Historical cultivated area, grain yield and production of rice in Brazil and in the states of Rio Grande do Sul (RS) and Santa Catarina (SC), from 2002 to 2012.
The annual rice production in Brazil is 11.6 million tons , occupying an average area of 2.43 million ha per year with yields averaging 4.73 t ha-1 (Table 1). The southern states of Rio Grande do Sul (RS; 1.05 million ha) and Santa Catarina (SC; 0.15 million ha) contribute with more than 77% of the rice production with about 51% of the cultivated area in Brazil. Average grain yields obtained in the last five years in the RS and SC were around 7.26 t ha-1, almost 55% higher than the national average 
The intensification of rice cropping systems in the same area promotes an increase in infestations by weeds. The fields of irrigated rice in southern Brazil provide a special habitat for weeds. During some months of the hot season, in addition to temperature and luminosity suitable for plant growth, there is also abundant soil moisture, which favors the development of weeds. This makes weeds responsible for losses in yield and grain quality, due to the direct interference they cause to the crop . The weeds also cause other indirect negative effects in the production system, such as losses in nutritional value of pastures, interference in cover crops and even depreciating the land value [4-6].
In the fields of southern Brazil, the increase in weed occurrence is well characterized, mainly due to the fact that the irrigated rice was – until recently – almost the only cultivated crop in lowlands. To reduce the impact of weeds in rice, farmers have adopted some technologies. At first, there were modifications in the soil management system, shifting from a conventional plough-and-harrow to other forms of soil cultivation, such as minimum-till, no-till and the water-seeded rice system. Secondly, there was the adoption of ALS-tolerant rice cultivars (Clearfield technology - CL®) and last, the increase in the area of Roundup Ready soybeans in drained lowlands has also contributed to the weed management in rice fields. Herbicides, however, are still heavily used as the main form of weed control in almost all irrigated rice fields in RS state. In complement, organic rice is growing in adoption, but actually is restricted to small fields. The certified organic smallholders account for 400 producers, in an area of about 3,400 ha dispersed in the RS state.
It is known that the average regional yields (7.26 t ha-1) are below those obtained in field trials and in high technology farms. Even though new cultural techniques are often used to control weeds, poor weed control is one to be highlighted among the probable causes of grain yield variability. According to results of  and  it is estimated that about 1 million tons of rice are lost annually in Brazil, which is roughly equivalent to 8% of the national production of this cereal, even after using all methods available for weed management. This corresponds to an annual loss estimated of about US$ 200 million.
Due to the particular regional characteristics, there are many ways of soil, water and plant management in irrigated rice in southern Brazil. The main system is minimum-till (around 60% of the area) in which the soil is plowed, harrowed, leveled and the levees are done in the autumn, right after the harvest of the summer crop, with chemical desiccation in spring before rice planting, done with a no-till drill in dry soil. Another system is the conventional seeding, where all the tillage is done just before planting rice, in dry soil. Finally, about 20% of the fields are cultivated with the water-seeded system, performed mainly in small farms (up to 30ha) in which rice is sown pre-germinated over a field already flooded (schemes on Figure 1). The system of manual or mechanic transplanting rice seedlings from the nursery to the puddled and flooded field – very common in the Asian paddies – is almost not used in Brazil.
In the last few years, there was a continuous increase in the soybean area in the lowlands of RS, and currently this crop occupies around 250,000ha in rotation with rice (all RS state have approximately 4.19 million hectares of soybean). Probably in the following years, soybean will spread up to 0.5 million hectares in the lowlands of RS, limited by poor soil drainage conditions. Glyphosate-tolerant soybean has changed the scenario of resistant-weeds in rice fields and will be discussed later in this article.
1.1. The main weeds of irrigated rice in southern Brazil
The main weeds in flooded rice fields in Brazil are commonly classified into narrow- and broad-leaved weeds. The major representatives of narrow leaves are weedy rice (
Recently, there was an increase in the occurrence of Alexander grass (
As broadleaved weed representatives, there are the jointvetches (
Many of these species are difficult to control and severely compete with the crop for resources available in the environment if no control method is adopted. In addition, barnyardgrass, weedy rice, globe fringerush, arrowhead and some sedges have acquired resistance to herbicides (Table 3).
1.2. How does resistance to herbicides appear in rice fields?
The adoption of herbicide-tolerant rice has increased considerably in the last few years. The results of this unprecedented change in agriculture have been many, but perhaps most dramatic is the simplification of weed-control tactics; growers can now apply a single herbicide group (ALS-inhibitors) at higher rates of active ingredient without concern for injury to the crop. Regardless, the number of chemical groups of herbicides applied has declined, thus increasing the ecological implications such as reducing the biodiversity of arable land, facilitating population shifts in weed communities and the evolution of herbicide-resistant biotypes. Historically, a number of significant changes in agricultural systems have occurred with significant impact on weed communities.
The use of herbicides for weed control has become a common practice in agriculture worldwide. Once, this technology was used mainly by big farmers; it is currently becoming a common practice even among smallholders. Nowadays, weed control in irrigated rice relies almost exclusively on herbicides, mainly because chemical control has been efficient, relatively cheap, readily available and professionally developed. Thus, other methods of control have been left as a second choice or under certain circumstances may present themselves unattractive or unfeasible. It needs to be noted that the strong presence of pesticide suppliers has almost banned the use of other forms of weed management but the herbicides in irrigated rice fields. The widespread and almost exclusive use of the chemical method of weed control in rice promotes changes in the weed flora, from quite easily controlled broadleaved weeds to more hostile grass weeds [8-9]. The recurrent use of herbicides with the same site of action can select individuals that are genetically capable of surviving a dose of a given herbicide which normally would kill or suppress the species . Herbicide resistance is the inherent ability of a species to survive and reproduce following exposure to a dose of herbicide normally lethal to its wild type. Resistance is not directly caused by herbicides, rather, it appears from the selection of natural mutation or minor pre-existing population of herbicide-resistant plants (selection pressure imposed by herbicides)  or in rice cases, gene flow from herbicide-resistant to weedy rice [12-14].
