UCCE Ventura County- Blogs
Avocado Phenology
Farm Advisor UCCE Ventura County
Plants, therefore avocados, go through different growth stages, so called phenological stages, regular periods where they grow and differentiate from seed to various vegetative stages, flowering and finally seed production. Avocado has a preset pattern of phenology that occurs depending on variety and where it is grown, driven by light, temperature, water availability and often by different stresses, such as cold, heat, and heavy or light crop load.
The successive stages of avocado phenology are demonstrated in the photomontage below, from bud break to harvestable fruit:
Main phenological growth stages of ‘Hass' avocado according to the extended BBCH scale. From: http://avocadosource.com/journals/elsevier/scientiahort_2013_164_434-439.pdf
And, depending on where in California the avocado is growing, the latitude, or on what side of the slope (in the shade or full sun, on the top of the slope, etc.), the tree will go through these successive stages at different times of the year, offset by weeks or even months. A general plan for the California coastal region was developed from accumulated experiences and tests by a variety of groups and is shown below:
Research-based information that allows producers to anticipate the regionally appropriate times for major phenological evets is limited in California. From work conducted at South Coast Research and Extension Center in Irvine, the onset of flowering in early March extends into May, normally, and the main fruit set period is between mid-April and May. In later work from the same location, a mean beginning bloom date for “on” and “off” crop years differed between Julian date 66 (March 7) and 80 (March 21), respectively. From avocado research in Carpinteria, flower abscission (as a measure of bloom) during “on” and “off' crop years peaked on two different Julian dates, (May 4 and June 2). Mid-June has been reported as the middle of the commercial ‘Hass” season for the Irvine area. Harvest in Santa Barbara and San Luis Obispo Countries may just be staring in mid-June and continue through November in the most northern growing areas.
Difference in crop development impact the timing of cultural practices, such as fertilization, irrigation, phytophthora treatment, pollination and gibberellin sprays. For instance, nitrogen fertilization is often recommended by month of the year, rather than growth stage of the tree. Several recent efforts indicated that the timing of nitrogen fertilizer may have significant impacts on yield and that two times the fertilizer rates in April and November may result in substantial yield increase. Available information indicates the April timing might correspond to fruit set for the Irvine area compared to early bloom for Santa Barbara and San Luis. By November, Irvine's current year's crop may have been harvested three months previously. In San Luis Obispo, harvest may have just ended. So just going by date is insufficient for guiding many horticultural activities.
California's trees often have two crops maturing at the same time. It becomes especially pronounced the further north the production. The management of multiple crops on each tree becomes more important and more confusing as the length of time the fruit remains on the tree. Carrying two and even three loads of crop increases the potential for alternate bearing. Reduction in alternate bearing has been determined to be an important strategic requirement for California's growers. Understanding the impacts of cultural practices on alternate bearing is important. For example, the chart below demonstrates a stylized calendar of the avocado growth cycle for California. Rate and application timing of nitrogen as predicted by the Avocado Nitrogen Model proposed by Rosecrance et al. (2013 and Calculator) are noted for a 15,000 per acre yield outcome. The “on” year suggests nitrogen rate for the late fruit growth/harvest/summer and fall flush period is 15 lbs. This application coincides with the fruit set timing for 16 lbs of N for the “off” bloom crop during the later bloom/fruit set/spring shoot growth phase. Rates and timings to support these crops ought then be combined and represent the 2X fertilizer rate that Lovatt (2001) found to have significant effects on yields.
Calendar of avocado growth cycles with both “on” and “off” years represented when they overlap, and suggested nitrogen fertilization timings and amounts.
Taking into account the actual phenology, what is happening in your trees, then is important for assessing when to make N applications. In the winter and spring of 2023, it seems like everything was on a different cycle. Thrips delayed their appearance, flowering was erratic. Honeybees seemed to have found somewhere else to hang out, because they were not flying in the avocado trees. And then suddenly, we had some fruit set in Ventura in late June. This is a really clear example of the problem of following a cookbook to farming avocados. The point here is that just going by the calendar is not going to meet the needs of the tree. The phenological stages of the tree in your environment needs to be taken into consideration.
