The tool could also be effective in performing model-based vineyard designs in which the optimal design is determined under a set of constraints such as slope aspect or minimum row spacing. Although this means that the optimal design is likely to be case-specific, the tool was used to examine general trade-offs in various designs, which are summarized below. While the N-S row orientation on flat terrain was effective in balancing daily berry light interception and heat accumulation between opposing sides of the vine, it is also susceptible to temporally localized berry temperature spikes on the west side that could be managed by applying dense shade cloth. For cases with no shade cloth, the NE-SW orientation was likely the best compromise between berry temperature reduction and balance between opposing sides of the vine, although it still had significant imbalance in heat accumulation and extreme berry temperatures. Addition of sloped terrain tended to exacerbate berry temperature extremes and imbalance when the slope was facing south or west, which in several cases could not be well managed using shade cloth. The shade cloths were more effective in reducing berry temperatures in cases with greater row spacing relative to plant height because adjacent rows could potentially provide their own shade. The simulation experiment in this work used the new modeling tool to examine general trends in berry temperature and light interception as vineyard architecture and shade cloth density were varied.
Because of the challenge in concisely presenting results of a very large number of simulated cases, growing raspberries in container results are limited to a limited number of architectures, a narrow time period, a single latitude, and site-specific weather conditions. As such, care should be taken in direct application of the simulated values for vineyard design, as they may change for a certain site or design. However, the model itself provides a tool that could be used to provide quantitative guidance for vineyard design or management at a specific site.Together, Chapters 2-4 motivated and carried out the development of a modeling tool that can be used to identify strategies for mitigating the effect of excess sunlight and unfavorable temperatures on grape berries. The tool was then used to study how vineyard design and management strategies related to berry shading interacted to influence berry temperature and light interception. Chapter 2 evaluated widely used assumptions when modeling solar radiation interception in plant canopies, namely assumptions of vegetation homogeneity and isotropy. Because of their simple, tractable form, one-dimensional turbid medium models of radiation interception that assume homogeneity or isotropy are used across a broad range of disciplines. However, it is relatively well-known that with varying levels of vegetation sparseness and preferential leaf orientations , the implicit assumptions of vegetation homogeneity and isotropy in this simple class of 1D models are frequently violated. Yet it is not well-known how this assumption violation translates into model errors in a given situation.
Results of this work provided quantitative guidance for when a simple 1D model can be appropriately used to estimate light interception. For complex canopies like grapevines, the results highlighted the need to use a 3D radiation model because these models can represent the vertical and horizontal variability in the canopy and their effect on light interception accurately. Chapter 3 developed and validated a three-dimensional model for grape berry temperature to understand whether the effect of excess sunlight on grape production can be mitigated by designing and managing vineyards in a way that effectively creates a favorable berry microcli-mate. For the first time, a 3D vine-resolving structural model was coupled with a high-resolution energy balance model for providing accurate and spatially-explicit predictions of berry temperature dynamics. The developed 3D model accurately simulated the spatial and temporal temperature fluctuations of grape berries in vineyards with different climate, topographies, and trellises. Chapter 4 explored different scenarios to mitigate the effect of excess sunlight and temperature. Previously developed models for grape temperature have not been used to evaluate the interacting effects of different management strategies to reduce grape berry temperature. This chapter measured the effect of vineyard design and shade cloth on berry temperature and quantified trade-offs between the different management strategies to maintain optimal berry heat balance and reduce the elevated berry temperatures. Altering light interception by using shade cloths affected the reduction of elevated berry temperatures depending on the vineyard design. A great effect of the shade cloths was found in clusters exposed to direct sunlight for prolonged hours, which tended to be in cases where the vines had greater plant spacing relative to plant height, and where rows were oriented NS and NW-SE in either a flat or sloped terrain facing W or SW, respectively.