As at other places worldwide, in the rice fields of south of Brazil, the continuous use of herbicides has led to the evolution and appearing of herbicide-resistant (HR) weeds, and this is an additional problem in the pest management context. Chemical weed control is used in almost all areas and the scenario in the short-past, at present – and probably to the future – is a continuous intensification of the rice cropping systems. This intensive system, combined with the continued use of herbicides with the same mechanism of action, has resulted in the development of resistant weeds. The resistance of weeds to herbicides in that region was confirmed by several institutions, namely EMBRAPA, EPAGRI, IRGA, UFRGS, UFPEL and UFSM.
2. Main herbicide resistant weeds occurring in rice in Southern Brazil
There are already reported cases of herbicide-resistant biotypes of the main weeds such as
2.1. First cases
Weed resistance to herbicides in rice fields of Southern Brazil was first registered in 1999 , with a biotype of arrowhead (
2.2. The case of
Echinochloa crus-galliresistance to the herbicide quinclorac
This species is a monocotyledon that survives in flooded environments, occurring normally in high levels of infestation. It is widely distributed in almost all rice fields of SC and RS. In addition, barnyardgrass presents morpho-physiological similarities with the crop in the early stage of development. The negative effects of its presence in rice include: the high capacity to compete with rice by resources as light and nutrients; the intrinsic difficulties related to control; the increases in the production costs; it causes rice lodging, difficulties in the harvest and depreciation of the product; it is a host of some pests in rice and this species can even decrease the commercial value of arable areas [3,19-20].
Barnyardgrass is also one of the most widely distributed weeds in the grain crops grown in rotation with rice in lowland areas, mainly represented by soybeans, some sorghum  and a little portion of areas with maize. In reference  reported that many of the ALS-resistant biotypes of
Due to the continuous use of herbicides with the same mode of action, often in the absence of crop rotation and lack of integrated management, barnyardgrass evolved resistance to several herbicides  and some biotypes have multiple resistance . In reference  reported a biotype of barnyardgrass presenting cross-resistant to quinclorac (auxin-mimic herbicide) and to ALS inhibitors. Herbicides represent the main tool for weed control within the program of integrated management in rice fields of Southern Brazil. Among those used in rice, quinclorac (auxin-mimic) combines flexibility in the application (pre- and post-emergence) and normally offers good efficiency to
2.3. The cases of weed resistance to ALS inhibiting herbicides
Similar to what happened with quinclorac in the past, in more than a half of all cultivated rice areas in RS state, the ALS-inhibitors were (and still are) vastly applied in the fields. This scenario was aggravated by the use of varieties tolerant to the herbicides belonging to this group (CL technology), aiming to achieve efficient control of weedy rice and barnyardgrass. The repetitive use of some ALS-inhibiting herbicides for 4 to 5 years after the launch of the CL technology resulted in resistance of barnyardgrass to the herbicides bispyribac-sodium, penoxsulam, imazethapyr+imazapic and imazapic+imazapyr .
2.4. Arrowhead —
This is an aquatic weed often found in water-seeded or transplanted rice systems. Arrowhead is characterized as a weed that occurs in high levels in most areas of flooded rice in Santa Catarina . This weed presents a low capacity to compete with rice as compared to other species which infest the crop . However, the frequency of high infestations by arrowhead has resulted in increased use of herbicides for its control. In the RS, rice is mainly drill planted in dry soil, and flood irrigation starts about 20-25 days after emergence; in the State of SC almost 100% of its rice area is grown in the water seeded system, which favors arrowhead.
Several biotypes of arrowhead were found to be resistant to ALS inhibitors . In Brazil, populations with cross-resistance to the sulfonylurea and pyrimidinyl thiobenzoates were identified in 1999 in areas treated with these products for about five consecutive years . In reference  the authors found that the resistant biotype of arrowhead showed faster emergence, higher seed vigor and absorption of herbicides preferably by shoots instead of roots, when compared to the susceptible population.
Rice areas with arrowhead resistant to ALS inhibitors are common in Brazil due to the extensive and repetitive application of herbicides with this mechanism of action. A recent study revealed the occurrence in SC State of populations of this weed with cross-resistance to several ALS-inhibiting herbicides and multiple resistances to PSII inhibitors . Currently, arrowhead resistant to ALS inhibitors is present in almost all municipalities which grow rice in Santa Catarina State.
In rice fields where the ALS-resistant biotype of arrowhead occurs, the herbicides carfentrazone-ethyl or bentazon can be used as alternatives for chemical control. Both herbicides applied alone or in tank mix allowed control levels of arrowhead superior to 92% at the pre-harvest of water-seeded rice in SC State . It should be emphasized that planting rice at low- or lower-densities that the recommended  allows a more favorable environment for aquatic rice weeds, especially arrowhead. In reference  it was observed that a strong negative correlation between the planting density of the rice variety BRS 6-Chui and the infestation by arrowhead; in other words, the infestation was more serious as rice density was decreased. According to the authors, this suppression caused by higher rice densities is due to the increased ability of the crop to compete for light, which prevented the weeds from having access to adequate levels of radiation.
2.5. Nutsedges —
Cyperus difformis, C. iriaand globe fringerush — Fimbristylis miliacea
Some weed species of the family
The weed control in rice fields can be accomplished with the use of herbicides due to its ease of use and high efficiency. There are difficulties, however, in chemically controlling species of the genus
The control of
From the 1980's, the ALS-inhibiting herbicides have become very important tools for agriculture, and the widespread use of these products was mainly due to its high efficiency at low doses, low toxicity to animals, high selectivity for some crops and reduced environmental impact when compared to other pesticides . These traits contributed to the increased use of these herbicides in various crops. Two years after these products were made available in the market, however, appeared the first case of a weed with resistance to this mechanism of action. Currently, there are 95 resistant species, distributed in 34 countries .
