Graduation date: 1995

I conducted field studies to determine the effect of insect herbivory and intraspecific plant competition on ragwort Senecio jacobaea. The objectives were to determine the patterns and causes in the distribution of the ragwort flea beetle Longitarsus jacobaeae foraging among varying densities of ragwort, to measure the behavioral and numerical responses of the beetle to changes in ragwort density, and to estimate the impact of insect herbivory and intraspecific competition on ragwort performance. Host density was manipulated by planting 1, 4, 8, or 16 plants per 0.5 x 0.5 m patch. Beetles were counted in each patch to assess the effect of host density on the beetle population. I measured four components of reproductive success represented by growth rate, development rate, reproduction, and annual survivorship to assess the effect of herbivory and intraspecific plant competition on ragwort performance In the first experiment, beetle populations were manipulated by establishing equal numbers of beetles in patches with unequal number of hosts (1, 4, 8, 16 plants per patch), which were then subsequently allowed to move freely about. Beetles rapidly re-distributed themselves, such that the number of beetles was strongly and positively correlated with the number of hosts. This indicates that ragwort flea beetles are highly sensitive to local distribution of their food plants. In the second experiment, host density was manipulated by planting ragwort in densities of 1, 4, 8, 16 plants per patch, and beetles were then allowed to colonize the experimental patches. Beetle behavioral response to a change in host density was dependent on host population size: the numbers of colonizing beetles increased asymptotically with increasing plant density. The number of beetle-days ranged from 261 for 1-plant patches to 1822 for 16-plant patches. In contrast, the numerical response (represented as observed multiplication rate per capita per generation per year) appears to be inexplicably low in the single plant population and levels off in the 4, 8, and 16 plant patches (grand mean for multiplication rate 1 was 5 and for multiplication rate 2 was 10.4 progeny per individual per generation). Combining these results, the beetles apparently respond to spatial variation in the density of hosts primarily by changes in their movement behavior rather than by changes in their per capita reproductive rates. These results highlight the importance of a natural enemy's colonizing behavior for controlling a sudden upsurge in pest abundance. Both insect herbivory and intraspecific competition had an effect on ragwort performance. For example, over approximately one year, ragwort's rate of biomass accumulation was 48% lower, and seed-head production was 18% lower in exposed compared to protected plots, while intraspecific competition reduced ragwort's rate of biomass accumulation and seed-head production, such that a 16-fold increase in host density (in protected patches) led to a 12-fold decrease in biomass per plant and a 11-fold decrease in the number of seed-heads per plant. Herbivore effects were independent of host density: variation in plant density from 1 to 16 plants led to no detectable change in magnitude of the herbivore effect. This suggests there is no density-dependent refuge for host plants operating at these local scales of observation. Keywords: Host density effects, behavioral response, reproductive response, biological control agent, Longitarsus jacobaeae, Senecio jacobaea. / Graduation date: 1995

The GRASS (V. 4.0) geographical information system (GIS) was used to test the hypothesis that pheromone trap based predictions of Helicoverpa zea (Boddie) damage in processed sweet corn could be improved by considering spatial patterns of corn plantings and wind blocking features around the trap. Wind blocking features include: tree rows, wooded areas, large buildings close to the trap, and abrupt hillsides. Pheromone traps were monitored at 29 and 30 sites in 1990 and 1991. Corn development through the year and damage levels at harvest (percent infestation) were also recorded for these locations. Maps of all corn plantings and wind blocking features within 2.5 kilometers of the trap were created, digitized, and entered into the GIS for each site. A stepwise regression analysis considering 18 spatial and two non-spatial variables resulted in a highly significant (P<0.001) four variable regression model with an R�� of 0.82. Spatial input variables used in this model included the total number of hectares of corn within 2.0 kilometers of the trap as well as the average distance to wind blocking features on the north side of the trap. The non-spatial variables used were cumulative trap catch and date of first silk. A dynamic simulation model was also created. This was designed to filter from the trap catch those moths coming from plantings outside of the trapped planting. This model functioned by creating map surfaces in the GIS showing for each day the relative contribution to catch for each location around the trap. This map surface was the product for each location of relative moth population levels and the likeliness that a moth positioned there would be captured by the trap. The modified cumulative trap catch was expected to correlate more strongly to damage levels than the unmodified trap catch, but no run of the model produced a significant improvement in the correlation. In the process of collecting data for this project, circumstantial evidence was obtained which indicated that high synchrony between valley-wide moth catch levels and valley-wide timings of silking in corn could be used as an indicator of high damage years. / Graduation date: 1994

