Integrated Weed Management in Chili under Rice fallow Situation

CONTENTS

ABSTRACT

I INTRODUCTION

II REVIEW OF LITERATURE

III MATERIALS AND METHODS

IV EXPERIMENTAL FINDINGS

V DISCUSSION

VI SUMMARY AND CONCLUSION

BIBLIOGRAPHY

ANNEXURE

APPENDICES

PLATES

LIST OF TABLES

3.1 Physico-chemical properties and available nutrients in soil before planting of chili

3.2 Schedule of plant protection measures

4.1 Weed flora associated with chili crop

4.2 Weed density at various days after planting of chili as affected by treatments

4.3 Weed dry weight at various days after planting as affected by treatments

4.4 Plant height at various growth stages of crop as affected by treatments

4.5 Number of branches per plant at 60 days after planting as affected by treatments

4.6 Days to flower initiation and 50 per cent flowering in chili as affected by treatments

4.7.1 Fruit characteristics of chili as affected by treatments

4.7.2 Fruit girth and number of seeds per fruit as affected by treatments

4.7.3 Yield attributing characters of chili as affected by treatments

4.7.4 Fruit yield (fresh and dry) of chili as affected by treatments

4.8 Biochemical parameters of chili as affected by treatments

4.9 Organic carbon and available nutrient content in soil after harvest of chili

4.10 Economics of different treatments

LIST OF FIGURES

3.1 Meteorological data during period of experimentation (January 2012 to May 2012)

3.2 Plan and layout of the experimental plot

4.1 Weed dynamics associated to chili under rice fallow situation

4.2 Effect of weed management on weed density and weed dry weight of chili

4.3 Fresh and dry yield of fruits as affected by treatments

LIST OF PlateS

1 General view of the experimental plot

2 Metribuzin @ 500 g/ha + Garden hoe 30, 60 DAP

3 Quizalofop-p-ethyl @ 50 g/ha + Garden hoe 45, 75 DAP

4 Garden hoe 20, 40, 60, 80 DAP

5 Weedy

6 Harvested Chili

ACKNOWLEDGEMENT

At the very outset, the authoress would like to express her deepest sense of gratitude to the people who have been instrumental in the successful completion of her thesis. With immense pleasure, the authoress would like to thank her major advisor Dr. J. Deka, Principal Scientist & PI, DWSR, Department of Agronomy, who motivated her, encouraged every time and shown his keen interest. It was his zeal and enthusiasm, which made it possible for the authoress to complete the works.

The authoress is pleased to express her gratitude to Dr. P.K. Gogoi, Professor and Head, Department of Agronomy and Director of Post Graduate studies, Assam Agricultural University, Jorhat for providing necessary facilities during the course of experimentation.

The guidance and support received from all the members of her advisory committee, Dr. I. C. Barua, Principal Scientist, Department of Agronomy, Dr. S. Baishya, Associate Professor, Department of Biochemistry and Agricultural Chemistry, Dr. K. Das, Associate Professor, Department of Crop Physiology, Assam Agricultural University for their genuine concern, valuable advice and encouragement throughout the research work.

The authoress would also like to offer her sincere gratitude and special thanks to Dr. H. C. Bhattacharya, Director of Extension Eduation, Dr. N. Borah, Professor, College of Horticulture and Dr. A. M Baruah, Associate Professor, Department of Biochemistry and Agricultural Chemistry for their support and help in her research work.

She is also grateful to the people who helped in her field experimentation Dr. K. Hazarika, Farm Manager, ICR Farm and all staff who assisted in her work.

The authoress has no words to express her gratitude and sense of obligation she feels for her members of her family. Papa, Maa, Gautam bhaiya, and Kavita, to whom this manuscript is dedicated for showering their blessings, love and support and for being a part of strength without which it could not have been possible for her to bring mammoth task to completion.

Above all, the authoress expresses her sincere thanks to almighty God for his heavenly blessings, sufficient Grace & strength that He bestows on her.

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ABSTRACT

A field experiment was conducted at the Instructional-cum-Research (ICR) farm of Assam Agricultural University in 2012 to study the effect of weed management practices on growth and yield of chili after winter rice. The treatments comprised of ten different weed management practices including control. The experiment was laid out in Randomized Block Design (RBD) with three replications.

The study revealed that the weed density as well as dry weight were lowest in the treatments with metribuzin @ 500 g/ha combined with garden hoeing at 30, 60 or 30, 50, 60 or 30, 60, 80 days after planting over the rest of the treatments. Among the weed management treatments, a higher weed density was observed in the three treatments of quizalofop-p-ethyl @ 50 g/ha followed by garden hoeing at 45, 75 or 60, 80 or 50, 80 days after planting. Plant height, days to 50 per cent flowering, numbers of primary and secondary branches were highest in metribuzin treated plots. Length of fruit and stalk, fruit girth, number of seeds per fruit, number of fruits per plant and yield per plant were relatively higher with treatments involving metribuzin. The fruit yield (fresh and dry) was also found to be higher in the metribuzin treated plots. Mechanical weeding with garden hoe alone closely followed metribuzin treatments in respect of fruit yield. The available nutrient was found to be lower in the plots with metribuzin treatment or mechanically weeded with only garden hoeing at different intervals. The yield loss due to uncontrolled weeds in weedy check (287 kg/ha) as compared to the highest yield (3417 kg/ha fresh chili) obtained from metribuzin 500 g/ha + garden hoeing at 30, 50 and 80 DAP was 91 per cent. The benefit-cost ratio was found to be highest (Abbildung in dieser Leseprobe nicht enthalten 2.60) in metribuzin @ 500 g/ha along with garden hoeing 30, 50, 80 days after planting. The biochemical attributes like ascorbic acid (62.1 mg/100g) and capsaicin content ( ~ 60.6 mg/100g) were found to be significantly higher in metribuzin @ 500 g/ha with garden hoeing at 30 and 60 or 30, 50 and 80 days after planting over the above treatments.

