- (Focus Area) Agriculture
- Author: Ben Faber
Old crop, new crop. What's up there in the trees? Are they big enough to sell? Is there a good set for next year? These are questions every avocado grower has every year, and often all year long. What is up there in the trees is confounded by what is called the "Avocado Illusion".
And boy was I reminded of the issue the other day when harvesting a GEM planting density trial. You don't see GEMs, you feel them, sense them being somewhere near your hand. There's a mass that's different from all the leaves near your hand, and you reach for it with your clipper and by golly you got a live one. But how many have you missed? You really need to search.
In a Science Magazine Letters to the Editor in Dec 1990, Paul Sandorff commented on a book written by Maurice Hershenson called The Moon Illusion. In the book Hershenson described the illusion of why the moon seemed so much larger when it was on the horizon than when it rose to its zenith on the same night. http://science.sciencemag.org/content/250/4988/1646.1
Sandorff said that this illusion applied to avocados since it was so hard to gauge the size of avocados when they were in the tops of the tree canopy. It is the surrounding environment that puts a context to size according to this theory of illusion.
Hershenson added to this observation in the March 1991 Science letters section with the comment that the leaves surrounding the fruit changes our depth perception and so changes our idea of the fruit size.
A further addendum to the avocado illusion theory is that since the fruit are the same color as the leaves (they are both dark green and the fruit unlike most other fruit continues to photosynthesize), it is hard to actually make out the fruit. You can be looking right at the fruit and not see it, confusing it with a leaf.
This illusion makes for difficult fruit estimation. To compensate for this illusion, I will eye the canopy in quadrants, counting the number of fruit, then arbitrarily doubling that total number. It usually gives a pretty close number to the real number of fruit that are in the tree.
By the way, with all the low down fruit in the skirt and with the wet winter, there were a heck of a lot of snails in the canopy dining on fruit.
Photo:
Can you count the number of fruit in this Hass canopy?
Photo: a mess of GEM fruit revealed hiding in the skirt.
- Author: Pamela S Kan-Rice
- Author: Mike Hsu
- Author: Saoimanu Sope
To help more Californians address challenging issues, University of California Agriculture and Natural Resources has hired UC Cooperative Extension experts to work in communities stretching from Humboldt and Siskiyou counties in the north, and south to San Diego County. State funding has enabled UC ANR to expand its expertise.
Since 1914, UC Cooperative Extension's researchers have been working directly with community members to improve the lives and livelihoods of Californians.
The nine recently hired UC Cooperative Extension specialists and advisors bring expertise in forestry, pest management, water, plant disease, horticulture, toxicology, economics, rice farming and wildfire.
To see a list of UC Cooperative Extension advisors who have joined in the past few months, visit https://ucanr.edu/About/DirectorySearch/Recent_Hires. The most recently hired scientists are introduced below.
Gill joins UCCE as environmental horticulture advisor
Haramrit Gill joined UC Cooperative Extension on April 1 as an environmental horticulture advisor for Tulare, Kings, Fresno and Madera counties.
She will be identifying landscape plants that are heat-tolerant, disease-resistant and fire-resistant. Gill will be researching California native plants with sustainable attributes that include superior adaptation, biodiversity enhancement, water efficiency and soil health benefits.
A native of Punjab, India, Gill earned her undergraduate degree in agriculture followed by a master's degree in horticulture at Punjab Agricultural University, where her research focused on micropropagation and haploid production in muskmelons. She earned a Ph.D. from the Department of Horticultural Sciences at Texas A&M University.
Her early research investigated the impact of nitrogen on spinach root architecture. Her doctoral work concentrated on rose breeding and deciphering the genetic underpinnings of flower color transition traits, fragrance and dwarfing in roses, with a particular focus on the intriguing phenomenon of flower color transformation from yellow to dark pink as blooms matured. She also collaborated on projects aimed at enhancing heat tolerance and disease resistance in roses.
Gill is based at the UCCE office in Tulare and can be reached at hamgill@ucanr.edu.
Jordan joins UCCE as forestry and natural resources advisor
Christian Jordan joined UCCE on March 18 as a forestry and natural resources advisor for Shasta, Siskiyou and Trinity counties. He will work to advance forest resilience and sustainable management on private and public lands, with a focus on conifer forest resource management and sustainable natural resources.
