Weed Science

Field dodder (Cuscuta campestris) is an annual obligate stem parasite belonging to family Cuscutaceae. The genus Cuscuta is comprised of about 175 species worldwide. Out of 12 species reported from India, C. campestris and C. reflexa are more common. It is a major problem in pulses, oilseeds and fodder crops in the states of Andhra Pradesh, Chhattisgarh, Gujarat, Orissa, West Bengal and parts of Madhya Pradesh under rainfed as well as in irrigated conditions. It reproduces mainly by seeds and unlike root parasites, Cuscuta seeds do not require a specific stimulant to induce germination. The yield reductions due to Cuscuta are reported to the tune of 60-65% in chillies, 31-34% in greengram/blackgram, 60-65% in niger, 87% in lentil, 86% in chickpea, 72% in tomatao and 60-70% in alfalfa depending upon its intensity of infestation. Cuscuta can be controlled by using Cuscuta free crop seeds, harrowing in crop rows before it parasitizes the host, cultural practices like tillage, planting time, crop rotation and intercropping, selection of Cuscuta tolerant varieties and use of selective herbicides like pendimethalin, fluchloralin and pronamide. If the infestation is in patches, it can be easily controlled by spraying non-selective herbicides such as glyphosate and paraquat. In this paper, an attempt has been made to review the research work done on biology and management of Cuscuta in India and elsewhere.

Effect of basil leachate on the emergence of 10 weed species, beggarweed (Desmodium tortuosum), crabgrass (Digitaria ciliaris), guineagrass (Panicum maximum), Johnsongrass (Sorghum halepense), milkweed strangler vine (Morrenia odorata), pigweed (Amaranthus retroflexus), sicklepod (Senna obtusifolia), Spanish needles (Bidens pilosa), teaweed or prickly sida (Sida spinosa) and yellow nutsedge (Cyperus esculentus) alongwith basil (Ocimum sanctum) was studied in Petridish and under pot conditions. In another study, intra- and interspecific competition between basil and 10 weed species (guineagrass) substituted with crowfoot grass (Dactyloctenium aegyptium) was carried out in pots under greenhouse conditions in a replacement series with four plants per pot. Effect of weed : basil mixture on fresh weight and plant height was observed. Relative crowding coefficients (RCC), relative yield total (RYT) and agressivity index (AI) was calculated. Basil leachate collected from soil influenced weed emergence (both inhibitory and stimulatory), but the differences between leachate or water used for irrigation in pots and Petri dish studies were not large enough except on some species, indicating any significant role of allelochemicals. Basil leachate inhibited the emergence of basil itself. Similarly, soil incorporation of basil root/shoot matter in 1 : 12 ratio (basil : soil) had no inhibitory effect on the emergence of D. tortuosum, S. halepense, M. odorata, A. retroflexus, S. obtusifolia, B. pilosa and C. esculentus. Basil suppressed the growth of all weed species, except yellow nutsedge, but plant height of basil was unaffected by weeds (when data averaged over weed species and plant ratio). Plant height of basil increased when growing with weed species compared to monoculture due to inter-specific competition. Even single plant of basil (with three of weeds) was competitive enough to reduce the plant height of D. aegyptium, S. spinosa, A. retroflexus and M. odorata; plant height increased significantly when weeds were growing in monoculture. RYT values of 1.04 in 1 : 3 mixture of basil with weeds compared to 0.83 in 3 : 1 or 2 : 2 ratio indicated some degree of resource complimentarity. Highest RYT value of 1.64 was derived for D. aegyptium followed by D. tortuosum (1.22), S. spinosa (1.14) and C. esculentus (1.06) when growing in 1 : 3 ratio with basil. RCC (basil on weeds and weeds on basil) values were significantly different for C. esculentus compared to other weed species when growing in 2 : 2 ratio. The aggressivity index of basil significantly decreased when one plant of basil was growing with three of weed species compared to 2 : 2 or 3 : 1 ratio (basil : weeds); lowest being with C. esculentus. The results suggest that insignificant effect on weed seed emergence with basil leachate may not be due to any allelopathic effect as the growth inhibition (plant height and fresh weight) does not support this hypothesis, but suggests dominant role of competition when weeds and basil were growing in different plant ratio.

