapidly adopted in California over the past decade, and is now used on approximately 90% of the production area. The economic necessity of maintaining the beds and replanting with only minimal tillage for multiple seasons has created a system where field bindweed (Convulvulus arvensis) has become more prevalent. Beginning in 2011, field studies were conducted at University of California Davis campus to evaluate the efficacy of registered herbicide combinations in controlling established field bindweed in processing tomatoes; parallel studies were conducted at the UC West Side Research and Extension Center using drip irrigation. The treatment design was a randomized block split-plot with four replications. Main plots consisted of pre-emergent and pre-plant incorporated (PPI) applications of pendimethalin, trifluralin, sulfentrazone, and rimsulfuron at label rates. Split-plot treatments were post-emergent applications of rimsulfuron or carfentrazone, applied after transplanting to emerged bindweed. Concurrently, additional herbicide treatment combinations included sequential post applications of rimsulfuron, carfentrazone, or carfentrazone + glyphosate; trifluralin applied PPI and again at lay-by, sulfentrazone + S-metalochlor PPI, trifluralin + S-metalochlor + rimsulfuron combination, as well as untreated and hand weeded controls. Overall, trifluralin was the most effective pre-emergence treatment for suppressing established field bindweed, however, this effect was not significantly different than the other treatments or the untreated control by the end of the season. Post-emergent applications of rimsulfuron and carfentrazone significantly improved bindweed control about 21% in most instances. The combination of trifluralin PPI and either rimsulfuron or carfentrazone applied post emergence, or applying trifluralin both pre and at layby, have been the best treatments for controlling field bindweed in these trials, with bindweed control of 50-80% compared to the untreated control. No significant differences were noted for tomato crop growth or yield; however, concerns remain about this herbicide program for its potential crop phytotoxicity and plant-back restrictions.

Design, Synthesis and Biological Activity of Novel Sulfonylurea Derivatives Containing Dimethoxymethyl-substituted Pyrimidine Moiety†

Acetolactate synthase( ALS) has been regarded as an attractive target for fungicide and herbicide discovery. Furthermore,sulfonylurea( SU) as one of the most active ALS inhibitors were used as herbicides in crops protect. In order to discuss the multi-biological activity of SU,two series of novel SU derivatives containing phenyl-substituted pyrimidine moiety were designed,synthesized and their antifungal activity and herbicidal activity were evaluated. The bioassay results indicated that some title compounds showed excellent antifungal activity against Physalospora piricola and Rhizoctonia cerealis in vitro at the dosage of 50 mg / L. Particularly,compound 9f exhibited more than 65% inhibitory activity against five phytopathogens. On the basis of advanced screening test,the EC50 value of compound 8f against P. piricola was 8. 63 mg / L,which was a little higher than Chlorothalonil( EC50= 7. 33 mg / L),the EC50 value of compounds 8k( 5. 48 mg / L) and 9k( 6. 09 mg / L) against R. cerealis were similar to Chlorothalonil( EC50= 4. 26 mg / L). In addtion,the title compounds showed favorable pre-emergence treatment herbicidal activity against Brassica napus and Amaranthus retroflexus at the dosage of 75 g / ha. For example,compounds 8d and 9d showed 86% and 73% inhibition activity respectively against Brassica napus; compound 9h exhibited 100% herbicidal activity against Amaranthus retroflexus,which was better than that of Chlorsulfuron( 96%). The results provided useful information for designing new SU with highly fungicidal activity and herbicidal activity.

Weed Control in Irrigated Corn with Combinations of Corvus, Balance Flexx, Capreno, Laudis, Harness, Atrazine, Glyphosate, Dual, and Diflexx

Most preemergence treatments followed by postemergence treatments provided better Palmer amaranth control than preemergence treatments alone or early postemergence treatments alone (Table 2). The better treatments provided good control of Palmer amaranth, kochia, Russian thistle, crabgrass, green foxtail, and shattercane. All treatments elevated yield over the untreated control.