In 2020, Jordan completed a Master of Forestry at UC Berkeley, with an emphasis on forest resilience in the context of increasingly severe wildfires. Prior to joining UC ANR, he worked in the private sector in defensible space and home hardening, installing residential exterior sprinkler systems for ember defense.
Jordan brings a diverse educational and work background to the position. In 2014, he earned a bachelor's degree in geography from UC Berkeley, writing a thesis on future climate and viticulture in Napa and Sonoma counties. Upon graduating, he worked in the wine industry before returning to natural resources.
Jordan is based at the UCCE office in Redding and can be reached at cjordan@ucanr.edu.
Pastrana joins UCCE as plant pathology advisor
Ana Pastrana joined UCCE on Jan. 16 as a plant pathology advisor serving Imperial, Riverside and San Diego counties.
In her role, Pastrana will collaborate with pest control advisers and support growers with disease management. In addition to identifying high priority concerns, she will conduct research and develop educational content that addresses growers needs.
Before moving to Southern California, Pastrana worked as a research scientist on plant pathology at the University of Seville, Spain, and at Vineland Research and Innovation Center in Canada. Previously, she completed a postdoctoral assignment in the Department of Plant Pathology at UC Davis in the Thomas Gordon Lab, where she specialized in soilborne diseases affecting strawberries and blackberries.
While attending the University of Seville, Pastrana earned master's and bachelor's degrees in biology. At Investigación y Formación Agraria, Pesquera, Alimentaria y de la Producción Ecológica, a government institution in Spain, she earned a Ph.D. and completed her dissertation on strawberry diseases.
“At that time, Europe banned methyl bromide and other soil disinfectants. Strawberries rely on these disinfectants so plenty of soilborne diseases emerged,” Pastrana said.
Originally from Seville, Spain, Pastrana said that her small hometown is surrounded by plum and citrus trees. Her mother, like many others, worked in the agricultural industry and Pastrana wondered how plant life works, inspiring her to study biology.
As a Ph.D. student, Pastrana didn't know she would pursue plant pathology specifically because she was open to studying diseases in general whether it be humans, animals or plants.
“Plant pathologists are like doctors. Not everyone is happy to work with us because it usually means that there is some sickness involved,” said Pastrana. “But if growers work with pathologists from the beginning, we can focus on preventative care and helping to protect plants from getting sick.”
Pastrana is based at the UCCE office in Holtville and can be reached at ampastranaleon@ucanr.edu.
Mokwunye named area IPM entomology advisor
Idongesit Mokwunye joined UCCE on Jan. 3 as an area integrated pest management entomology advisor.
She will be studying insect pests of economic importance affecting tree fruit and nut crops, such as pistachio, almond, walnut, table grapes and stone fruit. Major pests include navel orangeworm, mealybug, carpophilus beetle, mites and scale insects.
Prior to joining UC ANR, Mokwunye worked as a nut crop entomologist at the Cocoa Research Institute of Nigeria for over 15 years and headed its Crop Protection Division.
“My journey into entomology as a career started when I was posted to the Cocoa Research Institute of Nigeria for the mandatory one-year National Youth Service Corp,” Mokwunye said.
“I was really fascinated at the diversity and economic importance of the insect species (both beneficial and pests) on agricultural crops and natural landscapes generally,” she said. “The hands-on lab experiments and field activities were exciting, engaging and inspiring. I was actively involved in setting up experiments, data collection, data entry and informal discussions on research projects. I was seeing the insect world in an entirely different perspective.”
She already held a bachelor's degree in zoology from the University of Lagos, Nigeria.
“The then-head of the department observed my interest and encouraged me to get a master's degree,” said Mokwunye, who then earned a master's degree in entomology from the University of Ibadan, Nigeria. “During the course of the second degree, I got a job in the same institute and today the rest is history.”
Mokwunye holds a Ph.D. in entomology from the Federal University of Agriculture Abeokuta, Nigeria. Her research interests include integrated pest management, chemical ecology, extension entomology and economic entomology. She has worked on the population dynamics of the cashew stem girdler as it correlates with weather parameters, its damage potential, semiochemical interactions and chemical control of insect pests.
She has served as a resource person engaging stakeholders in outreach activities and facilitating training programs on good agricultural practices. In addition to publishing more than 25 research articles, she is a fellow of African Women in Agricultural Research and Development, Orange Knowledge Program of the Netherlands Government, and Scientific Exchanges Program of the USDA.
