Modelling the Effect and Variability of Integrated Weed Management of Phalaris minor in Rice-Wheat Cropping Systems in Northern India

Phalaris minor Retz. (littleseed canarygrass) is the most problematic and herbicide-resistant weed in the rice-wheat cropping system in India. As such, it poses a severe threat to wheat yield and food security. A number of herbicidal and agronomic practices have been identified for the effective control of P. minor. These include crop rotation, crop establishment methods, herbicide spray technology, sowing time, weed seed harvest and effective herbicide mixtures. A population model of P. minor was built based on the life cycle of the species, herbicide resistance mechanisms and the effects of weed control practices. The model simulated the interactions of these factors and provided the best management recommendations for sustainably controlling this noxious weed species. Model results indicate that integration of chemical and non-chemical control methods was the most effective and sustainable strategy. For example, the integration of a happy seeder (a tractor-mounted mulching and sowing machine) with an effective post-emergence herbicide reduced the probability of weed control failure by 32% compared to the scenario with a rotavator and the same herbicide. Similarly, more conventional crop establishment methods such as a rotavator and conventional tillage could be accompanied by pre- or post-emergence applications of herbicide mixtures. Adoption of good herbicide spray technology and weed seed harvest delayed the onset of resistance evolution by up to four years. Furthermore, effective crop rotation such as the inclusion of sugarcane in place of rice in the summer season reduced the risk of resistance evolution by 31% within the 10 year simulation period. In addition to the scenarios using representative parameter values, the variability of model predictions was investigated based on some field experiments. The model provided a powerful tool for promoting Integrated Weed Management and the sustainable use of herbicides. Pragmatic ways of dealing with uncertainty in model prediction are discussed.

EFFECTIVE MODE OF ESSENTIAL OIL APPLICATION OF TAGETES MINUTA L. TO MANAGE PHALARIS MINOR RETZ.

Essential oil (EO) of Tagetes minuta L. extracted from aerial parts of plant through hydro-distillation was tested for its chemical composition by GC-MS. In order to explore the allelopathic potential of the oil, it was tested under laboratory conditions on a common agricultural weed Phalaris minor. The modes of oil application were volatile form (VB), solution form (SB) and oil mixed with agar-agar (AAB). Bioassay studies revealed a dose-dependent inhibitory effect of EO of T. minuta on growth of P. minor. Most effective mode of treatment was VB followed by AAB and minimum effect was observed in SB. Thus, volatile form of EO is best suitable for managing P. minor in agroecosystems

Effects of various nitrogen regimes on the ability of rapeseed (Brassica napus L.) to suppress littleseed canarygrass (Phalaris minor Retz.)

Background: Littleseed canarygrass (Phalaris minor Retz.) is one of the most troublesome invasive weeds infesting winter crops in Yunnan Province, China. Our previous study found that rapeseed (Bassica napus L.) was a logical candidate crop to control littleseed canarygrass in agroecosystems. Nitrogen (N) could impact plant community composition by altering competitive interactions, however, the effects of different N regimes on weed control efficacy of rapeseed were unknown. Here, we report the effects of different N regimes on the competitiveness of rapeseed with littleseed canarygrass and accompanying differences in photosynthetic characteristics. Results: The results showed that the rapeseed yield and its control efficacy on littleseed canarygrass were significantly affected (P<0.05) under different N regimes, and the control efficacy of littleseed canarygrass by rapeseed increased first and then decreased with the increase of basal nitrogen rates, while increasing topdressing N rates increased control efficacy of littleseed canarygrass by rapeseed. In fact, yield and weed control efficacy of rapeseed was most ideal when both basal and top-dressing N was 90 kg·ha-1. We also found that N significantly impacted the competitive ability of rapeseed to littleseed canarygrass and rapeseed had the highest competitive ability when both basal and top-dressing N was 90 kg·ha-1. With the increase of basal nitrogen rates, competitive balance index (CB) of rapeseed increased initially but decreased beyond an optimal level. CB continually increased with increasing of topdressing N rates. Our research also showed level and period of N application had a significant effect (P<0.01) on the photosynthetic rate (Pn) and chlorophyll content (Chl) of both rapeseed and littleseed canarygrass. Under the same N application regime, the Pn and Chl of littleseed canarygrass were higher than that of rapeseed in December, while the Pn and Chl of rapeseed was higher than that of littleseed canarygrass in February. Our study indicated that photosynthetic characteristics of rapeseed and littleseed canarygrass in different growth stages differ in their sensitivity to N regimes, creating a dynamic competitive relationship. Conclusions: Together, our results demonstrated that optimal application of fertilizer N could help rapeseed produce higher yields and greater weed control efficacy, suggesting that future modeling or experimental studies on utilizing crops to control invasive weeds should carefully consider both timing and placement of N.

Formulation, Characterization and Evaluation of Encapsulated Bioherbicide on Echinochloa cruss galli and Phalaris minor

Weeds management under organic agriculture demands organic herbicides / bioherbicides.to address this issue an experiment was conducted in Centre of Environment Sciences and Technology, Central University of Punjab, Bathinda to study the effects of different concentration and bioassay of encapsulated essential oil extracted (EOs) from Callistemon viminalis on Echinochloa cruss galli and Phalaris minor under lab conditions. Encapsulation efficiency of gum arabic and maltodextrin (GAMD) EOs increased from 26 to 31% for 4 to 8% of EOs concentration. The sizes of all the particles were found in the range of 1-10 μm. The reduced size in case of EOs loaded GAMD-EOs encapsulates may be due to the application of spray drying method used during the preparation. Maximum germination inhibition was observed with P. minor as compared to the E. crus-galli L. The probable reason behind this may be the relatively smooth seed coat, smaller weight to volume ratio of P. minor as compared to the E. crus-galli L. Among all the treatments basal application of encapsulates with 8 % essential oil was found more lethal and result in maximum phyto-toxicity by registering less shoot length and root length and fresh biomass weight. Also, the individual constituents of the EOs can be explored for their use as herbicides and then their encapsulated formulations can be used for scale up in the field conditions.