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Oleg Daugovish and Michi Yamomoto

California leads national strawberry fruit production with annual value in Ventura County alone near $300 million. Bird damage to fruit routinely accounts for 3–5% losses and may exceed 50% in some fields. Conventional bird control tools have limited or no effect on fruit damage and may contribute to noise pollution. A four-site study at Oxnard, Calif., from Jan. to Apr. 2005 (highest value fresh market season) showed that release of Peregrine, Saker, or Barbary falcons in combination with helium balloon launching (site 4) in response to fruit damage reduced fruit damage from 80–90% to 15–20% after 1 week. When fruit damage increased again (>20%) a repeated 1-week daily program completely reduced fruit damage during the rest of the season. Falconry alone at site 2 (near man-made structures) for two consecutive days reduced fruit damage from 70–80% to 10–20%, however, at site 3, near giant reed, three weeks of daily releases did not eliminate the damage, but confined it to the strawberry beds adjacent to reed shelter (reducing overall damage from 100% to 25–50%). High frequency of release is likely unfeasible and destruction of shelter habitat may be justified. Falconry alone before damage occurrence (site 1) seemed to prevent fruit damage; however, lack of birds and fruit damage before, during, and after releases made it difficult to draw conclusions about the success of the preventive program. In April, no fruit damage occurred even during bird presence suggesting the change in their diet. The study showed that seed-eating birds were the main pests at Oxnard, Calif., and that trained falcons can disperse them, thus, reducing fruit damage. The success of falconry was site-specific and depended on proximity of suitable habitat and availability of food sources for pest birds.

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Oleg Daugovish and Kirk Larson

Total and marketable yield, fruit size and fruit rot were evaluated for `Camarosa' and `Ventana' strawberries grown with or without protected culture in southern California in 2003 and 2004. In both years, bareroot transplants were established on 5 Oct. using standard “open field” production methods. Fifty-five days after transplanting, metal posts and arcs were positioned over portions of the field and covered with 0.0324-mm-thick clear polyethylene (Tufflite Thermal, Tyco Plastics, Inc., Minneapolis, Minn.) to create “tunnel” structures 5 m wide, 25 m long, and 2.5 m high. Each tunnel covered three contiguous strawberry beds, and experiment design was a randomized complete block with four replications, with individual plots consisting of 20 plants. In 2003, early season (Jan.–1 Apr.) marketable yields in tunnels were 90% and 84% greater than outdoor culture for `Ventana' and `Camarosa', respectively. In 2004, use of tunnels resulted in a 140% marketable yield increase for `Ventana' and 62% for `Camarosa' (Jan.–31 Mar.); however, unusually high temperatures (38 °C) in April resulted in reduced yields in tunnels thereafter. In both years, increased early production coincided with highest fresh market fruit prices, resulting in $5700–7700 greater returns per-acre compared to open field production. For both cultivars, tunnel production resulted in 37% to 63% fewer non-marketable fruit due to less rain damage, better fruit shape, and decreased incidence of gray mold. For all treatments, fruit size decreased as the season progressed and was more pronounced in tunnels after April. Overall, these studies indicate that tunnels have potential for enhancing early-season production and profitability of strawberries in southern California.

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Oleg Daugovish and Doug Gubler

Strawberry anthracnose caused by Colletotrichum acutatum may kill strawberry plants or reduce plant vigor and marketable yield, resulting in multimillion dollar losses to strawberry industry. The fungus is often carried with transplants from nurseries to production fields undetected. The studies in one summer and two winter seasons near Oxnard, Calif., evaluated 30-second pre-plant dipping in ten fungicide solutions or water washing of transplants inoculated with C. acutatum as a means of reducing infection and improving fruit yield. In summer-planted `Baeza,' the pathogen caused severe die-back and reduced marketable fruit yield 89% in inoculated, untreated controls compared to non-inoculated plants while plants dipped in Switch (cyprodynil + fludioxynil) at 0.38 g/L had 33% yield reduction. Other fungicides provided even less protection, resulting in 53% to 89% yield losses. During cooler winter seasons the pathogen remained latent and lesions appeared on `Camarosa' when the day-night air temperatures reached 16 °C or more, 7–14 days after rain. None of the treatments reduced fruit lesion development, however, among plants dipped in strobilurin fungicides only 3% had C. acutatum symptoms (including early die-back) as opposed to 26% in inoculated, untreated controls. Plants dipped in Switch, Quadris (azoxystrobin), or Pristine (pyraclostrobin + boscalid) yielded similar to non-inoculated, untreated controls in 2003 and 10% to 12% more in 2005. These studies showed that strobilurin fungicides did not prevent fruit infection (indicating need for foliar in-season control) but improved marketable yield compared to the inoculated, untreated plants. Temperatures over 16 °C and precipitation may significantly increase disease development.

