- Author: Ben Faber
And doing it in the dark?
In a recent paper, David Pattemore and associates reveal some fairly different observations about avocado flowering. One, that the female stage can be open and potentially receptive to pollination at night. And Two, that moths and crane flies amongst other nocturnal insects are visiting the flowers and carrying pollen!!! These are two very new observations, made possible by the digital world we live in.
Of course, insect visitation doesn't mean fruit set. Is there pollination, transfer of pollen to the female stage? Is there enough pollen? Is it the right pollen? Is it the right temperature for fertilization to occur? Whatever else needs to happen for fruit set, is it happening?
But these observations are opening up new discussion topics for the avocado world.
LOW OVERNIGHT TEMPERATURES ASSOCIATED WITH A DELAY IN ‘HASS' AVOCADO (PERSEA AMERICANA) FEMALE FLOWER OPENING, LEADING TO NOCTURNAL FLOWERING
David Pattemore1,2*, Max N. Buxton1, Brian T. Cutting1, Heather McBrydie1, Mark Goodwin1, Arnon Dag3
1The New Zealand Institute for Plant & Food Research Limited, Ruakura Research Centre, Hamilton 3210, New Zealand
2School of Biological Sciences, University of Auckland, Auckland, New Zealand
3Gilat Research Center, Agricultural Research Organization, 85280, Israel
Abstract—Avocado (Persea americana) has synchronously protogynous flowers: flowers open first in female phase before closing and opening the next day in male phase. Cultivars are grouped based on whether the flowers typically first open in female phase in the morning (type A), or in the afternoon (type B). However, it is known that environmental factors can alter the timing of flower opening, with cold temperatures being shown to affect the timing of flowering. The aim of this study was to investigate how low spring temperatures in New Zealand affect the flowering cycle of commercial avocado cultivars, focusing primarily on the receptive female phase of ‘Hass', a type A cultivar. Time-lapse photography was used to assess flower opening times of ‘Hass' over three years. Decreasing minimum overnight temperatures were associated with a delay in the timing of ‘Hass' female flower phases and resulted in nocturnal flowering of both male and female phase flowers. We recorded insects visiting female flowers at night, and some nocturnal flower visitors collected were carrying avocado pollen. Our study suggests that nocturnal pollination needs to be considered for avocados grown in temperate regions. Furthermore, as the timing of the female phase of ‘Hass' varied significantly with overnight temperature, the activity patterns of potential pollinators need to be considered to ensure adequate pollinator activity across the range of times in which ‘Hass' flowers are receptive.
Eight different invertebrate orders were captured from avocado flowers at night. Coleoptera, Diptera and Lepidoptera were the most frequently caught floral visitors, but it was coleopteran, dipteran and neuropteran individuals that carried the greatest number of pollen grains on average. This is an important distinction to make, as not all floral visitors behave as pollinators: visitation does not necessarily infer pollination. Species such as Costelytra zealandica (Coleoptera), Micromus tasmaniae (Neuroptera), along with Tipulidae and Sylvicola species (Diptera) may be especially important, as these were both frequently caught and often carried a high number of pollen grains. Compared with diurnal pollination, nocturnal pollination is poorly understood and relatively little research in New Zealand has tested assumptions that nocturnal floral visitors can act as pollinators.
This is an interesting read and introduces further areas of pursuit to understanding what brings on fruiting in the wild avocado.
Read On:
click on Download this PDF file
Rhapsa scotosialis – a potential avocado pollinator?