While changing the row orientation to NE-SW can be an effective long-term practice to reduce the effect of elevated temperature, for cases where changing the vineyard design is not possible, the shade cloths presented an alternative to reduce unfavorable berry temperatures in many cases. The variables that determine cluster exposure to direct sunlight, such as topography, trellis systems, row orientation, and shade cloths should be considered carefully to develop management strategies for optimizing grape quality. The primary novel outcome of this dissertation that advances the current state-of-the-art is the development of a new tool that could be used to address the role of agricultural management in climate adaptation. Technologies that increase the rate of adaptation to climate change are of great value to farmers, the wine industry, policymakers, and the scientific community. In future studies, the 3D model could be used to evaluate the effect of vineyard designs on berry temperature under changing environmental conditions, to assess the effect of different irrigation strategies on grape production, and to relate the spatial and temporal variability in berry temperature to variations in berry quality traits.Drosophila suzukii , also known as the spotted wing drosophila , is a vinegar fly originating from Southeast Asia. SWD was first detected in North America in August 2008 in Santa Cruz County, California, where it was observed infesting strawberries and caneberries.1,2 In 2009, SWD was detected in Washington, Oregon, and Florida. By 2010, SWD was detected in Utah, Mississippi, North Carolina, South Carolina, Wisconsin, and Michigan in the United States, and Alberta, Manitoba, Ontario, and Quebec in Canada.3 Recent trapping indicates that SWD can be found in virtually any region of North America where host fruit are available. A coincidental invasion of SWD with a genetically distinct population has also been observed in Europe, with initial detections in both Spain and Italy in 2008, followed by its spread throughout the continent.2,4,5 In North America, SWD is primarily a pest of berries and cherries. In Europe, it is reported to also damage a number of stone fruits and grapes. Unlike native vinegar flies in North America and Europe, female SWD possess a serrated ovipositor that can pierce the skin of healthy, soft-skinned fruits to lay eggs. These eggs quickly develop into larvae, which consume the fruit and render it unmarketable. The only other Drosophila species known to oviposit in sound, marketable fruit is Drosophila pulchrella Tan. This species is native to Japan.1 Growers have attempted to mitigate crop damage risk by applying additional insecticide, harvesting more frequently, performing field sanitation, and implementing trapping programs to detect SWD populations. These management practices are costly and many growers still face significant yield losses from SWD infestations. We examine the economic impact of SWD infestations in the California raspberry industry. Raspberry producers are perhaps the most affected by SWD’s invasion amongCalifornia commodities, although producers of blueberries and cherries have experienced substantial losses too. Strawberry producers have experienced lower damage rates and primarily on the lower-value fruit produced for processing. SWD-related losses in these industries vary by year and crop depending on management practices, weather conditions, time of the year, raspberry container size and geographic location. A primary motivation for focusing on the California raspberry industry is that California accounts for the majority of raspberry production in the U.S. and the raspberry industry accounts for the majority of economic losses due to SWD among berry crops. 6 A second motivation is the magnitude of change in pest management practices; few of the SWD control practices used by raspberry producers were needed to prevent injury from other pests prior to its establishment. Economic losses in the California raspberry industry include the cost of managing SWD and the value of the fruit lost due to SWD infestations despite management efforts. First, we compute the cost of the chemical management programs and the labor-intensive sanitation practices implemented to mitigate SWD-related yield losses. Second, we calculate the industry level yield losses due to infestation. These components form an estimate of the full economic cost of SWD’s invasion into California raspberry production.
In 2013, raspberries were estimated to be the twenty-seventh largest crop in California by value of production. California accounted for 74% of all raspberry production in the United States. The United States is the third largest producer of raspberries in the world, producing 91,300 tonnes, after the Russian Federation and Poland, which produce 143,000 and 121,040 tonnes,respectively. Across all counties, California’s raspberry production was worth an estimated $239 million according to the United States Department of Agriculture’s National Agricultural Statistics Service , and $437 million according to California County Agricultural Commissioners’ Reports. The difference in these estimates reflects that the NASS data report cash receipts to producers while the Agricultural Commissioners’ Reports estimate the total value of production. Figures 1, 2, 3, and 4 plot California raspberry hectares, production, yield per hectare, price per kilogram, and the total cash receipts between 2004 and 2013. Note that raspberry hectares multiplied by yield per hectare is equivalent to production, and production multiplied by price per kilogram is equivalent to total cash receipts. Four counties account for virtually all commercial raspberry production in California: Ventura, Santa Cruz, Santa Barbara, and Monterey. In 2014, Ventura County produced approximately 52% of California’s raspberry crop by value, $241 million, on 1,873 hectares. Raspberries are the third most valuable crop in Ventura County. Santa Cruz County produced approximately 28% of California’s raspberry crop by value, $131 million, on 979 hectares. Raspberries are the second most valuable crop in Santa Cruz County. Santa Barbara County produced approximately 10% of California’s raspberry crop by value, $45.2 million, on 591 hectares. Raspberries are the ninth most valuable crop in Santa Barbara County. Monterey County produced approximately 10% of California’s raspberry crop by value, $45 million, on 316 hectares. Raspberries are the sixteenth most valuable crop in Monterey County. Table 1 summarizes California raspberry production by county. Counties are listed from north to south along the Pacific Coast. Figure 5 identifies these berry-producing regions with a stylized map of California.Most commercial raspberry plantings in California have had an 18-month lifespan. The crop is planted in the winter and then harvested twice, first in the fall following planting and then in the subsequent summer. Both harvest seasons last approximately three months, with crews harvesting fruit every three days on average. Variations in harvest frequency depend on yields and pest management activities. Yields are low at the beginning and end of a harvest season, and peak near the middle of a season. Pesticide applications may require an interval of time, depending on the particular pesticide, before normal harvesting activities can resume. This period is known as the pre-harvest interval , and it is determined by the U.S. Environmental Protection Agency. Occasionally, low yields are realized during the harvest season due to crop damage resulting from weather, pest activity, or other external factors. The summer harvest is typically larger than the fall harvest. Organically produced raspberries represent a significant share of total California raspberry production. In 2008 and 2011, California’s organic raspberry production was valued at $11.4 million and $8.98 million, respectively, according to the USDA-NASS. In 2012, 408 hectares of California raspberries were organically managed according to the University of California Agricultural Issues Center. Raspberry prices vary throughout the year, but on average organic raspberries are sold at a price premium. In 2015, the national average retail price of organic raspberries over the entire year was $3.52 per six ounce tray according to the USDA Agricultural Marketing Service. The average retail price of conventional raspberries over the same period was $2.55 per tray. The average California terminal market prices for organic and conventional raspberries were $3.29 and $1.97 per tray, respectively. California raspberries are a major export crop. In 2013, the combined category of raspberry, blackberry, mulberry, and loganberry exports was the twentieth largest export crop category by value in California.