Graduation date: 1993

During the springs of 1988 1989, experiments were conducted to determine effective methods of controlling damage by ring-necked pheasants (Phasianus coichicus) to sprouting corn in southwestern Idaho. Plot evaluations (1988) failed to demonstrate the ability of Miller Hot Sauce Animal Repellent, Isotox Seed Treater (F), provision of alternate food, and bird scaring reflective tape to reduce damage. When evaluated using entire production fields for replicates (1989) firecrackers on fuse rope, bird scaring reflective tape, hawk-kites, and provision of alternate food all significantly reduced the number of seedlings disturbed by ring-necked pheasants. No treatment in either experiment significantly increased the number of surviving corn seedlings. Fields were damaged from germination until the average sprout height exceeded 10 cm, but damage was greatest (69%) when sprouts were less than 5 cm tall. Management recommendations to avert damage include establishing treatments prior to the onset of damage and avoiding early planting dates. / Graduation date: 1991

Verticillium wilt of 'Willamette' hops (Humulus lupulus) was investigated to identifY the causal organism, to determine the incidence of the disease, and to explore the possibility of interactions with soil fertility and/or nematodes. In the first year of a three year study, sampling of yards followed a "searching for extremes approach". Selection of yards was based on a preliminary survey of all (35) hop growers in the Willamette Valley. Participating growers (10) were asked to identify one "good" and one "not-so-good" yard. Each of the 20 specified yards was subdivided into 4 plots; two representing a "good" and two representing a "not-so-good" area. In all 80 plots, data were collected to determine incidence of vascular colonization by Verticillium and stem necrosis in vines; soil and root parasitic nematode populations; concentrations of nitrate-N, ammonium-N, P, K, Ca, Mg, and pH in the soil surface, and nitrate-N, ammonium- N , and K in the subsoil; concentrations of total-P, K, and Zn in the leaves; and concentrations of nitrate-N, phosphate-P, and K in the petioles. The causal agents of the wilt were Verticillium dahliae in 13 yards and V. albo-atrum in one yard. Recovery of the pathogen within a yard ranged from 0 to 50% of sampled vines, while stem necrosis ranged from 0 to 68%. The frequency of infection was not significantly different among plots or yards, which suggests that the disease is present in all hop growing districts in Oregon. Soil nematode populations ranged from 0 to 3000 juveniles/100 g of dry soil. Heterodera humili (hop-cyst nematode) was the predominant parasitic nematode, while Pratylenchus (root-lesion nematode) and Paratylenchus (pin nematode) were recovered only occasionally. Densities of nematodes extracted from roots ranged from 0 to 2000 juveniles/g of moist root material and were primarily H. humili. A significant association between nematode populations and Verticillium incidence was not detected. Soil nutrient concentrations exhibited a high degree of variability among yards. The nitrate-N content, measured to a depth of 36" (90 cm) for individual hop yards, ranged between 65 (73) and 417 lb/A (468 kg/ha) with a mean value of 270 lb/A (302 kg/ha). Concentrations of ammonium-N were determined to be approximately one-fourth of the nitrate concentrations. Phosphorus and potassium concentrations ranged from 55 to 155 ppm and 118 to 799 ppm, respectively, in the surface soil. For the same depth, soil pH ranged from 5.15 to 6.78. Petiole concentrations of nitrate-N and potassium ranged from 0.16 to 1.3% and from 1.26 to 6.84%, respectively. While it is believed that the duration of the sampling period may have been responsible for the wide range in nitrate-N values, petiole potassium concentrations are thought to reflect the potassium content in the soil. The concentrations of K in petioles increased steadily with increasing soil test values up to 350 ppm K. Soil and tissue nutrient concentrations found within and among hop yards did not correlate significantly with the incidence of Verticillium wilt. However, petiole nitrate-N concentrations were significantly higher (p < 0.05) in plots infected with Verticillium (0.73%) as compared to noninfected plots (0.56%). / Graduation date: 1991