Results in reference  are shown in Figure 1. One biotype of
The mechanism involved in the resistance of
|Pyrazosulfuron-ethyl||15 b2||6 b||1,59 a|
|Bispyribac-sodium||6 bc||13 b||2,31 a|
|Imazapyr + imazapic||2 c||2 b||2,31 a|
|Penoxsulam||3 c||10 b||1,48 a|
|No application||0 c||0 b||2,79 a|
For rice fields infested with biotypes of weeds resistant to ALS inhibitors, the most effective strategies are pointed out in the following. The application of glyphosate alone or mixed with pendimethalin or clomazone at the so-called “needle point” will ensure that the rice emerges free from the infestation of
Although effective, a delay in the application of glyphosate + pendimethalin or clomazone for a single day from the needle point may cause severe damage to rice. This is particularly a problem if there are frequent rains forecasted for the five days following planting. So, technicians are highly encouraged to evaluate carefully the risk of this practice before recommending it for farmers. In addition, the application of glyphosate should not be done only at the needle point. There is the need for a previous desiccation of the area between 20 and 10 days before planting, which will allow control of the older weed plants.
Another option defined in  is the use of PSII inhibitors like bentazon or carfentrazone-ethyl in post-emergence. Carfentrazone, however, may cause severe damage to rice. In addition, both chemicals are contact-only herbicides, which means that a good coverage of the plants by using higher water volumes than the usual followed by flooding on the following day, should allow good results.
There were only three reports of resistance of
2.6. The case of weedy rice (red rice) resistant to ALS-inhibiting herbicides
Among the major weeds infesting rice, weedy rice can surely be highlighted as the one which most limits the potential yield of rice . The direct losses resulting from competition exerted by weedy rice in rice paddy fields is estimated at about 20% .
There are also several indirect losses, such as raised cost of production, depreciation of the market value of cultivated areas and of the harvested product, equipment damage and reduction in generation of jobs, further reducing the profitability of farming . The degree of interference of weedy rice varies with the level of infestation, soil and climatic conditions, cultivar traits, coexistence period and biotype found in the area .
The control of red rice with herbicides has become possible after the development of rice genotypes tolerant to the herbicides from the imidazolinone group (ALS-inhibitors) . The same authors also reported that effective chemical control of red rice is almost impossible using conventional genotypes, because of the morpho-physiological similarity between the cultivated and the weedy rice. Despite the Clearfield® system providing a great advantage in terms of weed control, the adoption of herbicides from the ALS group associated to this technology resulted in selection of resistant genotypes of this weed . Thus it is evident that the continued use of the Clearfield® system in rice areas of Rio Grande do Sul favored the development of populations of red rice resistant to imidazolinone due to its repeated use in the absence of crop rotation or others tools.
The introduction of rice cultivars tolerant to imidazolinone herbicides probably resulted in gene flow of the resistance to wild rice genotypes [47-48]. The occurrence of weedy rice populations resistant to herbicides may be caused by gene flow between cultivated varieties and weedy rice [12,13]. A research at RS has indicated that pollen dispersal occurs between cultivated rice and transgenic rice at levels below  and others studies [50-51] showed gene flux between rice CL varieties and weedy rice rates of 0.042 and 0.065%, respectively. It should be noted that even with low rates of gene flow, there might be a considerable increase in the frequency of resistant individuals in the population, given the high degree of infestation of cultivated areas . Another study shows that the gene flow as low as the rate of 0.008% originated 170 individuals of red rice per hectare with resistance .
In reference  with populations of red rice from the six most rice-producing regions of the RS, the occurrence of resistant biotypes to herbicides from the imidazolinone group (imazethapyr and imazapic) was confirmed to occur in all regions under the Clearfield® system. The predominant mechanism of herbicide resistance in weedy rice in RS and SC is the target site insensitivity due to changes in nucleotide sequence of the ALS enzyme [14,52]. Gene flux was the main origin of imidazolinone herbicide resistance, but independent selection occurred in 1.1 % of the evaluated weedy rice plants . The high frequency of weedy rice resistant plants carrying the G654E mutation, which is the same mutation responsible for the resistance in the rice cultivar largely used in Southern Brazil when the weedy rice plants were collected, suggests that gene flow is occurring from the rice cultivar to weedy rice .
2.7. A retrospect of the ALS-inhibiting herbicides and ClearField® technology use in irrigated rice fields of Southern Brazil
The use of Clearfield® (CL) technology in rice areas of southern Brazil began in 2002 with imidazolinone-resistant cultivars. Ten years later, more than 60% of irrigated rice in Rio Grande do Sul State carry the CL technology and are treated with these herbicides. The combined use of imidazolinone-resistant rice cultivars with the correspondent herbicides is often very effective, providing more than 95% of control of weedy rice in most cases . This technology had permitted immediate benefits in terms of efficiency and easiness of weed control, mainly for weedy rice and the
Even though some weeds presented resistance to ALS-inhibitors before the adoption of the CL technology (Table 3), the selection pressure caused by the increasing use of the ALS-inhibitors should be associated with the emerging of weedy rice (
|arrowhead||Azimsulfuron, bentazon, bispyribac-sodium, cyclosulfamuron, ethoxysulfuron, imazapic+imazethapyr, metsulfuron, penoxsulam, pyrazosulfuron-ethyl||[16, 17, 31]|
|barnyardgrass||Quinclorac||[4, 18, 25, 54]|
|Bispyribac-sodium, flucarbazone, imazapyr, imazethapyr, imazethapyr+imazapic, imazapyr+imazapic, nicosulfuron, penoxsulam, quinclorac||[55, 56, 60-65]|
|nutsedges||Azimsulfuron, bispyribac-sodium, cyclosulfamuron, ethoxysulfuron, penoxsulam, pyrazosulfuron-ethyl||[35, 36, 39, 65]|
|nutsedges||Bispiribac-sodium, Ethoxysulfuron, imazapyr+imazapic, imazethapyr+imazapic, penoxsulam, pyrazosulfuron-ethyl||[40, 41, 57, 58]|
|globe fringerush||Azimsulfuron, bispyribac-sodium, cyclosulfamuron, ethoxysulfuron, penoxsulam, pyrazosulfuron-ethyl||[66-67]|
|weedy rice||Imazethayr +Imazapic|
2.8. Prevention of herbicide-resistant weeds in irrigated rice of Brazil
An herbicide-resistant weed biotype usually occurs in areas where the common practice for weed control is the repeated use of the same product, or the use of different herbicides but with the same mechanism of action. This is the main scenario at the beginning of the weed-resistance cases in rice fields - the high selection pressure - as reported by . This situation is very common in the RS, where rice still is continuously grown as a mono-crop in most parts of the area. In the state of Santa Catarina, the areas are smaller and the management more varied, with farmers using both herbicides and cultural practices on weed management.
