Environmental and physiological factors that affect the efficacy of herbicides that inhibit the enzyme protoporphyrinogen oxidase: a literature review

Herbicides that inhibit the enzyme protoporphyrinogen oxidase (PROTOX) are usually effective to control dicotyledonous weeds and their agronomic efficacy is affected by environmental and physiological factors. The objective of this review is to summarize the knowledge of those factors available in the scientific literature in the last decade. Environmental factors that influence PROTOX inhibitors include temperature, irradiance and relative humidity. The most relevant physiological factors are the activity of enzymes that can detoxify herbicides and also of enzymes that mitigate the effects of oxidative stress in plants. The study also suggests some possible management strategies that could optimize the activity of PROTOX-inhibiting herbicides.

First report of Amaranthus viridis resistance to herbicides

Due to the limited number of herbicides registered for the control of dicot weeds in cotton crops, ALS inhibitors have been used on an intensive and recurrent basis. Given that, cases of poor weed control have been described after application of these herbicides in the main cotton producing areas in Brazil, the purpose of the present work was to evaluate the occurrence of resistance to ALS herbicides in Amaranthus viridis biotypes from those areas. Dose-response curves were prepared after pre-emergence applications of trifloxysulfuron-sodium (0; 1.8; 3.7; 7.5; 15 and 30 g ha-1) and pyrithiobac-sodium (0; 35; 70; 140; 280 and 560 g ha-1), equivalent to 0, ¼, ½, 1, 2 and 4 times the recommended commercial rates. The selection of trifloxysulfuron-sodium resistant biotypes of A. viridis was confirmed in samples from Bahia (BA 7, BA 8, BA 9 and BA 11). However, no resistance to pyrithiobac-sodium was found for biotypes either from Bahia or from Mato Grosso do Sul.

Sensibility of plant species to herbicides aminocyclopyrachlor and indaziflam

Aminocyclopyrachlor and indaziflam are under development in Brazil and there is no information about their behavior in Brazilian soils. This study aimed to evaluate the sensitivity of plant species to these new molecules, trying to select plants that can be used as bioindicators for testing the behavior of these herbicides in the soil. Two experiments were conducted, one for each herbicide. The treatments were arranged in a 8 x 6 factorial design, the factors being represented by eight species used as bioindicators cotton, maize, soybean, sorghum, sunflower, millet, cucumber and beet, and six doses of herbicides (aminocyclopyrachlor - 0, 10 , 20, 30 , 40 and 50 g ha-1 and indaziflam 0 , 20, 40 , 60, 80 and 100 g ha-1). Among the species studied, soybean and beet were quite sensitive to the two new herbicide molecules, being great alternatives for bioassays in order to detect low concentrations of aminocyclopyrachlor and indaziflam in the soil.

Potential of plant species for bioremediation of soils applied with imidazolinone herbicides

Imidazolinone herbicides present physicochemical characteristics that allow them to persist longer in environment, with increased chances of soil and water contamination, as well as carryover effects on subsequent crops. Phytoremediation is shown as a promising technique to decontaminate soils polluted by herbicides. The aim of this study was to assess the potential of some winter grown species in removing residuals from soils contaminated with imazethapyr + imazapic and imazapic + imazapyr, using pre-emergence to control weeds in summer grown rice fields. The experiment was conducted in a completely randomized design, with four replications. All species were subjected to herbicide application at different doses. Imazethapyr + imazapic and imazapyr + imazapic were applied at doses of 0.0, 1.0 and 2.0 L ha-1, and 0.0, 140 and 280 g ha-1, respectively, in pre-emergence of the species. Brassica napus and Festuca arundinaceae are not tolerant to herbicides, with 100% of phytotoxicity (plant death) for all doses assessed. The herbicide imazapyr + imazapic proved to be less selective, causing the highest phytotoxicity in the species tested. The most tolerant species to the herbicides was Vicia sativa, which may be the most suitable one for phytoremediation programs in areas contaminated with imazethapyr + imazapic and imazapyr + imazapic.

