Weed Science

Growth cabinet studies were conducted on the effect of temperature, pH and light exposure on seed germination of Brazil pusley, common ragweed, Florida beggarweed, hairy beggarticks, ivyleaf morningglory, Johnson grass, prickly sida, redroot pigweed, sicklepod, strangler vine, tall morningglory and yellow nutsedge. When averaged over all species and temperatures, highest weed seed germination was recorded in the temperature regime of 25 to 35OC, maximum being at 30OC. Lower temperature of 15OC inhibited germination of Johnson grass, Brazil pusley, Florida beggarweed, redroot pigweed, prickly sida and yellow nutsedge. Germination of common ragweed and ivyleaf morningglory was highest at 20OC, and significantly decreased above 35OC. Higher temperatures (30 to 40OC) were less inhibitory to germination of redroot pigweed, Johnson grass, Florida beggarweed, prickly sida and yellow nutsedge compared to other weed species. Tall morningglory and hairy beggarticks had high germination rates from 15 to 35OC. Germination of prickly sida and Florida beggarweed was highest between 25 to 40OC and sicklepod from 20 to 40OC. Strangler vine germination was highest at 30OC and decreased significantly with any increase or decrease in temperature. No weed seed germinated at pH 3, except yellow nutsedge. A pH range of 5 to 11 had no adverse effect on germination, when data were averaged over species. Germination of prickly sida was highest at pH 9 and any increase or decrease in pH resulted in reduced germination. Yellow nutsedge seed germinated 14% at pH 3 compared to 47% at pH 7. Germination was not inhibited for any test species in dark, except Brazil pusley. After 168 h, germination of Brazil pusley ranged from 2 to 10% with light exposure of 0 and 16 h, respectively, before placing them in dark. Under alternate light and darkness cycle of 12 h, germination of Brazil pusley increased to 59%. Other than Brazil pusley no other species exhibited the photoblastic effect.

Laboratory experiments were conducted to study germination, emergence and establishment of yellow sweet clover (Melilotus indica). The seeds showed poor germination in Petri dishes due to a hard seed coat. Mechanical scarification, acid scarification and scarification by a short term exposure (4-5 min) to boiling water resulted in 100% germination of 1-, 2- and 3-year old seeds. Seedling emergence from non-scarified seeds was observed within 15 days. The emergence from surface sown seeds in pots was >80% and the emergence declined significantly with an increase in the seeding depth. Germination percentage, hypocotyl and radical growth of seedlings from seeds scarified by boiling were not inhibited by an osmotic potential upto -0.8 MPa .The growth was, however, inhibited by a salt stress of 40 mM NaCl indicating that the species is drought tolerant and salt sensitive. Plant growth was slow during the initial 60 days i. e. from November end to January end. The information could be exploited for developing strategies for the management of this weed.

Growth cabinet studies were conducted on the effect of water potential and interaction of temperature and water potential on germination of Brazil pusley, common ragweed, Florida beggarweed, hairy beggarticks, ivyleaf morningglory, Johnsongrass, prickly sida, redroot pigweed, sicklepod, strangler vine, tall morningglory and yellow nutsedge. Decreasing water potential from 0 to -0.1, -0.2 -0.4 and -0.8 MPa caused 12, 32, 75 and 96% reduction in germination of the test species, 3 WAS. A lower water potential of -0.1 MPa resulted in significant reduction in germination of common ragweed, strangler vine, hairy beggarticks and redroot pigweed. Decreasing water potential further to -0.4 MPa caused 77 to 100% inhibition in germination of all the test species, except Florida beggarweed, yellow nutsedge and tall morningglory. No weed seed could germinate at -1.2 MPa, whereas 28, 9 and 3% seeds of Florida beggarweed, yellow nutsedge and tall morningglory were able to germinate at -0.8 MPa. Water stress of -0.1 and -0.2 MPa delayed the germination of Johnsongrass by one and two weeks, respectively. Germination of tall morningglory, Florida beggarweed, ivyleaf morningglory, sicklepod and prickly sida was faster than Brazil pusley, strangler vine and beggarticks. Water stress of -0.2 MPa reduced the germination of ivyleaf morningglory and prickly sida, whereas tall morningglory, Florida beggarweed and sicklepod required -0.4 MPa osmotic potential to significantly reduce germination. Increasing the temperature from 15 to 20 and 30OC increased germination of weed species from 11 to 22 and 34%, respectively. Increasing water stress from -0.1 to -05 and -1.0 MPa resulted in 37, 6 and 0.3% germination compared to 47% with no water stress. Increasing temperature from 15 to 20 and 30OC resulted in 18, 36 and 56% germination at -0.1 MPa osmotic potential. Lower temperature and water stress was more inhibitory than high temperature and increased water stress to many weeds species. Decreased osmotic potential of -1.0 MPa resulted in complete germination inhibition of all species, except Florida beggarweed (11%). An increase in temperature of 5 or 10OC increased germination of tall morningglory from 10 to 34 and 43% at -0.5 MPa osmotic potential. At -0.5 MPa, Florida beggarweed had no germination at 15 or 20OC compared to 43% at 30OC, which was similar to 20OC and lower water stress (-0.1 MPa).