Bispyribac-sodium was evaluated against mixed weed flora in transplanted rice at Karnal, Haryana. Major associated weeds were Echinochloa glabrescens and E. colona (L.) Link among grasses, Ammannia baccifera L. and Euphorbia sp. among broad-leaved weeds and Fimbristylis miliacea (L.) Vahl, Cyperus iria L., C. rotundus L. and C. difformis L. among sedges. Weeds allowed to grow throughout crop season caused 68 and 27% yield reduction during 2006 and 2007, respectively. Bispyribac applied at 15 or 25 DAT was found equally effective against grassy weeds, but control of broad-leaved weeds and sedges was comparatively more when applied at 15 DAT. Bispyribac 25 g/ha applied at 15 or 25 DAT was adjudged the most suitable herbicidal treatment resulting in 174-199% and 37-41% increase in the rice grain yield over weedy check during 2006 and 2007, respectively. There was no phyto-toxicity of bispyribac on rice and no residual toxicity on succeeding crop of wheat during both the

years of study.

Penoxsulam was found effective especially against Echinochloa species and Cyperus difformis as compared to butachlor and pretilachlor and it recorded lower weed dry matter. Highest grain yield was obtained with penoxsulam at 22.5 and 25 g/ha at 3 DAT during 2005 and 2006, respectively. Penoxsulam at 22.5 and 20.0 g/ha was found better against weeds than butachlor and pretilachlor. Weedy plot recorded 41.0 and 34.3% lower grain yield as compared to the treatment having highest grain yield during both the years. Based on two-season studies, it can be concluded that penoxsulam at 20-25 g/ha applied as pre-emergence (3 DAT) as well as early post-emergence (10 DAT) effectively controlled weeds in transplanted rice and it had no phytotoxicity effect on rice crop upto 25 g/ha dose.

Field experiments were conducted on loamy sand soils of Department of Agronomy, Punjab Agricultural University, Ludhiana during kharif season of 2006 and on sandy loam soil of the seed farms of Ladhowal and Kapurthala during 2007 to find out optimum seed rate and weed management practices in irrigated direct dry-seeded rice. A seed rate of 37.5 to 45 kg/ha depending upon varieties was found optimum for successful cultivation of direct-seeded rice (DSR). Weeds in DSR can be controlled effectively with the integration of post-emergence (25-30 DAS) application of bispyribac 25 g/ha or azimsulfuron 20 g/hawith pre-emergence application of pendimethalin 0.75 kg/ha. Application of pendimethalin alone was found inadequate for controlling complex weed flora of DSR. Integration of pre-emergence application of pendimethalin 0.75 kg/ha with post-emergence application of bispyribac 25 g/ha or azimsulfuron 20 g/ha produced 61.7 and 42.1% higher yield, respectively, than alone application of pendimethalin 0.75 kg/ha.

Field experiment was conducted at CCS HAU College of Agriculture Farm, Kaul, Haryana during kharif 2005 and 2006 to find out effective and viable system of controlling complex flora of weeds in direct seeded rice. Among different herbicidal treatments, pendimethalin at 1.5 kg/ha (PE) and cyhalofop butyl at 90 g/ha controlled Echinocloa very effectively but failed to check Cyperus, whereas pretilachlor+safener at 0.5 kg/ha provided excellent control of Cyperus. The grain yield was almost similar under the treatment of pendimethalin at 1.5 kg/ha fb HW at 30 DAS in all the sowing methods. Under wet seeding methods, pre-emergence application of pretilachlor+safener resulted in significantly higher grain yield of rice, whereas under dry seeding methods higher grain yield was recorded in the treatment of pre-emergence application of pendimethalin

Field investigation was carried out during two consecutive years (2005-06 and 2006-07) at Kanpur to find out direct and residual effects of atrazine application with regard to weed growth and crop growth of maizegreengram cropping system. Manual weeding followed by earthing operation done at 20 days after sowing (DAS) prevented weed competition (85.98% WCE) resulting in higher values of growth attributes viz., plant height 30.99%, culm girth 36.81%, leaf area index 76.19%, dry weight of plant 41.55% and crop growth rate 37.63% than weedy check which recorded lowest values of growth characters. Atrazine 0.50 kg/ha showed at par results with two manual weedings done at 20 and 40 DAS. Atrazine applied in maize had no residual effect on weed emergence and crop stand of succeeding greengram

Field experiments were conducted during rabi 2005-06 and 2006-07 at the Regional Agricultural Research Station, Lam, Guntur, Andhra Pradesh to find out the most effective weed management practice in zero-till sown maize crop grown after rice. Uncontrolled weed growth throughout the crop growing period caused 43% reduction in grain yield. All the weed control treatments significantly reduced the weed growth and increased maize yield by 22 to 62% over weedy check without any crop injury. Highest maize grain yield was recorded with two hand weedings and pre-emergence application of atrazine 1.5 kg/ha followed by (fb) hand weeding at 30 days after sowing (DAS). Maize grain yield did not differ significantly among the treatments with hand weeding and herbicide integration. Highest gross and net monetary returns and benefit : cost ratio were recorded with two hand weedings and with pre-emergence application of atrazine 1.5 kg/ha followed by (fb) hand weeding at 30 DAS.