“I am delighted to be here as a UC Cooperative Extension advisor and I hope to bring my expertise and experience in pest management to bear,” she said. “I plan to connect and engage meaningfully with my clientele in order to understand their needs, priorities and perspectives regarding pest management issues.”
Mokwunye is based at Kearney Research and Extension Center and can be reached at (559) 807-0257 and imokwunye@ucanr.edu.
UCCE water advisor Garza hopes to foster ‘spirit of shared responsibility'
Laura Elisa Garza Díaz joined UC ANR on Jan. 3 as the UC Cooperative Extension water quality, quantity and climate change advisor for Lake and Mendocino counties, focusing on how intensified droughts, floods, wildfires and other climate impacts affect water supply and quality.
She aims to address Sustainable Groundwater Management Act requirements and enhance local water resilience in collaboration with farmers and natural resource managers, local government water agencies, water districts and other key stakeholders.
In addition to guiding policymakers in creating comprehensive water-resiliency plans covering development, storage, alternative sources and conservation, Garza – who is fluent in Spanish – will share water research with a diverse range of communities.
“I aim to empower local stakeholders by providing them with the knowledge and tools needed to navigate the complex landscape of water quality, quantity and climate change,” she explained. “My goal is to foster a spirit of shared water responsibility, and ensure that water management practices consider the needs of all – for a more just and inclusive environment for everyone.”
Originally from Monterrey, Mexico (“the city of the mountains,” as she puts it), Garza earned her bachelor's degree from Tecnológico de Monterrey. After completing an Erasmus Mundus joint master's degree program in applied ecology, Garza worked as a specialist with the Water Center for Latin America and the Caribbean.
While pursuing her Ph.D. at UC Davis, she served as a scientific advisor for Pronatura Noroeste, an environmental protection organization, and started the Women in Science Interview Sessions at the Permanent Forum of Binational Waters, where she volunteered. It is an initiative to interview women who have worked or researched water topics in the Rio Grande/Rio Bravo Basin.
After obtaining her Ph.D. in hydrologic sciences from UC Davis, Garza worked as a project manager for the Washington Water Trust in Washington.
At every step of her journey, Garza has been motivated by a deep passion for safeguarding water resources and fostering resilient ecosystems and communities.
“I find inspiration in the intersection of science, community engagement and sustainable water management,” she said. “The opportunity to contribute to the well-being of local communities and the environment drives my commitment to addressing water challenges in a changing climate.”
Based at the UCCE office in Ukiah, Garza can be reached at legarza@ucanr.edu and (707) 463-4495.
Agyeman joins UCCE as economics advisor for Butte, Glenn and Tehama counties
Domena Agyeman joined UCCE Jan. 3 as an agriculture and natural resources economics advisor for Butte, Glenn and Tehama counties.
Prior to joining UC ANR, he was a postdoctoral associate at the Virginia Seafood Agricultural Research and Extension Center at Virginia Tech University.
As a UCCE advisor, Agyeman will provide insights that ensure economic profitability of all agriculture activities, including orchards, rice, forestry and other natural resources-based businesses in those counties. He will also promote broadband access and contribute to regional economic development.
“I am excited to leverage my expertise to highlight the economic contributions and impacts of the agriculture and natural resources industries in Butte, Glenn and Tehama counties,” Agyeman said, “and to provide producers and other stakeholders in the region with research-based information that will help them navigate their business challenges and opportunities.”
His research interests encompass natural resources and environmental policy impact assessments, economic contributions and impacts analyses, producer decision-making assessments, and consumer preferences assessments.
“To get started, I will be doing a needs assessment, focus group meetings and surveys of target groups,” he said.
Agyeman earned a Ph.D. in agricultural economics from the University of Kentucky, a master's degree in agricultural economics from Mississippi State University and bachelor's degree in agricultural science from University of Cape Coast in Ghana.
Agyeman is based at the UCCE office in Oroville and can be reached at dagyeman@ucanr.edu.
Marsh named rice advisor for Colusa and Yolo counties
Sarah Marsh joined UCCE on Jan. 3 as a rice farming systems advisor serving Colusa and Yolo counties.
Prior to joining UCCE, she worked in rice breeding research and integrative pest management with several row crops in the Upper Gulf Coast region.