From this study, it could be inferred that application of metribuzin @ 500 g/ha with garden hoeing at 30, 50, 60 days after planting controlled the weeds in chili effectively and resulted higher fruit yield, quality of chili and economic return.

CHAPTER IINTRODUCTION

Chilies are cultivated as vegetables as well as condiments and used around the world as sweet pepper, pungent chili pepper, or as source of dried powders of various colours and is cultivated as an annual crop worldwide. Chili (Capsicum annuum L.) is one of the most important vegetable-cum-spice crops valued for its aroma, taste, flavour and pungency. A wide range of variability reportedly exists in this crop (Nandi, 1992; Munshi and Behera, 2000). Chili varieties are generally classified based on fruit characteristics, i.e. color, pungency, flavour, shape, size and use (Smith et al., 1987). Chilies are a rich source of vitamin A and C, also called capsule of vitamin C and contain appreciable amount of calcium, phosphorus and iron. The pungency of chili or chili heat is due to capsaicin (C9H14O2) which is a complex of seven closely related alkaloids or capsaicinoids (Bosland, 1992). Chili is included in the genus Capsicum that belongs to family Solanaceae. Capsicum annuum is a variable herb or sub- shrub sometimes woody at base, erect, much branched, 0.5-1.5 m high, annual with strong taproot usually broken or arrested in growth on transplanting and numerous profusely branched laterals develop, extending to about 1m.

Asia produces 65.8 per cent of world green chilies and pepper and stands at the top, in contrary to 12.1 per cent by Europe and 9.5 per cent by Africa. India is the largest producer of chilies in the world contributing 25 per cent (11 lakh tons) of the total world production. Assam contributes 0.10 lakh metric tons of chili from 0.15 lakh ha area with an average yield of 654 kg/ha. Chili is used as an essential condiment in foods for its pungency and red colour. It is used in homeopathy also. A non-conventional use of chili is in the self-defence sprays, which are gaining popularity in USA. The spray consists of capsicum oleoresin at ultra high emission rate, which temporarily immobilizes the attacker. India is exporting chilies to a large number of countries spread all over the world in the form of chili powder, dried chilies, pickled chilies, chili oleoresins and many more.

Even if India ranks first among the chili producing countries over the world, certain production constraints are present in chili like incidence of diseases and pest, absence of hybrid technology, absence of varieties rich in capsaicin, oleoresin, capsanthin and problems of weed.

Weeds emerge fast and grow rapidly competing with the crop severely for growth resources viz. nutrients, moisture, sunlight and space during entire vegetative and early reproductive stages of the crop. They transpire lot of valuable conserved moisture and absorb large quantities of nutrients from the soil depriving the crop. Further, wide space planting provided to the chili allows fast growth of weed species causing considerable reduction in yield by affecting the plant growth and yield components. Presence of weed reduces photosynthetic efficiency, dry matter production and its mobilization to economical parts, which finally reduce the sink capacity of crop resulting in poor fruit yield. The extent of reduction in fruit yield due to weeds has been reported to be in the range of 60 to 70 per cent depending on the intensity and persistence of weed density in standing crop (Patel et al., 2004). It is now well established that 30 to 60 days after transplanting is the most critical period for crop-weed competition in chili (Frank et al., 1988) and hence managing weeds during this period is most critical for higher yields. Clean and weed free cultivation is pre-requisite for successful crop production. However, effective weed management practices require large human labour and therefore it is be costly as well as time consuming. Hence, integrated weed management by integrating chemical control with mechanical weeding is one of the effective and timely operations to reduce crop-weed competition. Herbicides not only control weeds but also offer a great scope of minimizing the cost of weed control irrespective of situation mainly in the states like Assam where there is a huge biodiversity of flora and faster weed growth rate due to high rainfall and lesser bright sunshine hours. However, there is no documented evidence of any work or research on chili as a succeeding crop after winter (sali) rice in medium land situation as well as management of weeds in chili under such situations. Hence, considering the above facts a research programme was undertaken with the following objective.

v To study the effect of integrated weed management practices on growth and yield of chili after winter rice

CHAPTER – II REVIEW OF LITERATURE

Various factors that are responsible for quality and yield of chili are needed to be explored without hampering the environment. It is important to maximize the utilization of available resources to enhance yield of chili. Chili experiences a wide range of weeds during its critical growth stages, which interferes with the crop and reduces both the quality and yield of chili. However, proper management practices can reduce the impact of weeds on the crop. A short review of background literature on various aspects on weed management in chili is presented below.

The following heads are covered in this chapter:

2.1 Weed flora of chili

2.2 Effect of weed on growth and yield of chili

2.3 Methods of weed control and their effects on weed growth, yield attributes and yield

2.4 Phytotoxicity of herbicide in chili

2.5 Biochemical parameters in chili

2.6 Economics of weed control

2.1 Weed flora of chili

Chili is a summer as well as winter season crop and it is infested with diverse weed flora comprising various grasses, broad leaved and sedges. Different works on the study of weed flora associated with chili from Tamil Nadu, Punjab, Karnataka, Haryana, Himalayan region, Uttaranchal, Arid regions, America, California are reviewed and presented below.

