Mireya Molina, a rising senior at El Diamonte High School, joined UCCE Tulare County as a 2024 summer research intern serving the nut, olive, and prune research and extension program. Mireya has a strong science background and is an active member of her high school horticulture and FFA programs. She has served as a volunteer at fundraisers for the local SPCA and at Happy Trails Riding Academy as well as at a youth science fair hosted by the Visalia Unified School District. Mireya has taken advantage of the AP and agricultural education coursework at El Diamonte High School and expresses an interest in pursuing a BS in animal science at Chico State University in fall 2025. During the summer of 2024, Mireya served as a volunteer intern in the research and extension program of Elizabeth Fichtner, UC ANR Farm Advisor, working on enumerating insects for a pest management study on walnuts. Mireya's work contributes to the understanding of the best timing for application of insect growth regulators (IGR) for management of walnut scale, specifically determining the value of dormant applications versus delayed dormant application of Centaur^®, an IGR produced by Nichino America. Her work will help walnut growers gain the maximum value out of each application of the insecticide, thus reducing overall insecticide inputs for management of the pest.

UCCE Tulare County recently joined an international group of scientists focused on leveraging pecan genetics to develop trees adapted for the diverse geographic regions in which the trees are cultivated and for tree resilience in the advent of climate extremes. Tulare County boasts over 1,000 acres of pecan and is home to one of the state's pecan handlers. Walnuts, a historic nut crop of Tulare County, are in the same plant family as pecan (Juglandaceae); consequently, the relatedness of the two crops has facilitated an overlap of specialization in the grower community, with many long-time walnut growers also managing the state's pecan acreage. 

In 2022 the team of 26 scientists was awarded an $8 million USDA NIFA Specialty Crop Research Initiative grant entitled ‘Trees for the future: Coordinated development of genetic resources and tools to accelerate breeding of geographic and climate adapted pecan trees.' Led by Dr. Jennifer Randall at New Mexico State University, the grant provides 4 years of research funding to USDA and major land grand institution scientists, as well as researchers at University of Tokyo and the HudsonAlpha Institute for Biotechnology. From California, Karlene Hanf of Mid-Valley Pecan sits on the advisory board, and Elizabeth Fichtner, UCCE Tulare County nut, olive, and prune advisor, serves as a principal investigator.

In some permanent cropping systems, climate conditions such as low winter chill may affect the overlap of the female and male bloom, affecting crop productivity. To mitigate this risk, pistachio growers sometimes plant multiple pollinizer varieties in orchards.  In Tulare County pecan growers rely on two varieties, ‘Western' and ‘Wichita,' to satisfy the reproductive needs of the crop.  One goal of the USDA NIFA-funded project is to assess the timing and overlap of the male and female bloom of co-planted varieties over years characterized by different climate conditions. Researchers across the United States are utilizing standardized techniques to assess bud break, shoot development, and bloom on many cultivars to provide phenotypic data that can be utilized by geneticists striving to breed climate resilience in pecan. Additionally, researchers are quantifying damage cause by pecan leaf scorch, a disease caused by a bacterial plant pathogen. The disease has been detected in California; however, it does not appear to be as severe in California orchards as in other regions of the United States.

The USDA NIFA-funded program fosters development of UC ANR competency in pecan production, a smaller acreage nut crop in California. California is the nation's largest producer of almond, pistachio, and walnut, but produces approximately 2% of the USA's total pecan crop. As a north American native plant, pecan is well adapted to cultivation in diverse regions of the United States. Its native range includes the forested lands surrounding the Mississippi River, as well as rivers in southeastern Texas and Mexico. Outside of its native range, pecan remains an economic crop in New Mexico, Arizona, the southeastern United States, and California, particularly in Tulare County.

Walnuts and pecans represent two of the four major nut crops grown in California. The California walnut industry dwarfs the state's pecan industry in acreage, with over 300,000 acres dedicated to commercial walnut production and approximately 3,000 acres to pecan. The relatedness of the two crops has facilitated an overlap of specialization in the grower community, with many long-time walnut growers also managing the state's pecan acreage. 

Walnuts and pecans are both in the same plant family (Juglandaceae); consequently, they have similar reproductive habits. They are both monoecious, meaning that male and female flowers are borne on the same tree. Also, both pecan and walnut produce male flowers called ‘catkins' (Figure 1), and the non-showy female flowers are produced at the terminus of a preformed shoot (Figure 2) that emerges from a compound bud.  On walnuts, the catkin buds are visible at nodes, sometimes with two catkins occupying a single node as a primary and secondary bud (Figure 1A). Conversely, the catkin buds on pecan are not readily visible before bud break (Figure 1B). During the delayed dormant phase on pecan, the catkins are hidden behind a scale sheath that covers the catkins and compound shoot bud (Figure 1 B and C). As a result, the catkins only emerge as the entire bud assemblage pushes, generally in late March-early April in California. The compound bud, containing the current season's shoot and female flowers, is assembled with catkins that emerge in groups of three (Figure 1C and 2B).  As a result, groups of catkins mature at the base of the current season's shoot (Figure 2B).

The compound buds of walnut and pecan are similar in that the bud contains the preformed shoot and preformed leaves as well as the female (pistillate) flowers. The female flowers are located at the apex of the preformed shoot (Figure 3 A and B). Walnuts and pecans both have variable numbers of pistillate flowers in each compound bud. Walnut flowers are readily visible with the naked eye, whereas pecan flowers are smaller, and observation of the stigmatic surface may be enhanced with the aid of a hand lens. The final nut set of each compound bud varies based on the number of initial pistillate flowers and the success of pollination and fertilization processes. 