Glutathione-Responsive Carboxymethyl Chitosan Nanoparticles for Controlled Release of Herbicides

Glutathione-responsive carboxymethyl chitosan nanoparticles cross-linked with disulfide bonds were developed for controlled release of herbicides. The nanoparticles were synthesized by selfassembly of amphiphilic carboxymethyl chitosan derivative (CMCS-MUA) in aqueous solution and subsequently producing disulfide cross-linking bonds by ultrasonic treatment. TEM showed that the nanoparticles had a spherical core-shell configuration with a size of about 250 nm. Assessment of stability of the nanoparticles (considering mean diameter, polydispersity, and Zeta potential) was conducted over a period of three months, and the nanoparticles were found to be stable in solution. Herbicide-loaded nanoparticles were prepared using diuron as a model herbicide. In vitro release study revealed that diuron can be released from nanoparticles in a controlled manner depended on the glutathione concentration. Herbicidal activity assays performed with preemergence treatment of target species (Echinochloa crusgalli) showed the effectiveness of diuron- loaded nanoparticles. Assays with nontarget species (Zea mays) showed that the diuronloaded nanoparticles did not affect plant growth. The results indicate that the glutathioneresponsive nanoparticles prepared in this work will be a promising candidate for controlled release of herbicides in agriculture.

Sequential Treatments of Rimsulfuron, Mesotrione, Thifensulfuron, Balance Flexx, Cinch, Cinch ATZ, and Prowl H2O Mixtures for Weed Control in Irrigated Corn

No treatment with less than 1.5 lb/a atrazine provided commercially acceptable Palmer amaranth control. The best level of Palmer amaranth control was produced by treatments that had good preemergence control augmented by a postemergence application with two or more modes of action that contained 0.5 lb/a atrazine. All treatments provided excellent kochia control. The best Russian thistle treatments provided from 77 to 88% control. The best foxtail or crabgrass treatments provided from 91 to 94% control. Combinations of preemergence treatments followed by a postemergence treatment achieved excellent shattercane control.

Effect of sequential application of metribuzin on selectivity and weed control in soybean

Post-emergence treatments are often the keys to efficient weed control, and could be a substitute or supplementary to pre-emergence treatment. Accordingly, this study was designed to test the selectivity and efficacy of sequential (pre- + post-emergence) applications of metribuzin on weeds in soybean, and to optimize the dose, volume rate and time of application. We observed that sequential metribuzin treatments were more toxic to soil micro-organisms and caused greater inhibition in photosynthesis, acetylene reduction activity and nodulation of soybean compared to only pre-emergence applications of metribuzin or pendimethalin. The negative effects, however, were mitigated by increased activities of superoxide dismutase and ascorbate peroxidase in soybean. The sequential applications left negligible residues at harvest. A sequential application of metribuzin 0.25 kg ha−1 2 days after sowing and 0.1 kg ha−1 20 days after sowing with 200 Lha−1 of water gave a higher seed yield. This ensured the possibility of sequential application of metribuzin with an optimized dose, volume rate and time of application.

Phytotoxicity levels in a wet year in an experiment on maize sensitivity to herbicides

The phytotoxic effects of herbicides applied pre-, early post- and post-emergence were studied in maize in a herbicide sensitivity experiment were set up in Martonvásár and Törökszentmiklós. The herbicides were applied in normal and in double doses to 37 Martonvásár inbred lines and to six parental single crosses. The small-plot experiments were set up in two replications. The wet weather that followed the pre- and early post-emergence treatments promoted the appearance of phytotoxic symptoms on maize. The degree of phytotoxicity was recorded on the 14th day after post-emergence treatment and on the 14th and 28th days after the pre- and early postemergence treatments. Herbicides applied pre-emergence only caused slight symptoms on maize. Although the double dose increased the damage, it was still not more than 5% on average. The symptoms caused by herbicides applied in the early post-emergence stage were more intensive than those detected in the pre-emergence treatments. However, the damage caused by the double dose of isoxaflutol + thiencarbazone-methyl and by the split treatment with nicosulfuron remained below 10%. The symptoms became somewhat more severe at the 2nd scoring date. Among the post-emergence treatments the maize genotypes had the least tolerance of the mesotrione + nicosulfuron combination of active ingredients, where the double quantities resulted in 13–14% damage in average.