Rajagopal et al. (1976) from Tamil Nadu recorded the weeds associated with chili crop as Trianthema portulacastrum L., Gynandropsis pentaphylla L., Cynodon dactylon L. pers, and Cyperus rotundus L. On the other hand, Saimbhi and Randhawa (1976) in Punjab observed Cyperus rotundus L., Tribulus terrestris L. Celosia argentea L., Digera arvensis Forsk., Digitaria sanguinalis L. Scop, Eragrostis spp., Eleusine aegyptium Desf., and Eleusine indica L. Gaertn. in this crop.

In the year 1984, Bullock et al. recorded the weeds of chili viz. Digitaria sanguinalis L. Scop, Panicum dichotomiflorum Michx, Eleusine indica L. Gaerth, Amaranthus retroflexus L. and Galinsoga spp., while Sharma et al. (1988) reported that Cyperus rotundus L., Cynodon dactylon (L.) Pers ., Commelina nudiflora L., Digitaria sanguinalis L. Scop., Echinochloa colonum L., Setaria glauca Beauv, Eleusine indica L. Gaertn, Chenopodium album L. and Ageratum conyzoides L., were mainly associated with chili. Dangol et al. (1988) confirmed the presence of Digitaria spp., Amaranthus viridis L., Eleusine indica L. Gaertn., and Cynodon dactylon L. Pers. Later on Masiunas (1989) identified the weed species found in chili as Digitaria spp., Panicum dichotomiflorum Michx., Eleusine indica L Gaertn., Chenopodium album L., Amaranthus spp. and Portulaca oleracea L. Lankroo et al. (1990) reported similar weed flora in chili

Schroeder (1992) reported that most common weeds in chili (Capsicum annuum L.) field were Physailis wrightit, Amaranthus blitooides and Datura quercifolia L. in America. At Dharwad, Hosmani (1993) found the weed species viz. Cynodon dactylon (L.) Pers., Cyperus rotundus L., Convolvulus arvensis L., Digitaria marginata Link., Dactyloctenium aegyptium Beauv., Dinebra retroflexa (Rahl.) Panz., Panicum isachine Roth., Commelina benghalensis L., Cynotis spp., Phyllanthus niruri, L., Sida Spp., Celosia argentia L., Acanthospermum hispidum Dc., Trianthema portulacastrum L., Ageratum conyzoides L., Cuscuta Spp., and Orobanche Spp.

According to Singh et al. (1993a), the predominated weeds are Amaranthus viridis L., Trianthema portulacastrum L., Digitaria spp. and Dactyloctenium aegyptium Beauv in Haryana region. On the other hand, study done by Lanini and Strange (1994) in

abroad observed Echinochloa crus-galli L. Beauv, Amaranthus retroflexus L., Chenopodium album L., Portulaca oleracea L. and Solanum nigrum L. in Capsicum annuum L. fields.

Biradar (1999) from Dharwad reported some kharif season weeds in transplanted chili. They were Cynodon dactylon L. Pers, Cyperus rotundus L., Dinebra retroflexa (Vahl.) Panz., Echinochloa crus-galli, Eleusine indica L., Setaria italica L., Commelina benghalensis L., Acanthospermum hispidum Dc., Ageratum conyzoides, Amaranthus viridis L., Convolvulus arvensis L., Digera arvensis, Euphorbia spp., Parthenium hysterophorus L., Phyllanthus niruri L., Portulaca oleracea L. and Tridax procumbens L. Again, Narasalagi (1999) from Dharwad reported that most common weeds in chili (Capsicum annuum L.) field were Acalypha indica L., Ageratum conyzoides, Amaranthus viridis L., Argemone mexicana, Chenopodium album L., Convolvulus arvensis L., Commelina benghalensis L., Cynodon dactylon Pers., Cyperus rotundus L., Digera arvensis L. Euphorbia geniculata., Lactuca rancinata Dc., Legusca mollis Cav., Portulaca oleracea L., Phyllanthus niruri L., Solanum nigrum L., and Setaria italica L.

Prakash et al. (1999) studied the weed flora from the Uttaranchal and reported Ageratum conyzoides, Commelina benghalensis L., Celosia argentea L., Cyperus rotundus L., Cynodon dactylon Pers., Digitaria sanguinalis, Digera arvensis, Echinochloa colonum, Galinsoga parviflora Cav., Oxalis latifolia and Panicum spp. in transplanted chili plots. From the arid zone, Yadav (2001) repoted that dominant weed flora of chili comprised of Amaranthus viridis L., Trianthema portulacastrum L., Digitaria ciliaris Retz., Dactyloctenium aegyptium L. Another work from the desert region recorded the weeds like Cyperus rotundus L., Argemona mexicana L., Celosia argentea L., Digera arvensis L., Euphorbia hirta, Launea splinifolia, Cynodon dactylon (Rajput et al. 2003).

In Uttarakhand, Prakash et al., (2003) identified few new weed species viz. Galinsoga parviflora, Oxalis latifolia, Echinochloa colonum, Digera arvensis, Digitaria sanguinalis, Ageratum conyzoides, Commelina benghalensis L., Celosia argentena L., Cyperus rotundus L., Cynodon dactylon Pers., Digitaria sanguinalis in chili.