The adoption of best-practices in weed control is one of the main tools to prevent the occurrence of new cases of resistance. In reference [33, 68], some preventative measures to avoid or to minimize the risks are the use of crop rotation, the use of herbicides in the correct time and when necessary; to perform the rotation of herbicides, using those with distinct mechanisms of action; and be aware of the results of herbicide applications, checking for escapes and shifts in weed population. When an escaped plant is observed it must be immediately eliminated, preventing the spread of this suspected resistant biotypes. These recommendations are not always adopted in all fields due to the various difficulties. A good exception is the case of the seed-producers: these farmers really care with the weeds in your fields and adopt the best-management practices in terms of weed control, because there are some weed species whose seeds are expressly prohibited in lots of commercial rice seeds, and its presence would condemn the entire field, preventing it to be sold as seed.
In areas where herbicide resistant weed populations occur, some simple – but important – management strategies are issued. It is recommended not to plant very early in spring, because due to low temperatures, weeds will emerge and grow faster than rice, offering an additional difficultly for control and increased competition. The soil could be prepared, or chemically desiccated, immediately before planting rice to eliminate the weed seedlings already emerged; the machinery should be cleaned when leaving an infested area; the herbicides with proven resistant biotypes should not be used, and resistant escaped plants should not be allowed to produce seeds, by means of the localized chemical desiccation or by manual rouging.
In lowlands of Southern Brazil, rice is the main crop and commonly shares areas with cattle production. The cattle can occupy the fields in winter (between two cycles of rice) and consume cold-adapted grasses and broadleaves belonging to the genus
In recent years, however, soybean has increased in area in the lowlands, also being used as a cash-crop in these fields due to the high prices in the international market. Between one-fourth and one-third of the rice in RS is already rotated with soybeans and this crop is the main – and probably the best – option to the rotational scheme with irrigated rice in terms of increasing the soil fertility and reduction of some pests in rice. Almost all soybeans cultivated in RS are tolerant to glyphosate (Roundup Ready technology) and this herbicide offers very good control of annual grasses such as red rice and barnyardgrass. The consolidation of RR soybean was a step forward in the effectiveness of integrated pest management in irrigated rice in the RS state. The soybean is already used as the main tool of management in the cases of herbicide-resistant weeds occurring in irrigated rice fields, mainly in those well-drained areas. However, there are some concerns about the selective pressure driven by glyphosate, and about the spread of the resistant weeds to glyphosate, such as the Italian ryegrass (
In terms of herbicide rotation, in the fields with barnyardgrass resistant to ALS-inhibitors and/or auxin-mimic herbicides, the herbicides pendimethalin, trifluralin, thiobencarb, clomazone (in pre-emergence), quinclorac (in pre or post-emergence – avoid it in areas where auxin-mimic resistant biotypes occur), propanil alone or mixed with pendimethalin or clomazone (in early post-emergence) and ACCase inhibitors (in post-emergence of the crop) are good options . There are, however, reports about biotypes of
In reference  studying methods of application of clomazone and imazapic + imazapyr, reported that the application of clomazone alone or mixed with imazapic + imazapyr in the rice on “needle point” allow efficient control of ALS-resistant
Several rice farmers use residual herbicides in mixture with glyphosate in the pre-planting desiccation, mainly in areas under minimum- or no-till system (sod seeding) and/or with delayed flooding. In these cases, the elimination of existing weeds is accomplished with glyphosate and the new cohorts of seedlings are controlled by the residual herbicides. One of the most widely used herbicides for this task is clomazone, which presents residual effects over several grasses, especially barnyardgrass . Thus, the use of clomazone with glyphosate, either in the early pre-planting desiccation of sod seeding areas, or in the post-planting on “needle point”, is an effective tool for weed suppression. The application of glyphosate in the needle point was previously discussed, being illustrated in Figure 2.
Besides clomazone, pendimethalin may also be used at the “needle point” mixed with glyphosate aiming to suppress the emergence of
Managing herbicides properly within these options will allow farmers to have a 3-year rotation of herbicide, which will reduce both the occurrence of resistant biotypes, and the chance of appearance of a new resistant weed biotype. Farmers should request their technicians to plan the most proper herbicide rotation for every case. Used alone, none of the currently available cultural techniques provides an adequate level of weed control. However, when used in carefully planned combinations, extremely effective barnyardgrass control can be achieved .
Weeds resistant to herbicides have been of concern for scientists and farmers in the Rio Grande do Sul and Santa Catarina states of Brazil, since most herbicides used for chemical control are no longer effective in many fields. It is noteworthy to mention that the evolution of weeds resistant to herbicides is related to selection pressure, genetic variability of weeds, the number of genes involved, patterns of inheritance, gene flow and dispersal of the propagules. The elucidation of these factors becomes important for future predictions of proportions between resistant, tolerant and susceptible biotypes in the fields, and will require choosing more efficient management methods on these biotypes, aiming also to prevent the multiplication and dissemination of weed-related problems in the area.
