Port Hueneme in Snow. January 11, 1949, I.N. Duggan.
Hail and lightning and thunder are not common along coastal Southern California, and when it happens, it's worth stopping and looking. On March 11, 2021, it fell from Goleta to the LA beaches. And it hit especially hard in some orchards from Moorpark to Ventura where it scarred fruit, especially young lemon fruit
It looks like feeding damage by stinkbugs or earwigs, but there aint no stink here. It's just the physical damage of the hail striking the fruit. If the fruit is small enough, in this case about an inch in diameter, the scaring will disappear with time. It will heal over, like wind scaring on young fruit. Older fruit, if they were scared, will carry it to the packinghouse and be downgraded.
Fortunately, this doesn't happen very often around here. About the same time, there have been similar storms and freezes in the Mediterranean that have caused havoc amongst all tree fruit growers, from Spain to Turkey. Undoubtedly, there is more whacky weather to come.
UC Cooperative Extension advisor Ramiro Lobo has found that the unusually beautiful fruiting cactus - pitahaya or dragon fruit - thrives in Southern California's mild climate. Pitahaya do well in regions where avocados are produced, but use much less water. They can also make excellent landscape plants, adding interest to the garden while producing healthful fruit.
Pitahaya fruit begin as large, showy, nighttime-blooming flowers, each of which contain male and female parts. In many of the most-desirable varieties, the anthers (the male part with pollen) and the stigma (the female part that needs to be pollinated) are separated by a distance that prevents night-flying pollinators, such as moths, from consistently making the connection.
For a uniform and bountiful crop, Lobo suggests hand pollination. Pollen can be collected by shaking a bloom over a bowl or trimming the anthers into a cup with a pair of scissors. He stores pollen in the freezer until the night or early morning hours when cacti bloom. He dabs up pollen with an inexpensive makeup brush and lightly swishes it onto the flowers' stigma.
“It's easy and takes just a few seconds per flower," Lobo said. "If you don't hand pollinate, you end up with fruits that are very small. And uniformity isn't there."
Hand pollination also allows farmers to accurately project their pitahaya harvest and work in advance with fruit marketing companies to sell the crop. Lobo said he carries a mechanical counter to click as he pollinates flowers. Forty days later, that precise number of fruit will be ready for harvest.
And here's his chart of the characteristics of different selections.
Are you interested in learning more about Nitrogen Management?
Are you a Certified Crop Advisor seeking Continuing Education Units and/or preparing for the new California Nitrogen Specialty Exam?
Has your grower clientele asked you if you are eligible to sign off on a Nitrogen Management Plan?
Registration for the brand new UC Nitrogen Management course is now open at
The UC Nitrogen Course is taught online through a video series delivered by UC Researchers and Extension Specialists. Each module is eligible for Certified Crop Advisor (CCA) continuing education units (CEUs).
The course is open to anyone interested in learning more about N management in California. The curriculum addresses all the learning objectives set forth by the American Society of Agronomy (ASA) for the new California Nitrogen Management Specialty Exam.
The 7-part video series starts Monday May 10th.
Register at http://ucanr.edu/NitrogenCourse
You may join the course at any time up until July 31st.
Avocado Leaves - on the left, low N; on the right, sufficient
UC Cooperative Extension Ventura County presents
Trees Make a Better World
A free five-part webinar series with James Downer, Ph.D.
April 22 & 29 and
May 6, 13 & 20, 2021
12:30 – 1:30 PM PDT
Webinar I: April 22, 2021
The Benefits of Trees
Trees enhance our environment by reducing pollution, providing oxygen, and increasing the physical and psychological well-being of people. Trees also save energy, help capture water and provide habitat for animals, insects and soil microbes that help keep carbon from our air. We can enhance the services trees provide by planting more trees. Before you can plant a tree, you have to choose one. This involves understanding tree morphology - what forms and shapes are available - and how tree genetics regulates development. Once the choice is made, selecting a well-grown tree that will perform as expected is very important. Size, condition, freedom from disease and defect are critical selection parameters. Inspecting trees in the nursery requires careful observation and you need to have a checklist of what you are looking for.
Webinar II: April 29, 2021
Trees often fail to thrive because they are improperly planted. The first phase of planting is to analyze the planting site: space to grow, soil, water, and sunlight. The site should be suited to the tree selected. Once the planting location is identified, planting can begin. Root washing! We will discuss timing of planting, how to make the planting pit, the role of organic materials, what goes in the backfill, fertilizer, mulch, and watering devices.
Webinar III: May 6, 2021
Trees often require pruning from the day they are planted into old age. While there are many reasons to prune trees, not all are effective or helpful. Pruning requires knowledge of trees, their physiology and growth, and responses to bud removal. Pruning should be frequent but strategic. For those that do not want to prune trees they will need to hire a tree-pruning contractor (arborist and tree worker). Selecting a qualified tree pruning contractor can be daunting. By understanding the basics, you can tell if your contractor is doing good work.
