Southern and India crabgrass are important grass weeds of rice in many tropical countries. Environmental factors influenced seed germination and seedling emergence of these weeds. Seeds of both species germinated at a range of alternating temperatures (25/15, 30/20, and 35/25 C day/night), though the germination of southern crabgrass was reduced at the lowest alternating temperatures (25/15 C). Light stimulated germination of both species; however, a small proportion of southern crabgrass seeds germinated in the dark. Germination of India crabgrass was influenced to a greater degree by increasing salt and water stresses than was southern crabgrass. Seeds of both species germinated over a wide range of pH between 5 and 10. Seedling emergence of both species (98% for southern crabgrass and 94% for India crabgrass) was greatest for seeds placed on the soil surface. Seed burial depth of 2 cm completely inhibited emergence of India crabgrass, whereas for southern crabgrass, this depth was 8 cm. Knowledge gained from this study is expected to contribute to developing components of integrated weed management strategies for these species.

Crop residues acting as mulches can influence weed seedling emergence and weed biomass. A field study was conducted to evaluate the effect of rice residue amounts (0, 3, and 6 t ha−1) on seedling emergence of eight weed species in zero-till dry-seeded rice. The highest seedling emergence of spiny amaranth, southern crabgrass, crowfootgrass, junglerice, eclipta, goosegrass, and Chinese sprangletop was observed in the absence of residue. Seedling emergence of these weeds declined with increasing residue amounts; however, the greatest and most substantial reductions in emergence occurred with 6 t ha−1 of residue. The presence of residue also resulted in less weed biomass than with the no-residue treatment. The emergence and biomass of threelobe morningglory seedlings, however, were not influenced by residue amounts. The use of residue also increased the time taken to reach 50% of maximum emergence for some species, for example, spiny amaranth and Chinese sprangletop. The results of our study suggest that the use of residue at high rates can help suppress seedling emergence and growth of many weeds. However, there is a need to integrate other weed management strategies with residue retention to achieve season-long weed control.

Hand-held hyperspectral reflectance data were collected in the summers of 2002, 2003, and 2004 to differentiate unique spectral characteristics of common turfgrass and weed species. Turfgrass species evaluated were: bermudagrass, ‘Tifway 419’; zoysiagrass, ‘Meyer’; St. Augustinegrass, ‘Raleigh’; common centipedegrass; and creeping bentgrass, ‘Crenshaw’. Weed species evaluated were: dallisgrass, southern crabgrass, eclipta, and Virginia buttonweed. Reflectance data were collected from greenhouse and field locations. An overall classification accuracy of 85% was achieved for all species in the field. A total of 21 spectral bands between 378 and 1,000 nm that were consistent over the three data collection periods were used for analysis. Only centipedegrass, zoysiagrass, and dallisgrass were correctly classified less than 80% of the time. An overall classification accuracy of 69% was achieved for the greenhouse species. Spectral bands used in this analysis ranged from 353 to 799 nm. Creeping bentgrass and Virginia buttonweed were classified correctly at 96 and 92%, respectively.