The unusually wet winter and spring of 2023 has had unprecedented impacts on our local orchard systems. However, the cumulative impacts of a barrage of atmospheric rivers and persistent standing water in some flooded areas may not be realized for another year. Cold and rainy conditions during bloom limited pollinator activity and impeded orchard access for spray operations, creating the ideal conditions for the onset of plant pests and disease issues. The timing of bud and shoot development has likely also been impacted, as the buds for next year's crop are formed during the current year; therefore, the unusually wet and cold spring of 2023 may also influence the development of the 2024 crop.  

The bloom period for many Prunus species (almond, peach, cherry, plum, prune, etc.) was unusually protracted due to the high frequency of rain and cool temperatures. Saturated soil conditions limited orchard access, resulting in delayed shaking of mummy nuts in almond, an essential sanitation practice for management of navel orangeworm, a key insect pest (Figure 1A). With few bee flying hours available for pollination, and wet, cold conditions conducive to disease development (Figure 1 B,C and D), the crop outlook for 2023 remains uncertain.

Pistachio, walnut, and pecan, all wind-pollinated crops, are experiencing delayed bud break and shoot development. The progression of bud break appears to be at least 10 days behind the norm and the timing and synchrony of male and female flower maturity is yet unknown.

Orchards that have sustained flooding may be physiologically impacted by roots persistence in anoxic conditions and may also be exposed to waterborne plant pathogens. Over time saturated soil will become depleted of oxygen by the roots and microbial communities resulting in anoxic conditions that can lead to root mortality. The extent of damage to the roots may not be realized until the season progresses, and root damage may manifest with general canopy decline and anchorage issues. Many of the tree crops grown in California are grafted onto disease resistant rootstocks. If flood water rises above the graft union, the benefit of these rootstocks is largely negated. Many rootstocks have been selected over time for resistance to Phytophthora spp., a group of soilborne pathogens that create motile spores that swim at the water surface. These pathogens are common in surface water, and incite canker diseases, particularly when the water level persists above the graft union. Symptoms of infection include general canopy decline and cankers, many of which ooze or ‘bleed' (Figure 1C). The full suite of symptoms may not manifest until further into the growing season when the heat imposes stress on the trees.

The rainfall and flooding have additionally influenced the nutritional status of orchard soils. Cool,  wet soil conditions slow the chemical and biological reactions that control the availability of nutrients for tree uptake. Micronutrients, present in only trace concentrations in soil, become particularly limited as  the wet and cold create reductive conditions that promote lime-induced iron chlorosis, a common nutritional deficiency  in prunes, almonds, and citrus (Figure 1 E).  In sites that have undergone whole orchard recycling with incorporation of woody biomass into the soil, saturated, anaerobic conditions may moderate the microbial activity needed to stimulate wood chip decomposition and further restrict nutrient availability until the soil warms. 

As rivers breach their banks, rushing floodwater may transport the less-soluble nutrients, such as sulphate of potash (SOP) that is often applied in the autumn, away from the tree rootzone. As water moves through the soil profile, other nutrients, such as nitrogen, may be lost from the rootzone by leaching. The leaching will, however, ameliorate salt accumulation after years of drought, particularly in sites that have relied on saline groundwater for irrigation.

As the season progresses, growers should work closely with their PCAs, crop consultants, and UCCE farm advisors to observe and document orchard changes in the 2023 season. Photographs should be taken of anomalies, such as delayed bud break, so comparisons may be made to past and future years. Additionally, photos of putative disease and insect issues may easily be shared with representatives from private industry as well as researchers in the UC system for both diagnosis and discussion of best management strategies. A suite of photos and management options for the most common pest and diseases of agricultural crops can be found at the UC IPM website (www.ipm.ucdavis.edu).

The removal of nuts remaining on almond trees from the prior year's crop is an important winter sanitation practice for the management of navel orangeworm (NOW), Amyelois transitella. Residual nuts are called ‘mummies' and the process of removing the mummies is referred to as a ‘mummy shake' because they are mechanically shaken from trees. This practice is conducted during the dormant and delayed dormant season, a time when orchard access may be thwarted by the winter rains.

Most growers strive to have the mummy shake complete by mid-January when buds are dormant and less likely to abscise from the vibration caused by a mechanical shaker. As the flower buds progress toward bloom, they become more sensitive to the shaker vibration and more likely to abscise. Studies conducted in the 1980s (Sibbett et al.) established that the shaking of mummies by January 31 (approximately 8 days prior to bloom) at a Kern County site did not adversely affect yield; however, the authors cautioned growers of the risk of delaying mummy shakes further, particularly on early blooming varieties and in locations in the southern San Joaquin Valley¹. Because bud development and bloom date advance with increasing latitude, the potential risk of early and mid-February mummy shakes was investigated by W. Asai (Pomology Consulting, Turlock, CA) in the northern San Joaquin Valley. This work, conducted at a more northern latitude, suggested shakes conducted in early February may not compromise yield².

The lack of yield detriment attributed to a mummy shake-mediated bud loss may seem counterintuitive; however, simple concepts of tree physiology may help explain this phenomenon. Consider that only approximately 30% of the flowers on a tree set a crop. A given tree does not have the carbohydrate stores needed to set every flower. As a result, the loss of a subset of flower buds may have little effect on overall yield. Naturally, the risk of crop loss increases the closer the shake approaches bloom, and both research groups suggested that mummy shakes be complete prior to the pink bud stage of development.

