Data for this study were collected by the US Forest Service and the Pennsylvania Bureau of Forestry on nearly 600 plots in central Pennsylvania. Tree and stand characteristics recorded between 1978 and 1985 include estimates of percent defoliation on individual trees. Logistic regression using maximum likelihood estimation was employed to model individual-tree mortality of 15 species in central Pennsylvania that had been defoliated by the gypsy moth. Defoliation was estimated to the nearest ten percent for individual trees. Other variables used for prediction included stand basal area and an individual-tree relative basal area index. Success ranged from no fit for three of the species to an R value (a derivation of Akaike's information criterion) of .613 for white oak. The inclusion of defoliation in the models had a varied effect. For four of the species percent defoliation was not significant. For hickory and white oak respectively, percent defoliation raised the R value by .305 and .290 percentage points. As many as five models for each species were developed: one or two models with no defoliation measure in the model and one each for one, two or three consecutive years of defoliation measures. A beta and gamma function were used to model individual· tree basal area growth for the same 15 species. The models were fit using nonlinear least squares. Variables used include the relative basal area index, stand basal area, site index and a defoliation index that incorporated three years of individual-tree, percent defoliation. The beta and gamma functions fit equally well with values of (1 - relative mean square error) ranging from .1967 to .6290. Results for both models are presented for each species. The defoliation index was a significant variable for five of the fifteen species: white, chestnut, red, and black oak and sassafras. / Master of Science

The effects of gypsy moth defoliation on acorn production (the seed source for oak regeneration), and the forest floor regeneration environment were investigated. Parameters measured included: acorn quantity, weight, development, and viability; litterfall; and forest floor depth and biomass. Nineteen plots in north-central Virginia and western Maryland on which trees suffered heavy, moderate, or no defoliation were monitored over a two-year period. / Master of Science

Phytophthora parasitica is an important root rot pathogen of American and English boxwood, Buxus sempervirens and B. sempervirens var. suffruticosa, respectively, shrubs used extensively in the landscape in Virginia and North Carolina. Studies were undertaken to screen microorganisms for antagonism to Phytophthora in vitro; test two polymers, carboxymethyl cellulose (CMC) and methylcellulose (MC) for their suitability as carriers, storage media, and carbon substrates; and finally to determine the efficacy of selected antagonist pairs in controlling Phytophthora root rot on containerized American boxwood. On the basis of in vitro inhibition tests, 14 organisms were selected. These included six bacteria, five fungi and three actinomycetes. Populations of conidia-forming fungal isolates increased or remained fairly stable when stored in 0.25% suspensions of CMC and MC, indicating that spores may be a more suitable propagule than mycelial fragments when storing fungal isolates for more than 1 week. No significant or consistent changes in population viability occurred among the actinomycete and bacterial isolates. Carboxymethyl cellulose was a more readily utilizable carbon source than MC as indicated by the smaller specific growth rates of microorganisms in MC. Methylcellulose was not utilized by actinomycete and non-spore-forming fungal isolates. Six of seven antagonist pairs were efficacious in controlling root rot in the greenhouse when suspended in CMC. In general, application of antagonist pairs to boxwoods stimulated growth relative to control plants. The polymers may provide the biocontrol organisms with a protective environment and/or food base for establishment of stable population levels in the infection court, providing protection of the root system when challenged with the pathogen. / M.S.

Host range and symptomatology of peanut stunt virus (PSV), cucumber mosaic virus (CMV), the Blencowe isolate of tomato aspermy virus (TAV-B) and a chrysanthemum virus (CV-L) varies on selected hosts. In sucrose density-gradient centrifugation each virus has a sedimentation rate of approximately 100s. Purified preparations of PSV and CV-L are homogenous and stable while CMV and TAV-B aggregate and lose infectivity. In acrylamide gel electrophoresis, all the viruses move as a single component with CMV migrating faster than the other three. Formaldehyde-stabilization of PSV and CMV did not increase the titer of immune sera. Classical microprecipitin and gel diffusion tests were unsatisfactory because of nonspecific precipitation and antibodies to normal host antigens. Analysis of incubated homologous and heterologous virus-antibody mixtures by density-gradient centrifugation detected specific precipitation with surface antigenic sites on the virions. In reciprocal tests, CMV and CV-L show no serological relationship. CV-L and TAV-B react reciprocally and are strains. CMV antiserum reacts with TAV-B, but not conversely. PSV reacts reciprocally with the other three viruses, and thus is related at the strain level to all three. Of the viruses compared, PSV appears to be most like the hypothetical parent strain of the CMV group, since it possesses antigenic sites in common to at least three members of the group. / Master of Science

Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Paecilomyces Ii/acinus, ras 251 (geregistreer in terme van wet 36 van 1947 as Suid-Afrika se eerste natuurlike nematisiede en kommersieel beskikbaar as PI Plus) is as biologiese beheer agent getoets by aartappels en in geïntegreerde beheer programme by sitrus en wingerd teen respektiewelik Me/oidogyne species, Ty/enchu/us semipenetrans en verskeie ektoparasitiese nematodes. Die swam toon belofte vir die beheer van hierdie nematodes en het terselfdertyd nie 'n nadelige effek op nie-teiken, voordelige organismes in die grond nie. Veral in kombinasie met chemiese middels, as deel van geïntegreerde programme, kan dit lei tot verminderde gebruik van hoogs toksiese middels en dus meer omgewingsvriendelike landboupraktyke. Biological control of plant parasitic nematodes on potatoes, citrus and grapevine with the fungus, Paecilomyces liIacinus. Paecilomyces liIacinus, race 251 (registered in terms of act 36 of 1947 as South Africa's first natural nematicide, commercially available as PI Plus) was tested as a biological control agent on potatoes and in integrated control programs on citrus and grapevine against Me/oidogyne species, Ty/enchu/us semipenetrans and various ectoparasitic nematodes respectively. The fungus shows promise for the control of these nematodes, without having a harmful effect on non-target, beneficial organisms in the soil. Especially in combination with chemical products, as part of integrated programs, this can lead to less use of highly toxic compounds and thus to more environmentally friendly agricultural practices. / AFRIKAANSE OPSOMMING: Sedert die ontdekking van die swam, Paeci/omyces Ii/acinus (Thom.) Samson as 'n effektiewe eierparasiet van Meloidogyne incognita acrita en Globodera pal/ida (Jatala et al., 1979) het verdere veldproewe in Peru tot die effektiewe beheer van M. incognita en Tylenchulus semipenetrans gelei. Na verskeie suksesse in Peru is die swam onder verskillende klimaat- en grondkondisies in verskeie ander lande beproef. Die sukses behaal in die Filippyne het gelei tot die kommersiële produksie van die swam onder die handelsnaam Biocon. Anders as met chemiese middels vind die werking van biologiese agente stadig oor tyd plaas. Biologiese beheer sal nie chemiese beheer sonder meer kan vervang nie. Dit behoort egter deel te vorm van geïntegreerde nematode bestuur. Inkorporering van die natuurlike organismes, die oordeelkundige gebruik van chemiese nematisiedes, moontlik in kombinasie met die biobeheer agente, weerstand, en ander kulturele praktyke moet ernstig oorweeg word as ons hoop om die steeds groeiende wêreldbevolking te voed (Jatala, 1986). Paecilomyces liIacinus, ras 251, Suid-Afrika se eerste geregistreerde natuurlike nematisiede, kommersieel beskikbaar as PI Plus, is in die Olifantsrivier besproeiingsgebied geëvalueer vir die bestuur van ekonomies belangrike plantparasitiese nematodes by aartappels, sitrus en wingerd. Hierdie gewasse is belangrike bedryfstakke van die streek en is onderhewig aan skade deur nematodes wat die opbrengs nadelig beïnvloed. Chemiese beheer bied slegs 'n korttermyn oplossing vir nematode probleme en skadelike getalle word in 'n kort tyd weer opgebou. Boonop lei dié hoogs toksiese middels tot agteruitgang van die omgewing en sy waterbronne. Die toenemende besorgdheid hieroor en die groot potensiaal van biologiese beheer agente (Jatala, 1986) was die hoofrede vir die werk waaroor hier gerapporteer word.

No description available.

Includes bibliographical references (leaves 217-230). Details the biology and life history of the Quandong moth and investigates management strategies that would enable growers to manage the pest in an economically and environmentally sustainable program.

Includes bibliographical references (leaves 217-230). / 230 leaves : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Details the biology and life history of the Quandong moth and investigates management strategies that would enable growers to manage the pest in an economically and environmentally sustainable program. / Thesis (Ph.D.)--University of Adelaide, Dept. of Applied and Molecular Ecology, 2001

Characterization of the most frequently isolated virus found during a survey of eastern Ontario red clover fields, which was designated as the Ottawa isolate, was undertaken. Determination of the biological and physico-chemical properties of the virus showed that the virus studied differed in some respects from other WCMV isolates. An ultrastructural examination of virus localization of cytopathological changes in infected red clover and pea plants revealed various types of viral inclusions, including a membrane-bound mass of tubules, not usually associated with infection by potexviruses, in red clover leaves, and severe organelle disorganization within pea leaf tissues. WCMV infection significantly reduced several processes relevant to symbiotic nitrogen fixation, including plant growth, nodulation, nitrogenase activity, leghemoglobin content, and Rhizobium population, but nitrate reductase and acid phosphatase specific activities were increased. The correlation between leghemoglobin content and nitrogenase activity shown at ten-leaf and pre-blooming stages was absent during the flowering and senescence stages. Infectivity assays, immunosorbent electron microscopy, and an ultrastructural examination showed the presence of the virus in nodular tissues; the cytopathological changes seen in bacteroids suggested that virus infection accelerated nodule senescence. Application of a cytochemical technique using diaminobenzidine showed that the leghemoglobin was located in the peribacteroidal space.

No description available.