A field experiment was conducted at CCS Haryana Agricultural University Regional Research Station, Karnal during rabi 2007-08 and 2008-09 to evaluate the efficacy of sulfosulfuron tank mixed with carfentrazoneethyl against weeds in wheat. The treatments included tank-mix or sequential application of sulfosulfuron 25 g/ha with carfentrazone 20, 15 and 10 g/ha, alone application of sulfosulfuron 25 g/ha and carfentrazone 20 g/ha, sequential application of clodinafop 60 g/ha or sulfosulfuron 25 g/ha with metsulfuron 4 g/ha, sulfosulfuron+metsulfuron (ready-mix) 32 g/ha, pinoxaden 50 g/ha fb carfentrazone 20 g/ha, mesosulfuron+iodosulfuron (ready-mix) 14.4 g/ha, along with weed free and weedy checks. Tank mix or sequential application of sulfosulfuron with carfentrazone being at par reduced the density and dry weight of Phalaris minor similar to sulfosulfuron alone, mesosulfuorn+iodosulfuron, sulfosulfuron+metsulfuron (ready-mix) and sulfosulfuron fb metsulfuron during both the years and it was as good as weed free check during 2008-09. All the tank-mix and sequential applications of sulfosulfuron with carfentrazone were at par with carfentrazone alone and similar to weed free check in respect of density and dry weight of broadleaf weeds. Tank-mix and sequential application of sulfosulfuron with carfentrazone were at par with sulfosulfuron alone, all other check herbicidal treatments (except carfentrazone alone being inferior) and weed free check in respect of effective tillers and grain yield of wheat. There was no phytotoxicity of combination treatments of sulfosulfuron with carfentrazone except some brown freckles appearing on the leaves due to tank-mix treatments or carfentrazone alone, which disappeared within two weeks without any adverse effect on the crop. Hence, carfentrazone was found compatible with sulfosulfuron as tank mixture against complex weed flora in wheat with no loss of herbicidal efficacy.

The studies were conducted to determine the effect of straw retention and burning on Phalaris minor control. Reduced herbicide (isoproturon and pendimethalin) efficacy and increased P. minor infestation were observed with rice straw burning. A survey conducted in rice-wheat system revealed that majority of the farmers (65%) were burning rice straw in north-western Indian plains. For sustainability of rice-wheat system, instead of burning, residue should be either retained on surface or incorporated. The surface retention of rice residue of 5.0 and 7.5 t/ha reduced the weed dry weight in wheat by 23.4-30.3 and 35.5-44.1%, respectively. However, the yield and weed control were lower in various residue retention treatments without herbicides as compared to the herbicide application (sulfosulfuron 25 g/ha+metsulfuron 3 g/ha). Considering advantage of residue retention, efficient weed management options need to be evolved under such residue management practices