- Author: Ben Faber
This is the most recent activity summary of a group of organizations working on the Invasive Shot Hole Borers and their associated fungal symbionts. This pest/disease complex affects avocado along with a large number of native and landscape plants in California, as well as in other parts of the world (http://ucanr.edu/sites/pshb/; http://ucanr.edu/sites/pshb/files/238251.pdf):
Invasive Shot Hole Borers
Quarterly Situation Report
January through March 2018
Executive Summary
Overview
Education, outreach, and monitoring activities were robust during the cool damp winter months of 2018. Infestations continued to dominate Orange, San Diego, and Los Angeles counties, with lesser activity in Ventura and Santa Barbara counties. The need for funding of research, education, outreach, and waste management associated with ISHB was brought to the attention of state governance. Preventative efforts to increase awareness of ISHB in unaffected counties continued. Collaborative efforts of numerous agencies, educational institutions, and non-profit groups resulted in the successful efforts listed below.
Statewide
The two-day Invasive Species Summit was held in the State Capitol for legislators and their staff to learn about environmental pressures and costs created by these species statewide. Three pieces of proposed legislation were written either specific to or with components addressing ISHB. They are: AB 2054 (Gonzlez Fletcher), AB 2166 – California Farm Bill, AB 2470 (Grayson) – Invasive Species Council.
The Statewide SHB Network convened telephonically to discuss ISHB, spread, threat, and help educate those in unaffected counties. An ISHB presentation was given at a statewide horticultural convention in northern California.
The triennial California Native Plant Society Conservation Conference was held near Los Angeles International Airport. ISHB was addressed at a pre-conference invasive species workshop, throughout the conference by tabling and poster session, and during the Invasive Species Session.
Regional
UCCE San Diego helmed a two-part GSOB/ISHB-FD webinar, along with other UCCE and CALFIRE collaborators. The first installment streamed in March.
UCCE San Diego began work on an online ISHB survey assessment tool that will be accessible when completed on PSHB.org. This feature will help the public determine if tree symptoms may be due to an ISHB infestation. An added component will allow UCCE to monitor reporting. The decision tree that is part of the assessment takes the reporter to part of the site whereby photos can be submitted if the tool determines a probability of ISHB infestation. This tool will be completed, tested, reviewed, and posted to the website by summer 2018.
San Diego County
- Two ISHB public educational events were presented
- Buy It Where You Burn It campaign distributed literature countywide
Orange County
- Four ISHB public educational events were presented
- Numerous trap and monitoring sites are established throughout the county primarily in wildlands and parks
- Orange County Waste and Recycling learned 28% of all trees at Prima Deshecha Landfill in San Juan Capistrano are infested with ISHB/FD or Botryospaeria. Most of the vegetation at this site is comprised of native species
- A post-incident GSOB/ISHB reconnaissance was conducted in Weir Canyon, where the Canyon II Fire burned in autumn 2017
- Orange County Parks continued to track tree losses and costs associated with ISHB infestations on its properties. An economic report was publicly released
Los Angeles County
- Three ISHB public educational events were presented
- A funding request was submitted to County governance to continue the ISHB trapping program coordinated by the Resource Conservation District of the Santa Monica Mountains
- The Huntington continued monitoring and green waste processing at the 207-acre facility. An ISHB trapping trial by principal investigator at UC Riverside was initiated that utilizes castor wood as the attractant
Ventura County
- Twenty-six traps are established and monitored in the Santa Clara River watershed extending from the estuary to Piru
- Fifteen traps are established and monitored in the Ventura River watershed. This number is down by two after being lost during the Thomas Fire
- A new infestation was identified in the City of Santa Paula proximal to a known infestation in the Santa Clara River
- One ISHB educational event was presented to Master Gardeners
Santa Barbara County
- Seven traps are being monitored in Montecito and the City of Santa Barbara
- Three traps in Montecito were lost from the January debris flow disaster
- One ISHB educational event was presented to Master Gardeners
San Luis Obispo County
- One ISHB educational event was presented to Master Gardeners
Articles:
