The research programme undertaken at Rice Research Station, Moncompu, Kerala Agricultural University, for the post-emergence management of weedy rice by direct contact application (DCA) of broad-spectrum non-selective herbicides using specially designed novel hand held weed wiper device could selectively dry the panicles of weedy rice at 60–65 DAS, taking advantage of the height difference of 15–20 cm between weedy rice and cultivated rice. The study revealed that DCA can be effectively done in weedy rice infested cropped field using non-selective herbicides, viz. glufosinate ammonium, paraquat dichloride or glyphosate at 1015% concentration. Weed control efficiency by this method in terms of drying of the weedy rice panicles was as high as 83 to 88%. The device has been filed for Indian Patent at Patent Office, Chennai (Application No. 1763/CHE/2014 dated 01.04.2014). The technology can reduce the seed rain and buildup of soil seed bank of weedy rice. It is highly energy efficient, less labour intensive, and ecofriendly compared to hand weeding, cutting of weedy rice ear heads or application of large quantity of herbicides using sprayers. The device has become popular among the farming community of Kerala and transfer of technology of the device was done during 2015. The product is now marketed as ‘KAU Weed Wiper’ by M/s Raidco Ltd, for large scale manufacturing and sale to farmers.

Tropical and humid conditions of Kerala provide a favorable environment for emergence of a wide range of plant species. Reduction in crop yield due to weeds has been estimated to be 30–80% under varying intensities. Due to the severity of weed problem, hike in labour wages and acute labour scarcity during the peak period of demand, chemical weed control has become indispensable in rice cultivation. The increasing use of herbicides in rice and rice–based cropping systems is of great concern because these chemicals may act as pollutants which can cause soil-plant-animal health hazards, deterioration of soil quality and other residue related problems. Therefore, recommendations on weed control can be evolved only if the residue studies confirm that these chemicals are dissipated from the environment soon after their mission is accomplished. A long-term herbicide trial in rice- rice system showed that continuous application of butachlor/pretilachlor in rice for 13 years from 2001 to 2014 in a lateritic soil did not result in build-up of residues in soil, grain and straw. Farmyard manure application significantly improved the bioefficacy of herbicides. Increasing organic matter content increased the rate of adsorption of herbicides as well as degradation by soil micro flora. Research results indicated that indiscriminate use of 2,4-D in lowland paddy fields in Kuttanad region (lying below the sea level) resulted in the persistence of residues in water bodies. Long-term application of herbicides had no significant negative effect on the basic soil properties, viz. pH, organic C and available nutrients.

Mimosa invisa Mart. (Mimosaceae) is an alien invasive weed, spreading rapidly in all topographies of Kerala, especially in the open areas and pastures. Since its introduction to Kerala in 1964, it has emerged as a problem weed adversely affecting the biodiversity of the area of infestation. The heliophytic nature, high smothering index and allelopathic effects contribute to the adverse effects of the plant on the accompanying vegetation. Studies at the Kerala Agricultural University during 2002-2004 confirmed that the suppression of the native flora by M. invisa was more conspicuous on grass weeds (21%) compared to broad leaved weeds (11%). The smothering efficiency of M. invisa increased by 25 percent towards the third year of infestation in pastures, which is an indication of the competitive ability and aggressive nature of the plant. This study emphasises that adoption of proper control measures against M. invisa during the early years of infestation is necessary to contain the weed infestation.

Leptochloa chinensis (L.) Nees. (Chinese sprangletop or Red sprangletop) is one of the most important invasive weeds in direct-seeded rice fields (Chin 2001). In Kerala, Chinese sprangletop was reported as a new weed specific to the alkaline soils of Chittoor taluk (Vidya et al. 2004). Though this weed is listed as an indicator plant for alkaline conditions, it is now seen spreading rapidly in acidic soils of Kerala also with typical example of weed shift. Continuous use of bispyribac-sodium, which is one of the most popular rice herbicides among farmers in Kerala, to control barnyard grass resulted in the dominance of Chinese sprangletop. In view of the growing menace of Leptochloa chinensis in the rice fields of Kerala, it is important to develop a new herbicide strategy by making use of the new molecule herbicides or the preand postemergence herbicides already in use for effective control.

