No abstract

HighlightsHigher cereal productivity can be achieved with lower environmental footprint through conservation agriculture.Wheat productivity and profitability can be increased by zero-tillage and early sowing.Kharif maize appears to be a suitable and profitable alternative to rice in northwest India.Productivity and resource efficiency of transplanted rice can be improved by BMPs.Directly sown rice has potential to save water, energy and global warming potential compared to transplanted rice.

The response of littleseed canarygrass biotypes to isoproturon, pendimethalin, and diclofop-methyl was evaluated in India, in pot studies and the field during the winters of 1991 to 1992 and 1992 to 1993. Some biotypes of littleseed canarygrass were resistant to isoproturon but cross-resistance to pendimethalin and diclofop-methyl was not confirmed. The resistant biotype required a higher dose of diclofop-methyl than the susceptible biotype. Variations in the response of littleseed canarygrass biotypes were not due to isoproturon formulation. Resistant biotypes required 2 to 8 times more isoproturon than a susceptible biotype for the same level of control. Diclofop-methyl at 1.0 kg ai/ha applied at the 2- to 3-leaf stage of littleseed canarygrass in pot experiments and PRE pendimethalin at 1.5 kg ai/ha in field trials controlled resistant biotypes. Field surveys of the affected areas revealed that resistance in littleseed canarygrass is more prevalent in rice-wheat rotations compared to other crop sequences. Control of littleseed canarygrass with isoproturon dropped from 78 to 21% from 1990 to 1993.

In the rice–wheat (RW) systems of the Indo-Gangetic Plains of South Asia, conservation tillage practices, including zero-tillage (ZT), are being promoted to address emerging problems such as (1) shortages of labor and water, (2) declining factor productivity, (3) deterioration of soil health, and (4) climate change. Despite multiple benefits of ZT, weed control remains a major challenge to adoption, resulting in more dependence on herbicides for weed control. Alternative management strategies are needed to reduce dependence on herbicides and minimize risks associated with their overuse, including evolution of herbicide resistance. The objectives of this review are to (1) highlight and synthesize research efforts in nonchemical weed management in ZT RW systems and (2) identify future weed ecology and management research needs to facilitate successful adoption of these systems. In ZT RW systems, crop residue can play a central role in suppressing weeds through mulch effects on emergence and seed predation. In ZT rice, wheat residue mulch (5 t ha−1) reduced weed density by 22 to 76% and promoted predation of RW weeds, including littleseed canarygrass and barnyardgrass seeds. For ZT wheat, rice residue mulch (6 to 10 t ha−1) in combination with early sowing reduced emergence of littleseed canarygrass by over 80%. Other promising nonchemical approaches that can be useful in suppressing weeds in ZT RW systems include use of certified seeds, weed-competitive cultivars, stale seedbed practices, living mulches (e.g., sesbania coculture), and water and nutrient management practices that shift weed–crop competition in favor of the crop. However, more research on emergence characteristics and mulching effects of different crop residues on key weeds under ZT, cover cropping, and breeding crops for weed suppression will strengthen nonchemical weed management programs. Efforts are needed to integrate multiple tactics and to evaluate long-term effects of nonchemical weed management practices on RW cropping system sustainability.

Littleseed canarygrass, a troublesome wheat weed, has developed resistance against isoproturon in India. Laboratory, pot, and field experiments were conducted to quantify the level of isoproturon resistance in various littleseed canarygrass biotypes and to evaluate the response of isoproturon-resistant littleseed canarygrass to alternate herbicides. For quantification of resistance, 10 littleseed canarygrass biotypes were collected from fields with a varied history of cropping and herbicide use. Pot studies indicated that 6 out of the 10 biotypes tested were resistant to isoproturon. The resistant (R) biotypes had 50% growth reduction values, 5 to 10 times greater than that of the most susceptible biotype. The R biotypes were from areas where isoproturon had been used continuously for more than 10 yr in wheat under a continuous rice–wheat cropping system. The isoproturon resistance was not detected where crops and herbicides were rotated. Under field conditions, postemergence isoproturon at 1,000 g/ha 32 d after sowing failed to control littleseed canarygrass and as a result wheat grain yield decreased by 65% compared with the weed-free control. The herbicides observed to be effective in wheat against isoproturon-resistant littleseed canarygrass were CGA 184927 (50 to 60 g ai/ha), fenoxaprop-p-ethyl (100 to 120 g/ha), ICIA 0604 (350 g ai/ha), and MON 37503 (25 g ai/ha). The use of these herbicides increased the grain yield by 200% or more when compared with the weedy check. Among the herbicides tested, MON 37503 at 25 g ai/ha was the best because of complex weed flora control and produced wheat yield similar to that of the weed-free control. Based on this study, the absence of resistance when herbicides and crops were rotated indicates that growers should follow herbicide and crop rotation in order to avoid development of herbicide resistance in the near future. The integration of this system (crop and herbicide rotation) with cultural and mechanical means of weed control could be further targeted as a long-term strategy for resistance management.