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Oleg Daugovish, Hai Su and W. Douglas Gubler

Bare-root daughter plants of strawberry (Fragaria ×ananassa) were inoculated with Colletotrichum acutatum, the cause of crown rot, root rot, and fruit rot of strawberry in California. Plants were subsequently dipped in fungicide solutions or washed with running tap water immediately before planting in Summer and Fall 2002 and Fall 2004. Fungicide treatments reduced plant dieback by up to 92% in fruit production fields. Plants treated with azoxystrobin, the premixtures of boscalid + pyraclostrobin and cyprodinil + fludioxonil had 50% to 92% reduction in disease incidence, increased canopy size by more than 100%, and produced significantly higher marketable yields in all planting dates than the inoculated plants that were not treated with the fungicides. Chlorothalonil and captan also significantly reduced disease incidence but did not consistently increase marketable yield compared with the untreated, inoculated control. The effects of propiconazole and trifloxystrobin were inconsistent in reducing disease incidence. Water wash did not reduce root and crown disease incidence but significantly increased marketable yields by 13% over the untreated, inoculated controls in one of two plantings. No pretransplant treatments provided protection against fruit and foliar infection; thus, in-season fungicide applications would be necessary for disease control in commercial production fields if environmental conditions favored disease development.

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Jayesh B. Samtani, Husein A. Ajwa, Rachael E. Goodhue, Oleg Daugovish, Zahanghir Kabir and Steven A. Fennimore

Fumigants are used to control soilborne pests before planting high-value crops such as strawberry. The use of specialized tarps during fumigation can reduce fumigant emissions and mitigate the need for large buffer zone requirements mandated by regulators. Increased fumigant retention by use of barrier films during fumigant application may increase fumigant retention and allow use of lower fumigant rates to control soil pests than would be needed with permeable film. The objective of this study was to determine the minimum effective rates of the alternative fumigants, 1,3-dichloropropene (1,3-D) + chloropicrin (Pic), and Pic required under virtually impermeable film (VIF) and a high-density polyethylene (HDPE) tarp to provide weed control equivalent to methyl bromide:chloropicrin (67/33% v/v MBPic) standard soil fumigation at 392 kg·ha−1 under HDPE. A second objective was to determine fumigant rates under VIF and HDPE tarps needed to provide weed control and the economic costs of using VIF and reduced rates of the alternative fumigants. In 2002–2003 and 2003–2004 growing seasons, the fumigants 1,3-D + Pic and Pic were tested at 0, 56, 112, 224, 336, and 448 kg·ha−1 under HDPE and VIF tarps at Oxnard and Watsonville, CA. An untreated control and a MBPic standard at 392 kg·ha−1 were also included in the study. Weed control was assessed using weed propagule viability bioassays for four common weeds, time required for hand weeding, and weed fresh biomass. The fumigant rate that would be needed for a 90% reduction in viability (GR90) for all weeds was 21% to 84% less for 1,3-D + Pic under VIF compared with the HDPE tarp. For Pic, the GR90 values were 5% to 64% less under VIF compared with the HDPE tarp. Hand weeding times and weed biomass decreased with increasing fumigant rates. With the exception of Pic in 2002–2003 at Oxnard, VIF reduced the rate required for weed control compared with the HDPE tarp for both fumigants and at both locations. Economic benefits of VIF relative to the HDPE tarp were not consistent and additional work is needed to quantify these relationships and the production conditions under which VIF will be beneficial.

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Oleg Daugovish, Mark Bolda, Sukhwinder Kaur, Maren J. Mochizuki, Daniel Marcum and Lynn Epstein

Strawberry anthracnose caused by Colletotrichum acutatum is often asymptomatic on plants in sprinkler-irrigated nurseries but destructive after transplantation into fruiting fields. This study evaluated the impact of strawberry nursery sprinkler and drip irrigation in the presence or absence of C. acutatum on post-transplantation plant growth, mortality, and fruit yield in fruiting fields in California. In a 2005 nursery at Tulelake, CA, dip infestation of mother plants with C. acutatum reduced early-season mother plant canopy size by 21% and delayed runner production in mother plants but otherwise had no obvious disease symptoms. In comparison with sprinkler-irrigated treatments in the nursery, drip irrigation of infested nursery plots reduced plant losses in fruit production fields by 86% at Watsonville, CA, in 2005 and 50% and 75% at Oxnard, CA, in 2005 and 2008. Transplants from infested nursery treatments had a 33% to 60% smaller canopy and 11% to 42% lower yield than transplants from uninfested nursery treatments. However, transplant canopy size and yield from the infested and then drip-irrigated nursery treatment were similar to the sprinkler-irrigated, non-infested nursery treatment. Quantitative polymerase chain reaction measurements of C. acutatum in crown tissue of fruiting field plants seven weeks after transplanting showed significantly more C. acutatum (≈11×) in their crowns in sprinkler-irrigated than drip-irrigated, infested nursery transplant treatments. During the course of fruit production, the amount of C. acutatum in crown tissue increased in all treatments. However, at the end of the fruit season, there was still significantly more (≈8×) C. acutatum in the crowns of the plants produced by sprinkler irrigation than by drip irrigation in the nursery. These data suggest that if C. acutatum is present in the nursery, drip irrigation can reduce subsequent plant stunting and yield losses in strawberry production fields.