In the case of rice, there are some intrinsic difficulties for adoption of full-integrated weed management with crop rotation because the condition of soil, with its susceptibility to be flooded and difficulties for fast drainage. The weed resistance to herbicides may cause losses to the rice production in many regions of Southern Brazil. Without the introduction of new herbicide mechanisms of action or better herbicide-resistance management, a technology that has allowed increases in agricultural productivity is at risk . Despite the success attained in some cases, more research and investments must be directed to this field of study in irrigated rice in Brazil, especially in the Southern region, which is the main producer, so that the problem can be more understood and specific strategies to manage this problem can be established and applied by the farmers.
FAO. Food and Agriculture Organization. http://www.fao.org (accessed 22 October 2012).
CONAB. Companhia Nacional de Abastecimento. Arroz - Brasil. Série Histórica de: área, produtividade e produção. http://www.conab.gov.br (accessed 22 October 2012).
Agostinetto D, Galon L, Silva JMBV, Tironi SP, Andres A. Interference and economic weed threshold (Ewt) of barnyardgrass on rice as a function of crop plant arrangement. Planta Daninha 2010; 28(special issue) 993-1003.
Andres A, Concenço G, Melo PTBS, Schmidt M, Resende RG. Detection of Echinochloasp. Resistance to quinclorac in rice fields in southern Brazil. Planta Daninha 2007; 25(1) 221-226.
Galon L, Agostinetto D, Moraes PVD, Dal Magro T, Panozzo LE, Brandolt RR, Santos LS. Economic threshold level for barnyardgrass (Echinochloa spp .) control decision in flooded rice (Oryza sativa). Planta Daninha 2007; 25(4) 709-718.
Galon L, Agostinetto D. Comparison of empirical models for predicting yield loss of irrigated rice ( Oryza sativa) mixed with Echinochloaspp. Crop Protection 2009; 28(10) 825-830.
Oerke EC. Crop losses to pests. The Journal of Agricultural Science 2006; 144(1) 31-43.
Mortimer AM, Hill JE. Weed species shifts in response to broad-spectrum herbicides in sub-tropical and tropical crops. Brighton Crop Protection Conference 1999; 2(1) 425-437.
Olofsdotter M, Navarez D, Rebulanan M, Streibig JC. Weed-suppressing rice cultivars - does allelopathy play a role? Weed Research 1999; 39(6) 441-454.
Gressel J, Segel LA. Interrelating factors controlling the appearance of resistance: The outlook on the future. In: LeBaron, H.L. and Gressel, J. (eds.) Herbicide Resistance in Plants. New York: Wiley; 1982. p325-347.
Prather TS, Ditomaso JM, Holt JM. Herbicide Resistance: Definition and Management Strategies. University of California, Division of Agriculture and Natural Resources, Publication 8012. http://anrcatalog.ucdavis.edu/pdf/8012.pdf (accessed 10 October 2012).
Gealy DR, Mitten DH, Rutger JN. Gene flow between red rice ( Oryza sativa) and herbicide-resistant rice ( O. sativa): implications for weed management. Weed Technology 2003; 17(3) 627–645.
Shivrain VK, Burgos NR, Anders MM, Rajguru SN, Moore J, Sales MA. Gene flow between Clearfield rice and red rice. Crop Protection 2007; 26(3) 349–356.
Goulart ICG, Pacheco MT, Nunes AL, Merotto Jr. A. Identification of origin and analysis of population structure of field-selected imidazolinone-herbicide resistant red rice ( Oryza sativa). Euphytica 2012; 187(3) 437-447.
Menezes VG, Mariot CHP, Kalsing A, Goulart ICGR. Red rice ( Oryza sativa) resistant to the herbicides imidazolinones.Planta Daninha 2009; 27(special issue) 1047-1052.
Noldin JA, Eberhardt DS, Knoublauch R. Resistência de Saggitaria montevidensisa herbicidas: primeiras evidências. In: Embrapa Clima Temperado (ed.): proceedings of the I Congresso Brasileiro de Arroz Irrigado, 1-4 August 1999, Pelotas, Brazil, Pelotas: Embrapa Clima Temperado; 1999.
Noldin JA, Eberhardt DS, Knoublauch R. Sagitária resistente a herbicidas inibidores da enzima ALS, In: SBCPD (ed.): proceedings of the Congresso Brasileiro da Ciência das Plantas Daninhas, 6-11 June 2000, Foz do Iguaçú, Brazil, Foz do Iguaçú: SBCD: 2000.
Merotto Jr A, Vidal RA, Fleck NG, Reis B, Andres A. Resistência de Echinochloasp à quinclorac. In: SBCPD (ed.): proceedings of the Congresso Brasileiro da Ciência das Plantas Daninhas, 6-11 June 2000, Foz do Iguaçú, Brazil, Foz do Iguaçú: SBCPD: 2000.
Kissmann KG, Groth D. Plantas infestantes e nocivas. São Paulo: BASF; 1997.
Lopez-Martinez N, Salva AP, Finch RP, Marshall G, Prado RD. Molecular markers indicate intraspecific variation in the control of Echinochloa spp. with quinclorac. Weed Science 1999; 47(3) 310-315.
Andres A, Concenço G, Theisen G, Galon L, Tesio F. Management of red rice (Oryza sativa) and barnyardgrass ( Echinochloa crus-galli) grown with sorghum with reduced rate of atrazine and mechanical methods. Experimental Agricultural 2012; 48(4) 587–596.