Shaikh (2005) observed the dominant weeds in chili field, which were Brachiaria eruciform, Cynodon dactylon, Dinebra retroflexa, Cyperus rotundus, Parthenium hysterophorus, Digera arvensis, Merremia emerginata, Acalypha indica, Chrozophora rottleri, Euphorbia hirta, Convolvulus arvensis, Corchorus acutangulus, Lagasca mollis Cav., and Physailis minima L.

2.2Effect of weeds on growth and yield of crop

Due to the wider plant-to-plant spacing, slow vegetative growth of chili and shorter plant height, weed growth is very severe and they compete easily with the growing chili plants and dominate them. Crop plants vary greatly in their ability to compete with associate weeds. In addition, weeds can bring considerable reduction in fruit yield of chili. Weeds are the potential competitors with chili because of which they cause marked reduction in its fruit yield. The losses also vary with the density of weeds, duration of weed, type of weed species and crop competitive ability. A brief review about the research work done on this aspect is discussed below.

Eshel et al. (1973) reported that Capsicum annuum L. yields were reduced by 70 per cent when weeds infested during the first month in direct seeded crop. This was confirmed by the findings of Bhalla and Nakhatore (1980). On the contrary, Adigun et al. (1991) reported that yield loss in chili caused by the season long competition by weeds ranged from 40 to 90 per cent.

Labrada and Paredesh (1983) found that the critical period of weed interference in Capsicum annuum L. lies between 20 to 40 days after transplanting. When Echinochloa crus-galli (L.) Beauv interfered with the critical stage of chili, the critical period was found to be 25 to 30 days after transplanting (Tei, 1986). Frank et al. (1988) reported that the weed interference period was approximately 40 to 60 days reducing both the bell pepper fruit number and weight. When chili was transplanted at 50 cm row to row spacing the presence of black night shade (Solanum nigrum) resulted in yield loss of 48 per cent (Torner et al. 1993).

Singh et al. (1993a) studied that critical period for crop weed competition in chili and found that it was from 30 to 45 days after planting. A weed free period up to 60 days after transplanting was required for optimum yield of chili and weeding after 60 days of transplanting did not affect the fruit yield (Anon., 1996a). It was also reported that, unchecked weed growth throughout the season caused a yield reduction in the dry chili up to 75.86 per cent (Anon., 1997). Amador-Ramirez (2002) found that the maximum weed infested period in chili ranged between 0.7 and 3.2 weeks after transplanting (WAT) and weed should be removed during 0.9 to 2.1 WAT to prevent losses due to weeds and achieve highest marketable yields. The reasons cited for yield reduction in chili due to weeds as depletion of nutrients, water and light (Pandey, 2000). Besides, harbouring several diseases and pests and quality were also reported to be other harmful impacts of weeds in chili.

Prakash et al. (2003) reported that weed infestation is the major limiting factor causing reduction of the potential yield of capsicum as high as 78 per cent. Similarly, it was found that 60 to 70 per cent fruit yield losses could be observed depending upon the weed flora and intensity of weeds (Patel et al. 2004). Khokhar et al. (2006) reported that compared to weed free condition, weed-crop competition caused 30.1 and 46.4 per cent reduction in the fruit yield during the first and second year.

Adigun et al. (1987) reported that unchecked weed growth throughout the crop life cycle resulted in an 86-90 per cent reduction in potential chili fruit yield. However, Sharma et al. ( 1988) obtained an increase of 35.8 per cent in the fruit yield when the weeds were controlled during crop life cycle as compared to weedy check. Presence of Datura stramonium in sweet pepper severally affected the growth of the crop after 30-45 days competition (Medina and Zaragoza, 1992). Schroeder (1992) reported from the study in untreated plots of chili that weed Physalis wrightii and Amaranthus blitoides reduced chili pepper yield by 33 per cent, Flaveria trinervia by 19 per cent and Physalis wrightii, Amaranthus palmeri, Chenopodium album by 61 to 76 per cent.

Lanini and Strange (1994) studied that there was an increase in yield of 4 to 18 per cent in bell pepper when the weed-free condition was maintained for the entire season. A similar study done at APAU, Hyderabad (Anon., 1995) revealed that unweeded check recorded significantly the lower yield of chili due to the severe competition from weed. The study conducted at Kanpur (Anon., 1996) showed that competition with 5 and 10 plants/m2 of Commelina benghalensis caused 21.73 and 26.73 per cent reduction in fruit yield, respectively.

Reduction of 81–90 per cent chili fruit yield was observed by Adigun (2001), at Nigeria due to unchecked weed growth throughout the crop life cycle. There was a visible affect on internodes length, stem diameter and plant height after eight or more weeks of weed interference. At least four tones of weed dry matter per ha was recorded for treatments with increasing periods of weed interference. This was enough to decrease the crop yield up to 67 per cent. (Amador-Ramírez et al. 2005)

2.3 Methods of weed control and their effects on weed growth, yield attributes and yield

Timely weed management in chili crop is one of the important agronomic practices for increased productivity. In a tropical country like India, availability of abundant sunshine and adequate fertilizers applied to the crop after transplanting trigger fast and abundant growth of weeds in the chili fields. Results reported by different workers from the studies on weed management practices are summarized below.