A long term experiment of rice-wheat rotation system sprayed in wheat with clodinafop continuously and as a component of herbicide rotations has been conducted on a permanent plot at Regional Research Station, Karnal since 1999. During the rabi season of 2005-06, wheat rhizosphere soil samples of above experiment were analyzed for total bacterial, free living diazotrophs and nitrifying bacterial populations in green manured plots (GM) and in plots without green manuring (WGM). Total bacterial and free living diazotroph populations were more in GM plots than in WGM plots. At early stages after the application of clodinafop, bacterial population was significantly less in plots sprayed with clodinafop as a component of herbicide rotations than in plots sprayed with clodinafop continuously and weedy control. At 30 days after the clodinafop treatment (DAT), free living diazotroph count was less in clodinafop treated GM plots than controls (weedy and weed free). The nitrifying population was inhibited at early stages after the application of clodinafop under GM conditions.

A bioassay, based on the response of wheat roots, was used to quantify the concentrations of bioavailable S-metolachlor when applied at different timings. The application timings of S-metolachlor (0.48 kg/ha) were 20 days before crop sowing (DBS), at crop sowing (AS) applied either post-sowing pre-emergence (PSPE) or incorporated by sowing (IBS). The upper 0 to 5 cm soil layer was sampled from all treatments at 0, 8, 14, 23 and 33 days after crop sowing (DAS). The concentration of bioavailable S-metolachlor was similar between the application timings AS (IBS) and AS (PSPE) at both 0 DAS (94 to 96%) and 8 DAS (86 to 89%). After this period, herbicide bioavailability was significantly greater in the AS (IBS) than AS (PSPE). The bioavailabity of S-metolachlor was always greater for the herbicide applied AS (IBS) than applied at 20 DBS. The bioavailability of the herbicide applied at 20 DBS was 55% of the original applied herbicide at seeding. On the last sampling time (33 DAS) the bioavailability of S-metolachlor was 45, 27 and 28% of the original amount applied for application timings of AS (IBS), AS (PSPE) and 20 DBS, respectively. The implications of this information for weed management strategies are discussed.

The effect of different weed control methods on weed population, yield and yield attributes of soybean was studied at TNAU, Coimbatore, using pre-emergence application of pendimethalin, fluchloralin and alachlor each @ 1.0 kg/ha as well as integrated application of pre-emergence herbicide+one hand weeding at 35 DAS, and two hand weedings at 20 and 35 DAS. Alachlor @ 1.0 kg/ha+one hand weeding at 35 DAS was found to be the best treatment followed by pendimethalin @ 1.0 kg/ha+one hand weeding at 35 DAS and two hand weedings at 20 and 35 DAS treatments. The quality parameters of soybean seeds were not affected by weed control practices.

The uptake of nutrients by sunflower crop and its associated weeds was studied under two planting patterns (45 x 30 cm and 60 x 22.5 cm) and six weed management practices (fluchloralin 1.0 kg/ha, pendimethalin 1.0 kg/ha, fluchloralin 0.5 kg/ha+pendimethalin 0.5 kg/ha, fluchloralin 0.5 kg/ha+pendimethalin 0.5 kg/ha supplemented with one HW at 40 DAS and HW twice at 20 and 40 DAS including unweeded check). Planting pattern of 45 x 30 cm significantly reduced the nutrient removal by weeds and consequently nutrient uptake by crop was increased. Among the weed management practices tried, the nutrient uptake by weeds was significantly lower with HW twice and it was at par with fluchloralin 0.5 kg/ha+pendimethalin 0.5 kg/ha supplemented with HW at 40 DAS. On an average, weeds under unweeded check removed 42.0 kg N, 15.5 kg P and 45.4 kg K/ha and monetary loss in terms of nutrient removal by weeds was maximum in unweeded check with an amount of Rs.1133/ha, besides reducing the seed yield by 62% than the best weed management practice, HW twice.

A field experiment was conducted during the winter season of 2003-04 and 2004-05 at Udaipur to study the effect of integrated weed and nutrient management on weed density and productivity of coriander (Coriandrum sativum L.). Among the weed management practices, hand weeding twice (HW) at 30 and 45 days after sowing (DAS) and preemergence application of pendimethalin at 1.0 kg/ha+hand weeding at 45 DAS were at par. These treatments significantly reduced the density and dry weight of weeds over other treatments and significantly increased yield attributes of coriander resulting in higher seed yield (1.58 and 1.57 t/ha) and net return (Rs. 23,930 and 24,072 /ha) as a result of higher weed control efficiency (88.50 and 88.14%) and lower weed index (0.63% of pendimethalin+HW), respectively. Chenopodium murale Spergula arvensis and Melilotus indica were the most pre-dominant weeds. Nutrient management did not significantly influence weed density. Application of 60 kg N+30 kg P+30 kg K+30 kg S/ha significantly increased yield attributes, seed yield, net returns and B : C ratio in comparison to N+P and N+P+K fertilization owing to lower weed index and registered higher seed yield by 18.0 and 8.36%, respectively.