Ruiz-Santaella JP, Fischer AJ, De Prado R. Alternative control of two biotypes of Echinochloa phyllopogonsusceptible and resistant to fenoxaprop-ethyl. Communications in Agricultural and Applied Biological Sciences 2003; 68(4) 403-407.
Lopez-Martinez N, Marshall G, De Prado R. Resistance of barnyardgrass ( Echinochloa crus-galli) to atrazine and quinclorac. Pesticide Science 1997; 51(2) 171-175.
Mariot CHP, Menezes VG, Souza PA. Resistência múltipla e cruzada de capim-arroz a herbicidas na cultura de arroz irrigado no Rio Grande do Sul. In: SBCPD (ed.): proceedings of the Congresso Brasileiro da Ciência das Plantas Daninhas, 19-23 July 2010, Ribeirão Preto, Brazil. Londrina: SBCPD; 2010.
Eberhardt DS, Noldin JA, Gutierez M, Dittrich RC. Resistência de capim-arroz ( Echinochloa crusgalli) ao herbicida quinclorac. In: SBCPD (ed.): proceedings of the Congresso Brasileiro da Ciência das Plantas Daninhas, 6-11 June 2000, Foz do Iguaçú, Brazil, Foz do Iguaçú: SBCD: 2000.
Mariot CHP, Rubin R, Celmer A, Tormen N. Controle de capim-arroz resistente a imidazolinonas com a associação de Ricer + Clincher em arroz irrigado no Rio Grande do Sul. In: Epagri/SOSBAI (eds.): proceedings of the VII Congresso Brasileiro de Arroz Irrigado, August 2011. Balneário Camboriú, Brazil. Itajaí: Epagri/SOSBAI; 2011.
Noldin JA, Eberhardt DS, Rampelotti FT, Zunino J, Concenço G. Freqüência de plantas de Sagittaria montevidensisresistentes ao herbicida Only. In: SBCPD (ed.): proceedings of the Congresso Brasileiro da Ciência das Plantas Daninhas, 24-28 May 2004, São Pedro, Brazil. Londrina: SBCPD; 2004.
Gibson KD, Breen JL, Hill JE. California arrowhead is a weak competitor in water-seeded rice. Weed Science 2001; 49(3) 381-384.
Merotto Jr A, Kupas V, Nunes AL, Goulart ICGR. Isolamento do gene ALS e investigação do mecanismo de resistência a herbicidas em Sagittaria montevidensis. Ciência Rural 2010; 40(11) 2381-2384.
Concenco G, Noldin JA, Lopes N F, Comiotto A. Aspectos da resistência de Sagittaria montevidensisao herbicida pirazosulfuron-ethyl inibidor da ALS. Planta Daninha2007; 25 (1)187-194. http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-83582007000100021&lng=en&nrm=iso (access on 22 October 2012).
Eberhardt DS, Noldin JA. Multiple Herbicide-Resistant Sagittaria montevidensisPopulation in Santa Catarina State (Brazil) Rice Fields. WSSA Abstracts, 2011. http://www.weedscience.org/Case/Reference.asp?ReferenceID=1166 (accessed 22 October 2012).
Menezes VG, Kalsing A, Felin JP. Controle químico de Sagittaria montevidensis(SAGMO) em áreas de arroz cultivadas no sistema pré-germinado. In: Epagri/SOSBAI (eds.): proceedings of the VII Congresso Brasileiro de Arroz Irrigado, 9-12 August 2011. Balneário Camboriú, Brazil. Itajaí: Epagri/SOSBAI; 2011.
Sociedade Sul-Brasileira de Arroz Irrigado – SOSBAI. Arroz irrigado: recomendações técnicas da pesquisa para o Sul do Brasil. Porto Alegre: SOSBAI, 2012. http://www.sosbai.com.br/BoletimRecomendacoesTecnicas_2012.zip (accessed 22 October 2012).
Ferreira FB, Pinto JJO, Sperandio CA, Lamego FP, Resende AL, Lazaroto CA, Galon L. Influência da população de arroz na infestação de sagitária. In: SBCPD/Embrapa Clima Temperado (eds.): proceedings of the Congresso Brasileiro da Ciência das Plantas Daninhas, 29 July – 01 August 2002, Gramado, Brazil. Pelotas: SBCPD/Embrapa Clima Temperado; 2002.
Noldin JA, Eberhardt DS, Rampelotti FT. Cyperus difformis L. resistente a herbicidas inibidores da ALS em Santa Catarina. In: SBCPD/Embrapa Clima Temperado (eds.): proceedings of the Congresso Brasileiro da Ciência das Plantas Daninhas, 29 July – 01 August 2002, Gramado, Brazil. Pelotas: SBCPD/Embrapa Clima Temperado; 2002.
Galon L, Panozzo LE, Noldin JA, Concenço G, Tarouco CP, Ferreira EA, Agostinetto D, Silva AA, Ferreira FA. Herbicide Resistance of Cyperus difformisto ALS-Inhibitors in Paddy Rice of Santa Catarina. Planta Daninha 2008; 26(2) 419-427. http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-83582008000200019&lng=en&nrm=iso (accessed 25 October 2012)
Saari LL, Cotterman JC, Thill DC. Resistance to acetolactate synthase inhibiting herbicides. In: Powles SB, Holtur, JAM. (eds.) Herbicide resistance in plants: biology and biochemistry. Boca Raton: Lewis; 1994. p83-139.
Heap, I. International Survey of Herbicide Resistant Weeds. http://www.weedscience.org (accessed 22 October 2012).
Dal Magro T, Santos L, Schaedler CE, Agostinetto D, Vargas L, Noldin JA. Dose resposta de pyrazosulfuron-ethyl em biotipos de Cyperus difformisL. resistente e suscetível. In: SOSBAI/IRGA (eds.): proceedings of the VI Congresso Brasileiro de Arroz Irrigado, 11-14 August 2009. Porto Alegre, Brazil. Porto Alegre: SOSBAI/IRGA; 2009.