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Maren J. Mochizuki, Oleg Daugovish, Miguel H. Ahumada, Shawn Ashkan and Carol J. Lovatt

The objectives of this preliminary study were to optimize a carbon dioxide (CO2) application system for field-grown raspberry (Rubus ideaus) under high tunnels and then to compare plant photosynthesis, growth, and fruit yield with and without CO2. Based on plant photosynthesis measures before CO2 application, we placed the drip irrigation tape to apply CO2 in the middle of the plant canopy at 100 cm aboveground and split daily CO2 application from 0700 to 1100 hr and 1400 to 1800 hr. In the morning hours, CO2 concentration in the tunnel was 18% higher than in the afternoon; wind speed often increased later in the day, which may have moved the CO2 even in the tunnel. We maintained an average CO2 concentration of 436 ppm for 4 months, applying about 25 tons of CO2. In tunnels enriched with CO2, yield and berry size from plots 20 ft in length increased 12% and 5%, respectively, compared with untreated tunnels. We measured no corresponding differential response in the number of 6-oz baskets harvested from the full tunnel, leaf CO2 assimilation, stomatal conductance (g S), or fluorescence, raspberry cane height, pruned cane biomass, cane diameter, or carbohydrate content of the fruit after CO2 application. Documenting potential plant physiological changes should therefore be a focus of future research.

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Donald J. Merhaut, Lea Corkidi, Maren Mochizuki, Toan Khuong, Julie Newman, Ben Faber, Oleg Daugovish and Sonya Webb

Agriculture is a major industry in California, with cool-season crops grown along the state’s coasts, warm-season crops grown in the hot deserts, and many temperate crops grown in the state’s valleys. In coastal communities such as Ventura County, the Calleguas Creek and the Santa Clara River watersheds have 50,000 and 60,000 irrigated acres of farm crops, respectively. These watersheds are considered impaired by nutrients, salts, pesticides, and other agricultural contaminants. Mitigation of chemical and sediment runoff through grower-implemented best management practices (BMPs) is therefore one of the highest priorities in the Los Angeles Regional Water Quality Control Board Basin Plan. A 3-year project was designed to assist Ventura County growers in meeting regional water quality objectives. The University of California Cooperative Extension Ventura County and the University of California, Riverside, collaborated with the Ventura County Resource Conservation District and the Ventura County Agricultural Irrigated Lands Group (VCAILG) to address three project goals: increase grower and landowner understanding of local agricultural water quality issues; identify gaps or deficiencies in current management practices in agricultural operations; and reduce the contribution of nutrients, pesticides, and other pollutants to impaired water bodies. To achieve these goals, 469 surveys of agricultural water quality management practices were collected to assess the extent of current adoption of BMPs. Over 160 growers who farm more than 14,000 acres that drain into Calleguas Creek and 7,000 acres that drain into the Santa Clara River watersheds were assisted. Using the survey, growers developed site-specific farm water quality plans and received on-farm recommendations for BMPs. Additionally, 12 water quality educational programs, “including demonstrations of successful BMPs,” were developed and more than 2500 copies of educational materials published by the University of California, the Resource Conservation District, and the Natural Resources Conservation Service of the U.S. Department of Agriculture were distributed at on-farm visits, workshops, and other grower events. The project resulted in improved understanding, by growers and landowners, of water quality issues and significantly increased the implementation of appropriate on-farm BMPs to protect water quality. Nearly 100 new BMPs primarily aimed at managing erosion, sediment movement, and irrigation runoff were identified and documented through annual reassessments for more than 8000 acres draining into Calleguas Creek. A total of 518 people attended the educational programs, and over 90% of participants who completed evaluations rated the programs highly. In the final year of the project, 75% of attendees indicated they plan to implement new BMPs within the next 5 years, especially in the areas of irrigation, erosion, and pest management.