No description available.

No description available.

Digitized by Kansas Correctional Industries

Digitized by Kansas Correctional Industries

Field studies were conducted during the 2003 and 2004 growing seasons to: 1) evaluate the control of silverleaf nightshade and western ragweed, and (2) assess the forage tolerance of Coastal and Tifton 85 bermudagrass hybrids using tank mix combinations of diflufenzopyr. Herbicides that were evaluated in each study included picloram, multiple rates of picloram with diflufenzopyr, triclopyr, triclopyr with diflufenzopyr, dicamba + diflufenzopyr, and diflufenzopyr alone. Visual ratings were taken on the weed control experiments approximately 30, 60 and 90 days after treatment. Phytotoxicity ratings were taken prior to each harvest of the Coastal and Tifton 85 varieties to determine influence of each herbicide treatment. Each bermudagrass variety was harvested twice during each growing season to determine dry matter yield and quality. Forage quality, including crude protein, acid detergent fiber, and neutral detergent fiber, was assessed using near infrared reflectance spectroscopy. Adding diflufenzopyr to triclopyr did not consistently increase control of silverleaf nightshade or western ragweed. In general, picloram + diflufenzopyr and picloram applied alone provided the greatest control of both species at the highest rate of picloram. Increased efficacy was more evident from the addition of diflufenzopyr to picloram in 2004 on western ragweed. By the final ratings in both experimental years, dicamba + diflufenzopyr provided no more than 76% control of either species. Both forage varieties showed significant variability in phytotoxicity between years. Although observed levels of growth reduction were relatively high at the first harvest in 2003, no treatment exceeded a 10% growth reduction by the second harvest for either forage variety. In addition, the only significant reduction in dry matter yield occurred at the first harvest of Coastal in 2003 from picloram + diflufenzopyr applied at the highest rate.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

No description available.

Broad-leaved weeds have generally been dismissed as less competitive than grass weeds in oilseed rape and therefore their competitive effect on the crop has been ignored. This has limited the development of cost-effective strategies for their control. A survey identified the main weeds of winter oilseed rape in north-east Scotland as chickweed, annual meadowgrass, volunteer barley, mayweed spp., field pansy and shepherd's purse. Of these, only the effect of volunteer barley has been previously researched. Field trials over five years showed that the effects of broad-leaved weeds on the growth and yield of oilseed rape varied between seasons, but clearly demonstrated that these weeds can be very competitive and can cause substantial yield losses. The start of crop stem extension in spring was identified as the critical time for broad-leaved weed competition in oilseed rape. Unless the crop is free of weed competition at this time or is sufficiently vigorous to outgrow weeds, yield losses will result. However, autumn proved to be the optimum time to control broad-leaved weeds and early treatments were found to be most efficacious. The variation in crop response between seasons was largely attributable to seasonal weather and its effects on crop vigour and weed growth. Seasonal weather also influenced the efficacy of reduced doses of herbicides. Metazachlor gave good weed control at reduced doses in vigorous crops, but not in less vigorous crops in poor growing seasons. This variability makes it difficult to predict crops responses to weed competition and the justification for herbicides. Thus a semi-prophylactic approach is proposed, based on a reduced dose of metazachlor applied early with the option of a reduced dose follow-up post-emergence treatment in autumn, if necessary. This is a practical approach which could be adopted on many farms and would benefit the farmer in terms of improved cost-effectiveness and go some way towards satisfying the demand for reduced pesticide inputs.

This research programme sought to establish whether crop varieties had different competitive abilities against weeds and what the characteristics of competitive cultivars might be. A series of experiments studied the relative competitiveness with fat hen (<I>Chenopodium album</I>) of four spring wheat varieties Alexandria, Tonic, Canon and Baldus selected to represent different heights, tillering potentials and leaf angles. Additional experiments examined aspects of seed production, seed germination and seedling establishment of fat hen. In the glasshouse, all the wheat varieties were of similar competitive ability and no plant character was related to crop aggressivity index. In field experiments, the variety ranking of aggressiveness against fat hen was Alexandria > Tonic > Canon > Baldus. Crop aggressivity was positively related to crop plant height, leaf area and tillers per plant when grown in mixture with fat hen, and negatively related to fat hen height, leaf area and dry matter per plant. Physiological attributes such as absolute and relative growth rates, net assimilation rate, specific leaf area and leaf area ratio of wheat were rarely related to crop aggressivity at any single harvest but changed with time. Relationships of aggressivity with wheat characters measured in monocultures were generally poor. Crop aggressivity was positively related to relative loss of weed dry matter, and negatively related to relative loss of wheat dry matter and grain yield. The most competitive variety was associated with the lowest weed seed production and seed return to the soil. Wheat varieties were less competitive when fat hen emerged 15 days earlier but were highly competitive when fat hen emerged 15 days later. Light interception by crop canopies in mixture was positively related to crop aggressivity. It is suggested that plant breeders should use greater height, greater leaf area, more droopy leaves and greater number of tillers as selection criteria for competitive wheat cultivars.

Laboratory experiments were conducted to characterise the germination of some tropical weed seeds. Field experiments in Sri Lanka characterised the seed bank and monitored seedling emergence after sugarcane planting. In laboratory experiments, final germination, median germination time and rate of germination were determined on a Temperature Gradient Plate and used to define values for optimum temperature (T_o), base temperature (T_b), and upper temperature limit for germination (T_m). Final germination, median germination time and rate of germination were also evaluated to study germination response to water availability. Field studies were conducted in Sri Lanka to estimate the seed rain and the bank and also to monitor seedling emergence after sugarcane planting. Taylor's Power Law (TPL) parameters were used to describe the spatial distribution of seeds in the seed bank. The Principal Components Analyses (PCA) was used to summarise the variation between samples and species. The Shannon-Weaver diversity index was used to estimate species diversity in the seed bank. Chi-square analyses (x²) were performed to assess the species similarity of the seed bank and the emerged vegetation. Seedling emergence in the field was examined for relationships with rainfall, soil moisture and soil temperatures. The seed rain fluctuated with time. The higher seed rain in fallow land increased the density of the seed bank particularly near the surface. Ploughing substantially reduced the seed bank (by about 80%) and mixed seeds more evenly through the ploughed layer. The majority of seedlings (98%) emerged from the top 4.0cm of soil. Hot and humid conditions favoured the germination and emergence of weed seedlings. This was seen not just in comparison of plantings in October 1995, January 1996 and April 1996 but also more seedlings emerged in the furrows than on ridges. There was no similarity of the species composition of the seed bank and the seedling population arising. Also, the abundance of common species in the seed bank and emerged vegetation was poorly correlated. There was a little relationship between seedling emergence and soil temperature in this investigation.