Although rainy years make it difficult for growers to access orchards and complete orchard sanitation tasks, the heightened soil moisture adversely affects NOW survival in comparison to dry winters. Mummy nuts on the ground support enhanced NOW survival on a dry orchard floor than on moist soil with winter vegetation in the row middles. The next step in managing overwintering populations of NOW is destruction of mummies by flailing or mowing. Flailing and mowing should be completed by March 1, prior to the emergence of NOW. The emergence profile of NOW varies by location, but the first flight generally starts in late March.

Growers who have not completed their winter sanitation practices by the end of January should walk their orchards to assess bud development in consideration of a delayed mummy shake. Winter sanitation can reduce now damage by up to 80%, so an early February shake may be worth the effort if orchard access is possible and bud development has not advanced into pink tip. For more information on NOW management, visit www.ipm.ucdavis.edu.

As California's nut industry has grown, so too have the opportunities for UC ANR farm advisors and specialists to present the latest innovative research topics to the state's nut growers, crop consultants and farm managers. UCCE farm advisors utilize large industry-sponsored trade show venues and magazines to extend unbiased, third-party generated data to our primary clientele groups who produce California's almonds, pistachios, walnuts, and pecans. The partnerships between our applied research community and agricultural marketing companies such as Malcolm Media and Jason Scott Marketing, publishers of Pacific Nut Producer (PNP) and West Coast Nut (WCN), respectively, magnifies the reach of UCCE's extension efforts beyond county lines, thus fostering regional and statewide impacts of otherwise local programs.

Annual trade shows such as the California Tree Nut Conference, the Tree and Vine Expo, and the California Walnut Conference attract hundreds of growers to centralized locations in the Central Valley. The educational content at these conferences, including presentations and oversight of panel discussions, is contributed by UC ANR academics with wide-ranging research expertise. The value of this partnership is underscored by the unbiased role of UC scientists in the research arena, particularly at venues designed primarily as marketing events. These trade show events generally engage over 1000 growers per event, allowing UC-generated information to reach greater numbers of contacts than that of our local meetings or newsletter publications. The added benefit is that the costs of the venue and associated luncheon are covered by the corporate sponsors presenting their products in the trade areas.

The farm advisor community similarly capitalizes on the high subscriber numbers of serial publications to extend written extension materials to our clientele base through the state. PNP, established in 1995, reaches nearly 10,000 subscribers and has relied on the UC ANR farm advisor community for relevant, science-based editorial content. For example, Brent Holtz, PhD, UC ANR has authored the monthly Almond Tasks editorial for 15 years. The promulgation of information is heightened by both the circulation volume and the availability of an online archive of articles.

The rich editorial provided by trade magazines includes articles written by UC academics and associated collaborators, as well as articles composed by journalists based upon the work or presentations conducted by UC academics. Subscribers should always take note of article authorship in trade magazines. Articles written by journalists are not proofread or edited by the UC research community; consequently, small errors may be unintentionally propagated in the trade literature.  In the past decade, the demand for editorial on nut crops has increased so dramatically that the research community cannot meet the demand. Consequently, trade magazines have had to rely on technical articles composed by freelance journalists. Researchers appreciate the work of the ag- journalism community and do their best to provide information, quotes, and figures for such articles. Regardless, there should be a distinction between articles written by the research and extension community and those authored by our peers within the journalist community.

The written and spoken content presented for industry functions may vary considerably from the content farm advisors print or post in UC forums, such as UC newsletters and grower meetings. Trade shows are funded by marketing; therefore, research that demonstrates a lack of product efficacy (or perhaps even a product detriment to a crop or commodity) will not be welcome at trade shows. As a result, certain topics may be excluded from the agendas at trade events. Similarly, higher emphasis may be placed on agenda items qualifying for continuing education credits than on horticultural practices or techniques. Rest assured, UC ANR academics continue to provide third party, unbiased extension materials by maintaining UC-sponsored meetings for growers and publishing our newsletter editorials both in print and online. UC extension resources include our website, UCCE San Joaquin Valley Trees and Vines (https://www.sjvtandv.com/about-the-authors), individual farm advisor websites and blogs, and as well as the UCCE Growing the Valley podcast (https://www.growingthevalleypodcast.com/).

The dairy and nut industries are dominant contributors to Tulare County's agricultural economy, with milk consistently ranking as the highest valued ag product, followed close behind by pistachio and almond in the top 10.  The dairy industry provides economic value to a biproduct of the almond industry-- almond hulls. Almond hulls are incorporated in the herd diet, thus reducing the quantity of forage required for feed in a region sustaining a multi-year drought. This practice increases the water use efficiency of both the dairy and orchard systems.

In October 2022, the UCCE Tulare County Orchard Systems Program, led by Dr. Elizabeth Fichtner, provided an opportunity for cross-disciplinary dialogue between the animal science and plant science communities. Dairy researchers from across the United States visited Tulare County as part of a USDA-funded research team focusing on the economic and environmental sustainability of dairy enterprises. The team was hosted by Dr. Noelia Silva del Rio, UC ANR Dairy Herd Health Specialist, at the UC Davis Veterinary Medicine Research and Extension Center in Tulare, CA. The group had the opportunity to visit a commercial walnut orchard during harvest operations, using the field site as a platform for discussion of cross-disciplinary topics including nutrient management, food safety, composting protocols, and water use efficiency. Additionally, dairy researchers observed the extensive damage on walnut trees caused by Agrobacterium tumefaciens, an organism familiar to all scientists for its role in revolutionizing molecular biology, but infamous to walnut growers and plant pathologists as a bacterial plant pathogen causing crown gall.