Volunteer RR® corn management in roundup ready® soybean-corn succession system

The present study evaluated the effects of cover crops (Pennisetum glaucum, Crotalaria spectabilis and Urochloa ruziziensis) associated with the application of herbicides {glyphosate; (glyphosate + haloxyfop-R); (glyphosate + fluazifop-p-butyl); (glyphosate + imazethapyr) and (glyphosate + imazaquin)} in soybean desiccation management for volunteer RR® corn control. The experiment was conducted under field conditions at Sinop-MT, during the 2013/2014 crop season, in a randomized complete blocks design with factorial scheme and four replications. The following parameter were evaluated: dry matter of cover crops and ground coverage rate, control of volunteer RR® corn present at the time of desiccation, dry matter, height and intoxication level on soybean plants caused by herbicides at 7, 14 and 28 days after emergence (DAE), control of volunteer RR® corn derived from emergence fluxes subsequent to desiccation management and soybean yield. The joint application of (glyphosate + haloxyfop-R) provided the best level of volunteer RR® corn control present at the time of desiccation. Satisfactory control (80%) of volunteer corn was obtained with the application of (glyphosate + imazethapyr). This treatment displayed an additional residual effect of imazethapyr, which efficiently controled volunteer RR® corn derived from fluxes subsequent to desiccation management, especially in treatments performed under U. ruziziensis straw. None of the herbicides used in desiccation management caused any significant effect on dry matter, height and phytotoxicity of soybean plants at 7, 14 and 28 DAE nor on grain yield.

Dose-response curve to soil applied herbicides and susceptibility evaluation of different amaranthus species using model identity

Greenhouse studies were conducted in 2008-2009 with the objective of adjusting dose-response curves of the main soil-applied herbicides currently used in cotton for the control of Amaranthus viridis, A. hybridus, A. spinosus, A. lividus, as well as comparing susceptibility among different species, using the identity test models. Thirty six individual experiments were simultaneously carried out in greenhouse, in a sandy clay loam soil (21% clay, 2.36% OM) combining increasing doses of the herbicides alachlor, clomazone, diuron, oxyfluorfen, pendimethalin, prometryn, S-metolachlor, and trifluralin applied to each species. Dose-response curves were adjusted for visual weed control at 28 days after herbicide application and doses required for 80% (C80) and 95% (C95) control were calculated. All herbicides, except clomazone and trifluralin, provided efficient control of most Amaranthus species, but substantial differences in susceptibility to herbicides were found. In general, A. lividus was the least sensitive species, whereas A. spinosus demonstrated the highest sensitivity to herbicides. Alachlor, diuron, oxyfluorfen, pendimethalin, S-metolachlor, and prometryn are efficient alternatives to control Amaranthus spp. in a range of doses that are currently lower than those recommended to cotton.

Imidazolinone Degradation in Soil in Response to Application History

Accelerated herbicide degradation consists in its faster degradation in areas where it has been previously applied, due to the adaptation of microbial population to that particular compound. Accelerated degradation can reduce herbicide persistence and reduce its efficacy in soil. The objective of this study was to investigate if imidazolinone herbicides have enhanced microbial degradation in rice paddy soils. A laboratory experiment was conducted, evaluating the CO2 evolution rate from soils with and without history of herbicide application (imazapyr + imazapic and imazethapyr + imazapic), incubated with imidazolinone herbicides: imazethapyr, imazapyr, imazapic, imazamethabenz, imazamox and an untreated check. The amount of CO2 released from the soil was measured. As a result, the prior application of imidazolinones does not stimulate microbial degradation of herbicides from the same chemical group.

ANNUAL GRASSES CONTROL WITH TOPRAMEZONE IN MIXTURE WITH ALS-INHIBITING HERBICIDES

ABSTRACTPanicoid grasses are major weeds of maize and sugarcane as well as of several other important grains, including sorghum, pearl millet, and foxtail millet. Pot trials were conducted to study the activity and potential interactions of topramezone in mixture with recommended rates of rimsulfuron or nicosulfuron on three annual panicoid grasses (i.e. Echinochloa oryzoides,E.phyllopogon, and Panicum miliaceum). Target weeds were treated at the four- to five-leaf growth stage. On the basis of fresh weight reduction, topramezone alone provided 78% control of E.oryzoides, 68% control of E.phyllopogon, and 99% control of P.miliaceum. Topramezone plus rimsulfuron or nicosulfuron provided decreased control of both Echinochloa spp. compared with topramezone alone. The decreased control of E.oryzoidesand E.phyllopogon was more pronounced with rimsulfuron as a companion herbicide in the mixtures. Slightly decreased control of P.milaceum was observed with topramezone plus rimsulfuron compared with topramezone alone, but this was not the case for topramezone plus nicosulfuron. Increased topramezone rates mixed with rimsulfuron or nicosulfuron did not improve control of E.oryzoides and E.phyllopogon compared with the lowest topramezone rate. Also, increased topramezone rates mixed with rimsulfuron or nicosulfuron showed decreased control of both Echinochloa spp. when compared with either rimsulfuron or nicosulfuron alone, suggesting a two-way interaction between topramezone and the ALS-inhibiting herbicides. The above-mentioned interaction was not observed in P.miliaceum, probably related with species sensitivity to the herbicides tested. Newly introduced or naturalized panicoid grasses in maize fields may complicate selection of companion herbicides and rates for effective weed control.

