Makhan S. Bhullar

Control of Morningglories (Ipomoea spp.) in Sugarcane (Saccharum spp.)

Abstract Morningglories are summer annual or perennial dicots, and are troublesome weeds in sugarcane cultivated in northern India. If not controlled, they may compete with sugarcane, interfere in the harvest operation, and reduce yields. Managing morningglories in sugarcane continues to be a serious challenge for sugarcane growers. Field experiments were conducted during the 3-yr period from 2007 to 2009 to evaluate herbicides applied PRE and POST for control of morningglories in sugarcane. The herbicides applied PRE included diuron, metribuzin, and atrazine at 1.6, 1.4, and 1.0 kg ai ha−1, respectively, applied alone or followed by 2,4-D amine salt (0.58 or 1.16 kg ae ha−1) or 2,4-D sodium salt (0.8 or 1.6 kg ae ha−1) applied POST. Herbicides applied PRE controlled morningglories ≤ 87% at 15 d after treatment (DAT); however, control reduced to ≤ 56% at 90 DAT. Control improved when herbicides applied PRE were followed by POST application of 2,4-D amine or sodium salt. For example, diuron applied PRE followed by 2,4-D amine salt applied POST at any rate provided 100% control of morningglories at 15 and 30 DAT. At 90 d after POST application, control ranged from 68 to 82% with the PRE followed by POST herbicides, compared to 0% control when metribuzin or atrazine were applied PRE alone. The density and biomass of morningglories was also reduced to zero in treatments that included 2,4-D amine salt. The number of millable canes, cane height, and single cane weight was superior in PRE followed by POST herbicide treatments compared to herbicides applied PRE alone. Maximum cane yield was recorded for the treatments that included 2,4-D amine or sodium salt compared to only PRE treatments, and it was usually comparable with the nontreated weed-free control. It is concluded that a combination of PRE and POST herbicides were effective for control of morningglories; however, more research is required to evaluate other herbicides and their tank mix partners for control of morningglories in sugarcane. Nomenclature: Japanese morningglory, Ipomoea nil (L.) Roth.; obscure morningglory, Ipomoea obscura L. Ker Gawl.; sugarcane, Saccharum spp.

Development of cross resistance in isoproturon resistant Phalaris minor Retz. in Punjab

Seeds of isoproturon resistant Phalaris minor were collected from wheat fields and field experiments were conducted during winter season of 2012 and 2013. The biotype was found resistant to clodinafop-propargyl, fenoxaprop-pethyl and also showed cross resistance to pinoxaden. Mesosulfuron + iodosulfuron and sulfosulfuron provided 65 and 90 per cent control of the weed, respectively. Metribuzin recorded above 90 per cent weed control during both the years. Plants sprayed with metribuzin showed a sharp decrease in chlorophyll fluorescence (Fv/Fm ratio) of about 65 per cent as compared to control after 24 hours of spray even when there were no visible symptoms of herbicide injury. By this time, reduction in Fv/Fm ratio was less than 10 per cent for plants treated with ACCase and ALS inhibitors. At 15 days after spray, Fv/Fm ratio decreased by 11 to 13 and 23 to 30 per cent as compared to control for ACCase and ALS inhibitors, respectively.

Weed management in conservation agriculture in India

Conservation agriculture (CA) involves minimum soil disturbance, permanent soil cover through crop residues or cover crops, and crop rotations for achieving higher productivity. Even though the adoption of CA in India is still in an early stage, it has been successfully used in the irrigated rice-wheat cropping systems of the Indo Gangetic Plains (IGP) and recently been demonstrated in parts of central India. Increased weed problems during the ‘transition period ’tends to be the most common hurdle in adoption of CA by farmers. Research has shown that cover crops could play an important role in weed management in CA systems; however, their level of adoption at present is fairly low. Changes in patterns of tillage, planting systems, and other management strategies can alter the soil environment and lead to a major change in weed flora. Herbicide use has been an extremely important component of weed management in CA systems but greater effort is needed to integrate non-chemical weed control tactics with herbicides. Farmer-participatory model of research has proved highly effective in developing CA in rice-wheat system in the IGP. Efforts are required to increase the rate of adoption of direct seeded rice and zero-till wheat throughout the IGP. At present, residue retention on farmer fields tends to be low. Greater awareness of the benefits of residue retention for improved soil health is worthy of an extension campaign in particular and in India in general. Research effort needs to be enhanced to develop CA and promote its adoption in non-rice-wheat cropping systems in India.