Notes:
Lovatt, C.J. 2001 Properly Timed Soilapplied Nitrogen Fertilizer Increases Yield and Fruit Size of ‘Hass' Avocado. J. Amer. Soc. Hort. Sci. 126(5): 555?559.
Rosecrance, R., Lovatt, C.J., 2013. Management tools for fertilization of the 'Hass' avocado. FREP final report.
Calculator: https://rrosecrance.yourweb.csuchico.edu/Model/AvoModel/Avo2NKModel.html
Phytoplasma Diseases in Palm?
Phytoplasma Diseases of Palms in the USA
Robert R Krueger1 and Brian W Bahder2
1USDA-ARS National Clonal Germplasm Repository for Citrus & Date, Riverside, CA
2Dept of Entomology & Nematology, University of Florida Fort Lauderdale Research & Education Center, Davie, FL
Phytoplasmas are plant pathogenic bacteria that lack cell walls and have reduced genomes. Their taxonomy has historically been based upon 16S ribosomal gene sequences. Since they have not been cultured to date, they are classified as Candidatus Phytoplasma spp. Phytoplasmas of various taxonomic designations have been associated with or shown to cause diseases in a wide range of cultivated and wild plant species. In recent years, long-established and newly reported declines or diseases of palms have been associated with phytoplasmas. Although there are reports of phytoplasma-associated diseases of palms in both the Eastern and Western Hemispheres, this brief review will focus on reports from the United States.
The earliest reported disease of palms that was later associated with Phytoplasma infection was Lethal Yellows (LY). LY is a disease which attacks and kills coconut palms (Cocos nucifera). LY was first reported in Jamaica in 1891 and much later (1972) associated with a phytoplasma (Tsai and Harrison 2003), which was later identified as being in the taxonomic sub-group 16SrIV-A (Harrrison et al. 2002a). An epiphytotic of LY occurred in southern Florida in the 1960's to 1970's (Tsai and Harrison 2003). During this outbreak Phoenix spp., which in Florida were planted as ornamentals or present in germplasm collections or botanic gardens were also shown to be susceptible. This was evidenced by the presence of mycoplasma-like bodies observed in tissues via electron microscopy (Thomas 1974, 1979; Howard et al. 1979). Phoenix dacytlifera was more susceptible to decline than other Phoenix spp., being equivalent in this regard to C. nucifera (Howard and Barrant 1989), although the symptomology was distinct compared to that in C. nucifera (McCoy et al. 1983). The vector of LY in Coconut palm was demonstrated to be the planthopper Haplaxius crudus van Duzee, and this was assumed to be the vector transmitting LY to Phoenix spp. as well (Howard et al. 1983, 1984).
There's a lot more to this story: https://ceventura.ucanr.edu/Com_Ag/Subtropical/?newsletteritem=100493
Foliar yellowing symptoms of Lethal Yellows on Coconut palm. Photo credit: NA Harrison
Phytoplasma disease palm
Watch Out for Fruit Flies
California inundated with invasive fruit flies
Bodil Cass
Extension Subtropics Entomologist, Dept of Entomology, UCR
California is experiencing an unusually high number of invasive fruit fly infestations. There are seven active regional quarantines in different areas of the state for four different species of exotic fruit flies in the family Tephritidae: Medfly (Ceratitis capitata) and Tau fly (Zeugodacus tau) in Los Angeles, Queensland fruit fly (Bactrocera tryoni) at the border of Ventura/Los Angeles, and four separate quarantine areas for the Oriental fruit fly (‘OFF'; B. dorsalis) in Riverside/San Bernardino, Contra Costa, Sacramento, and Santa Clara counties. A quarantine just ended following the successful eradication of an infestation of Mexfly (Anastrepha ludens) in San Diego County.