She earned a master's degree in horticulture and agronomy at UC Davis, where she worked with Kassim Al-Khatib, professor of plant sciences, studying weeds and herbicide resistance in rice agroecosystems. She holds a bachelor's degree in plant and environmental soil science from Texas A&M University.
“I grew up on a diversified row-crop and orchard farm in Arbuckle and am grateful for the opportunity to serve the community in which I was raised,” Marsh said. “I hope to spend the first few months getting to know the growers and community of this region and learning what the unique needs of our area are.”
Marsh is based at the UCCE office in Colusa and can be reached at smarsh@ucanr.edu and (530) 415-7052.
Woelfle-Hazard joins UCCE Humboldt-Del Norte as fire advisor
Cleo Woelfle-Hazard joined UCCE on Jan. 3 as a fire advisor for Humboldt and Del Norte counties. He will support residents, landowners, planners, land managers, tribes and Native fire practitioners in making North Coast communities more resilient in the face of intensifying wildfires.
His research and extension programs focus on climate resilience, cultural burning, fire-water interactions and training a diverse fire workforce.
Woelfle-Hazard collaborates on research with Native nations, agencies and local community members. In collaboration with the Karuk Department of Natural Resources, he is exploring future fire scenarios in the Klamath Basin and how streamflow would change. They are also exploring how fire and flooding can be renewed to revitalize habitat for ecocultural species such as willow, grape, salmon, elk and eel.
His past projects have included community-directed river research with frontline communities in Seattle, the Yukon-Kuskokwim Delta and Sonoma County. Using his expertise in home water and wastewater systems, he evaluated health and economic aspects of water delivery in Oakland and Hubli-Dharwad, India.
As a co-investigator on the Humanities Education for Anti-Racism Literacy project, Woelfle-Hazard collaborated on creating pathways to higher education for Native youth, and for training students to engage in respectful collaborations with Native partners.
He earned a master's degree and Ph.D. in energy and resources at UC Berkeley, where he convened scientists and Sonoma County residents to experiment with capturing winter rain to increase summer streamflow to benefit juvenile salmon, and exploring the possibilities of working with beavers to create cool refuges for coho. He also holds a bachelor's degree in interdisciplinary geosciences from the University of Montana.
Woelfle-Hazard is based in Eureka and can be reached at cwhaz@ucanr.edu.
Jegede joins UCCE as agricultural toxicology specialist
Olukayode “Kayode” Jegede joined UC ANR on Jan. 2 as an assistant professor of Cooperative Extension for agricultural toxicology with the Department of Molecular Biosciences, School of Veterinary Medicine and Department of Environmental Toxicology in the College of Agricultural and Environmental Sciences at UC Davis.
Jegede will be studying contaminants of agricultural importance in California, such as pesticides, metals, microplastics, veterinary pharmaceuticals, PFAS, fertilizers and their effects on humans, animals (including aquaculture) and environmental health of soil and plants.
“I will also be looking at various exposure pathways of these contaminants and interactions through food, water, soil and how climate change or other major environmental change events can influence toxicity of these contaminants and mitigation strategies,” Jegede said. “My research will also have a “one-health” perspective to it.”
Prior to moving to California, Jegede was a postdoctoral research associate at the Department of Soil Science, University of Saskatchewan, Canada for a year before moving to Wageningen University and Research in the Netherlands to work as a research scientist focused on terrestrial ecotoxicology.
His past research has examined the effects of metals, pesticides and mixture toxicity on soil biota (mites, springtails, snails, earthworms) and soil enzymes, related ecosystem service function and generating data for environmental risk assessment of metals and pesticides.
“I look forward to helping solve toxicology issues in California through research, advising on and promoting good health for everyone and everything connected to small and large-scale agriculture in California.” Jegede said.
He earned his Ph.D. in toxicology at the University of Saskatchewan in Canada and bachelor's and master's degree in zoology at the Obafemi Awolowo University in Nigeria.
Jegede is based at UC Davis and can be reached at ojegede@ucdavis.edu.
- Author: Jorge Antonio Angeles
- Posted by: Gale Perez
Silverleaf nightshade, Solanum Elaeagnifolium, is perennial weed that is native to South America, Mexico, American Southwest and Southern States. This herbaceous and woody summer weed belongs to Solanaceae just like other weeds such as black nightshade (Solanum nigrum), hairy nightshade (Solanum physalifolium) and horsenettle (Solanum carolinense). It can be found throughout California and in grows in desert and semi-arid areas. Silverleaf nightshade is often found growing in different cropping systems, rangeland, pastures, roadsides, and disturbed areas. Silverleaf nightshade is highly adaptable and can tolerate a wide range of soil and climatic conditions such as high temperatures, low rainfall, saline and drought conditions. The leaves and berries produced by silverleaf nightshade plants have glycoalkaloid compounds that can be toxic to livestock and humans if consumed (UC IPM) (Boyd 1982).