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

In the past 10 years we have witnessed the beginnings of the study of soil ecology as a unified science, and the general realization by soil scientists, farmers, and land managers that many of the most important economic aspects of soil health are controlled by biological factors. This research focuses on alterations in a tropical soil microarthropod community under differing intensive agricultural protocols: native vegetation, pastures and cropland, during June, July and August 1998. The effect of pesticides in potato cultivation was also studied. In the Ecuadorean montane forest, 361 morphospecies of soil arthropods, were classified during the three sampling months. August was the month with highest abundance and diversity. Acari, Coleoptera, Collembola, Diptera and Homoptera were the most abundant orders present in all the three types of land management. The native vegetation had the most abundant and diverse representation of all soil arthropod taxa compared to the pastures and croplands. Coleoptera, Diptera, Diplopoda, Diplura and Hemiptera were significantly more diverse in native vegetation than in pastures and croplands. The most abundant functional groups were the fungivores, herbivores and predators. The abundance of functional groups was significantly higher in the native vegetation for predators, herbivores and detritivores. 115 morphospecies of soil arthropods were identified in the study of arthropod response to pesticides in a complete randomized potato plot. Seasonal effects were documented for Acari, Collembola, Diptera, and Homoptera. Predators were most abundant in July and fungivores decreased in September. Neither arthropod orders nor functional groups showed a significant change in abundance between different treatments. Only Homoptera showed an increase in its abundance in the third sampling date and only in the Antracol plots. The potato plants in the whole block showed poor productivity, suggesting that the whole system was stressed by the fungal pest. / Graduation date: 2000

This thesis addressed the potential of endemic predaceous and parasitic arthropods of the Hood River Valley, Oregon to suppress the pear psylla, Cacopsylla pyricola F8rster. Natural enemies adequately suppressed psylla in three of seven unsprayed orchards of differing vegetational settings, orchard age, and size. Relatively few psylla natural enemies dispersed to unsprayed pear mini-orchards, dspite abundant populations on surrounding noncultivated vegetation. Pear psylla natural enemies were more abundant on arboreal rather than herbaceous non-pear hosts. Selective programs of pear pest control based on diflubenzuron were moderately successful in controlling the pear psylla, with natural enemies aiding in suppression in six of fourteen commercial trials of selective programs. In both unsprayed and commercial pear orchards, late-season psylla densities appeared to be best suppressed when levels of natural enemies were high during early-season. Classification analysis confirmed that orchard site, chemical regime, type (mini- or commercial), and season affected proportions of natural enemies and their pear psylla prey. Complexes of natural enemies and pear psylla immatures from commercial orchards where biological control was successfully demonstrated were taxonomically similar. Effective natural enemy complexes in commercial orchards were characterized by earwigs, lacewing larvae, and moderate proportions of pear psylla immatures during early season and Deraeocoris brevis, earwigs, and lacewings during mid-season. Plagiognathous guttatipes (Uhler) or Diaphnocoris provancheri (Burque) dominated effective natural enemy seasonal complexes at each of two mini-orchards. The functional response to pear psylla eggs was measured for five predaceous mirids. Functional response parameters differed among species and their life-stages, but all destroyed large numbers of psylla eggs. Further experimental directions for the implementation of pear psylla biological control are proposed. General investigative strategies include: (1) augment natural enemies on non-pear vegetation adjacent to the target orchard, and (2) modify the orchard habitat to both encourage natural enemy colonization and allow permanent complexes of natural enemies to develop. Specific tactics include: plant hedgerows of filbert or willow, cultivate snakeflies, introduce Anthocoris nemoralis, adjust early season psylla densities with suitable timing and kind of delayed dormant sprays, using a more effective selective psyllacide, and reduce winter pruning to allow development of natural enemies which overwinter in the egg stage. / Graduation date: 1992

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.