A field study was conducted at Punjab Agricultural University Regional Station, Bathinda during 2005-06 and 2006-07 to evaluate the effect of different weed control treatments on germination, growth of onion seedlings and weed spectrum in onion nursery. All the treatments reduced weed growth significantly over the unweeded control except plastic mulching and oxyfluorfen at 0.062 kg/ha. Pendimethalin at all the three levels significantly reduced weed population but adversely affected the germination of onion seedlings. The most adverse effect of pendimethalin was observed at 1.0 kg/ha. However, partial control of weed was observed in case of oxyfluorfen. There was significant reduction in weight of 100 seedlings at all the oxyflourfen levels. So, pendimethalin at 0.5 kg/ha and oxyfluorfen at 0.125 kg/ha can be used for better weed control and higher seedling production in onion nursery

Field experiments were conducted at S. V. Agricultural College, Tirupati for two consecutive rabi seasons of 2005-06 and 2006-07 to study the influence of graded levels of nutrients, time of N application and weed management practices on bulb yield of onion. Yield attributes and bulb yield were highest with the higher nutrient level i. e. 120-60-50 kg N, P, K over the other nutrient levels. Time of N application did not exert any significant influence on bulb yield, economic returns and weed dynamics of onion. Among the weed management practices, hand weeding twice at 20 and 40 DAT significantly reduced the density and dry weight of weeds, resulting in improved weed control efficiency, elevated stature of yield attributes and higher bulb yield and it was comparable to other weed management practices. Higher bulb yield was realized even at lower level of nutrients with weed management practices.

Explosive seed dispersal, viability and germination in Euphorbia geniculata have been determined. Plant disperse seeds explosively upto 6 m but dispersal was affected by temperature, humidity and radiation load. Seed viability was not affected by dry storage (X±SE=93.6±0.67) and low temperature (X±SE= 9I.6±0.7). Seeds lacked primary dormancy, however, low temperature enforced secondary dormancy. Seed dispersal began at 1100 h and finished at 1500 h with peak at 1300 h (52.3%) during September. During November when temperature drops, dispersal began at 1100 h and finished at 1400 h with peak at 1200 h (40.7%). However, there was no significant correlation between temperature and seed dispersal. The distance peak of explosively dispersed seeds was observed between 100-200 cm (26%) and tail of distribution reached upto 677 (X±SD=243.6±148.8) cm and dispersal distance was not dependent on seed weight.

Field studies were carried out under non-cropped situations using tank mix applications of some herbicides against Canada thistle (Cirsium arvense) during 2007-08 and 2008-09. Tank mix applications of carfentrazone 20 g/ha with glyphosate 1.0% (0.75% repeat year) plus 0.25% non-ionic surfactant (NIS) provided 95 (95) and 87% (82) control of Canada thistle compared to 95 (97) and 83% (82) control by glyphosate alone at 2.0+0.25% NIS, 8 and 13 weeks after treatment (WAT), respectively. Carfentrazone alone was not effective. In another experiment, tank mix applications of carfentrazone 20 g/ha+glyphosate 0.75+0.25% NIS+2,4-D amine 500 g/ha provided 98, 99, 96 and 89% control of Canada thistle compared to 85, 95, 92 and 79% control by tank mixing of 2,4-D 500 g/ha+glyphosate 1.0+0.25% NIS and 89, 92, 88 and 78% control by glyphosate alone 2.0+0.25% NIS, respectively, at 21, 42, 56 and 75 DAT. The mortality of Canada thistle was similar when glyphosate 1.0 or 1.5% was tank mixed with 20 or 40 g/ha of carfentrazone. Effect of 2, 4-D amine was significantly lower when used alone or tank mixed with carfentrazone compared to their mixture with glyphosate. The effect of herbicides was significantly higher in the second year compared to first year of spraying. Tribenuron alone at 25 g/ha+0.25% NIS or its tank mixture at 20 g/ha with 2,4-D ester 250 g/ha, metsulfuron 4 g/ha or carfentrazone 20 g/ha was not effective against Canada thistle. Similarly, tank mix applications of metsulfuron 2 or 4 g/ha with 2,4-D 250 or 500 g/ha failed to satisfactorily control Canada thistle. Glyphosate 1.0% alone or with metsulfuron 4 g/ha provided similar control of Canada thistle, but effect was significantly lower than alone application of glyphosate at 2.0+0.25% NIS