Life Cycle
Impacts
Silverleaf nightshade is becoming a problematic weed in some young pistachio orchards in Tulare, Kings and West Fresno. This perennial weed is mostly found in young orchards that are planted on west Fresno and Kings County by interstate 5 highway (Figure 3). In Tulare County, silverleaf nightshade is found pistachio orchards that were planted in unmanaged fallow land or in fields near roadsides where it's commonly found. One of the major impacts of silverleaf nightshade is that it competes with young pistachio orchard for resources such as water, light and nutrients. If left unmanaged, silverleaf nightshade can also interfere with irrigation operations and potentially reduce crop vigor in young pistachio trees (Figure 2). Since silverleaf nightshade can adapt to alkaline and saline soils, it will also outcompete many of the summer annual weeds and become the dominant weed in the population.
Management
Silverleaf nightshade can be a weed that is difficult to control with the available management methods in orchards. Tillage is not recommended as that is one of the ways that rhizomes can be spread across the orchard (Ensby 2011). Mechanical control methods such mowing can be an effective control method to prevent weeds from setting seed. Flail mowers are often used in orchards and vineyards to mow weeds in between tree rows. It is important to note that, new silverleaf nightshade shoots will potentially sprout from the root system after the tops are mowed (Stanton 2011). Even though mowing can be an effective weed control method during the growing season, most commercial mowers will miss the weeds that grow in between trees that directly compete with young trees. Hand weeding can be used to remove some of the weeds around the trees, but extra precaution needs to be taken. Mature silverleaf nightshade plants are covered in reddish prickles that can be harmful if weeds are handled with bare hands. Weeding tools such as shovels and hula hoes can damage surface drip hoses if the user is not careful.
Herbicides can be an effective weed management method to control silverleaf nightshade in different tree crops. There are a twelve pre-emergent and thirteen post-emergent herbicides with different sites of action that are registered for use in pistachios (Table 1). Pre-emergent herbicides are normally applied during the dormant season and most only control weeds before they germinate. Pendimethalin, rimsulfuron, mesotrione, flumioxazin, isoxaben, and flazasulfuron are herbicides that have great control over black and hairy nightshade. Isoxaben can suppress silverleaf nightshade, but cannot be used in pistachios that have not been established for at least three years. Pre-emergent herbicides will not control silverleaf nightshade that emerges from rhizomes in the summer. Post-emergent herbicides can be used to control silverleaf nightshade that emerges in the summer and early fall before harvest. Glyphosate, glufosinate, pyraflufen, and carfentrazone are post-emergent herbicides with different sites of action that can be used to control different weeds and can be used up to two weeks before harvest. 2, 4-D is another post-emergent herbicide that is registered for use in pistachios, but needs to be applied to trees that have been established for at least one year and has a pre-harvest interval of 60 days. Research work from other researchers has shown that glyphosate and 2, 4-D have excellent control of silverleaf nightshade (DiTomaso 2013) (Gitsopoulos 2017). Glyphosate is a systemic herbicide that can potentially kill the root system of silverleaf nightshade, when applied at the correct timing and rate. Since Silverleaf nightshade has extensive rhizome root systems, the root systems need to be killed to fully control this weed. In the summer months, a combination of mowing and the use of post-emergent herbicides can kill the aboveground tissues of silverleaf nightshade weeds and deplete the root bank in the soil (Heap 2018). Post-emergent herbicides need adjuvants such as nonionic surfactants, crop and seed oils, to increase their efficacy. Furthermore, always consult the herbicide labels on information regarding information on the required adjuvants, pre-harvest intervals, application rates and maximum applications per seasons.
