Progress 11/01/01 to 11/01/06
Outputs
Prior to this study, it was unknown what impact the glassy-winged sharpshooter (GWSS), Homalodisca coagulata, had on fruit yield, fruit size, and quality as well as tree vigor. The goals of this project were to determine the usefulness of management of GWSS to prevent yield loss, fruit size reduction, and degraded fruit quality. This information is paramount before we can even begin to incorporate these into conventional IPM programs. Prior to this study, efforts to manage GWSS in citrus were primarily to suppress populations to limit the spread of Xylella fastidiosa in areawide management programs. The effects of the high feeding populations of GWSS on navel orange peel nutrient status and metabolism have been consistent for the four years of the study. High GWSS feeding populations significantly reduced peel Ca and Mg concentrations all years of the study: year 1 (P<0.05) and year 2 compared to the low GWSS population (control trees treated with Admire) (P<0.001).
High GWSS feeding populations significantly disrupted N metabolism causing high peel nitrate-N or total N in years 1 and 2, respectively (P0.05). High GWSS feeding populations significantly increased peel arginine and putrescine concentrations in four years of the study with the magnitude of the difference between the two treatments greater in year 2 and 3 (P<0.05). High GWSS feeding populations resulted in a numerically higher concentration of proline in year 1 and a significantly higher proline concentration in year 2 (P<0.05). Although GWSS feeding causes changes in peel Ca, Mg and N status, high levels of feeding and the induced changes occur after maximum peel thickness and, thus far, have not affected external fruit quality. The changes in metabolism induced by GWSS feeding are indicative of tree stress. The increased magnitude and statistical significance of these metabolic changes over the first two years of high GWSS feeding pressure is consistent with cumulative
stress to the trees. At the beginning of the study in January 2002, there were no significant differences in Washington navel orange yeild and fruit size distribution. There were significant differences in yield and size distribution in January 2003 and 2004.
Impacts
The data from the four seasons of this study indicate that chronic high feeding of more than 1000 GWSS per orange tree during mid-June to mid-September trees significantly reduces overall orange yield. While rind pitting was a postharvest physiological disorder that occurred in both treatments following simulated transPacific shipments, it wasn not attributed to heavy GWSS feeding. Finally, soil applied Admire 2F (active ingredient imidacloprid) seemingly has know effect on tree physiology, yield or fruit quality. It does provide some control of some species of plant parasitic nematodes which may prevent some yield loss. In fact, nematodes are on the label of the new formulation Admire Pro. An additional harvest will be conducted in January or February of 2006 to further evaluate tree recovery to compliment the 2005 recover data.
Publications
- No publications reported this period
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Progress 01/01/04 to 12/31/04
Outputs
Glassy-winged sharpshooter (GWSS) vectors the bacterium that causes Pierce's Disease in Grapes. Therefore, GWSS has the potential to devastate the California grape industry. Detecting and determining GWSS populations in the agro-ecosystem is a major weakness of area wide programs to contain this vector. Electrophysiological measurements will be and are being used to determine the visual sensitivity GWSS to different wavelengths of light. Electroretinogram techniques will be and have been employed to accomplish this. Unpublished data indicate that GWSS is moderately attracted to commercially available yellow sticky traps and that the GWSS attraction to the traps varies with the shade of yellow on the traps. (At present in CA over 6,000 of these commercially available traps is being used to initiate insecticide treatments to manage GWSS in area wide programs.) This research will determine the color of yellow that is most attractive to GWSS and how GWSS trap catches
relate to populations in vineyards and citrus groves. Our studies demonstrate that GWSS is attracted to at least one band of ultraviolet light and at least one band of visible light with four peaks suspected. These measurements will allow us to determine the best shade of yellow for GWSS monitoring. Yellow sticky traps based on optimum reflectance and behavioral assays will be deployed in commercial vineyards and citrus groves to evaluate their effectiveness for attracting GWSS.
Impacts
To have an easier method of monitoring GWSS populations and therefore increasing our ability to reduce this vector's numbers in the agro-ecosystem.
Publications
- No publications reported this period
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