Landscape palms (Arecaceae) are pruned (i.e., leaves removed) to avoid the hazard of falling fronds, to remove diseased or brown leaves, and, in some cases, to minimize growth by diminishing photosynthetic capacity. In studies at two California locations (Long Beach and Irvine), even complete leaf removal every 3 to 4 months for 18 to 21 months resulted in similar new leaf production by queen palm (Syagrus romanzoffiana) or windmill palm (Trachycarpus fortunei) compared with no pruning or “10 and 2” pruning (industry standard pruning referring to the palm canopy visually beginning at the 10 o'clock position and ending at the 2 o'clock position on a clock face). By contrast, complete leaf removal reduced the number of new leaves of california fan palm (Washingtonia filifera), young mexican fan palm [MFP (Washingtonia robusta)], and taller, more mature MFP by 30%, 23%, and 21% compared with no pruning and “10 and 2” pruning. Leaf petiole length, leaf blade length, leaf blade width, and total palm height were also reduced 19% to 43% after complete leaf pruning compared with no and “10 and 2” pruning of young and more mature MFP. Although “10 and 2” pruning did not reduce growth of any palms, pruning all but the four newest leaves reduced leaf petiole length by 21% for the taller MFP. An important consideration for palm disease control is that tools used for pruning may harbor pathogen inoculum. Flaming pruning saws with a propane torch for 10 s reduced total fungal colonies and palm pathogenic fungi recovered on a selective medium by 95%. Increasing our understanding of palm response to leaf removal and how to minimize unintended consequences of pruning, such as the spread of disease, is an important part of improving palm maintenance.
A. James Downer, Donald R. Hodel, and Maren J. Mochizuki
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.
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.
Maren J. Mochizuki, Anusuya Rangarajan, Robin R. Bellinder, Thomas Björkman, and Harold M. van Es
Vegetable producers are increasingly interested in adopting conservation tillage practices to maintain or enhance productivity and soil health, but reducing tillage may reduce yields in cool climates. Strategies to transition from full-width tillage to zone tillage systems for cabbage (Brassica oleracea L. Group capitata) were tested with the goals of overcoming soil temperature and compaction limitations and producing crop yield and quality equivalent to conventionally tilled. Designed to achieve differential soil temperature and compaction levels, the treatments were factorial combinations of two widths of zone tillage (15 and 30 cm) and two depths of zone tillage (10 and 30 cm) plus a conventional rototilled treatment (full width and 20-cm depth) as a control. To assess the effect of treatments in the transitional year to reduced tillage, the experiment was conducted in 2003 and 2004 at different fields that were previously conventionally tilled. Increasing tillage width from 15 cm to 30 cm increased soil temperature by 1 °C in both years but had a limited effect on cabbage growth and no effect on yield. Tillage width and soil temperature may have greater impact on an earlier planting. By contrast, increasing tillage depth from 10 cm to 30 cm reduced soil penetrometer resistance by up to 1 MPa, increased plant growth by 28%, and increased yield by 22%. Growth and yield in 30-cm depth treatments were similar to conventional tillage, indicating the undisturbed, between-row areas in zone tillage treatments did not restrict growth. Zone tillage did not affect cabbage maturity or quality. Tillage depth was more important to the success of this system than tillage width; vertical tillage to 30-cm depth left between 60% and 80% of the soil surface area undisturbed and can be an effective transition to conservation tillage for transplanted cabbage.
Maren J. Mochizuki, Anusuya Rangarajan, Robin R. Bellinder, Harold M. van Es, and Thomas Björkman
If benefits of conservation tillage can be quantified even in the transition year from conventional tillage, growers will more likely integrate practices that maintain or enhance soil quality and productivity. The management of surface residue is an important component of conservation tillage, especially in cool, rainy climates where vegetable growth and yield reductions have been observed when heavy residue is present. Cereal rye (Secale cereale L.), grown until flowering, was killed with glyphosate and was then cut and removed (stubble treatment) or rolled or chopped to form a surface mulch (mulched treatment) before transplanting cabbage. Rolled mulch increased soil wet aggregate stability by 4% and reduced soil penetrometer resistance by up to 0.5 MPa compared with rye stubble treatments in 2003. In 2004, frequent rains saturated soils and may have accelerated the decomposition of chopped mulch, minimizing treatment effects. Rolled mulch reduced soil temperatures by up to 2 °C in 2003, but June transplanting of cabbage probably minimized the impact of soil temperature. Mulched treatments did not delay cabbage maturity or affect head quality characteristics such as color or uniformity. Although rolled mulch reduced cabbage growth by as much as 30% and yield by 21% in 2003, chopped mulch did not affect growth or yield in 2004. Yield reduction may be overcome by killing the rye relatively early in the spring or retaining only the surface stubble; these strategies may maintain or measurably improve soil quality even in the transition year to conservation tillage.
Ben A. Faber, A. James Downer, Dirk Holstege, and Maren J. Mochizuki
Soil testing is an important component of a plant nutrient management program for farmers, home gardeners, and agricultural service personnel. Results from five commercially available colorimetric soil test kits were compared with standard laboratory analyses for pH, nitrate–nitrogen (NO3), phosphorus (P2O5), and potassium (K2O) content for Salinas clay loam soil with three cropping histories. The kits ranked in accuracy (frequency of match with analytical laboratory results) in the following sequence: La Motte Soil Test Kit, Rapitest, Quick Soiltest, Nitty-Gritty, and Soil Kit at 94%, 92%, 64%, 36%, and 33%. NO3 was most accurately determined by Rapitest and Quick Soiltest, P2O5 by Rapitest, and pH by La Motte Soil Test Kit. K2O was determined with equal accuracy by all but Soil Kit. The composition of the extractants may be an important factor affecting the accuracy of the test kit. For example, all kit extractants for K2O were composed of the same chemical and matched analytical laboratory results 82% of the time. By contrast, kits using an acid-based extractant for NO3 analysis more frequently matched the analytical laboratory results than kits using a zinc-based extractant (P ≤ 0.0001). La Motte Soil Test Kit had the largest range of pH measures, whereas Rapitest was relatively easy to use and interpret and is a practical choice for home gardeners or landscapers; both were more than 90% accurate for this soil type. Although an important limitation of commercial test kits is the approximate or categorical value of nutrient content (i.e., low, medium, high), accurate test kits can yield results quickly and economically for improved nutrient management.
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.