2.3.1 Mechanical and cultural methods

Mechanical and cultural methods of weed control are most common methods used all over the world. These methods of weed control are labour intensive and costly but until now, these are practiced more widely. Herbicides are more effective, cheaper and chemical method of weed control is fastly replacing the traditional, mechanical and cultural methods of weed control in India. Nevertheless, prevention is still a good option of weed management and it can supplement other methods for an effective and economic control of weeds. The changes in the planting date and spacing have been recognized as important agronomic measures to control weeds (Phillip, 1960). In addition to these practices, emphasis is also given to use of certified seeds, removal of source of infestation, use of well-decomposed manure, clean cultivation, proper crop rotations, proper maintenance of water channel and bunds, as some of the preventive methods of weed control. (Asalam et al. 1989)

Rangaswami (1984) opined that tractor ploughing followed by harrowing reduced the weed weight, increased root weight and yield (11.10 q/ha) of chili, as compared to no tillage (9.00 q/ha). Similar results were obtained by Lanini and Strange (1994) where weed cover in hand weeding at 2, 4, 6 and 8 weeks after transplanting was significantly lower (74.5, 36.0,30.5 and 11.5 per cent, respectively) than untreated plot and it was on par with the hand weeding at 2, 4 and 6 weeks after transplanting. The yield of green chili was produced in hand weeding at 2, 4, 6 and 8 weeks after transplanting was maximum (17915 kg/ ha) but it was on par with hand weeding 2, 4 and 6 weeks after transplanting.

Patel et al. (2004) during his study reported the effect of cultural and chemical methods on weeds in transplanted chili. There was higher green fruit yield in chili from the treatment with three hand weeding + three hand hoeing. Amador-Ramirez et al. (2006) who opined that weeds are mainly controlled by mechanical means such as cultivation and hand hoeing which increased production costs.

Field experiments were conducted at Agricultural Research Station (TNAU), Kovilpatti during rabi season of 1991–93 to find out the effect of cultural control of weeds by intercropping with chili (Muthusankaranarayan et al., 1997). The result indicated that the intercropping of coriander in chili effectively checked the weeds recording lower weed density and weed dry matter production than chili + onion system. The effect was more pronounced at 40 DAS as the intercrop canopy spreading was higher at that stage.

2.3.2 Chemical method of weed control

Wherever labour is scarce and expensive, use of herbicides hold a good promise for timely, effective and efficient weed control. Since most weeds emerge either before or along with the crop, the use of pre-sowing incorporation and pre-emergence herbicides is a better management practice. The choice of herbicides for a particular situation will depend upon the climate, soil type, prevalent weed species, crop cultivar, method of propagation and management practices.

Rajagopal et al. (1976) conducted a study on chili and they reported that alachlor 1.5, 2.0 & 2.5 kg/ha resulted in early control of annual weeds. However, higher yield was recorded in pre-emergence application of alachlor 1.5 kg/ha + one hand weeding at 30 DAT compared to application of pendimethalin alone. Pre-plant application of alachlor @ 2.0 kg/ha + one hand weeding recorded the lowest dry weight of weeds, increased. The yield and maximum weed control efficiency as compared to weedy check in chili (Bhalla and Nakhatore, 1980).

Singh et al. (1985) opined that pendimethalin, fluchloralin and oxadiazon applied @ 1.0 kg/ha controlled the weed effectively and increased the growth and yield of chili. Singh et al. (1992) repoted that the highest yield with pendimethalin (1.0 kg/ha) + oxyfluorfen (0.15 kg/ha). The weed control efficacy was found to be increased with increasing levels of herbicides. Another record of using a pre-plant herbicide oxyflurofen @ 0.14 kg/ha alone or combined with metolachlor @ 2.24 kg/ha and pendimethalin at 1.65 kg/ha gave excellent control over broad-leaved weeds during first 3 weeks after application of herbicide. Application of oxyfluorfen @ 0.40 kg/ha together with one hand weeding at six weeks after transplanting resulted highest chili yield (Semidey et al. 1989).

Singh et al. (1992) concluded that combined application of fluchloralin @ 1.0 kg/ha + pendimethalin @ 0.15 kg/ha + oxyfluorfen @ 1.0 kg/ha reduced the population and weed dry weight on an average by 41, 76, and 30 per cent as compared to weedy check and hand weeding at 20 and 40 days after transplanting. Ajay Kumar and Thakral (1993) recorded minimum weed dry weight (2352 kg/ha) with pre-emergence application of pendimethalin @ 1.25 kg/ha which was significantly lower than oxyfluorfen @ 0.25 kg/ha with or without hoeing or hand weeding twice 30 and 60 DAT (3248 kg/ha and 3555 kg/ha, respectively).

Joshi et al. (1995) reported that application of alachlor @ 1.25 kg/ha or pendimethalin @ 0.75 kg/ha as pre-emergence suppressed the weeds significantly and recorded higher yield of chili pepper.

The study conducted at Hyderabad (Anon., 1995) showed that pre-emergence application of butachlor @1.0 kg/ha followed by one intercultivation 30 DAS (days after sowing) significantly reduced the weed dry weight and increased the crop growth and chili fruit yield. Later on, report from Narasalagi (1999) confirmed that the weed free check reported lowest weed dry weight and highest weed control efficiency followed by treatment with butachlor @ 1.0 kg/ha coupled with weeding at 45 DAS. In addition, this experiment was found to be confirmative with Patil (1999).