Manual cono weeding in rice is a tedious job requiring more labour and energy. An effort was made to develop prototype of a self propelled cono-weeder under the AICRP on Weed Management at the College of Horticulture, Kerala Agricultural University, Vellanikkara, Thrissur with an objective to reduce drudgery involved in manual cono-weeding in rice. Main components of the newly developed self propelled cono-weeder are the main frame, a prime mover, front and rear floats and a rotor. Field experiment was conducted at Pattambi in Palakkad district to study the performance of the prototype in comparison with manual cono weeding and conventional weeding methods in rice. The weed density, weed dry weight and the grain and straw yields of rice at various treatments were observed. It was found that self propelled cono-weeder had a field capacity of 0.1 ha/h at an operating speed of 2.0–3.0 km/h. The weeding efficiency of the unit in rice was at par with that of the manual cono-weeder operated twice at 15 and 30 days after transplanting.

An experiment was conducted to assess the performance of rice under the system of rice intensification (SRI) in comparison with the conventional system of cultivation. The field studies were carried out during the rabi seasons of 2007 and 2008 in the lateritic sandy clay loam soils of RARS, Pattambi, Palakkad district in Kerala, having pH 5.00 and medium fertility, in RBD with 16 treatments replicated thrice. The weed density and dry weight were higher in SRI. Growth parameters such as plant height, number of tillers hill-1 and dry matter production hill-1, and yield parameters like number of productive tillers hill-1 and length of panicle were significantly higher in the SRI treatments, whereas the tiller density, dry matter production per unit area, the grain yield per hectare and the B:C ratio were higher in the conventional system. Hence it is concluded that in the irrigated rice tracts of Kerala conventional system of rice cultivation is more advantageous than the SRI in terms of crop yield and economics of cultivation.

The present study was conducted to find out the extent of leaching of butachlor, pretilachlor, 2,4-D and oxyfluorfen in two soil types, viz. Type I [coarse textured low organic matter soil (Mannuthy–Ultisol] and Type II [fine textured high organic matter soil (Alappad-Inceptisol]. Intact soil columns were collected from the paddy fields after the harvest of second crop. Butachlor, pretilachlor, 2,4-D and oxyfluorfen were applied in moist soil columns at the recommended rate of application. Soil samples from different depths up to 10 cm (top 5 segments of 2 cm each) and the leachate at 30 and 60 cm depths were analyzed for herbicide residues using gas chromatography. Among the four herbicides tested, 2,4-D registered highest level of residue in the leachate (0.20 ppm at 60 cm depth). Pretilachlor and butachlor followed the same trend in the pattern of movement of residue through the soil columns. However, the leachate of pretilachlor registered much lower quantity of residue (0.006 ppm). Fine textured organic matter rich soil recorded lower residue levels compared to the soil with coarse texture and poor organic matter. It could be attributed to the high adsorptive power of the soil, especially at the top layers with high organic matter content. Oxyfluorfen residues could not be detected in the leachate, because of its poor water solubility.

A long-term trial was conducted in the coconut plantation at Thrissur, Kerala, India from July 2008 to June 2013. Time series analysis was performed with monthly weed count data to determine seasonality of selected weeds of a coconut garden. A multiplicative model was assumed for the time series and the seasonal index was worked out for each weed species. The results revealed that Axonopus compressus, Biophytum sensitivum and Mimosa pudica dominated during the South West monsoon season while Curculigo orchioides and Desmodium gangeticum were seen germinating during the North East monsoon period from September - October and were predominant in the field till February. Hemidesmus indicus and M. pudica were the weed species seen throughout the year. However, their predominance was the field was between November to April and July to November, respectively.

The persistence and bioefficacy of butachlor and pretilachlor in rice-rice system in a lateritic soil with and without farm yard manure (FYM) is reported. Initial residues (at one and 15 d after spraying, DAS) of butachlor and pretilachlor in soil were significantly higher in the treatments with organic manure. However, at 30 DAS and at the time of harvest, the residues did not differ significantly among the treatments. The enhanced degradation of herbicides over time in the presence of organic matter is apparently responsible for it. Higher levels of pretilachlor residues compared to butachlor were observed (0.121 and 0.056 μg g−1 for the treatments pretilachlor+ FYM and butachlor + FYM respectively) at 15DAS. The enhanced retention in the FYM treated plots was reflected in the weed control and crop yield.

