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Biocontrol has been critized because the target effects of biocontrol introductions have not been studied rigorously. The objectives of this thesis were 1)to assess quantitatively the efficacy of a classical biocontrol agent after its release and 2)to suggest factors that affect the density and distribution of the biocontrol agent. In 1997, Aphthona lacertosa, a root-feeding flea beetle that is native to Europe, was released for the biological control of leafy spurge in Alberta. The beetles had established at more than 75% of the release sites that were monitored in 1999. In 2000, the peak abundance of A.lacertosa across release sites ranged from low (<10 beetles m-2) to high (>70 beetles m-2). Sites with high beetle densities had a significantly greater local (ie. within 5m of release point) reduction of leafy spurge than sites with low beetle densities. The density and distribution of A. lacertosa are affected by cumulative degree-days (CDD) at the release site and plant lacertosa are affected by cumulative degree-days (CDD) at the release site and plant morphology, respectively. Beetle population growth may be enhanced by releasing A. lacertosa at sites where there are more CDD. It is expected that high densities of A. lacertosa will effectively control leafy spurge populations. / 93 leaves : ill. (some col.) ; 29 cm.

This study examined the effect of density on rhizome bud production in quackgrass (Elytrigia repens (L.) Nevski). The treatments consisted of two biotypes (L8 and L9), and nine density levels ranging from 1 to 22 plants m$ sp{-2}$. The results showed that bud production per plant diminished with increasing density in both biotypes. However, biotype L8 was less productive at low densities, but almost equal to L9 at higher densities. A second experiment was undertaken to measure the expansion of clonal colonies and the distribution of shoots within these colonies. For both biotypes the growth rate was highest in late summer and early fall, but colonies of L9 grew more rapidly. Biotype L9 had 59% of its total biomass located within 40 cm of the centre as compared with 81% in L8. Overall, Biotype L9 produced more rhizome buds, responded more strongly to intraspecific interference, and grew more rapidly as a colony.

Field trials were conducted to evaluate the effect of quizalofop-ethyl on quackgrass plants in a potato cropping sequence. Fall and summer applications were compared for their quackgrass control potential. Season-long quackgrass control was obtained with quizalofop-ethyl at 96 g/ha following summer application. An increase in the rate of quizalofop-ethyl did not further improve control. Yields with quizalofop-ethyl at 96 g/ha were similar to standard treatments sethoxydim and fluazifop-butyl at recommended rates. Quackgrass control following a summer application was not maintained through to the following season. Fall applications did not result in adequate control of quackgrass the following season at any of the quizalofop-ethyl rates tested.

Typescript. / Thesis (Ph. D.)--University of Hawaii, 1966. / Bibliography: leaves 76-80. / v, 80 l mounted illus., tables

MSc. (Geography) / Growing concerns with regards to the environmental and economic impacts related to the application of herbicides to control the spread and abundance of weeds in agricultural crops have created a need for the development of novel agricultural management systems that are less dependent on herbicide usage and tillage. Such concerns have given rise to the need for the variable spatial treatment of croplands aimed at the minimization of requirements for the application of herbicides and the subsequent minimization of excess materials released into the surrounding environment. Remote sensing provides an opportunity for the fast and cost-effective delineation of weed patches in croplands over large areas where traditional scouting techniques would be impractical. The differences in spectral reflectance from different plants at certain wavelengths due to species specific variations in biochemical and physical characteristics is what lays the basis for the distinction of vegetation species within remotely sensed images and ultimately the potential detection of weed-species in croplands. This study investigates the potential spectral characterisation of maize and commonly occurring weed-species by (1) making use of reflectance spectra collected at leaf-level to identify statistically significant differences in reflectance between individual species throughout the visible (VIS), Near-Infrared (NIR) and Shortwave-Infrared (SWIR) regions of the electromagnetic spectrum, determining the potential of the Red-Edge Position (REP) and slope for this particular application and testing the accuracy at which reflectance spectra may be classified according to vegetation species based on spectral reflectance at specific wavebands and REP as input predictor variables, (2) testing the potential effect of mixed spectral responses and soil-background interference through the analysis of reflectance spectra collected at canopy-level, and (3) determining the potential effect of the spectral generalisation associated with multispectral reflectance through the analysis of spectral responses resampled to the spectral band designations of representative high spatial resolution multispectral sensors. The results showed that maize may be spectrally distinguished from all of the weed-species included in the analysis based on leaf-level hyperspectral reflectance throughout the Visible-to-Near-Infrared (V-NIR) and SWIR-regions of the electromagnetic spectrum, however, the unique characterisation of weed-species is not possible for all species and where it is possible, it is highly wavelength-specific and would require high spectral resolution hyperspectral data. The wavelengths most suitable for the spectral characterisation of maize-crops and weed species in the study area were identified as: 432.1nm, 528.2nm, 700.7nm, 719.4nm, 1335.1nm, 1508.1nm, 2075.8nm, 2164.5nm and 2342.2nm. The output predictor model was able to classify reflectance spectra associated with maize crops and weeds in the study area at an overall accuracy of 89.7 per cent and it was shown that the inclusion of the REP as predictor variable did not improve the overall accuracy of the classification, however, may be used to improve the classification accuracies of certain species...

In the Northern Great Plains (NGP), weed management within organic systems remains a challenge. Experiments were conducted at two distinct sites in North Dakota to investigate effects of deep mulch no-till (NT) on soil quality indices, weed densities, and weed seedbank densities. We hypothesized that alfalfa mulch no-till and arbuscular mycorrhizal fungi (AMF) inoculant would be associated with reductions in weed densities and improvements to soil quality and vegetable yield. NT treatments were associated with reductions in weed densities and time required for weeding, with improvements in soil quality, such as increased AMF biomass, and yield for snap pea, onion, beet, and butternut squash compared to tilled treatments. Our findings suggest deep mulch no-till using alfalfa residue may be a viable option for small-scale organic vegetable producers in the NGP. Additional research is required to determine costs associated with sowing, harvesting, baling, and applying alfalfa mulch compared to tilling.

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