Singh et al. (1995) reported that oxyfluorfen @ 0.3 kg/ha significantly reduced the weed density compared with fluchloralin @ 1.0 kg/ha, oxyfluorfen @ 0.1 kg/ha and metolachlor @ 0.5 and 0.75 kg/ha.

At Dharwad, Narasalagi (1999) showed that pre-emergence application of butachlor @ 1.0 kg/ha followed by one hand weeding at 45 DAS significantly lowered weed dry weight and increased the crop growth and yield in direct seeded chili + onion intercropping. The study revealed that most of the weeds except Cynodon dactylon, Cyperus rotundus, Ageratum conyzoides, Commelina benghalensis and Cynotis cristata were found susceptible to pendimethalin 1.5 kg/ha.

Prakash et al. (1999) observed that alachlor @ 3.0 kg/ha + hand weeding at 45 DAT resulted in excellent control of weeds closely followed by alachlor @ 2.0 kg/ha + hand weeding at 45 DAT. Along with that, pendimethalin was effective against grassy as well as broad leaf weeds, where as fluchloralin was effective against broad leaf weeds in chili. Under rainfed condition, Singh et al. (2001) showed that the performance of herbicides viz. butachlor and alachlor were good to excellent than that of diclosulam, pendimethalin, haloxyfop and oxyflurofen which gave slight toxic injury to the crop. Significantly lower weed population, weed dry weight and higher weed control efficiency (WCE) was recorded in weed free check and butachlor @ 1.0 kg/ha at all the stages crop growth. Rajput et al. (2003) concluded that alachlor 3.0 kg/ha + hand weeding 45 DAT significantly reduced the weed population and dry-matter accumulation. Alachlor @ 2.0 kg/ha + hand weeding 45 DAT was equally effective in reducing the dry weight of weeds in chili compared to its higher concentration.

Yadav (2001) concluded that oxyfluorfen (0.2 kg/ha) combined with two hoeing at 30 and 60 DAT significantly reduced the dry weight of both grassy and broad leaf weeds compared to oxyflourfen (0.2 or 0.3 kg/ha) with one hoeing. Pendimethalin (1.0 kg/ha) + one hoeing controlled grassy weeds as effectively as the oxyflourfen @ 0.2 or 0.3 kg/ha with two hoeing but oxyflourfen (0.3 kg/ha) + one hoeing was more effective on broad-leaved weeds compared to pendimethalin.

A study by Prakash et al. (2003) revealed that the weed-control efficiency with different integrated weed control methods. Except pendimethalin @ 1.0 kg/ha and fluchloralin @ 1.0 or 2.0 ka/ha , all the other weed control treatments significantly reduced the weed density and weed biomass and in turn increased the yield of chili significantly. Under repeated weeding, the highest fruit yield of 201.3 q/ha. Among the different herbicidal treatments, application of alachlor @ 3.0 kg/ha, followed by handweeding at 45 DAT (days after transplanting) proved the best in terms of yield (168.5 q/ha), net returns (Rs 73, 326/ha), the lowest weed index (16.2) and the highest weed-control efficiency.

Frost and Hingston (2004) in Australia reviewed that there are limited effective weed management practices for capsicum and chili producers. Current weed management practices included the use of plastic mulch, selective herbicides against grasses, hand weeding or tillage. There are currently no herbicides registered for broadleaf weed control in capsicum or chili. Potential new herbicides were screened and efficacy, crop safety and residue data were generated. The most effective herbicides identified from this work were pendimethalin, clomazone and oxadiargyl, all of these gave satisfactory results when applied as pre crop transplanting. All the three products provided effective pre-emergent control of a range of common broadleaf and grass weeds across a number of sites.

Patel et al. (2004) reported that dry weight of weed recorded at 45 DAT was significantly lower in three handweeding and was at par with three hand weeding and hand hoeing and application of pendimethalin @ 1.0 kg/ha as pre – transplant supplemented with hand-weeding at 45 DAT. Weed control efficiency was between 89.4 to 97.3 per cent in these treatments among herbicidal treatments; significantly lower weed dry weight was recorded in pre-transplant application of pendimethalin, which was at par with all the herbicidal treatments except pre-transplant or post-transplant application of metolachlor due to non control of Boerhavia diffusa.

At Ludhiana, chili fruit yield was significantly higher in oxyfluorfen than other herbicides. The yield ranges from 142.4 q/ha to 170.2 q/ha (Anon., 2005). In the same year, Shaikh (2005) studied that weed control efficiency (>80per cent) was recorded in hand weeding, oxyfluorfen @ 0.10 kg/ha and pendimethalin @ 0.75kg/ha supplemented with hand weeding at 45 DAT. The mean chili yield was higher in pendimethalin (9.62 t/ha) @ 0.75 kg/ha.

Weeding at 45 DAT and oxyfluorfen @ 0.1 kg/ha, Drill sown chili yield was found to be higher (298.30 kg/ha) with pendimethalin @ 1.0 kg/ha as pre emergence spray + hand weeding and was on par with oxadiargyl @ 0.09 kg/ha + hand weeding (Agasimani and Channappagoudar, 2005). However it was also found that the black polyethylene mulch along with pendimethalin @ 1.0 kg/ha provided good control over weeds and resulted in the highest yield (241.9 q/ha) followed by sole plastic mulching treatment (219.4 q/ha). The unweeded control treatment reported only 30.2 q/ha red chili yield. (Marajan et al., 2006)

2.4 Phytotoxicity of herbicides in chili:

The use of different herbicide sometimes shows phytotoxic symptoms to the plants. Since, chili is very sensitive crop, therefore, some studies regarding the phytotoxic symptoms generated due to herbicide is reviewed here.