Weedy rice (Oryza sativa f. spontanea) is the complex of morphotypes of Oryza species, evolved largely by natural hybridization between wild and cultivated rice. With diverse biotypes, weedy rice has already infested large rice growing areas across the globe. It has also become a threat in major rice tracts of eastern and southern India. The weed has distributed in the commercial rice fields especially in areas where farmers have switched to direct-seeding due to labour shortage and high cost. Weedy rice has competitive advantage over cultivated rice as it grows taller and faster, tillers profusely and competes with cultivated rice for nutrients, light and space. It flowers much earlier than cultivated rice and produces grain that shatter easily thus enhancing the weed seed bank. Survey conducted has revealed the presence of weedy rice variants with respect to morphological characters like number of tillers per plant, height of plant, length of ligule, panicle characters, colour of grains, and length and colour of awns. Management of weedy rice infestation is complex mainly because of its morphological similarities to cultivated rice and lack of herbicides for selective control of weedy rice in cropped fields. Management options found effective for the control of weedy rice in direct seeded puddled rice include pre sowing surface application of oxyfluorfen 0.3 kg/ha, three DBS in thin film of water and selective drying of weedy rice panicles by direct contact application of glufosinate-ammonium or glyphosate or paraquat 15–20% concentration at 60–65 DAS using specially designed wick applicator. Stale seedbed technique with dry and wet ploughing followed by the application of a broad spectrum herbicide and flooding proved to be effective in exhausting soil seed bank. Integrated management strategies are to be adopted for effective control of weedy rice.

The influence of source of organic matter on the dissipation of two chloroacetamide herbicides butachlor and pretilachlor, in a lateritic soil under flooded condition is reported. Two exogenous sources of organic matter viz., farm yard manure (FYM) and vermicompost, and soil alone (control) were taken as treatments under each herbicide. The soil was kept under submerged condition in mud pots by maintaining 3 cm water above the soil surface. The herbicides, butachlor and pretilachlor were applied @ 1.25 and 0.45 kg ai ha−1 respectively and each manure @ 5.0 t ha −1. The results showed that butachlor as well as pretilachlor with FYM dissipated slowly compared to soil alone and vermicompost. At one day after application of herbicides, significant variation in the dissolved organic carbon (DOC) content was noticed among the organic manure treatments. The initial concentration of residues in soil (1 day after spraying, DAS) was lowered by DOC released from the farmyard manure, However, total organic carbon content was significantly higher under FYM treatment up to four weeks after herbicide application. The half life of both the herbicides was also higher in FYM treatment as compared to vermicompost and control (soil alone). The results indicated superiority of FYM in retaining the herbicides for longer period of weed control in rice.

A study to identify the prevalence of co-morbidity among Chronic Obstructive Pulmonary Disease patients seeking treatment in outpatient department of Bhopal Memorial Hospital & Research Centre, Bhopal. Objectives:

Experiments were carried out in the field and laboratory during 2001-02 to study the persistence of three herbicides, namely butachlor, pretilachlor (Rifit) and 2,4-D in a rice – rice system and the effect of their residues on soil micro flora. Irrespective of the seasons and treatments, all the three herbicides dissipated quickly from soil and no residues were detected at the time of harvest. Even in the plots where butachlor was sprayed continuously for the four crop seasons without addition of organic matter, more than 96.20 per cent of the applied herbicide disappeared from the soil by 30 days after spraying. Therefore, alternate application of butachlor or pretilachlor between years or seasons could not exert any influence on their persistence in soil. The results also indicated that considerable variation in the microbial population would result from the application of herbicides. However, the change was observed only for a short period. Drastic decline in the population of soil bacteria noticed at one day after the application of herbicides extended up to 30 to 45 days in the first crop and 15 to 30 days in the second crop. In all the treatments, microorganisms attained the initial (normal) level of population by the time of harvest. Inhibitory effect of the herbicides was more on soil bacteria than soil fungi or actinomycetes and the extent of inhibition was more manifested by the application of butachlor than pretilachlor. The treatments with farmyard manure had higher population of micro flora at all the sampling intervals and they registered higher rate of degradation of butachlor, pretilachlor and 2,4-D in the soil.

