Weed Science

Clodinafop-propargyl was compatible with metsulfuron-methyl and carfentrazoneethyl as tank mixture with respect to the control of Phalaris minor and Chenopodium album in wheat. Fenoxaprop-p-ethyl was compatible with carfentrazone-ethyl and not with metsulfuron-methyl. Clodinafop as well as fenoxaprop had no compatibility with 2, 4-D. The mixed population of P. minor and C. album caused 66% reduction in wheat grain yields in weedy plots, whereas competition with C. album caused 22% reduction in wheat yield.

Tank mixture of clodinafop+sulfosulfuron (3 : I) at 60 g ha- ' and fenoxaprop+ sulfosulfuron (4 : I and 5 : I) at 120 g ha- I provided 85-90% control of Avena ludoviciana and Phalaris minor and 60% control of broadleaf weeds like Chenopodium album. Melilotus indica and Rumex retrojlexus. None of the herbicide combinations was effective against Convolvulus arvensis. Clodinafop+sulfosulfuron at lower dose of 50 g ha- I and fenoxaprop+sulfosulfuron at 100 g ha- I although provided good control of broadleaf weeds but poor control of grassy weeds. Maximum grain yield (5240 kg ha- ') was obtained in weedfree treatment which was at par with clodinafop+sulfosulfllron (3 : I) at 60 g ha- I and fenoxaprop+slllfoslllfuron (4 : I or 5 : I) at 120 g ha- ' .

Fenoxaprop at 120 g ha", clodinafop at 60 g ha" and sulfosulfuron at 25 g ha" significantly reduced the density of Phalaris minor and increased number of spikes and grain yield of wheat over their lower doses. Density of broad leaf weeds decreased significantly with sulfosulfuron or metribuzin or tank mixture of metribuzin with fenoxaprop or c1odinafop compared to weedy check. Tank mixture of clodinafop+metribuzin at 45+ 140 g ha'I recorded lowest weed biomass fotlowed by fenaxoprop+metribuzin at 90+ 140 g ha'i and clodinafop+metribuzin at 30+140 g ha". Increasing the dose of metribuzin in the mixture from 100 to 140 g ha'i reduced wheat yield; the effect was more pronounced with fenoxaprop than with clodinafop.

Addition of power activator increased the efficacy of fenoxaprop-p-ethyl at 80 and 100 g ha- ' on grassy weeds in wheat. The efficacy of this herbicide at 120 g ha- ' was not affected due to addition of surfactant. Fenoxaprop at 100 g ha- ' with or without surfactant produced wheat grain yields at par with weed-free treatment and clodinafoppropargyl at 400 g ha- ' .

Dithiopyr at 360 g ha- I proved superior in reducing the density of Phalaris minor than the lower doses and was at par with trifluralin at 1250 g ha-' and isoproturon at 1000 g ha- I. Density of broad leaf weeds was significantly lower in the plots treated with dithiopyr at 240 g ha- 1 compared to trifluralin at 1250 g ha- 1 • Tank mixture of dithiopyr+isoproturon at 120+ 1000 g ha- 1 reduced the total dry weight of weeds by more than 90% over weedy check and provided similar yield to that of isoproturon and weed-free treatment. It was observed that at higher dose (480 g ha- I) of dithiopyr crop lodged due to thin stem and increased length of internodes.

Alone application of chlorsulfuron at lower doses (20 and 30 g hao' ) was not effective against Phalaris minor but it was at par with sulfosulfuron in reducing the broad leaf weeds at lowest (20 g hao' ) dose. Tank mixture of chlorsulfuron either with pendimethalin or tritluralin at 1430+70 g ha" provided effective control of both P. minor and broad leaf weeds. The number of spikes and wheat yield increased with the increase in dose of chlorsulfllron from 20-40 g ha· ' . Tank mixture of pendimethalin or tritluralin with chlorslllfllron did not increase grain yield of wheat over their alone application at corresponding doses.

Sulfosulfuron (except at 100 g ha- ' ) did not control wild oat population but reduced its dry matter significantly as compared to isoproturon and weedy check. Sulfosulfuron (either of its doses) was not effective against C(chorill/ll illtybus but gave effective control of Phalaris minor and Medicago hispida. Isoproturon was less effective against wild oat but gave very good control of C. album. Sulfosulfuron at 50 and 100 g ha- ' was phytotoxic to wheat crop during 2001-02. Isoproturon (1000 g ha- ' ) gave the maximum grain yield of wheat in absence of wild oat, while sulfosulfuron (50-100 g ha") in presence of wild oat.