SELECTION OF HERBICIDES TARGETING THE USE IN CROP SYSTEMS CULTIVATED WITH SHOWY CROTALARIA

ABSTRACT The increase in the area planted with Crotalaria spectabilishas occurred by several factors, highlighting the potential to reduce the nematodes, nitrogen fixation and the high production of biomass. By becoming a species sown as a crop, it is necessary to control the weeds that coexist with showy crotalaria. This change in the use of this crop creates the possibility of this specie becoming a weed. The aim of this study was to assess the potential use of herbicides applied in preemergence and postemergence of C.spectabilisfor different purposes (control of volunteer and selectivity plants). Three experiments were installed in a greenhouse (two with herbicides applied in preemergence - in soils with distinct textural categories; and one experiment with herbicides applied in postemergence). The results of the experiments with herbicides applied in preemergence showed that: amicarbazone, atrazine, diuron, metribuzin, prometryn, fomesafen and sulfentrazone showed effectiveness for control of C.spectabilis in clayey soil. Besides these, flumioxazin and isoxaflutole also showed potential to be used in the control of showy crotalaria in soils with loam texture. In relation to the postemergence herbicides, atrazine, diuron, prometryn, flumioxazin, fomesafen, lactofen, saflufenacil, amonio-glufosinate and glyphosate can be used aiming the chemical control of C.spectabilis. Herbicides chlorimuron-ethyl, diclosulan, imazethapyr, pyrithiobac-sodium, trifloxysulfuron-sodium, clomazone, pendimethalin, S-metolachlor and trifluralin applied in preemergence, and imazethapyr, pyrithiobac-sodium, flumiclorac, bentazon and clethodim applied in postemergence caused low levels of injury to C.spectabilis plants, making necessary the development of new searches to ensure the selectivity of these products.

WEED MANAGEMENT WITH HERBICIDES APPLIED IN PRE AND POSTEMERGENCE ON CASTOR CROP

ABSTRACT The aim of this work was to evaluate the weed management with herbicides applied in pre and postemergence on castor crop. The treatments were constituted by management systems using herbicides in pre (PRE) and postemergence (POS): 1) S-metolachlor at 576 g ha-1 (PRE 1) and chlorimuron-methyl at 15 g ha-1 (POS 1); 2) PRE 1 + clomazone at 650 g ha-1(PRE 2) and POS 1; 3) PRE 1, POS 1 and halosulfuron-methyl at 112.5 g ha-1(POS 2); 4) PRE 1, POS 1 and ethoxysulfuron at 60 g ha-1 (POS 3); 5) PRE 1, POS 1 and ethoxysulfuron at 120 g ha-1 (POS 4); 6) PRE 1 + PRE 2, POS 1 and POS 2; 7) PRE 1 + PRE 2, POS 1 and POS 3; 8) PRE 1 + PRE 2, POS 1 and POS 4; 9) hand-hoeing control and 10) non-weeded control. The experimental design was randomized blocks with four replications. The association of the herbicides in PRE combined to sequence applications of chlorimuron-ethyl and halosulfuron-methyl or ethoxysulfuron in POS resulted in the highest control levels of Richardia scabraand Cyperus ferax. Mild phytointoxication symptoms to the crop were more persistent with ethoxysulfuron at 120 g ha-1. The acceptable control of the weed species and similar yield to the hand-hoeing control permitted to conclude that S-metolachlor + clomazone PRE, followed by chlorimuron-ethyl and halosulfuron-methyl POS proved to be more adequate as a weed management strategy on castor crop.

APPLICATION HEIGHT IN HERBICIDES EFFICIENCY IN BEAN CROPS

ABSTRACTInadequate herbicide application can result in failures in weed control and/or poisoning of the crops, resulting in yield losses. In this research were assessed the effects of the sprayer nozzle boom height in the distribution of the spray solution for weed control, influencing intoxication of beans and crop yield. Experiments were conducted in laboratory and field conditions. In laboratory, the performance of flat spray tip TT 11002 was assessed at heights 0.20, 0.30, 0.40 and 0.50 meters with respect to the target surface. In the field the same heights were assessed in applications of herbicides fomesafen, fluazifop-P-butyl and fomesafen + fluazifop-P-butyl. There was an inverse relationship between the height of the spray boom and the coefficients of variation of the patterns. The mixture better efficiency in a tank of fluazifop-P-butyl + fomesafen was obtained with the height of 0.50 m from the target. This treatment resulted in better weed control, lower poisoning of the bean plants and better crop yield rates.

