An important disease of Vitis vinifera production in Oregon and all other
commercial growing regions is powdery mildew of grape, caused by the obligate fungal
pathogen Uncinula necator (Schwein.) Burril. Grape production can be characterized as
a long-term investment in the establishment and maintenance of the vineyard.
Establishment times have been reduced with the use of plastic vine shelters, but powdery
mildew disease pressure within vine shelters had been an unaddressed issue. Control of
the pathogen requires frequent spray applications and costly cultural management of the
grape canopy. Industry interest in forecasting programs have shown promise in
regulating spray applications to times when they are most effective, or needed. The
timing of when to begin spray programs is believed to be a point of weakness in the
forecasting programs currently available for grape powdery mildew.
The influence of vine shelter use on the development of powdery mildew was
investigated in the field during the 1998 and 1999 growing season. Industry standard
installations of various brands of vine shelters were tested against modified installations
for both incidence and severity of Uncinula necator infection. The industry standard
installation of 76 cm high tubes hilled with 8 cm of soil at the bottom to prevent airflow,
were effective in reducing the incidence of powdery mildew in both field seasons.
Disease reduction was associated with prolonged temperatures above 36��C and the
exclusion of infective spores by the artificial barrier created by the vine shelters.
The effectiveness of three forecasting programs for predicting the initial spray
application was investigated for three seasons. Actual disease onset dates were
determined by using trap leaves or plants. The forecasting programs consistently
predicted initial spray dates between 31 and 44 days prior to the detection of powdery
mildew with the trapping system. Modifications to the existing forecasting programs
were attempted to adjust the forecasting programs to more closely predict the actual
detected disease onset dates. The UC-Davis program performed the best over the three
years of the study, but improvements will be necessary for an adequate forecasting
program in the region. Flag shoots were reported for the first time in Oregon. / Graduation date: 2000
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33174 |
| Date | 07 February 2000 |
| Creators | Hall, Tyrone W. |
| Contributors | Mahaffee, Walter F. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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