Disease control is a crucial aspect of plant breeding for researchers as well as commercial producers. After samples from OSU's tomato breeding program tested positive for Columnea latent viroid in a screen done by a private company, secondary testing was done by the USDA laboratory in Corvallis which suggested that...
Three species of true firs in the Pacific Northwest--Abies gran-dis, grand fir; A. amabilis, Pacific silver fir; and A. lasiocarpa,
subalpine fir--are severely damaged or killed by an imported insect
pest, the balsam woolly aphid (Chermes (Adelges) piceae Ratz.), Infestations of this insect cause abnormalities in the wood and, in...
Knowledge of the viruses which are mechanically transmitted
from pear to herbaceous plants and the diseases they cause in pear
is not complete. This thesis discusses the means used to mechanically
transmit pear viruses, the properties of those viruses and their
relationships with latent viruses of apple.
Herbaceous plant virus...
A disease of sweet cherry (Prunus avium L.) known as "cherry
rosette" has threatened production of cherries in Oregon. In 1961
this disease was observed in widely separated orchards. Rosette
occurred in isolated trees or in spreading patterns, often from
identified single trees or from one section of an orchard....
Verticillium wilt of hops in Oregon, caused by Verticillium
dahliae Kleb., was first reported in 1956. Later, V. albo-atrum
Reinke & Berth. was also isolated from infected hop plants, and thus
both species of the fungus were shown to be the causal agents of the
disease in Oregon.
The purpose...
Verticillium dahliae Kleb. causes a wilt disease of peppermint.
Attempts to control the disease by soil fumigation, crop rotation,
flaming of stubble, and deep plowing have met with only limited success.
Development of resistant varieties through conventional breeding
procedures is difficult because commercial peppermint is male-sterile.
Several strains of commercial...
The fungus Phoma menthae Strasser causes black lesions and
cankers on stems and rhizomes of Mentha piperita L. The purpose
of this thesis was to: 1) study the production of polygalacturonase
(PG) and macerating enzymes (ME) by P. menthae in vivo and in
vitro, 2) study the effects of phenolic...
The extent of the competitive effect of wild oats on winter wheat
yield was estimated in field studies on three commercial wheat farms in
the Willamette Valley. The morphological development of the wild oat
plants was also documented.
Wild oats were removed from stands of wheat in six different treatments;...
Race identification of stripe rust (Puccinia striiformis West. )
is influenced by environment, pathogen variability and host age.
Isolates of stripe rust were collected in the Pacific Northwest and
characterized on two sets of differential varieties; the "Oregon" and
the United States. Six of the seven isolates tested on the...
In vitro tests showed mycelial growth of Pyrenochaeta
terrestris was inhibited by root and bulb extracts from the pink root
resistant onion cultivar Nebuka, but not by extracts from the susceptible
Southport White Globe. The active principle was shown to be
fungistatic rather than fungicidal. It is present in both...
Trifluralin (a, a, a - trifluoro -2, 6 -dinitro-N, N-dipropyl-ptoluidine)
is effective in controlling downy brome (Bromus tectorum
L.) and wild oat (Avena fatua L.) but does not severely affect the
growth of wheat (Triticum aestivum L.). Studies were conducted
using germination chamber and greenhouse facilities to investigate
possible factors...
Root rot of ponderosa pine caused by Armillaria mellea was
studied in a pine forest that had been under management for 30 years
in Klickitat County, Washington. Information sources included
disease survey, detailed observation and description of specific
disease situations, and examination of roots in situ and removed.
Roughly circular...
In 1967, Lophodermella morbida Staley and Bynum, a recently described
hypodermataceous needle-cast fungus, became destructively
epidemic in a knobcone pine (Pinus attenuata Lemm.) plantation in
Del Norte County, California, and in several ponderosa pine (P.
ponderosa Laws.) plantations in western and southwestern Oregon.
This thesis presents information on this currently...
Self-interactions (effects of reinoculation with the same nematode)
in Meloidogyne hapla and Heterodera schachtii on Beta vulpris at
different levels of inocula with various population combinations were
studied. In M. hapla, the only significant increase of galls was
noted in treatments when 250+250 larvae were inoculated at 10-day
intervals. Longevity...
Studies were conducted on the mechanisms contributing to
resistance in broccoli, Brassica oleracea italica, to the garden
symphylan, Scutigerella immaculata (Newport). Differences in
resistance to symphylan injury were shown between five selected
broccoli cultivars. The hybrid cultivars, Crusader, Green Duke
and Bravo, showed a higher level of resistance to symphylans...
The seasonal development and habits of Labops hesperius Uhler
were studied in rangeland seeded to intermediate wheatgrass (Agropyron
intermediurn (Host) Beauv. ) in Baker County, Oregon, The
first nymphs appeared on March 22, and required about one week to
complete each of the five nymphal stadia. Most small nymphs stayed...
Footrot of wheat (Cercosporella herpotrichoides Fron) is a
major disease of winter wheat in certain areas of the world having a
cool, damp winter and early spring climate. In Oregon, it is an
economic problem in the higher rainfall wheat-growing areas in the
eastern portion of the state. This study...
Observations of bacterial soft rot of onions in the Lake Labish
area in the Willamette Valley of western Oregon showed that two distinct
symptom types occur during the growing season. The most
prevalent symptom type appears in infected plants as a wilting and
chlorosis of two or more lower leaves...
A series of field experiments was conducted during 1975 and
1976 to examine peppermint tolerance and Canada, thistle response to
Dowco 290 (3, 6- dichloropicolinic acid). Peppermint oil yield and
Canada thistle density were considered most important in evaluating
experimental results.
Peppermint tolerance to Dowco 290 was studied in weed-free...
Hop varieties were compared under field and greenhouse conditions to determine their relative susceptibility to the twospotted spider mite, Tetranychus urticac Koch. A fertility schedule was prepared for mites on resistant and susceptible varieties, and tests were conducted to compare sex ratio, oviposition rate, survival rate, and developmental rate of...
A light and electron microscope study of Corylus avellana L.
vegetative buds infested with the eriophyoid mites, Cecidiophyopsis
vermiformis Nal. and Phycoptella avellanae Nal., is reported. Descriptions
are given of changes in infested stipule tissue. The
nipple-like proliferations (enations) which arise on the infested
stipule surface are covered by a...
Benomyl-tolerant Botrytis cinerea was found in snap
bean fields throughout the Willamette Valley while no tolerant
isolates of Whetzelinia sclerotiorum were detected.
Thirty-five benomyl-tolerant isolates of B. cinerea had
slower radial growth rates than eighteen benomyl-sensitive
isolates. Sporulation of an aggressive tolerant isolate
was not stimulated when grown on benomyl-treated...
The transmission of strawberry mottle virus (SMV) to Fragaria vesca
L. by Chaetosiphon thomasi and C. fragaefolii was studied to determine
differences between the two species. Acquisition, inoculation, and
retention phases of transmission were described. In all phases, C.
fragaefolii was found to be the more efficient vector.
Mean transmission...