Ulguim AR, Agostinetto D, Vargas L, Manica-Berto R, Westendorff N, Rubin R, Danielowski H. Resistência de Cyperus iria l. (CYPIR) aos inibidores de acetolactato sintase (ALS) no Rio Grande do Sul. In: Epagri/SOSBAI (eds.): proceedings of the VII Congresso Brasileiro de Arroz Irrigado, 9 – 12 August 2011. Balneário Camboriú, Brazil. Itajaí: Epagri/SOSBAI; 2011.
Scherer MB, Dornelles, SHB, Sanchotene, DM, Macedo LCP de, Espíndola EFS, Cirolini AN. Manejo químico alternativo de Cyperus iriaresistente aos herbicidas inibidores da enzima ALS. In: Epagri/SOSBAI (eds.): proceedings of the VII Congresso Brasileiro de Arroz Irrigado, 9 – 12 August 2011. Balneário Camboriú, Brazil. Itajaí: Epagri/SOSBAI; 2011.
Kissmann KG. (ed.). Plantas infestantes e nocivas. São Paulo: BASF Brasileira S.A.; 2007.
Fleck NG, Agostinetto D, Galon L, Schaedler CE. Relative competitivity among flooded rice cultivars and a red rice biotype. Planta Daninha 2008; 26(1)101–111
Menezes VG, Silva PRF. Manejo de arroz-vermelho através do tipo e arranjo de plantas em arroz irrigado. Planta Daninha 1998; 16(1) 45-57.
Agostinetto D, Fleck NG, Rizzardi, MA, Merotto Jr A, Vidal RA. Red rice: Ecophysiology and Strategies of control. Ciência Rural 2001; 31(2) 341-349.
Croughan TP. Application of tissue culture techniques to the development of herbicide-resistant rice. Louisiana Agriculture 1994; 37(3) 25–26.
Zhang W, Linscombe SD, Webster E, Tan S, Oard J. Risk assessment of the transfer of imazethapyr herbicide tolerance from Clearfield rice to red rice ( Oryza sativa). Euphytica 2006; 152(1) 75-86.
Shivrain VK, Burgos NR, Sales MA, Mauromoustakos A, Gealy DR, Smith KL, Black HL, Jia M. Factors affecting the outcrossing rate between ClearfieldTM rice and red rice ( Oryza sativa). Weed Science 2009; 57(4):394–403.
Magalhães Jr AM, Franco DF, Andres A, Antunes P, Luzzardi R, Dode LB, Tillmann MAA, Silva MP. Método para identificação de sementes de arroz transgênico resistente ao herbicida glufosinato de amônio. Agropecuária Clima Temperado 2000; 3(1) 31-38.
Ramírez HB. Polinização cruzada em arroz irrigado. Doctoral thesis. Universidade Federal de Pelotas, Brazil; 2003.
Villa SCC, Marchezan E, Avila LA, Massoni PFS, Telo GM, Machado SLO, Camargo ER. Arroz tolerante a imidazolinonas: controle do arroz-vermelho, fluxo gênico e efeito residual do herbicida em culturas sucessoras não-tolerantes. Planta Daninha 2006; 24(4) 761-768.
Roso AC, Merotto Jr A, Delatorre A, Menezes VG. Regional scale distribution of imidazolinone herbicide-resistant alleles in red rice ( Oryza sativaL.) determined through SNP markers. Field Crops Research 2010; 119(1) 175-182.
Burgos NR, Norsworthy JK, Scott RC, Smith KL. Red rice ( Oryza sativa) status after 5 years of imidazolinone resistant rice technology in Arkansas. Weed Technology 2008; 22() 200–208.
Menezes VG, Ramirez H. Resistance Echinochloa crus-galliL. to quinclorac in flooded rice in southern Brazil. In: IWSC (ed.) proceedings of the III International Weed Science Congress, 6 - 11 June 2000, Foz do Iguaçu, Brazil. Corvalis: IWSC; 2000.
Menezes VG, Mariot CHP, Oliveira CAO, Kalsing A, Soares DC. Resistência de capim-arroz a herbicidas do grupo químico das imidazolinonas no sul do Brasil. In: SOSBAI/IRGA (eds.): proceedings of the VI Congresso Brasileiro de Arroz Irrigado, 11-14 August 2009. Porto Alegre, Brazil. Porto Alegre: SOSBAI/IRGA; 2009.
Ulguim AR, Westendorf N, Noldin JA, Agostinetto D, Manica-Berto R, Ludtke R, Thurmer L. Resposta de biótipos de Echinochloa crusgalli(L.) Beauv. resistentes e suscetível aos inibidores de ALS. In: Epagri/SOSBAI (eds.): proceedings of the VII Congresso Brasileiro de Arroz Irrigado, 9 – 12 August 2011. Balneário Camboriú, Brazil. Itajaí: Epagri/SOSBAI; 2011.
Dornelles SHB, et al. Controle pré-emergente de Cyperus iriaresistente a herbicidas inibidores da enzima ALS. In: Epagri/SOSBAI (eds.): proceedings of the VII Congresso Brasileiro de Arroz Irrigado, 9 – 12 August 2011. Balneário Camboriú, Brazil. Itajaí: Epagri/SOSBAI; 2011.
Dornelles SHB, et al. Cyperus iriaresistente a herbicidas inibidores da enzima Aceto Lactato Sintase. In: Epagri/SOSBAI (eds.): proceedings of the VII Congresso Brasileiro de Arroz Irrigado, 9 – 12 August 2011. Balneário Camboriú, Brazil. Itajaí: Epagri/SOSBAI; 2011.
Concenço G, Melo PTBS, Ferreira EA, Silva AF, Aspiazú I, Galon L, Ferreira FA, Silva AA, Noldin JA. Competitividade de biótipos de capim-arroz resistente e suscetível ao quinclorac. Planta Daninha 2008; 26(1) 195-202.