Both walnut and pecan tend to exhibit apical dominance as evidenced by the stronger, and often earlier, growth of the apical bud.  In walnut, two buds (primary and secondary) may be present at each node. Usually, one bud will dominate and grow, while the weaker bud will remain static or die off. Occasionally, both primary and secondary buds grow, resulting in branching at acute angles, often referred to as “forking”.  In walnut, nut set can be evaluated by early June and buds for the next year's crop may already be visible in May (Figure 4A). In vigorous orchards, in-season growth may be produced beyond the position of the nuts (Figure 4B). In-season (neoform) growth is less common in pecan. Researchers speculate that the neoform growth observed in walnut may be related to the use of vigorous hybrid rootstocks.

Although pecan and walnut are related species hailing from the same plant family, their growth and reproductive habits do have notable differences. Growers with a lifetime of experience with walnuts may be baffled by the lack of visible catkins on pecan during the dormant season. A bit of patience in the spring, however, reveals the reproductive structures upon bud break. The need for patience in pecan cultivation is also notable at harvest time. In California, the pecan harvest generally commences after the walnut harvest is complete and often continues into the successive year as fall rain events may impede orchard access.

Within the past decade a wood decay fungus with no prior record in North America has emerged as a pathogen of almond, prune, and peach (rootstock) in the San Joaquin Valley. Since 2016, Ganoderma adspersum, has been associated with decay symptoms on almonds in Kings, Tulare, Kern, and Madera counties. Unlike other endemic species of Ganoderma that were previously recognized in California almond orchards, G. adspersum appears to be aggressive on young trees, particularly those on ‘Nemaguard' rootstock. Additionally, G. adsperum infection appears to be prevalent in orchards with high incidence of crown gall caused by Agrobacterium tumefaciens, leading plant pathologists to suspect that the bacterial disease may predispose infected almond trees to the decay fungus. After a recent farm call with almond growers and crop consultants, UCCE Advisors Mohammad Yaghmour, Elizabeth Fichtner, and Raymond Mireles have initiated a series of studies to further investigate the potential relationship between crown gall and G. adspersum in the field, as well as evaluate techniques to limit the spread of G. adspersum in orchards.

Ganoderma adspersum is a wood decay fungus that infects the roots and butts of trees causing white rot and leading to tree blow-over and mortality especially after windy and rainy storms, hence, it is also called butt rot. Infected trees may appear healthy but are more likely to collapse during storms or harvest activities than uninfected trees.

 Infection by G. adspersum can be identified by the fruiting bodies, known as conks. The conks are thick-based, semi-circular, or hoof-shaped, shelf-like fruiting bodies found on tree trunks mainly at the base of the tree. Once fruiting bodies are visible, the fungus has already colonized the tree; consequently, removing fruiting bodies has little potential to affect the health of infected trees. Because Ganoderma fruiting bodies may produce 30 billion spores a day, the removal of fruiting bodies may reduce disease spread by limiting the inoculum level in affected orchards. Fruiting bodies generally regrow three to four months after removal; therefore, repeat removal of conks will be necessary to maintain reduced inoculum levels in orchards. Recent studies indicate that sporulation is highest in August and September, suggesting that harvest related activities may also contribute to spore dispersal.

In February 2024, Yaghmour, Fichtner, and Mireles established new research studies in Tulare County orchards to address the hypothesis that G. adspersum infections are more prevalent on trees infected with A. tumefaciens. With the assistance of Santosh Bhandari, Associate Specialist with UC ANR, over 6,000 trees were surveyed across two orchards and rated for incidence of each disease. Both orchards were on ‘Nemaguard' rootstock and included ‘Nonpareil,' ‘Monterey,' and ‘Fritz' varieties. Results of statistical analyses indicate a significant association between G. adspersum and crown gall infection on all varieties in both orchards.  For each incident of crown gall, the probability of infection with G. adspersum increased by over 80-fold across all varieties in both orchards.

Studies conducted by Daisy Hernandez, a PhD student in the Department of Plant Pathology at UC Davis, suggest that stem infections with crown gall do not alter the tree's susceptibility to future infection with G. adspersum at another location on the stem. This work suggests that the association of the two diseases may not be related to a physiological change in the plant resulting from prior infection with A. tumefaciens; however, it does not rule out other mechanisms of predisposition. Mireles, Yaghmour, and Fichtner are interested in studying whether the crown gall itself presents a unique infection court (ie. opening) that facilitates infection with windblown spores of G. adspersum that may encounter the gall years after crown gall development.

In 2024, new studies will be initiated to evaluate the potential benefit of phosphites (ie. K-Phite^®) in limiting the progression of new infections of G. adspersum in affected almond orchards. Phosphites offer a cost-effective approach at managing several plant diseases, including Phytophthora on almonds. Phosphites are known to induce plant defense responses to disease and are often better at preventing than curing disease. Additionally, some growers have expressed interest in using conk-removal as a strategy for reducing G. adspersum inoculum in orchards. UCCE Advisors plan to evaluate the influence of phosphite treatment on the rate of fruiting body regrowth with the anticipation of identifying multiple techniques that growers may employ to mitigate the economic effects of these diseases in California orchards.