Effect of repeated application of pendimethalin on its persistence and dissipation kinetics in soil under field and laboratory conditions

ABSTRACT The repeated application of herbicide can alter its persistence in the environment. In India, wheat fields are exposed to herbicide application at least once in the cropping season. The present study investigated the dissipation behavior of pendimethalin applied annually to a wheat field over four cropping seasons from 2012 to 2016. The dissipation studies were also conducted under laboratory conditions during 2015–2016. Pendimethalin from soil and wheat grain samples was extracted using matrix solid-phase dispersion and quantified using high-performance liquid chromatography and gas chromatography–tandem mass spectrometry. The average recoveries of pendimethalin from soil and crop produce ranged from 81.3% to 103.1%. The half-life of pendimethalin ranged from 20.9 to 31.3 days and 9.4 to 60.2 days under field and laboratory conditions, respectively. Dissipation of pendimethalin varied significantly over the years under field conditions and was comparatively faster than under laboratory conditions. On the other hand, non-significant variation in the dissipation of pendimethalin in soils under laboratory conditions was observed. The residues of pendimethalin in crop produce at harvest were below the maximum residue limit set by EPA.

Weed Management in Common Cottonwood (Populus deltoides) Nursery Plantation

Abstract Common cottonwood-based agroforestry system is widely adopted in Indian Indo-Gangetic plains. The stem cuttings of common cottonwood are raised in a nursery 10 to 12 months in rows spaced 0.5mx 0.5 m, before re-planting in the field. The longer duration of 10 to 12 months and wider spacing of stem cuttings in the nursery makes the entire transplants highly vulnerable to weed competition, especially during early establishment stages. The efficacy of preemergence herbicides and plastic and straw mulches for weed management in common cottonwood nursery was investigated at two sites in years 2014 and 2015. The major weed flora in the experimental field consisted of three grass weeds (crowfootgrass, feather lovegrass, and southern crabgrass), and four broadleaf weeds (scarlet pimpernel, garden spurge, niruri, and lesser swinecress). The integrated use of pendimethalin or alachlor applied PRE with paddy straw mulch significantly reduced density and biomass of both grass and broadleaf weeds compared to herbicide or straw mulch used alone, and provided similar level of weed control to hand weeding at both locations. Spreading of plastic mulch in the whole field after punching holes for common cottonwood stem cuttings, or in row spaces recorded similar weed control to hand-weeding. The integrated use of herbicides with straw mulch, and or plastic mulch alone significantly improved plant height, stem diameter, below- and aboveground biomass of common cottonwood plants compared to unweeded check. The study concluded that integrated use of herbicides plus paddy straw mulch or plastic mulch alone could be adopted for weed management in common cottonwood nursery plantations. Nomenclature: Alachlor; pendimethalin; crowfootgrass, Dactyloctenium aegyptium (L.) Willd.; feather lovegrass, Eragrostis tenella (L.) Beauv. ex Roemer & J.A. Schultes; garden spurge, Chamaesyce hirta (L.) Millsp.; lesser swinecress, Coronopus didymus (L.) Sm.; niruri, Phyllanthus niruri L.; scarlet pimpernel, Anagallis arvensis L.; southern crabgrass, Digitaria ciliaris (Retz.) Koel.; common cottonwood, Populus deltoides Marshall.

Ecological Methods for Weed Management

Weed ecology is influenced by the plant community composition, the evolution of weeds, allelopathy and competition. Climatic, edaphic and biotic factors determine the distribution of weed species, their type, prevalence and intricate relationships resulting in association of weeds whose ecological requirements tally with the crop. Environmental factors such as temperature, osmotic potential, pH, salinity, light, burial depth and management practices affect seed germination and emergence of weeds. These factors are important for the development of integrated weed control strategies. We review ecological weed association, germination ecology of weeds, crop-weed competition, weed flora in different crops and ecological approaches for weed management. We discuss shifting the focus from weed control to weed management and how the integration of cultural, mechanical and chemical practices can reduce weed establishment. Weeds reduce crop yield by competition for light, water, nutrients and space, interfering with harvesting operations and increasing the cost involved in crop production. Cultural practices can be manipulated for eliminating or reducing the population of major weeds. Overall, knowledge of weed ecology can be used as a tool for effective weed management.

