Improving almond orchard management by integrating cultural practices, pest and disease controls, and vegetation management has been a goal of Univ. of California research and extension efforts for more than 25 years. Alternative cultural practices related to orchard floor management, fertilizer applications, and pest and disease control are currently important components of the almond production system. Nontillage, with or without a seeded cover crop, has improved potassium uptake and reduced pest problems. In-season fertilizer applications reduced the potential for nitrate pollution of groundwater. Minimizing dust, early harvest, and destruction of overwintering refugia are all cultural practices that reduce crop damage caused by pests. New methods of pest and disease monitoring using pheromone traps, egg traps, or a better understanding of disease life cycles have reduced unnecessary chemical applications. Degree-day phenology models have improved the timing of needed sprays. Expanded use of selective spray materials, such as narrow-range oils and Bacillus thuringiensis, reduce impacts on non-target species while natural predators and parasites are encouraged. Augmentative releases of beneficial insects are currently being evaluated as an additional alternative to in-season spraying. Cultivar and rootstock choices for new plantings present alternatives that can help avoid pests or diseases. Planting pattern affects productivity and is another factor to consider when evaluating alternative production practices for almond as new orchards are established.
Joseph H. Connell
Joseph H. Connell
Almond, [Prunus dulcis (synonym Prunus amygdalus)] planted on approximately 595,000 acres (240,797 ha), is California's largest acreage tree crop. California's Central Valley accounts for nearly 100% of the U.S. domestic production of almonds. Integrated pest management (IPM) programs that integrate cultural practices and pest and disease monitoring with selective controls have improved plant protection in almond. Methods of orchard floor management and their effects must also be taken into account. Minimizing dust reduces mites while harvesting earlier and the destruction of overwintering refugia are cultural practices that reduce worm damage. Improved methods for field sampling and monitoring have reduced the need for pesticide applications while improving timing and effectiveness of needed crop protection sprays. Selective controls have further reduced the impact on nontarget species. Augmentative parasite releases have also helped manage navel orangeworm (Ameylois transitella). Effective use of new selective fungicides will require precise application timing and greater knowledge of diseases and resistance management. A better understanding of disease life cycles leading to improved monitoring of the fungal diseases, shothole (Wilsonomyces carpophilus), almond scab (Cladosporium carpophilum), and anthracnose (Colletotrichum acutatum) have reduced fungicide applications. Future challenges include the potential loss of effective pest control products, the need to continually develop improved utilization strategies, and maintaining economic sustainability.
Joseph H. Connell
California almonds [Prunus dulcis, (Mill.) D.A. Webb, syn. Prunus amygdalus Batsch] are self-incompatible requiring cross-pollination to produce a commercial crop. Within seven known pollen groups, they also display cross-incompatibility. Coincidence of bloom between compatible cultivars is essential for cross-pollination. Since almonds are pollinated primarily by honeybees [Apis mellifera L.], arranging pollinizers in close proximity to one another promotes maximum pollen transfer. Almonds are frequently subject to inclement weather during their February bloom period. Strong honeybee colonies are better able to forage during marginal weather conditions than are weak colonies. Honeybee management can encourage pollen foraging and placement of colonies can affect flight activity and ultimately nut-set. Weather permitting vigorous honeybee flight activity is the most important factor for setting a good crop. Temperature also affects anther dehiscence, pollen germination, and pollen tube growth. The sooner an almond flower is cross-pollinated after opening, the greater the chance of fertilization and nut-set. Optimizing all of these pollination factors is therefore essential to achieve maximum production in almond orchards.
Joseph H. Connell and Richard L. Snyder
Almond (Prunus dulcis Mill.) cultivars vary in tolerance to cold with flowers at pink bud more tolerant than at full bloom or than small nuts. Branch samples 60 cm long with 30-100 blossoms or nuts were cut, sprayed with water, and artifically frozen. Subsamples were removed after exposure to 4 to 6 successively lower temperatures for 30 minutes. After 48 hours of ambient temperatures, flowers or small nuts were sectioned and examined for visual evidence of injury. Of the early cultivars, `Peerless', is most sensitive at full bloom and `Sonora' is most hardy. `Sonora' is especially hardy at pink bud. `NePlus Ultra' is intermediate. Of the mid-blooming cultivars, `Carmel' is most sensitive to cold while `Nonpareil' is most tolerant. `Price' is intermediate. The late blooming cultivar, 'Mission' is most sensitive while 'Padre' and 'Butte' appear similar. This study compared several popular new cultivars to older industry standards.
Joseph H. Connell, K. Uriu, W. Micke, and J. Uyemoto
Boron(B) deficiency in almond (Prunus dulcis Mill.) is characterized by leaf tip scorch, leaf drop, twig dieback, brown gummy areas in the endocarp, and embryo abortion followed by nut drop in May. Additional symptoms revealed by our work include failure of flowers to set nuts and lateral bud drop. Lack of production in part or in all of the free canopy causes spurs to elongate leading to a “willow twig” symptom on the small fruitwood. This can be confused with the nonproductive “bull” syndrome or with virus bud failure (ABFV or PRSV). Comparative leaf, pericarp, or kernel analysis in May gave a better indication of low B than did leaf analysis in August. In August, analyzing the hulls (mesocarp and exocarp) gave better separation between deficient and adequate trees than did leaf, kernel, or shell analysis. B critical levels for almond leaves should be re-evaluated since deficiency symptoms occur at currently accepted “adequate” levels.