A field experiment was conducted during rabi season in a farmer’s field in the Kole lands at Pullu in Thrissur district during the period November 2012 to March 2013. The treatments included application of both pre emergence and post emergence herbicides. The pre emergence herbicides selected were oxyfluorfen sprayed at 3 days after sowing (DAS) and butachlor and pretilachlor sprayed at 6 DAS. Pyrazosulfuron-ethyl, an early post emergence herbicide, was sprayed at 8 DAS. The herbicides cyhalofop butyl, fenoxaprop- p-ethyl, metamifop, penoxsulam, bispyribac sodium and azimsulfuron, are post emergence in action and were sprayed at 20 DAS. Hand weeded (handweeding at 20 and 40 DAS) and unweeded controls were also included for comparison with the herbicide treatments. The best herbicide for control of grass weeds was either fenoxaprop-p-ethyl @ 60 g a.i. ha-1 or cyhalofop butyl @ 80 g a.i. ha-1, both applied at 20 DAS. Broad spectrum weed control can be made possible by spraying herbicide combinations that could give higher yield and B:C ratio.

An experiment was conducted to assess the efficacy of different weed management practices in rice grown under the System of Rice Intensification (SRI) in comparison with the conventional system. The study was carried out during 2007 and 2008 in the lateritic sandy clay loam soils at Pattambi, Kerala. Density and dry weight of weeds were higher in SRI especially when weed control was done through repeated cono weeding, while they were lower in the conventional system. Conventional system with cono weeding at 10 DAT followed by hand weeding at 30 DAT, and post-emergence herbicides alone reduced the weed dry weight significantly. Net returns and B:C ratio were also the highest in the conventional system with post-emergence application of cyhalofop-butyl 0.1 kg/hafollowed by metsulfuron-methyl + chlorimuron-ethyl. In SRI, the weed density and dry weight were the lowest with pre-emergence herbicide followed by hand weeding at 30 DAT, and cono weeding at 10 DAT followed by post-emergence herbicides. However, weed control with post-emergence application of cyhalofop-butyl, followed by metsulfuron-methyl + chlorimuron-ethyl gave higher B:C ratio in both systems.

Weedy rice are complex of Oryza morphotypes widely distributed in the commercial rice fields in more than 50 countries of Asia, Africa and Latin America, especially in areas where farmers have switched to direct seeding due to labour shortage and high cost. Wild and weedy forms of different species coming under the genus Oryza are also known as wild rice, red rice, padi angin, windy rice, air rice, varinellu, wild rice etc. Southeast Asia has been identified as the centre of origin of rice and many wild and weedy relatives are present in different rice growing areas of this region. Indian weedy rice is identified as Oryza sativa f. spontanea which belongs to the indica group. They are major threat to irrigated rice production systems in Southeast Asian countries because of their great adaptability to emerge at low temperature and from deep soil or water depths. Weedy rice is problematic, especially in Asian rice bowls. The spread of wild rice takes place in West Bengal, Andhra Pradesh, Assam, Bihar, Karnataka, Madhya Pradesh, Orissa, Tamil Nadu and Uttar Pradesh. Wild and weedy forms are problematic in Eastern India (Eastern U. P., Bihar, Orissa, Manipur, and West Bengal) and Southern India (Kerala). In North Western states like Punjab and Haryana, weedy rice is rarely seen. Heavy infestation of weedy rice in rice fields during the recent years is forcing farmers to abandon the crop due to huge reduction in crop yield (around 40-70 per cent) depending on the severity of infestation (5-15 or even more mature weedy plants per square meter). Genetic and morphological similarity of weedy rice to the cultivated species makes it difficult to control and chemical methods alone are unlikely to be effective.Origin and spread of weedy riceCultivated rice is included in the genus Oryza of the grass family (Poaceae). This genus includes two cultivated species (Asian rice - Oryza s ativa, and African rice - O. glaberrima) and more than 20 wild species with ten different genome types, i.e., AA, BB, CC, BBCC, CCDD, EE, FF, GG, JJHH, and JJKK. The wild relatives of rice with different genome types usually have significant reproductive isolation, making them unlikely to hybridize under natural conditions. The AA genome weedy and wild relatives are highly compatible sexually with cultivated rice. Their interspecific F hybrids could form complete chromosome pairing in meiosis and have relatively high pollen 1 and seed fertility to produce viable offspring. It is widely hypothesized that weedy rice has a variety of origin.Weedy plants are adapted to a wide range of environmental conditions. The spread is generally favoured by the planting of commercial rice seeds that contain grains of the weed. The spread of weedy rice is likely to be accomplished by several means, including water, cattle, farm machinery, and as contaminants of new varieties. Disk cultivation also helped to move the seeds downward to the 3 - 15 cm soil layer resulting in serious infestations and difficulties in control.