Key weed species in the experimentaJ field were Phalaris minor, Avena ludoviciana, Chenopodium album. Melilotus indica. Coronopus didymus and Convolvulus arvensis. On an average, prometryn at 2.0 kg ha· 1 provided 73-82% control of grassy as well as broad leaf weeds. Efficacy of prometryn against grassy weeds was higher than isoproturon but lower than clodinafop and sulfosulfuron. Inspite of good efficacy of prometryn against weeds, wheat grain yield and number of spikes were significantly less than clodinafop and sulfosulfuron due to toxicity to crop.

Depth and periodicity of Phalaris minor emergence were recorded in wheat sown under different establishment methods after rice which was also planted adopting various establishment methods. Maximum depth of emergence of P minor was 5.92 cm under conventionally tilled wheat sown after transplanted rice, whereas minimum depth of 0.91 cm was recorded in zero tillage wheat after direct seeded rice without puddling (DS). Maximum P minor population emerged from 0-3 cm depth under all the wheat establishment methods. In both conventionally tilled and zero tilled wheat after direct seeded unpuddled and puddled rice, there was no emergence of P minor from 6-9 cm depth but still 5% population could emerge from this layer after transplanted rice. Conventionally tilled wheat had more weed population than zero tilled wheat after any rice establishment method. Under conventionally tilled wheat field before irrigation, there was 16% increase in P minor density during 15 to 20 DAS but after first irrigation, the density of this weed increased by 175% during 20 to 40 DAS. In zero tilled wheat, the density of this weed increased by 61% before irrigation and after irrigation this increase was only 102%.

Dry matter of Phalaris minor recorded at the time of harvest was found to be 100~er in the wheat crop sown after giving deep/inverted tillage with mould board plough dUring the start of the experiment and consequently the number of seeds of P minor in the top 0-15 cm soil depth was found to be significantly less in these treatments as compared to the plots of continuous zero till sown crop for three years. Post-emergence application of clodinafop 60 g ha- I, sulfosulfuron 25 g ha- I and fenoxaprop-p-ethyl 100 g ha,l was found to be at par with respect to dry matter accumulation by P minor. However, seed bank recorded during the year of termination was found to be significantly less in clodinafop, sulfosulfuron as compared to fenoxaprop-p-ethyl treated plots. Wheat sown after giving inverted tillage (during 2001-02) produced significantly higher grain yield as compared to the crop sown with zero tillage or zero tillage followed by normal tillage.

Puddling of soil significantly influenced the vertical distribution of weed seeds. Weed seeds were observed upto 20 cm depth but their intensity varied. While Chenopodium alhum was distributed mostly upto 5 cm depth, Medicago hispida and Phalaris minor were found in large numbers upto higher depth (10 cm). Avena ludoviciana was mostly abundant from surface to shallow depth (2.5 cm). Maximum emergence of P minor at 2 cm and A. ludoviciana at 4 cm depth was recorded upto two weeks. Red light increased the germination of P minor but reduced the germination of M. hispida. Lowest germination of Asphodelus tenuijblius and P minor was observed in dark but there was no effect of darkness on germination of M. hispida. Maximum germination of A. lucloviciano was recorded in green light.

SensulfuTOn-methyl at 30 to 60 g ha" applied alone or as tank mixture with butachlor at 1.0 kg ha" reduced the density of all the sedges as well as Caesu/ia axillaris and Comme/ina benghalensis. At higher doses of bensulfuion methyl (50 and 60 g ha"), there was almost complete control of sedges and non-grassy weeds. The differences in grain yields due to various doses of bensulfuron-methyl were non-significant and yields were at par with weedfree treatment. Bensulfuron-methyl was compatible with butachlor with report to control of various weeds.

Weed density and yield of rice in western IGP were examined in transplanted rice crop under rice-wheat, rice-pea-rice and rice-sugarcane=ratoon-wheat/fallow cropping systems. Echif/ochloa crusgalli was dominant after rice-wheat and rice-pea-rice sequence, but it was completely suppressed after the sugarcane sequence. Among sedges, Fimbristylis milliacea was dominant after rice-wheat and Cyperus difJormis after rice-pea-rice. [n the sugarcane system. Cyperlls rotllf/dlls became the main weed. The yield loss from weeds in unweeded plots was highest in the rice-wheat system. followed by rice-pea-rice, and was least in the sugarcane system. Under fanners' weed management practices, there were yield losses due to weeds ranging from 13.1 to 22.4'Yo. The total cost of weed management in transplanted rice was higher in rice-wheat system than in rice-pea-rice or rice-sugarcane system.