Thomas M. Gradziel, Bruce Lampinen, Joseph H. Connell, and Mario Viveros
Joseph H. Connell, Warren Micke, James Yeager, Janine Hasey, Bill Krueger, and Craig Weakley
High orchard establishment costs require greater production early in an orchard's life. Our goal was to develop temporary trees at the least cost with the best early production. Health and longevity of permanent trees is essential. Six pruning treatments were evaluated in five-tree plots using a randomized complete block design. Each treatment was replicated four times on the `Butte' and `Mission' almond cultivars. After six years, temporary trees receiving the least pruning had the highest yields. Permanent trees had lower yields since more pruning was done in the second through fourth dormant seasons to develop branch framework for the long term. `Butte' and `Mission' responses to treatment varied due to varietal growth habits. Effects on tree development and the need for later corrective pruning were noted. After four harvests, yields were greater with less pruning.
Maria J. Berenguer, Paul M. Vossen, Stephen R. Grattan, Joseph H. Connell, and Vito S. Polito
A comparative study was conducted to evaluate the influence of seven different levels of irrigation applied to `Arbequina I-18' olive (Olea europaea L.) trees grown in a super-high-density orchard (1,656 trees/ha) in the Sacramento Valley of California. Water was applied differentially by drip irrigation at rates of 15%, 25%, 40%, 57%, 71%, 89%, and 107% evapotranspiration (ETc) in 2002, and 28%, 33%, 55%, 74%, 93%, 117%, and 140% ETc in 2003. Each treatment was replicated three times. Olives were harvested on two different dates each year from each of 21 plots. Three of four harvest dates showed a decrease in maturity index with increasing irrigation levels. Oils were made from olive samples collected from each plot and analyzed for oil quality parameters. Total polyphenol levels and oxidative stability decreased as the trees received more water, especially for the three lowest irrigation treatment levels in 2002, but few differences were noted between treatments in 2003 when all the trees were irrigated more heavily. Average oxidative stability was correlated very closely with total polyphenol content with r 2 = 0.98 in 2002 and 0.94 in 2003. In 2002, free fatty acid levels increased and peroxide levels were unchanged, but in 2003, free fatty acid levels were unchanged and peroxide levels decreased in treatments receiving more water. Saturated fatty acids did not significantly change in 2002, due to tree irrigation level. The mono-unsaturated fatty acid levels and oleic–linoleic relationship declined while poly-unsaturated fatty acid levels increased in 2002 with increased irrigation. In 2003, there was no notable difference in the ratio of mono to poly unsaturated fatty acid levels. The individual fatty acid most consistently affected by more irrigation water was stearic, which decreased in both years. Total sterol content (mg·kg–1), percentages of cholesterol and erythrodiol were significantly influenced by tree irrigation levels, but increased in one year and either decreased or were unchanged the next. Oil sensory properties of fruitiness, bitterness, and pungency all declined in oils made from trees receiving more water. The lowest irrigation levels produced oils that were characterized by excessive bitterness, very high pungency, and woody, herbaceous flavors. Intermediate irrigation levels (33% to 40% ETc) produced oils with balance, complexity, and characteristic artichoke, grass, green apple, and some ripe fruit flavors. Higher irrigation levels lowered oil extractability and produced relatively bland oils with significantly less fruitiness and almost no bitterness or pungency.
John P. Edstrom, Joseph H. Connell, Warren C. Micke, and James T. Yeager
Bridget M. Lamp, Joseph H. Connell, Roger A. Duncan, Mario Viveros, and Vito S. Polito
Scanning electron microscopy was used to examine almond [Prunus dulcis (Mill.) D.A. Webb (syn. Prunus amygdalus Batsch, Amygdalus communis L.)] flower bud development for three cultivars (Nonpareil, Carmel, and Butte) from four California locations (which span the range of almond production in California) for 2 years, and for `Nonpareil' in a single location for a third year. The objectives were to document timing of floral developmental events and to better understand the extent of variation that exists within and among cultivars, locations, and years. Results indicated that the time of floral initiation relative to hull split varied among cultivars. Median time for floral initiation in `Nonpareil' was more than 3 weeks after the onset of hull split. For `Butte' and `Carmel', median time of floral initiation preceded the onset of hull split. Extensive variation in the timing of bud development events within a cultivar was apparent. Timing of developmental events varied among locations, but no patterns emerged consistent with the north to south range which spanned 4°15' latitude and 520 km. Among years, development occurred earliest in 1997, a relatively warm year, and was delayed in 1998 and 1999, relatively cool years. Results indicate an earlier onset of floral initiation than reported in the classical literature on the subject.