Presentations: North American Strawberry Symposium (NASS) 2023
Blauer K. and Holmes, G. 2023. Multi-year summary of fungicide efficacy on botrytis fruit rot and powdery mildew. Annual NASGA Meeting & North American Strawberry Symposium, San Luis Obispo, CA. 7-10 March.
This poster contains efficacy ratings for 59 different fungicides for use on strawberries in California and 2 pending registration. Results are compiled from 28 trials over an 8-year period conducted at the Cal Poly Strawberry Center. Efficacy trials for Botrytis fruit rot consisted of five weekly applications followed by at-harvest and post-harvest evaluations. Efficacy trials for powdery mildew were conducted in the greenhouse on raised tabletop benches and consisted of five weekly applications with weekly severity and incidence ratings on the foliage. Each trial included a non-treated control and grower standard as a positive control. Fungicide efficacy was averaged across multiple trials and given a relative fungicide efficacy score. Fungicide efficacy scores range from 5 (excellent and consistent) to 0 (ineffective). There are 15 products that are excellent and consistent against powdery mildew and 9 that are excellent and consistent against Botrytis fruit rot.
Fink, C., Mendez, M., Rodriguez, J., Lobo, C., Molinar, A. and Lin, J. 2023. Recommended spray rig designs for California strawberries. Annual NASGA Meeting & North American Strawberry Symposium, San Luis Obispo, CA. 7-10 March.
Spray rig coverage is important to pest management efficacy. It depends on multiple factors including weather, operating parameters, and sprayer design. This work compared 30 spray rig designs used in California strawberry production. Field evaluations were conducted in beds with 4 canopy lines in Santa Maria, CA on 162 cm beds and in Oxnard, CA on 172 cm beds as well as in beds with 2 canopy lines in Watsonville, CA on 122 cm beds and 132 cm beds. Pressure, number of nozzles, nozzle type, and nozzle spacing were evaluated with water-sensitive spray cards (n=2,000). Spray rigs were properly maintained and calibrated before each evaluation. Cards were placed both horizontally and vertically on plant canopies near the middle and edge of the beds. The results indicated that increasing nozzle pressure and positioning the nozzle closer to the canopy level could potentially increase coverage by 30%.
Holmes, G. J. 2023. The California strawberry industry: current trends and future prospects. Annual NASGA Meeting & North American Strawberry Symposium, San Luis Obispo, CA. 7-10 March.
California grew 16,187 hectares of strawberries in 2022 in three growing districts located along California’s Central Coast: Oxnard, Santa Maria, and Watsonville-Salinas. Transplants are grown on approximately 2,023 hectares at high and low elevation nurseries located hundreds of miles from fruit growing districts. In 2022, there were 13 public cultivars grown, with the most popular being Monterey, Portola, Fronteras, Cabrillo, and San Andreas, grown on 28%, 11%, 10%, 5%, and 3% of the planted acres, respectively. Proprietary cultivars made up 38% of the planted acres. The most important diseases are Macrophomina root rot, Fusarium wilt, Verticillium wilt, Phytophthora root rot, Botrytis fruit rot, and powdery mildew. The most important arthropod pests are twospotted spider mites and Lygus bug. Labor issues, loss of fumigants, and water quality (nitrates and saltwater intrusion) are current challenges. Increased regulation, increased urbanization and drought magnify these concerns.
Kraemer, W., Lin, J., Wells, J. and Fink, C. 2023. Optimized Lygus bug vacuum. Annual NASGA Meeting & North American Strawberry Symposium, San Luis Obispo, CA. 7-10 March.
Lygus spp. are major pests of the California strawberry industry and have prompted growers to purchase and use machines called “bug vacuums” to mitigate damage throughout the production season. Field tests of the two new vacuum models were conducted in Guadalupe, California and Watsonville, California on raised strawberry beds with fully developed canopies. Results indicated that the vacuum significantly increased removal of Lygus spp. compared with a conventional vacuum. The average number of Lygus spp. removed on each pass by the Double Barrel Bug Vacuum was 2.2 times greater than that of the conventional vacuum, and the Single Barrel Bug Vacuum was 3.0 times greater. The elimination baffle located at the outlet of the conventional vacuum was observed to significantly reduce air speed, and raising it 30.2 cm above the outlet increased air speed by 17% (3.0 m/s) at the vacuum inlet.
Kraemer, W., Lin, J. and Ahmadi, M. 2023. Plastic mulch hole burning and cutting for strawberry planting. Annual NASGA Meeting & North American Strawberry Symposium, San Luis Obispo, CA. 7-10 March.
Creating wide holes in plastic mulch on strawberry beds in preparation for planting helps with preventing plants from growing under the plastic and increases the amount of water and sunlight available. Currently, this process is performed by hand, either using a knife to cut open the plastic mulch or burning it with a handheld burner, which makes it a labor-intensive operation in strawberry production. To assist growers in reducing the effect of labor shortages, two new mechanical hole-cutting systems have been developed. The first device was designed to be retrofitted on conventional hole punchers, which would make perpendicular cuts on the plastic mulch. The second device was developed as a new implement to automate the hole-burning process. The first and second apparatuses have been tested successfully to cut holes in the plastic for around 5 and 35 acres (about 46 football fields) of strawberry beds, respectively.
Schaap, G., Speth, G., Kraemer, W., Wells, J., Fink, C. and Lin, J. 2023. Automated hoop house arch removal. Annual NASGA Meeting & North American Strawberry Symposium, San Luis Obispo, CA. 7-10 March.
Hoop houses have been proven to protect strawberries from extreme weather conditions. Currently, the process of implementing and removing hoop houses is done by hand, resulting in high labor costs for growers and a mildly unsafe work environment. A solution to this problem is to design an agricultural implement that can safely and efficiently remove hoop houses from the ground to ensure optimal harvest timing, reduced labor costs, and a safe work environment. Three iterations were tested in grower and research fields. During final testing, the implement produced a 98% success rate in removing the hoop from the stake and a 68% success rate in racking the hoops after removal. The economic analysis revealed that the payback period of the implement would be roughly 100 acres of hoops.
Simard, S. Z., Blauer, K. A., Serpa, B. R. and Holmes, G. J. 2023. Farm-scale evaluation of UV-C for control of powdery mildew in strawberries. Annual NASGA Meeting & North American Strawberry Symposium, San Luis Obispo, CA. 7-10 March.
This study compared the efficacy of UV-C and a conventional fungicide program against strawberry powdery mildew within commercial strawberry production fields. A field of summer planted Portola in Nipomo, CA was used. Strawberry beds (73, 400 linear ft.) were divided into two treatments: grower standard and UV-C. The grower standard consisted of conventional fungicides applied via tractor-mounted sprayer at the grower’s discretion. UV-C treatment was applied twice-weekly between 9:00 PM and 1:00 AM using an autonomous robot. Weekly powdery mildew assessments occurred from 7 Jul through 15 Sep. Assessments consisted of leaf counts, disease incidence and severity. UV-C treated plants had significantly less powdery mildew incidence at five of the nine evaluation dates. Disease incidence peaked 26 Jul, reaching 16.1% and 37.8% for the UV-C treatment and grower standard treatment. These findings suggest that UV-C treatment, applied twice-weekly, significantly reduces powdery mildew incidence compared to the growers’ fungicide program.