Rice establishment methods had marked effect on weed density and their dry matter production. The highest weed density and dry matter production were recorded in DSR (dry direct seeding unpuddled) and least in WSR (wet seeding in puddled soil) and TPR (transplant) establishment methods at 30 days stage of growth. In weedy plots, the density of Echinoch!oa colona in DSR was higher than in WSR and TPR. Similarly, nongrassy weeds were more in number in DSR than in WSR and TPR. The population of sedges was more in DSR than in WSR, whereas it was not found in TPR. Uncontrolled weeds, on an average, caused 75.8, 70.6 and 62.6% reduction in grain yield of rice when compared with weeded situation in DSR, WSR and TPR, respectively. Thus, the potential yield loss due to weeds was higher in DSR than in TPR. The grain yield of rice was similar under the three establishment systems of rice when weeds were controlled effectively by herbicide application supplemented with weedings.

Pyrazosulfuron-ethyl at 25 g ha- I applied 10 days after sowing (DAS) was found most effective, recording 85.8% reduction in dry matter of weeds and 54.6% higher grain yield over weedy check. -The corresponding increase in grain yield was 45.7, 39.0 and 28,8% with pyrazosulfuron-ethyl at 20 g ha- I applied 10 DAS, two hand weedings done 20 and 40 DAS, and butachlor+safener at \.00 kg ha- I applied 3 DAS, respectively.

Pre-emergence application of pretilachlor with safener supplemented with one hand weeding at 40 days after sowing provided better weed control and higher grain yield than the two hand weedings done at 20 and 40 days after sowing. Intercropping of Sesbllnia aeu/eala and dual cropping of azolla with rice resulted in reduced density and dry weight of weeds. Regarding nitrogen management, 100% N+S. lIeu/eala intercropping+azolla dual cropping had a positive impact on yield attributes and thereby produced higher grain yield.

The highest weed control efficiency (45.3%) was recorded in sole maize crop with alachlor at 1.5 kg ha-' supplemented with hand weeding, closely followed by maize+blackgram intercropping with same weed control practice (37.1 %). Intercropping with soybean or blackgram increased the maize grain yield by 18.8 and 16.6% over sole maize crop. Significantly higher maize equivalent was recorded in maize+soybean intercropping with alachlor at 1.5 kg ha-' supplemented with hand weeding (8803 kg ha- I), followed closely by maize+soybean with alachlor alone (8103 kg ha-').

Crop rotation of l1lustard-wheat-wheat-mustard was most effeclive in arresting populalton of Asphodelus tenuifolius with similar effect on weed dry weight. As a result. It improved yield attributes and seed yield of mustard by 667 kg ha" compared with continuous mustard rotation. The herbicidal control (tluchloralin at 1.0 kg ha" in mustard and 2. 4-D at 0.5 kg ha" in wheat) in mustard-wheat-wheat-mustard rotation controlled A. tenuifolius and total weeds effecltvely and thus significantly enhanced the seed yield of mustard. On the contrary, use of tluchloralin alone without any herbicide rotation in continuous mustard did not control A. tenuifolius effectively and thereby, reduced the seed yield of mustard compared to all other rotations.

Parthenilll1l hysterophorus. Cyperus rotundus, Brachiaria ramosa, others as well as total weed density and total weed dry weight were lowest under atrazine at 2.0 kg ha" which was closely followed by two hoeings done at 50 and 80 days after harvesting of main crop and metribuzin at 1.0 kg ha". Uncontrolled weeds caused 63.6% reduction in the cane yield when compared with weed-free treatment. Atrazine at 1.0 and 2.0 kg ha" or metribuzin at 1.0 kg ha" applied just after hoeing and two hoeings at 50 and 80 days after harvesting of main crop produced cane yield at par with weed-free treatment.

The highest weed control efficiency (96.7%). dry root yield (558 kg ha"), seed yield (506 kg ha") and net profit (Rs. 18,450 ha") were recorded with three weedings at 20, 40 and 60 days after sowing (DAS), followed by pre-emergence application of isoproturon at 0.50 kg ha"+weeding at 45 DAS which was followed by glyphosate at 1.0 kg ha"+weeding at 45 DAS. Unchecked weed growth caused 57.2% loss in dry root yield and 53.6% loss in seed yield of asgandh. Higher doses of isoproturon (0.75 kg ha") and glyphosate (1.5 kg ha") gave 8.6 and 13.4% phytotoxicity tel asgandh crop, respectively.

Adsorption-desorption of sulfosulfuron on four Indian hill soils was studied using batch equilibrium technique. Freundlich constant log K was highest for mollisol-2 soil having low organic carbon, clay content and high pH. Adsorption was in the order inceptisol > mollisol-2 > mollisol-I > entisol. Sulfosulfuron showed S-type adsorption isotherm curves indicating hydrophilic nature of surface of soils due to which water molecules compete with the herbicide. Sulfosulfuron showed negative hysteresis or irreversiblc adsorption with hysteresis coefficient values more than I.