A. Raver. The tiny menace. Landscape Architecture Magazine. March 2018.
https://landscapearchitecturemagazine.org/2018/03/13/the-tiny-menace/
Images:
Shot Hole Borer galleries, cottonwood
Shot Hole Borer entry point, sycamore. Curtis Ewing, CAL FIRE
- Author: Ben Faber
At a recent grower meeting at South Coast Research and Extension Center in Irvine, Carol Lovatt gave a talk on the use of gibberellic acid to increase avocado fruit set and yield. The registration for the use only occurred this spring, barely in time for growers to use it, so not many applied it. Then we had this heat wave in July and a lot of fruit, whether it had been treated or not, fell off. A show of hands was asked of the growers present, who had applied it this spring. Of the 100 people or so in attendance, only five raised their hands. Of course, this is not a scientific survey, but most would try it again this coming spring, even though they might not have seen results this year.
The following are guidelines that were provided on how to use it, if you should so choose this coming spring:
Use of ProGibb LV PlusR Plant Growth Regulator on Avocado to Increase Fruit Size and Yield
Carol Lovatt
Professor of Plant Physiology, Emerita, and Professor in the Graduate Division, Department of Botany and Plant Sciences, University of California, Riverside carol.lovatt@ucr.edu
ProGibb LV PlusR. On March 27, 2018, gibberellic acid (GA3) was approved for use on avocado to increase fruit size and yield. The only material registered for this purpose is ProGibb LV PlusR, a low volatile organic compound (LVOC) formulation, manufactured by Valent BioSciences, Corporation (Libertyville, IL). Only this product may be used; the older formulation sold under the name ProGibbR and other generic GA3 products cannot be used. Note: (i)the restricted entry interval is only 4 hours; (ii) the preharvest interval is 0 days; and (iii) ProGibb LV PlusÒ can be used in certified organic orchards.
Application Time. ProGibb LV PlusR is applied as a foliar spray at the cauliflower stage of avocado inflorescence development. The applications should be made when 50% of the trees in the block have 50% of their bloom at the cauliflower stage. This means that 25% of the bloom will be at an earlier stage of inflorescence development and 25% will be approaching bloom (open flowers). If you are unable to make the application at this time, being slightly late in applying the treatment affords better efficacy than being too early. Note: applications made at full bloom are typically not effective.
ProGibb LV PlusR Dose and Dilution Rate. The sprays should be applied like a pesticide spray to give full canopy coverage, especially of the developing inflorescences, but not sprayed to run-off. For ground application, use 12.5 fluid ounces of ProGibb LV PlusR (25 grams active ingredient [g ai]) in 100 gallons of water/acre. For aerial (helicopter) application, use 12.5 fluid ounces (25 g ai) in 75 gallons of water /acre. The maximum allowable dose is 25 g GA3 (active ingredient)/acre. Note: the results of our research documented that lower and higher doses are less effective.
Spray Solution pH. The final pH of the spray solution in our research was between pH 5.5 to 6.0. ProGibb LV PlusR is stable at pH 4.0 to 8.5. The pH of the water used should be adjusted accordingly. Note: prolonged exposure of GA3 to a pH > 8.5 should be avoided to prevent breakdown of the material.
Additional Information on Spray Volume. In our research, for ground applications, we used the same amount of GA3 (25 g ai/acre) but a spray volume of 200 to 250 gallons of water/acre, depending on tree size, to achieve good coverage without causing the material to run-off the tree and with minimum spray volume left in the tank after application. Use of spray volumes greater than label rate of 100 gallons of water/acre for ground application is the decision of the Agricultural Commissioner for each county. Consult with your County Agricultural Commissioner, if you wish to apply ProGibb LV PlusR (25 g ai) in more than 100 gallons of water/acre as a ground spray. For the aerial (helicopter) application, the greatest efficacy was achieved with ProGibb LV PlusR (12.5 fluid ounces, 25 g ai) in 75 gallons of water/ acre.
Wetting Agent. In our research, we used the organosilicone surfactant Silwett L-77R or Widespread MaxR (Loveland Industries, Greely, CO) at a final concentration of 0.05%. Similar pure organosilicone type surfactants are acceptable.