Mariot CHP, et al. Resistência múltipla e cruzada de capim-arroz a herbicidas na cultura do arroz irrigado no Rio Grande do Sul. In: SBCPD (ed.): proceedings of the Congresso Brasileiro da Ciência das Plantas Daninhas, 19-23 July 2010, Ribeirão Preto, Brazil. Londrina: SBCPD; 2010. [CD-ROM].
Merotto Jr A, Kupas V, Nunes AL, Costa RF. Resistência de Capim-arroz ( Echinochloa crusgalli) aos herbicidas inibidores da enzima ALS. In: SOSBAI/IRGA (eds.): proceedings of the VI Congresso Brasileiro de Arroz Irrigado, 11-14 August 2009. Porto Alegre, Brazil. Porto Alegre: SOSBAI/IRGA; 2009. http://www.sosbai.com.br/admin/artigos/bk20100528133117.pdf (accessed 12 October 2012).
Perboni LT, et al. Controle de capim-arroz resistente e suscetível à ALS pela aplicação de herbicidas em diferentes épocas. In: Epagri/SOSBAI (eds.): proceedings of the VII Congresso Brasileiro de Arroz Irrigado, 9 – 12 August 2011. Balneário Camboriú, Brazil. Itajaí: Epagri/SOSBAI; 2011.
Noldin JA, Eberhardt DS, Andrade S, Pinheiro GF. Capim-arroz com resistência múltipla a herbicidas em Santa Catarina. In: SOSBAI/IRGA (eds.): proceedings of the VI Congresso Brasileiro de Arroz Irrigado, 11-14 August 2009. Porto Alegre, Brazil. Porto Algre: SOSBAI/IRGA; 2009. http://www.sosbai.com.br/admin/artigos/bk20100528133117.pdf (accessed 12 October 2012).
Pinto JJO, Noldin JA, Donida A da C, Piveta LB, Pinho CF de, Pohlmann TS, Batista DD. Controle de capim-arroz em áreas de arroz com suspeita da presença de biótipos resistentes a herbicidas inibidores da ALS. In: SOSBAI/IRGA (eds.): proceedings of the VI Congresso Brasileiro de Arroz Irrigado, 11-14 August 2009. Porto Alegre, Brazil. Porto Alegre: SOSBAI/IRGA; 2009.
Theisen G, Andres A. Tolerância de capim-arroz ( Echinochloa crus-galli spp.) ao herbicida imazetapir + imazapic em arrozais da região Sudeste do RS. Pelotas, Brazil: Embrapa Clima Temperado; 2010. http://www.cpact.embrapa.br/publicacoes/download/comunicados/comunicado_253.pdf (accessed 22 October 2012).
Rampelotti FT, et al. Monitoramento da resistência de Cyperus difformise Fimbristylis miliaceaaos herbicidas inibidores de ALS em Santa Catarina. In: SBCPD (ed.): proceedings of the Congresso Brasileiro da Ciência das Plantas Daninhas, 24-28 May 2004, São Pedro, Brazil. Londrina: SBCPD; 2004.
Noldin JA, Eberhardt DS, Rampelotti FT. Fimbristylis miliacea(L.) Vahl resistente a herbicidas inibidores da ALS em Santa Catarina. In: SBCPD/Embrapa Clima Temperado (eds.): proceedings of the Congresso Brasileiro da Ciência das Plantas Daninhas, 29 July – 01 August 2002, Gramado, Brazil. Pelotas: SBCPD/Embrapa Clima Temperado; 2002.
Empresa de Pesquisa Agropecuária e Extensão Rural de Santa Catarina – EPAGRI. Sistema de produção de arroz irrigado em Santa Catarina (pré-germinado). Florianópolis, Brazil: EPAGRI; 2010.
Marchezan E, Oliveira APBB, Avila LA, Bundt ALP. Red rice seed bank dynamics affected by cattle trampling and fallow duration. Planta Daninha 2003; 21(1) 55-62.
Valverde BE. Status and management of grass-weed herbicide resistance in Latin America. Weed Technology 2007; 21(2) 310-323.
Chaves ICPV, Garcia L. Avaliação da combinação de Aurora 400 CE + Gamit 500 CE, aplicada em mistura com glifosato, na dessecação de erva-de-bicho ( Polygonum persicaria) e seu efeito residual no controle de capim-arroz ( Echinochloasp.). In: SOSBAI (ed.): proceedings of the IV Congresso Brasileiro de Arroz Irrigado and XXVI Reunião da Cultura do Arroz Irrigado, 9 – 12 August 2005. Santa Maria, Brazil. Santa Maria: Orium/SOSBAI; 2005. [CD-ROM].
Riches CR, Knights JS, Chaves L, Caseley JC, Valverde BE. The role of pendimethalin in the integrated management of propanil-resistant Echinochloa colona in Central America. Pesticide Science 1997; 51 (3) 341-346.
Valverde BE, Riches CR, Caseley JC. Prevention and management of herbicide-resistant weeds in rice: experiences from Central America with Echinochloa colona. Costa Rica: Cámara de Insumos Agropecuarios; 2000.
Andres A, Machado SLO. Plantas daninhas em arroz irrigado. In: Gomes AS, Magalhães Jr AM (eds.) Arroz irrigado no sul do Brasil. Brasília: Embrapa; 2004. p.611-726.
Gill GS, Holmes JE. Efficacy of Cultural Control Methods for Combating Herbicide-Resistant Lolium rigidum. Pesticide Science 1997; 51(3) 352-358.
Vencill W, Grey T, Culpepper S. Resistance of Weeds to Herbicides, Herbicides and Environment, Dr Andreas Kortekamp (Ed.). Rijeka: InTech; 2011. http://www.intechopen.com/books/herbicides-and-environment/resistance-of-weeds-to-herbicides (accessed 22 October 2012).