Appearance of new weeds in Punjab

Weed monitoring and survey was conducted to detect appearance of new weed species. Ten new weed species namely Galium spurium Linn. (family Rubiaceae), Geranium nepalense Sweet (family Geraniaceae), Lamium amplexicaule Linn. (family Lamiaceae), Evolvulus nummularius (family Convolvulaceae), Euphorbia thymifolia Linn.(family Euphorbiaceae), Oenothera laciniata Hill (family Onagraceae), Soliva anthemifolia (Juss.) R. Brown (family Asteraceae), Verbesina encelioides (Cav.) Benth. and Hook. f. ex A. Gray (family Asteraceae), Nicotiana plumbaginifolia Viv. (family Solanaceae) and Portulaca oleracea L. (family Portulacaceae) have been recorded in the last decade from different places of Punjab State. Out of these, weed species namely, O. laciniata, L. amplexicaule, S. anthemifolia and G. nepalense were mainly observed inhabiting the crop fields. Three weed species namely, G. spurium, N. plumbaginifolia and V. encelioides were observed growing along roadsides, wastelands, canal banks and uncultivated areas. P. oleracea and E. thymifolia were observed growing on bunds of agricultural fields. E. nummularius is a serious weed of lawns and landscapes. These weeds have now domesticated in the studied ecological niche and may potentially harm the biodiversity of those areas.

Germination ecology of wrinkle grass (Ischaemum rugosum) population of Indo-Gangetic plain region

Wrinkle grass (Ischaemum rugosum Salisb.) is a highly competitive weed in rice production that can cause huge yield reductions. Information on germination ecology of this weed is essential for the development of effective integrated weed management systems. No information is available on germination ecology for populations of this weed from Indo-Gangetic plain region of India. This study was conducted to generate information on effects of major environmental factors, viz. light, temperature, burial depth, moisture, salinity and pH on germination/emergence of this weed. Seed germination was independent of light and more than 50% germination was recorded under a wide temperature range of 20/ 10 to 35/25 °C day/night (12/12 h). Maximum emergence was observed when seeds were placed on surface or buried up to 1 cm; but considerable emergence was also observed from deeper soil layers (up to 6 cm depth). Germination was above 75% at 160 mM but completely inhibited at 320 mM of NaCl. Germination was sensitive to moisture stress and was completely inhibited at water potential of -0.8 MPa. Seeds were able to germinate under wide pH range of 3-10.

Quantification of flufenacet residues in soil and wheat grain

The terminal residues of flufenacet were quantified in soil and wheat grains. Flufenacet was applied at 250 and 300 g/ha on 21 and 35 days after the sowing of wheat at the Research Farm of Punjab Agricultural University, Ludhiana. Matrix solid phase dispersion (MSPD) method was used for the extraction of flufenacet from soil and grain samples. The herbicide residues were quantified using High Performance Liquid Chromatography (HPLC) equipped with UV-Vis detector and were confirmed with gas chromatographic tandem mass spectrometry (GC-MS/MS). The average recoveries of flufenacet extracted from the matrix ranged from 80.9 to 93.0% and 88.0 to 96.2% when quantified using HPLC and GC-MS/MS, respectively with relative standard deviation less than 10%. Both HPLC and GC-MS/MS offer high reproducibility, however GC-MS/MS was more sensitive having limit of detection (LOD) and limit of quantification (LOQ) as 0.001 and 0.003 μg/g, respectively. Terminal residues of flufenacet in the soil and wheat grain samples were below the detectable limit. Thus, the use of flufenacet in wheat under sub-tropical humid conditions could be considered safe.

Control of mixed weed flora in wheat with sequential application of pre-and post-emergence herbicides

The field efficacy of pre-and post-emergence herbicides for control of mixed weed flora in wheat was evaluated in a field study conducted at Punjab Agricultural University, Ludhiana during Rabi seasons of 2014–15 and 2015–16. The season long growth of weeds reduced wheat yield upto 38.5%. Pendimethalin and metribuzin recorded 65–73 and 73–78% control of Phalaris minor, respectively and their tank-mix application enhanced P. minor control to 78–85%. Pendimethalin and metribuzin recorded 26–33 and 5863% control of Medicago denticulata, respectively and their tank-mix application enhanced control to 77–92% of this weed. Pendimethalin and metribuzin provided control of Rumex dentatus to the extent of 98–100% and 68–92%, respectively, while provided 98–100 and 63–72%, respectively control of C. album. Sequential application of pendimethalin as pre-emergence followed by sulfosulfuron as post-emergence recorded the highest weed control efficiency (96%) and wheat grain yield (4.8 t/ha), and it was at par to pre-emergence pendimethalin + metribuzin, post-emergence pinoxaden + metsulfuron, mesosulfuron + iodosulfuron, sulfosulfuron + metsulfuron and two hand weeding.