Photo: Cauliflower stage inflorescence. Source: Salazar-García et al., 1998.
- Author: Ben Faber
Wildlife isn't always restricted to wild spaces.
Avocado orchards and other agricultural landscapes also buzz with species that forage and reproduce in these spaces. Birds and herbivores are able to find food and shelter in these cultivated areas, but what about carnivores? In a study published in PLOS ONE, researchers at the University of Washington have discovered that mammalian carnivores also occupy avocado orchards in southern California.
The authors used motion-activated cameras to observe animals in orchards and in adjacent wild lands in Santa Barbara and Ventura. Avocado orchards were of particular interest due to their location near native vegetation.
Through their investigation, the researchers detected more carnivores in the avocado orchards than in neighboring wild land sites. At least 7 out of the 11 native carnivores in the area were spotted roaming the orchards, including bear, coyotes, gray foxes and bobcats.
Having delicious avocados handy may explain why some omnivores such as bears and raccoons are present in the area, however, little is known about why animals like bobcats and mountain lions might leave their wild habitat for cultivated land. One possibility is that the orchards provide water and fruits for herbivores, and an increased herbivore population could translate to more prey for the carnivores. The orchards may also serve as shelter, offering forest cover similar to oak woodlands in the area.
These native species cannot always persist in protected reserves, so it is important to learn how cultivated lands can serve their lifestyle and behaviors. The carnivores may not be searching for the perfect guacamole ingredient; however there is no doubt that the avocado orchards are serving as a habitat for a wide range of species.
Citation: Nogeire TM, Davis FW, Duggan JM, Crooks KR, Boydston EE (2013) Carnivore Use of Avocado Orchards across an Agricultural-Wildland Gradient. PLoS ONE 8(7): e68025. doi:10.1371/journal.pone.0068025
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0068025
- Author: Guy B Kyser
A recent request from the San Diego area has prompted the reposting of this blog by Guy Kyser, UC Davis Plant Sciences Specialist
http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=6296
A neighbor asked me to identify a robust perennial that keeps coming up in his garden. It had long, tropical-looking leaves and floppy racemes with small white flowers. This was a new one for me. Turned out it was common pokeweed (Phytolacca americana), a native of eastern North America. In the south some people eat it (poke salad), and a few southerners probably brought it west as a garden vegetable. But the whole plant is toxic if improperly prepared, so it's the fugu of weeds.
A couple of weeks later my daughter brought home a stalk of purple berries and asked if she could eat them. “No,” I said, “they contain numerous saponins and oxalates.” I began to wonder if there's more pokeweed around than I realized.
Then Gillies Robertson of Yolo RCD sent photos of a purple-berried plant found along a slough near Grimes. Common pokeweed again.
Pokeweed is in the Phytolaccaceae. This weed can grow to 10 feet tall. It dies back in winter then reemerges from the ground in spring, growing from a fat fleshy storage root. The leaves are large, 3 inches to a foot long and 1 to 5 inches wide, often with reddish stalks and lower veins. From August to October, pokeweed produces racemes of white flowers followed by reddish-purple berries. In its natural state, all parts of the plant, especially the root, are toxic to humans. Birds can eat the berries but sometimes act funny afterwards.
This plant can be found in most of the contiguous states. In drier regions, it prefers gardens and irrigated areas. Southerners with pokeweed experience suggest controlling it by digging up as much of the taproot as possible and/or by cutting off the stalks and painting the stubs with concentrated glyphosate (e.g. Roundup). Either way, treatments will probably have to be repeated until the plant's storage reserves are worn down. And it's a good idea to deal with pokeweed before it produces berries and seeds.
Since this is the first year I've seen it, and since I suddenly ran into it in three locations within a few weeks, I'm guessing that the common pokeweed population is expanding. This plant seems robust enough to cause some trouble if it becomes established in natural riparian areas.