Saimbhi and Randhawa (1976) opined that pre-plant application of linuron @ 0.30 kg a.i./ha showed adverse effect on seedling setting and thus a high percentage of seedling mortality was recorded in chili, particularly when these were combined with pre-plant application of EPTC @ 3.75 kg/ha. Some of the herbicides like aclonifen (1.5 kg a.i./ha), metribuzin (70 g/ha), isoxaben (40 g/ha) and fomesafen (170 g/ha) were phytotoxic to chili crop when applied as pre emergent and post emergent. Post emergent application of linuron (0.25 kg a.i./ha) was phytotoxic when the crop was 6-8 true leaf stage. However, ethalfluralin and rimsulfuron (0.83 kg/ha and 8 g/ha respectively) produced the temporary symptom of phytotoxicity in chili (Suso et al. 1995).

The study conducted at Anand (Gujarat) (Anon., 1996b) suggested that that oxyfluorfen @ 0.24 kg/ha was phytotoxic to chili plants of evidenced by drying of growing plants after transplanting. Another study by Cavero et al. (1997) showed that pre-emergent application of clomazone resulted in chloratic seedlings and at 2 kg/ha reduced the plant stand of chili but was selective when applied at 6-8 leaf stage of the crop. Pepper was tolerant to diethyl ethyl when applied as pre emergence, but caused severe phytotoxicity when applied as post emergent and when mixed with diphenamid.

Narasalagi (1999) studied that application of pendimethalin @ 1.50 kg/ha caused severe injury to the direct seeded chili crop and some stand loss at 15 DAS. Injury was more pronounced with oxyfluorfen @ 0.15 kg/ha during the initial stages but not persistent at subsequent stages. In butachlor, 1.0 kg/ha treated plots though slight stunting and injury was noticed the crop recovered soon. Pendimethalin @ 1.50 kg/ha maintained its hytotoxicity on chili even up to 90 DAS. At 60 DAS and thereafter, phytotoxicity of all herbicides disappeared except pendimethalin @ 1.5 kg/ha.

Patel et al. (2004) reported that post-emergent application of linuron (0.25 kg/ha) was phytotoxic when chili crop was 6-8 true leaf stage while, ethalfluralin and rimsulfuron (0.83 kg/ha and 8 g/ha, respectively) produced the temporary symptoms of phytotoxicity. Post-transplant application of oxadiazon, oxyfluorfen and metolachlor caused phytotoxicity to chili crop. Metolachlor applied even as pre-plant showed toxicity on chili. Crop growth was also severely affected under black polyethylene mulch treatment due to higher soil temperature as compared to no mulch (37.0 °C), which restricted root growth of chili at early stage.

Oxyfluorfen showed mild initial toxicity to the chili crop and was recovered in due course of time at PAU, Ludhiana (Anon., 2005).

2.5 Biochemical parameters in chili

The research works on effects of weeds on capsaicin content and ascorbic acid of chili has only few reports. Therefore, the review collected for capsaicin and ascorbic acid are related to properties, varietal difference, nutritional compositions, climate and various growth related factors. Capsaicinoids are alkaloid compounds that produce the hot flavor or pungency associated with chilies. Ascorbic acid is functional as well as nutritional component of hot pepper fruit and recognized as an antioxidant and biologically active compound (Simonne et al., 1997; McCall and Frei, 1999 and Rietjens et al., 2002).

The two most important biochemical attributes are capsaicin and ascorbic acid. Capsaicin is the pungent principle of chili. It is crystalline colourless alkaloid and known to be a stimulant, alternative, carminative and anticoagulant (Anon., 2005a). The difference in the nutritional content of chili varies from variety to variety (Kaur et al., 1980) and location-to-location (Raina and Teotia, 1985 and Teotia and Raina, 1986). The capsaicin and the allied pungent principles viz., dihydrocapsaicin and nor-dihydrocapsaicin are the most important pungent components of chilies. They have both antimicrobial and antioxidant properties. Chilies are used for carminative, tonic, stimulative and counter irritant properties in pharmaceutical industry (Mathew, 2002).

Higher weed incidence, weed dry weight and nitrogen uptake by the weeds resulted in reduced ascorbic acid. Shashidhara (1999) confirmed that higher availability of nutrients always improved the ascorbic acid content of chilli fruits.

The degree of pungency depends on the Capsicum species, cultivars and their concentration could be affected by different factors like fruit development stage (Sukrasno and Yeoman, 1993), genetic character and agro-climatic conditions of each cultivar (Cisneros-Pineda et al., 2007). Capsaicinoids concentration in hot peppers limits from 0.003 to 0.01 per cent while mild chilies had 0.05 to 0.3 and 0.3-1 percent was recorded in strong chilies (Perucka and Oleszek, 2000).