The compatibility of fenoxaprop-P-ethyl with carfentrazone-ethyl for the control of complex weed flora in wheat was evaluated during rabi 2005-06 and 2006-07 at CCS Haryana Agricultural University Regional Research Station, Karnal, India. The treatments included fenopxaprop + carfentrazone 100 and 120 g/ha in 4 : 1, 5 : 1 and 6 : 1 ratio, fenoxaprop+metsulfuron-methyl 100 g/ha in 30 : 1 and 40 : 1 ratio, fenoxaprop+2, 4-D Ester and Na salt 500 g/ha in 1 : 4 ratio, in comparison to fenoxaprop+A (adjuvant) 100 g/ha, fenoxaprop 120 g/ha and carfentrazone 20 g/ha along with weed free and weedy check. The density and dry weight of Phalaris minor decreased with widening of the ratio from 4 : 1 to 6 : 1 combination of fenoxaprop+carfentrazone at both the doses. In general, fenoxaprop+carfentrazone 120 g/ha was better than 100 g/ha in respect of density and dry weight of P. minor. Fenoxaprop+carfentrazone at 120 g/ha in all the ratios resulted in grain yield at par with weed free check during both the years. Among all the treatments, maximum number of effective tillers and grain yield were recorded with fenoxaprop+carfentrazone 120 g/ha (5 : 1) during both the years. Carfentrazone was compatible with fenoxaprop as tank mixture and there was no adverse effect on efficacy of both the herbicides. Fenoxaprop+carfentrazone 120 g/ ha (5 : 1) appeared to be the best combination for achieving maximum weed control efficacy and improved grain yield. Metsulfuron 2, 4-D Ester and Na salt had antagonistic effect on the efficacy of fenoxaprop when applied as tank mixture with it.

An experiment was conducted at experimental farm of Department of Agronomy, Punjab Agricultural University, Ludhiana (India) during rabi seasons of 2004-05 and 2005-06 in a split plot design comprising five planting techniques in main plots (conventional tillage, zero till sowing without stubbles, zero till sowing in standing stubbles, zero till sowing after partial burning and bed planting) and five weed control treatments in sub-plots (clodinafop 60 g/ha, clodinafop 60 g/hafb 2, 4-D 0.5 kg/ha, sulfosulfuron 25 g/ha, mesosulfuron+iodosulfuron 12 g/ha and unweeded control). Reduced dry matter of Phalaris minor Retz. and broadleaf weeds and higher wheat grain yield were recorded with zero till sowing in standing stubbles followed by zero till sowing after partial burning and bed planting. Clodinafop 60 g/ha alone controlled P. minor but did not control broadleaf weeds. Significantly reduced population of P. minor as well as broadleaf weeds and increased grain yield of wheat were observed with postemergence application of clodinafop 60 g/ha fb 2, 4-D 0.5 kg/ha, sulfosulfuron 25 g/ha and mesosulfuron+iodosulfuron 12 g/ha than clodinafop 60 g/ha alone and control. Among the planting techniques, zero till sowing in standing stubbles and among the weeds control practices sulfosulfuron 25 g/ha recorded highest wheat yield

The experiment was conducted at the Research Farm of the Punjab Agricultural University, Ludhiana in rabi seasons of 2005-06 and 2006-07 to study the efficacy of tank mix application of 2, 4-D, carfentrazone and metsulfuron with isoproturon in managing weeds of irrigated barley. Minimum weed dry weight was recorded in isoproturon 1000 g+metsulfuron 4 g/ha which was statistically on par with isoproturon 1000 g/ha, isoproturon 1000 g+carfentrazone 20 g/ha and isoproturon 1000 g+2, 4-D 500 g/ha during 2005-06. In 2006-07, minimum weed dry weight was recorded in two hand weedings which was statistically on par with isoproturon 1000 g+metsulfuron 4 g/ha, isoproturon 1000 g/ha, isoproturon 1000 g+carfentrazone 20 g/ha, and isoproturon 1000 g+2,4-D 500 g/ha. Highest test weight and barley grain yield were recorded in isoproturon 1000 g+metsulfuron 4 g/ha which were statistically on par with isoproturon 750 g+metsulfuron 4 g/ha, isoproturon 750 g+2,4-D 500 g/ha, isoproturon 1000 g+2, 4-D 500 g/ha and two hand weedings. The highest net returns of Rs. 29063 with isoproturon 1000 g+metsulfuron 4 g/ha and Rs. 39581 were recorded in isoproturon 1000 g+2, 4-D 500 g/ha as tank mix in 2005-06 and 2006-07, respectively.

