Navjyot Kaur

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.

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.

Allelopathic potential of rice varieties against major weeds of rice and wheat

Rice-wheat system is the major cropping system in Northern India. Direct-seeding of rice is receiving considerable attention because of decreasing availability of water and increasing labor costs. In rice shift from transplanted to direct-seeded cultural practices, weed problems are expected to increase since crop and weeds can emerge together (Rao et al. 2007). Yield losses of wheat due to weeds are estimated around 25-50% and in very severe cases the losses may go up to 80% (Singh et al. 2005). Production of large amount of straw by rice crop is one of the most serious problems in rice producing countries like India. The majority of rice straw is burnt in the fields causing environmental pollution and health hazard to public. Incorporating the residues of rice with high allelopathic activity can reduce the herbicide usage in rice-wheat system. Echinochloa crus-galli and E. colona in rice and Phalaris minor in wheat are the predominant and noxious grassy weeds in rice-wheat system (Walia et al. 2005). The use of rice germplasm that contains high allelopathic activity, combined with incorporating straw into the soil can suppress germination of weeds. So, the present study was undertaken to assess basmati and non-basmati rice varieties for their allelopathic potential against germination of E. crusgalli, E. colona and P. minor.

Herbicide resistance in weeds and its management

Repeated use of herbicides with similar modes of action for weed control in wheat has resulted in evolution of multiple herbicide resistance in Phalaris minor, which could threaten the sustainability of the rice-wheat cropping system in north-western India. Herbicide resistance could also become a problem in direct seeded rice and soybean crops, which rely heavily on acetolactate synthase (ALS) and acetyl coenzyme A carboxylase (ACCase) inhibiting herbicides. As discovery of new herbicide modes of action has slowed dramatically, all effort should be made to increase the effective life of existing herbicides and make weed management cost-effective and efficient. Early detection of resistance can facilitate timely adoption of alternative tactics and minimise the financial impact on farmers. Structured surveys of resistance affected areas can provide required information for site-specific recommendations as expression of herbicide resistance tends to be highly site-specific. Greater emphasis is needed on weed management systems based on sound knowledge of weed ecology. Refinement is needed in seeding machinery for high residues systems, improvements in equipment for inter-row cultivation and application technology of herbicides. Farmer-participatory research and adoption of improved agronomy could delay evolution of resistance in weeds and enhance the sustainability of Indian cropping systems. This paper has reviewed and discussed herbicide resistance in weeds in Indian context.

Germination Ecology of Herbicide-Resistant Population of Littleseed Canarygrass from North–Western India

ABSTRACT Littleseed canarygrass (Phalaris minor Retz.) is a most dominant weed of wheat (Triticum aestivum L.) in the north-western states of India. Little information is available on germination of littleseed canarygrass and wheat under similar ecological conditions. The present study was conducted under controlled conditions to study germination ecology of littleseed canarygrass population possessing multiple-herbicide resistance, along with wheat. Germination of littleseed canarygrass and wheat was independent of light. Optimum temperature for germination of littleseed canarygrass and wheat was 20°C. Germination of both species was completely inhibited at osmotic potentials lower than −0.4 MPa. Seeds of littleseed canarygrass and wheat were able to germinate even at NaCl concentration of 200 mM, with complete inhibition at 300 mM. Germination of both species was favored in a pH range of 5–8. Moisture, salinity, and pH stresses significantly reduced the speed of germination, with a concomitant increase in mean germination time, thus exposing seedlings to longer periods of less favorable conditions. This information should help in predicting potential distribution of littleseed canarygrass to new areas and also assist in formulating effective weed-management strategies for the future.