Experiments were performed to determine the nature of maize influence on bean disease in additive-type intercrops. Overall effects of intercrops on angular leaf spot (caused by Phaeoisariopsis griseola) in Kenya indicated >23% reductions (P<0.05) in area under the disease progress curve (AUDPC) in two of three season-site combinations. Fertilization tended to increase disease (135-205%, P<0.10), but changes in bean density or planting pattern had no effect. Intercrops reduced temperature and wind velocity, but increased relative humidity. A 27% AUDPC reduction (P=0.07) in bean rust (caused by Uromyces appendiculatus) due to intercropping was observed in Oregon in 1989 and 1990 in two of three locations. Mechanisms of maize influence on rust were also assessed in Oregon. Intercropping, and competition of maize with beans alone, consistently steepened dispersal gradients (P<0.10). Interference of maize with dispersal alone tended to flatten gradients. Spore retention in plots was increased in mid-season, then decreased late in the season, due to competition in both years (P<0.05). Intercropping reduced infection by 96% late in 1989 (P<0.05), probably due to microclimatic influence of maize. The data from these experiments were used as inputs for computer simulation to evaluate effects of specific mechanisms on disease dynamics. Combination of all mechanisms (= intercrop) reduced AUDPC to 32% of monocrop, using 1989 data. Infection efficiency reductions, and to a lesser extent dispersal effects, were responsible for these changes. Intercrop effects declined as pathogen multiplication rate (DMFR) increased. No intercrop effect occurred at any DMFR using 1990 data, although interference and competition effects of maize alone both increased AUDPC at low DMFR. Partitioning dispersal effects into those due to gradient slope changes and spore retention indicate that the latter accounts almost entirely for disease alteration. / Graduation date: 1992

Vineyard management strategies, including vineyard floor management and crop level management, can be used to influence vine vigor and fruit composition. Two studies were conducted to evaluate the impact of these practices on Pinot Noir in Oregon's Willamette Valley. Managing crop levels is common in cool climate vineyard production though it is a costly practice. With economic pressures, the premium winegrape industry is questioning whether they can reduce production costs and increase yields without compromising quality. A crop thinning trial was conducted in 2010 and 2011 to address these concerns and to better understand the role of vine balance on fruit composition. Crop levels were moderately (35% crop removed) or severely (65% crop removed) thinned at pre-bloom, fruit set, lag phase, or véraison and compared to full crop treatments. In both years, crop thinning reduced yields but had no effect on berry weight or cluster size. In 2010, poor fruit set reduced overall yields, and thinning treatments resulted in very few differences in vine growth, cluster architecture or fruit composition, including total soluble solids (TSS), pH, titratable acidity (TA), yeast assimilable nitrogen (YAN), anthocyanins, phenolics and tannins. In 2011, yields were much higher due to high fruit set and larger cluster size. No differences were found in vine growth (leaf areas or pruning weights) or fruit YAN, but thinned vines had higher TSS and pH and lower TA than full crop vines at harvest. Fruit thinned at lag phase and véraison had higher TSS and lower TA than fruit thinned pre-bloom. Intensity of thinning had a stronger influence on anthocyanin and tannin concentration than timing, while phenolics were not impacted by either factor. Ravaz index values (fruit yield/pruning weight) below 2.25 and leaf area to yield ratios of 2.25 to 3.25 m²/kg improved fruit composition in 2011 as did later season thinning, though data from the remaining years of this study will provide more insight into appropriate crop load metrics for cool climate Pinot Noir. A second study was implemented in 2011 to determine the impact of crop thinning in vines with different levels of vegetative vigor caused by three vineyard floor management techniques: permanent grass (Festuca rubra spp. rubra) cover (grass), alternating grass cover and tillage (grass & tilled), and tillage of every alleyway (tilled). Crop was thinned at the BB stage of berry development (EL stage 73) to one cluster per shoot (half crop) or not thinned (full crop); all cluster wings were removed at the time of thinning. Tillage treatments had been in place four years prior to the start of the study and competition for nitrogen in grass caused reduced early season vine growth, leaf chlorophyll and canopy size at both bloom and véraison while crop thinning increased canopy size at véraison. Yields were altered by tillage and crop thinning treatments, as grass had fewer clusters per shoot and berries per cluster, and crop thinning reduced yields to 64.7% of full crop across all tillage treatments. At harvest, grass had the lowest TA while TSS and pH were not affected by tillage. Crop thinning increased TSS but did not impact pH or TA. Anthocyanins were affected by both tillage and thinning and were found to be related to vine yield, YAN, leaf N, and leaf area index. Tannins were highest in grass but were not affected by crop thinning, and phenolics were not changed by either factor. Few interactions between tillage and crop thinning were found, but as variables such as yield per vine were impacted by both treatment factors, monitoring long term effects of crop / Graduation date: 2012