According to Bajaj et al. (1980), the chili on an average contains dry matter (22.02 per cent) ascorbic acid (131.06 mg/100g). Stage of harvest is one of the major factors that determine the compositional quality of fruits and vegetables. The range of ascorbic acid concentrations of mature green chili fruit was found to vary from 121.8 to 146.5 mg 100/g fresh weight and red succulent fruit had 233.3 mg 100/g (Howard et al., 1994 and Lee et al., 1995). The concentration of ascorbic acid in chili peppers increased after the mature green stage and peaked in red fruit with about 75 per cent moisture content. However, fully dry red fruit had 15-18 per cent moisture with lowest levels of ascorbic acid concentration among maturity stages (Osuna-Garcia et al., 1998).

Khadi et al. (1987) reported significant differences in ascorbic acid content in green and ripe fruits of 11 chili cultivars and revealed that green fruits contain lesser ascorbic acid content than ripened fruit. Further, they also found that ascorbic acid in ripe fruits was influenced by the number of days to ripening of fruits, fruit surface area and fruit length.

Ahmed et al. (1987) reported that capsaicin content was more in red ripened and dry fruit compared to green chilies and reported that the Byadagi cultivar had the highest capsaicin content followed by Chincholi and Sankeshwar. The capsaicin content ranged from 1.0 to 107.2 mg/100g fruit at ripe stage. However, fruit size and stage of maturity influenced the amount of capsaicinoind present in chili fruit. The capsaicin content was found to be inversely related to fruit diameter, length and thickness.

Estrade (1999) reported that environmental conditions such as water stress impart strong effect upon the accumulation of capsaicin, which could be the result of competition between biosynthesis of capsaicinoids and other phenyl propanoid metabolites in pedron pepper fruits. The above study proved that amount of capsaicinoids (capsaicin and dihydrocapsaicin) in pedron pepper fruits of water stressed plants was higher than that of control plants.

2.6 Economics of Weed Control

Sharma et al. (1988) reported highest net returns in chili of Abbildung in dieser Leseprobe nicht enthalten 13,000 /ha, when fluchloralin was applied as pre-plant application @ 0.48 kg a.i./ha and one hoeing 25 DAT. Fluchloralin @ 1.44 kg a.i./ha and fluchloralin @ 0.96 kg a.i./ha followed by one hoeing were next in order. Nitofen was also economical in checking weeds, when it was used as pre-plant incorporation spray and one hoeing but 2, 4-D in general showed poor performance because of its phytotoxic effect on plant. The minimum weed index was also found with fluchloralin @ 0.48 kg a.i./ha in addition with one hoeing in transplanted chili.

However, use of herbicides either alone at varied rate or in combination with hand weeding gave more profit compared to weedy check. Highest net profit of Abbildung in dieser Leseprobe nicht enthalten 18, 379 /ha was obtained from pre emergence application of pendimethalin @ 1.0 kg a.i./ha + oxyfluorfen @ 0.15 kg a.i./ha (Singh et al. 1991). Highest net income in chili was obtained in weed free check followed by glufosinate ammonium @ 0.90 kg a.i./ha and alachlor @ 2.0 kg a.i./ha, both in combination with intercultivation at 40 and 60 DAT (Biradar, 1999).

Narasalagi (1999) studied higher net returns were with weed free check and butachlor @ 1.0 kg/ha + Hand weeding at 45 DAS, but the latter treatment recorded the highest benefit-cost ratio in direct seeded chili. In 2001, Yadav evaluated that higher net return was obtained in oxyflourfen at 0.3 kg/ha + two hoeing (Abbildung in dieser Leseprobe nicht enthalten 24,992 /ha), closely followed by lower dose of oxyflourfen (0.2 kg/ha) with two hoeing (Abbildung in dieser Leseprobe nicht enthalten 24,515 /ha). However, higher benefit-cost ratio was obtained in lower dose of oxyflourfen (0.2 kg/ha) with two hoeing closely followed by oxyflourfen @ 0.3 kg/ha + two hoeing in transplanted chili.

Prakash et al. (2003) studied that repeated weeding treatment recorded the higher net return (Abbildung in dieser Leseprobe nicht enthalten 79, 890 /ha), followed by alachlor @ 3.0 kg/ha + hand weeding at 45 DAT (Abbildung in dieser Leseprobe nicht enthalten 73,326 /ha) however, later treatment provided better net profit/rupee invested (Abbildung in dieser Leseprobe nicht enthalten 8.2) than former treatment (Abbildung in dieser Leseprobe nicht enthalten 4.2). Application of alachlor 2.0 kg/ha alone proved the best from net profit/rupee investment point of view (Abbildung in dieser Leseprobe nicht enthalten 12.1) in transplanted chili. However, Patel et al. (2004) opined that three hand weeding and hoeing gave highest net profit (Abbildung in dieser Leseprobe nicht enthalten 65253 /ha) and benefit- cost ratio (Abbildung in dieser Leseprobe nicht enthalten 2.68) followed by three hand weeding (Abbildung in dieser Leseprobe nicht enthalten 63053 /ha) and pre-transplant application of pendimethalin supplemented with hand weeding at 45 DAT (Abbildung in dieser Leseprobe nicht enthalten 60080 /ha) in transplanted chili.

Shaikh (2005) reported higher net monetary returns (Abbildung in dieser Leseprobe nicht enthalten 55.70 thousand/ha in pendimethalin at 0.75 kg/ha followed by hand weeding at 45 DAT over weedy check and fluchloralin at 1.35 kg/ha. Simultaneously, Khokhar et al. (2006) found that application of herbicide oxadiazon one week before transplanting of chili in combination with one hand weeding at 45 DAT was found to be more effective in enhancing fruit yield and recorded the highest net returns than other treatments.

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