A field study was carried out at Kathalagere, Karnataka in red loamy soil to evaluate the effectiveness of azimsulfuron on weed control, crop safety and grain yield of transplanted rice. Associated major weeds were Echinochloa glabrescence, Cyperus sps., Scripus roylei, Fimbristylis miliacea, Ludwigia parviflora, Lindernia verbenaefolia and Glinus oppositifolius. Hand weeding twice (20 and 40 DAT) recorded lower weed dry weight and higher mean rice grain and straw yield. Among the herbicides, application of azimsulfuron @ 30 g a. i./ha+0.2% nonionic surfactant applied at 19 DAT recorded higher mean rice grain and straw yield

In a field experiment, all weeds including Trianthema portulacastrum L. (T. portulacastrum) and 200 plants/m2 of T. portulacastrum resulted in significantly higher weed/T. portulacastrum dry weight, growth rate and relative growth rate than those in other treatments except all weeds excluding T. portulacastrum. These treatments caused significant reduction in soybean dry weight, crop growth rate, relative growth rate, leaf area index, net assimilation rate and uptake of N, P and K by soybean. All weeds excluding T. portulacastrum were comparable with them on the reduction of most of these parameters. Competition by all weeds including T. portulacastrum resulted in significantly lower values of pods/plant, seeds/pod, seeds/plant and seed weight/plant of soybean than other treatments except 200 T. portulacastrum/m2. All the densities i. e. 25, 50, 75, 100 and 200 T. portulacastrum/ m2 and all weeds including and excluding T. portulacastrum resulted in significantly lower seed yield than weed-free check, but the reductions were greater in all weeds including T. portulacastrum and 200 T. portulacastrum/m2. There was significant negative correlation (at P≤ 0.01) between the T. portulacastrum density and soybean seed yield.

A field experiment was conducted at Udaipur during 2002-03 and 2003-04 with 11 weed and three nutrient management practices to study the effect on growth, yield and quality of coriander (Coriandrum sativum). Weed management practices significantly reduced weed density, dry matter and nutrient uptake by weeds and improved growth (plant height), yield attributes (umbels/plant and weight of seeds/umbel), seed and biological yield, quality parameters (essential oil content and oil out turn) and nutrient uptake by crop as compared to control. Two hand weedings (HW) at 30 and 45 DAS resulted in maximum reduction in weed density, dry weight and nutrient depletion by weeds and gave the highest seed (1.59 t/ha) and biological yield (4.11 t/ha) of coriander. However, maximum essential oil content, oil out turn and B : C ratio (2.13) were obtained by pendimethalin 1.0 kg/ha+one hand weeding at 45 DAS. Both the treatments remained at par in reduction of weed dry matter and nutrient uptake by weeds and resulted in maximum weed control efficiency (88.50%) as compared to rest of the practices. Balanced fertilization with 60 kg N+30 kg P+30 kg K+30 kg S/ha also significantly improved weed dry weight and nutrient uptake by weeds, but simultaneously enhanced crop nutrient uptake, plant height, umbels/plant, 1000 seed weight, seed and biological yield, essential oil content, oil out turn and B : C ratio over N+P and N+P+K application. Treatment of pendimethalin 1.0 kg/ha+one hand weeding at 45 DAS resulted in the highest seed yield, maximum weed control efficiency (88.50%) and B : C ratio (2.13). However, minimum nutrient uptake by crop and maximum nutrient removal by weeds were noted under weedy check.

A field experiment was carried out during 2005 and 2006 at Belvatagi, Karnataka to work out the weed management practices in drill sown onion+chilli+cotton relay intercropping in rainfed Vertisols. Pre-emergence application of oxyfluorfen @ 0.15 kg/ha and pendimethalin @ 1.0 kg/ha reduced the weed growth significantly but oxyfluorfen was toxic to onion and chilli. Pendimethalin @ 1.0 kg/ha with two or more hand weedings resulted in higher onion bulb yield and at par with farmers’ practice (88.37 q/ha). Chilli fruit yield was significantly higher with oxadiargyl @ 0.09 kg/ha with hand weeding at 20, 40, 60 and 80 DAS (11.8 q/ha), which was at par with weed free check (12.99 q/ha) and farmers’ practice (10.09 q/ha). Seed cotton yield was found better with oxyfluorfen @ 0.15 kg/ha alongwith hand weeding at 20, 40 and 60 DAS. Application of pendimethalin @ 1.0 kg/ha with three hand weedings at 20, 40 and 60 DAS was found better for onion bulb and chilli fruit yield and comparable with farmers’ practice for the onion+chilli+cotton relay intercropping system. This resulted in higher net returns (Rs. 64,390/ha) and B : C ratio (3.99).