VINASSE EFFECT ON HERBICIDES CLOMAZONE AND TEBUTHIURON AVAILABILITY IN DIFFERENT KINDS OF SOILS

ABSTRACT The objective of this study was to evaluate the availability of herbicides clomazone and tebuthiuron in the solution in different kinds of soils saturated with water or vinasse. Samples of 30 soils with different characteristics were arranged on trays to the herbicides spraying. Then they were homogenized, placed in plastic cartridges and saturated with deionized water or vinasse, and remaining at rest during 18 hours. Two extractions were made, the first one quantified the presence of the herbicides in the soil solution and in the second one the total extraction of herbicide remaining in the soil was taken to determine the recovery percentage of each herbicide tested. For quantification, a LC-MS/MS system was used, a compound of a high performance liquid chromatograph (HPLC) coupled to a triple quadruple mass spectrometer. Tebuthiuron was more available in the soil with the vinasse addition when compared to water. Vinasse applications resulted in no significant difference in availability of clomazone between treatments. Tebuthiuron showed the highest availability frequencies, and on average of all samples 32.49% were extracted from total herbicide applied, while for clomazone this value was 16.50%.

MULTIPLE RESISTANCE OF Sagittaria montevidensis BIOTYPES TO ACETOLACTATE SYNTHASE AND PHOTOSYSTEM II INHIBITING HERBICIDES

ABSTRACT The objective of this research was to evaluate the occurance of multiple resistance of Sagittaria montevidensis (SAGMO) biotypes to acetolactate synthase (ALS) and photosystem II (PSII) inhibiting herbicides through dose-response experiments. The experiment was conducted in a greenhouse from October 2012 to March 2013, in Pelotas, RS. The experimental design was completely randomized, with four replications. Treatments were arranged in a triple factorial design: two biotypes of S. montevidensis(SAGMO 35 - susceptible to herbicides and SAGMO 32 - suspected to be multiple resistance to ALS and PSII inhibiting herbicides), four herbicides (penoxsulam, (imazethapyr+imazapic), bentazon and saflufenacil) and 8 rates of these herbicides (1/32x, 1/16x, 1/8x, 1/4x, 1/2x, 0x, 1x, 2x, 4x, 8x, 16x, 32x and 64x). SAGMO 32 biotype presented high levels of resistance to penoxsulam, (imazethapyr+imazapic) and bentazon. For a 50% reduction in dry matter of the resistant biotype rate of 138 and 2.46 times higher than the label required for the susceptible biotype of the herbicides (imazethapyr+imazapic) and bentazon, respectively, are required. Saflufenacil may be used successfully to controlSagittaria montevidensis resistant in irrigated rice.

Changes in Photosynthesis and Oxidative Stress in Wheat Plants Submmited to Herbicides Application

The use of herbicides, even in tolerant crops, can cause stress evidenced by increase phytotoxicity affecting growth and development. The objectives of this study were to evaluate herbicides effect from different mechanisms of action in photosynthetic and oxidative stress parameters, as well visual phytotoxicity and wild radish control in wheat crop, cultivar Quartzo. Two trials were conducted where the first one evaluated the photosynthetic parameters on wheat plants in two seasons collection, following the application of herbicides bentazon, clodinafop, iodosulfuron, metribuzin, metsulfuron and 2,4-D; and the second one evaluated wild radish (Raphanus sativus) control, wheat phytotoxicity and yield due to bentazon, iodosulfuron, metribuzin, metsulfuron and 2,4-D herbicides application. Photosynthetic rate, stomatal conductance and transpiration were negatively affected by metribuzin, metsulfuron and 2,4-D herbicides at 24 and 120 HAS (hours after spraying) compared to control. Oxidative stress was similar or lower to control, when herbicide was applied and, in general, there was no difference between application times. Lipid peroxidation, catalase activity and phenols were higher in the first collection time. The application of herbicides iodosulfuron and 2,4-D reduces chlorophylls and carotenoids in wheat. Herbicides bentazon, iodosulfuron, metribuzin, metsulfuron and 2,4-D are selective to wheat, cultivar Quartzo and do not affect wheat yield. 2,4-D, metribuzin and iodosulfuron are more efficient for wild radish control.

Physiological and Genetic Bases of the Circadian Clock in Plants and Their Relationship with Herbicides Efficacy

In order to adapt to daily environmental changes, especially in relation to light availability, many organisms, such as plants, developed a vital mechanism that controls time-dependent biological events: the circadian clock. The circadian clock is responsible for predicting the changes that occur in the period of approximately 24 hours, preparing the plants for the following phases of the cycle. Some of these adaptations can influence the response of weeds to the herbicide application. Thus, the objectives of this review are to describe the physiological and genetic mechanisms of the circadian clock in plants, as well as to demonstrate the relationship of this phenomenon with the effectiveness of herbicides for weed control. Relationships are described between the circadian clock and the time of application of herbicides, leaf angle and herbicide interception, as well as photosynthetic activity in response to the circadian clock and herbicide efficiency. Further, it is discussed the role of phytochrome B (phyB) in the sensitivity of plants to glyphosate herbicide. The greater understanding of the circadian clock in plants is essential to achieve greater efficiency of herbicides and hence greater control of weeds and higher crop yields.