The weed management tools to control silverleaf nightshade in pistachio orchards are limited. Developing and maintaining field records before planting is a great way to determine the history of a field before planting. Conducting weed surveys in the winter and spring can help determine what weed species are present in a field. Silverleaf nightshade populations can be reduced by mowing in between tree rows and applying herbicides to weeds present in between trees. These management practices need to be done before the weeds set seeds to contribute to reduce the seedbank. To avoid introducing silverleaf nightshade to other fields, it is important to sanitize tractor equipment and manage the weeds that grow on the field edges or near irrigation canals (. To have an effective silverleaf nightshade management program, a combination of herbicides with different modes of action are needed decrease the possibility of it developing herbicides resistance. Silverleaf nightshade is difficult to control because of its tolerance to many herbicides (Gitsopoulos 2017). During the summer months, it is best to use a combination of systemic and contact post-emergent herbicides to get higher levels of control for silverleaf nightshade. To enhance the efficacy and herbicide absorption, post-emergent herbicides require adjuvants such as methylated seed oils, non-ionic surfactants, crop-oil concentrates, and nitrogen-based fertilizers.
Cited Literature
Boyd, J.W. and Murray, D.S. 1982. Growth and development of silverleaf nightshade (Solanum elaeagnifolium). Weed Science 30, 238-43.
DiTomaso, J.M., G.B. Kyser et al. 2013. Weed Control in Natural Areas in the Western United States. Weed Research and Information Center, University of California. 544pp.
Ensbey R. 2011. Noxious and environmental weed control handbook – A guide to weed control in non-crop, aquatic and bushland situations. 6th ed. New South Wales: Department of Trade and Investment, Regional Infrastructure and Services.
Gitsopoulos, Thomas & Damalas, Christos & Georgoulas, Ioannis. 2017. Chemical options for the control of silverleaf nightshade (Solanum elaeagnifolium). Planta Daninha. 35. 10.1590/s0100-83582017350100064.
Heap, J. & Wu, H. 2018. Silverleaf Nightshade: Australian best practice management manual. Primary Industries and Regions SA & NSW Department of Primary Industries: Adelaide.
Roberts J., Florentine. 2022. Biology, distribution and management of the globally invasive weed Solanum elaeagnifolium Cav. (silverleaf nightshade): A global review of current and future management challenges. Weed Res. 2022;62:393–403. doi: 10.1111/wre.12556.
Stanton, R. & Wu, Hanwen & Lemerle, D. 2011. Root regenerative ability of silverleaf nightshade (Solanum elaeagnifolium Cav.) in the glasshouse. Plant Protection Quarterly. 26. 54-56.
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- Author: Elizabeth J Fichtner
- Author: Santosh Bhandari
- Author: Jennifer Randall
- Author: Richard Heerema
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.
- Author: Ben Faber
So rain is great………as long as it doesn't cause problems like increased iron chlorosis, root rot, snails, erosion, too many weeds, etc., etc., etc, And now we are seeing more anthracnose. This disease is not normally much of a problem in dry California. Colletotrichum gloeosporioides, the causal fungus of the disease, is widespread in avocado and citrus groves. We see it frequently on small stems and branches, but It is normally of little importance on fruit because unusually large numbers of spores are required to produce damaging infections.
Disease on stems
Disease on leaves
Low humidity and no rain during much of the growing season limit disease development in California. With extended foggy or rainy conditions and mild winter temperatures, and where many dead leaves and twigs and mummified fruit accumulate in trees, the fungus can produce enough spores to cause a disease problem. Spores spread in splashing water and can cause infection anytime from fruit set to harvest. Once infected fruit starts to ripen, temperatures of 75°F and above will accelerate anthracnose development, while temperatures below 59°F retard disease development.
Disease on fruit - black speckles
Fuerte, Rincon, and Wurtz scion cultivars are more susceptible to anthracnose than Hass. Healthy trees often recover from foliar infections and defoliation once conditions become dry. Anthracnose becomes a postharvest problem after the grove has been excessively wet for extended periods. Poor growing practices and mishandling of fruit during or after harvest greatly increase the potential for significant fruit loss.
Anthracnose is controlled primarily with good cultural practices in the grove and proper preharvest and postharvest fruit handling.
- Prune out dead limbs and twigs where fungi sporulate. If many dead leaves are entwined in the canopy, knock them out of the tree.
- Prune low limbs to at least a foot off the ground to reduce humidity within canopies by improving air circulation.
- Prune and harvest only during dry conditions and minimize fruit contamination and injury.
More at UC IPM
https://ipm.ucanr.edu/agriculture/avocado/anthracnose/#gsc.tab=0
We do like the rain, so keep it up.