A field experiment was conducted during rabi seasons of 2007-08 and 2008-09 at the research farm of NRCSS, Ajmer (Rajasthan) to find out most suitable and economical method of weed control in fennel (Foeniculum vulgare).The experiment was laid in RBD. Based on two years’ study, it was revealed that besides weed free treatment, significantly highest plant height at all the growth stages, number of branches/plant, yield attributes like number of umbels/plant, number of umbellates/umbel, number of seeds/umbellate, seed and straw yields of fennel were recorded with pre-emergence (PRE) application of oxadiargyl @ 75 g /ha+one hand weeding (HW) at 45 DAS which being at par with PRE application of pendimethalin @ 1.0 kg/ha+HW at 45 DAS. Similarly, besides weed free treatment, the lowest dry weight of weed at harvest and weed index as well as highest weed control efficiency was also obtained with PRE application of oxadiargyl @ 75 g/ha (PE)+HW at 45 DAS. This treatment also exhibited highest net returns (Rs.104310/ha) and B : C ratio.

Greenhouse studies were conducted to examine the effect of non-ionic ‘Induce’ and the organosilicone ‘Silwet L-77’ adjuvants on the rainfastness of glyphosate applied to a broadleaf weed-wild mustard. Glyphosate was tank mixed with and without adjuvant at three different concentrations. No rainfall and six simulated rainfall treatments at 30 min, 1, 2, 4, 6 and 24 h after glyphosate treatment were applied to the treated plants. With the addition of either adjuvant, absorption of 14C glyphosate was enhanced, which presumably led to increased rainfastness as indicated by good control of wild mustard plants even when simulated rainfall occurred 30 min after application. Addition of both adjuvants also improved translocation of 14C glyphosate. Simulated rainfall immediately after glyphosate application washed off chemical from the foliage, leaving not enough chemical to have phytotoxic effects. Simulated rainfall that occurred 30 min after application did not affect the efficacy of glyphosate as a significant amount of 14C glyphosate had already been absorbed. Use of the organosilicone adjuvant achieved higher per cent control of weeds than the nonionic adjuvant, presumably through increased rainfastness of glyphosate. Addition of non-ionic adjuvant ‘Induce’ at 0.25% in and organosilicone ‘Silwet L-77’ at 0.1% was better in achieving effective control of wild mustard than other rates of adjuvants with glyphosate under different simulated rainfalls. Thus, addition of an adjuvant helped in absorption and translocation of 14C glyphosate as quickly as 30 min after treatment.

Perennial weed, Cynodon dactylon L. is one of the most troublesome weeds in mulberry plantations. Treatments comprising hand weeding and intercropping with cowpea recorded the lowest weed density and dry weight. The total weed control efficiency ranged between 76.6 and 52.6%, while the efficacy against C. dactylon ranged between 77.8 and 37.2%. The leguminous intercrop had a positive and significant influence on mulberry growth and yield.

Efficiency of Eisenia foetida, Amyanthes diffringens and Eudrillus eugineae in vermicomposting of plant biomass viz., rice straw, Ipomoea carnea, Eichhornia crassipes alone and in mixture was studied during summer and winter seasons. All the species were found efficient in vermicomposting of plant biomass. Time required for composting varied from 50-70 days and 55-75 days during summer and winter seasons, respectively. E. foetida was at par with E. eugineae as regards to their multiplication rate and composting period. The multiplication rate was lowest with A. diffringens which also took relatively longer time for composting. The compost recovery did not change with earthworm species. The highest compost recovery was obtained from Ipomoea biomass followed by mixture of rice straw, Ipomoea and Eichhornia biomass. The compost recovery was lowest with Eichhornia biomass. Irrespective of earthworm species, the population at maturity of the compost was increased by 8-12 times over the initial population. Earthworm activity substantially narrowed down the C : N ratio and increased the nutrient content in the compost over the initial value of the respective biomass. Different earthworm species could not show any significant variation in the nutrient content except for nitrogen and phosphorus, which were significantly higher with E. foetida and E. engineae compared to A. diffringens. Vermicompost prepared from Ipomoea biomass had the highest nutrient level followed by mixture use of rice straw, Ipomoea carnea and Eichhornia crassipes biomass. The lowest C : N ratio was recorded in the vermicompost from Ipomoea biomass, while the highest was recorded from rice straw.