The OFF infestation in San Bernardino/Riverside is especially serious in terms of the unprecedented number of flies found and the many acres of commercial production affected. For this species, six male flies/one mated female/one larva triggers a quarantine, but here we have detected more than 500 adult flies and are still finding more, even during winter. The affected area, including more than 550 square miles, encompasses not just residential properties but an important agricultural region with commercial farms. Farmers in the area are bringing in more trained pesticide applicators, and facing crop losses, delayed harvests, disruption to integrated pest management practices for other pests, and increased costs as they act to mitigate the damage. The unfortunate proximity of the epicenter of the outbreak to agricultural production is necessitating some problem solving and adaptation of mitigation protocols as we race to stop the fly population from establishing.
The quarantine boundary is also approaching the edge of the California Citrus State Historic Park and the University of California Riverside campus, with fly finds less than two miles from active subtropical fruit and biological control research plots, the Givaudan Citrus Variety Collection, and citrus trees of historical importance. Researchers are gauging how the infestation and mitigation protocols might impact current experiments being conducted, including delayed harvest dates, and scrambling to adapt research plans accordingly.
Usually, we have one or two small exotic fruit fly quarantines per year, so the current situation is a strain on resources statewide. The number of areas invested and the severity of the OFF infestation in San Bernardino/Riverside are stretching resources thin as the Department of Agriculture pulls insect detection specialists and staff from other projects to help place more traps, enact compliance agreements, and visit residential properties. San Bernardino County is providing yard signs to help encourage residents not to move produce while the quarantine is in effect.
Exotic fruit flies are one of the most serious threats to food production in the state, with the estimated economic cost of any one of these Tephritidae species becoming established running into the $100 of millions through crop losses, additional pesticide use, and collapse of export markets. These flies are of concern because the larvae/maggots feed on fresh fruit and vegetables prior to harvest. The immature flies chew through the fresh fruit, and it rots on the tree or vine, or drops prematurely to the ground. Fruit infested with large maggots is not marketable to consumers and not fit for human consumption. They are much more damaging than other flies, like smaller Drosophila species that develop on fruit that has already matured, been harvested and is in compost. Tephritidae flies are also highly polyphagous, with some species attacking more than 100 types of fruit, vegetables, and nuts, including the major food crops produced in the state; citrus, avocado, dates, tomatoes, bell peppers, figs, grapes, cucurbits and many specialty crops are all at risk.
We have a long-standing success record of keeping fruit flies out of the state, and fully expect to achieve eradication of all the current infestations through an approach that consists of biological control (mating disruption by sterile insect release), chemical control (targeted pesticide baits), and physical control (destruction of infested fruit from the current season and restrictions on movement of fruit from infested areas). If you have questions about a fruit fly quarantine/eradication, or if you think you have fruits and vegetables infested with fruit fly larvae, call the CDFA Exotic Pest Hotline at 1 (800) 491-1899, contact your local Agricultural Commissioner, or the University's Cooperative Extension. More information specifically for growers is available at regional Farm Bureau meetings and on the CDFA website: https://www.cdfa.ca.gov/plant/PE/InteriorExclusion/current_grower_info.html#INTRO
Image of Oriental Fruit Fly
oriental fruit fly image
Avocado Field Day
You may have missed it, or you may want to relive it. Here's a video of the June 25 Avocado Field Day at Jackson Ranch in North San Diego County:
Field Day at Jackson Avocado Ranch
avocado cluster
A Strawberry FaeireTale
The way the strawberry industry grows plants really makes them a subtropical plant. The industry is located along the coast from Monterrey to San Diego, with the bulk around Salinas, Santa Maria and Oxnard. Oleg Daugovish looks after this industry from our office in Ventura. He's written a story that illustrates the whole industry, from where the mother plants are grown near Mt Shasta to the fields along the coast. It's a story that every Caifornia kid should read about.
Mt Shasta