An experiment was conducted at Kole lands in Thrissur district, Kerala to study the efficacy of various post-emergence herbicides in wet-seeded rice. The results showed that cyhalofop-butyl + chlorimuronethyl + metsulfuron-methyl, fenoxaprop-p-ethyl + chlorimuron-ethyl + metsulfuron-methyl and bispyribac-sodium were best treatments with a lower weed biomass as well as high grain yield and B:C ratio. Maximum weed control efficiency of 97.1% was obtained in hand weeded plots followed by bispyribac-sodium (93.6%). The highest grain yield of 6.13 t/ha was recorded in hand weeded plot which was at par with cyhalofop-butyl + chlorimuron-ethyl + metsulfuron-methyl and fenoxaprop + chlorimuron ethyl+ metsulfuron-methyl (5.8 t/ha). From this study it can be concluded that, cyhalofop-butyl with a follow up spray of chlorimuron-ethyl + metsulfuronmethyl or fenoxaprop-p-ethyl with a follow up spray of chlorimuron-ethyl + metsulfuron methyl or bispyribac sodium alone can be recommended for effective post emergence weed control and higher yield in wet seeded rice. If grasses are the predominant weeds, cyhalofop-butyl or fenoxaprop-p-ethyl alone without follow up spray of chlorimuron-ethyl + metsulfuron-methyl can also be recommended.

Studies to assess the influence of plant population and management under the System of Rice Intensification (SRI) on crop-weed competition was conducted in farmer's field at Thrissur district, Kerala, during the second crop seasons (rabi) of 2005–06 and 2006–07. The experiment was laid out in split plot with two mainplot treatments of weeding and unweeding and five subplot treatments of spacing and management. Increase in crop density under closer spacing significantly reduced the number and dry matter production of weeds. Cono weeding was not effective in controlling weeds growing very close to the rice plants. Number and dry matter production of weeds were higher in SRI plots. The uptake of nutrients by weeds was minimum in closer spacing. Weed control efficiency was also maximum for closer plant spacing of 10 cm x 10 cm. The highest grain yields of 8858 kg/ha and 8358 kg/ha during first and second years of study were observed in closer spacing of 10 X 10 cm followed by 20 x 10 cm both under normal package of practices with weeding. The yield obtained from 20 x 10 cm plots with weeding and 10 cm x 10 cm without weeding were on par showing the importance of closer spacing as a weed management strategy. Among the weeded plots, the lowest grain yield of 5250 kg/ha was observed in SRI plots with cono weeding. Uptake of nutrients by the crop was higher in plots with closer spacing with weeding.

The traditional system of growing tall rice ( Oryza sativa L.) varieties during the monsoon season and prawn culture (prawn filtration) during summer season, locally known as pokkali , is a sustainable system of production harmoniously blended with natural processes like sea water inundation in the low-lying coastal zones of Kerala. A two year field study at Vyttila, Kerala, India evaluated spatial and temporal integration of high yielding pokkali rice genotypes with varying morphological characters (VTL3, culture-1026, and ‘Chettivirippu’ mutant) with fish [etroplus ( Etroplus suratensis Bloch), rohu ( Labeo rohita F. Hamilton) and tilapia ( Oreochromis mosambicus Peters)] and tiger prawn ( Peneaus monodon Fabricus) grown in succession. Culture-1026 showed better growth and yield (4391 kg ha–1) over VTL3 (2434 kg ha–1) and ‘Chettivirippu’ mutant (3950 kg ha–1). Among the fishes tried, all male population of tilapia outperformed etroplus and rohu in terms of survival (37.6, 0.0, and 16% respectively) and yield (216.7, 0.0, and 12.7 kg ha–1 respectively) when grown simultaneously with rice. Inclusion of tiger prawn as a rotational component during summer enhanced profitability (prawn yield 425 kg ha–1) and benefit-cost ratio (2.03). Although no direct effect of the components on pH, electrical conductivity, organic carbon content, available phosphorus, available potassium, and available sodium of the soil were noted, seasonal variations in water quality and consequent changes in soil properties were evident. Compatibility of the components, stable yields, favourable soil physico-chemical and hydrological parameters, and economic returns contribute to the sustainability of this production system.