Webinar IV: May 13, 2021
Caring for Trees
Once your new shade tree has been selected planted and had its first pruning, the work for its survival is just beginning. Trees need water, nutrients, oxygen (near their root systems), and sunlight to grow well. Tree horticulture requires an understanding of a tree's growing needs.
Webinar V: May 20, 2021
Managing Tree Pests and Diseases
Trees like all plants are at times susceptible to insect and plant pathogen attack. New pests are arriving with increasing frequency. These can be dangerous to both native and ornamental shade trees. The first step in fighting tree pests is recognizing their damage and the signs and symptoms associated with their presence. Once identified, a control program can be developed to reduce the impact of tree pests on tree performance./h3>/h3>/h3>/h3>/h3>/table>/h2>/h2>
By Christopher Vincent, Anirban Guha, Joon Hyuk Suh and Yu Wang
It may surprise you to learn that citrus trees can get too much sunshine in the Sunshine State. Manipulating the light environment around a plant can have several surprising benefits. Shade can suppress the HLB cycle and enhance citrus health and yield. Overall, a mildly shaded citrus plant is likely to have fewer signs of stress, less HLB-spreading psyllids, less severe HLB symptoms and higher yield.
Our groups have joined with several others at the University of Florida to assess how shade impacts the various dynamics of pests, disease, plant health and horticulture. HLB is spread by Asian citrus psyllids landing on trees. Previous researchers observed that low light reduced psyllids landing on trees in a laboratory and that the shaded sides of trees in the field had fewer psyllids.
In our initial study at a natural forest site, we found it was difficult to find psyllids on feral citrus trees in shaded hammocks, and very few trees were infected with Candidatus Liberibacter asiatius (CLas), the bacterium that causes HLB. We think fewer psyllids land on shaded trees because psyllids use light reflecting off distant trees to locate them. If there is less reflection, the trees are less likely to be spotted. We also found very few symptomatic leaves in the forest site. Leaves showed few signs of stress to their photosynthetic machinery, regardless of whether the trees had HLB.
We followed our forest study by examining sweet orange in the field with 4-year-old Hamlin trees that were all infected and showed strong HLB symptoms. We installed shade netting with 30, 50 or 70% shade over the trees in late 2018 and followed their growth and health over two years.
There is evidence that the trees' health has improved, though they are HLB infected. When we performed a whole leaf metabolomic analysis in spring and fall, we found many changes in the metabolic profile, including prominent changes in leaf hormonal balance and the metabolism of sugars and nitrogen. In association with the hormonal changes, the shaded trees have less intense flushes, though their canopies are not less dense. This indicates the leaves likely have longer lifespans in the shade, counteracting an important symptom of HLB: leaf drop.
The shaded leaves had less foliar starch, meaning shade mitigates the typical starch accumulation induced by HLB. Along with the reduction in starch, the shaded leaves also accumulated more of the sugars involved in carbohydrate export from the leaf, indicating that phloem may be functioning more effectively, though this point needs more research.
These results, combined with evidence that leaf water status has improved, suggest that CLas-infected trees in the shade are healthier than in full sun. Thus, it comes as no surprise that shade improved yields. Over the two years of the study, the trees under 30% shade produced twice the yields of those in full sun.
Of course, too much of a good thing is still too much. Increasing shade beyond 30% continued to mitigate stress in the leaves but did not improve yields. Based on work done by our predecessors at the Citrus Research and Education Center, increasing shade intensity too much leads to a reduction in the flowering needed to set a good crop. The shade needs to be sufficiently moderate to help avoid the worst of the sun- and heat-induced stress while still spurring the trees to make fruit.
Despite these benefits, there are challenges to using shade in horticulture. Although shade netting is frequently used in some international citrus regions, such as South Africa and Australia, installing large shade structures may not be cost effective for many Florida growers.
A notable exception to this is the construction of many citrus under protective screen (CUPS) structures and individual protective covers that are installed on young trees. Although these are implemented as exclusion netting to prevent the arrival of psyllids on the trees, the nets also provide the environmental benefits of shade, including a warm humid environment that does not overload the leaves with too much light.
Particle films can also provide temporary, sprayable shade. These consist of particles that can be put in suspension and sprayed on leaves, leaving them to dry as a film.
Our ongoing experiments with kaolin particle films have demonstrated that these treatments also reduce disease pressure and leaf water deficit while enhancing tree growth and yield. We studied the application of red and white kaolin particle films over the first four years of a planting, where we saw the kaolin treatments more than quadrupled the yield compared with a treatment that used foliar insecticides to control psyllids.
We have also found that these treatments in young trees lead to larger, denser canopies and help avoid water stress when the soil water depletes. These treatments are cheaper than other approaches to shading trees and may be more effective in keeping Asian citrus psyllid populations low. Thus, particle films may be more accessible to many growers.
There is still much to learn about how different approaches to shade affect the health, ecology and horticulture of citrus. However, recent promising results indicate that manipulation of the light environment in the canopy is an approach worth considering. In the next few years, we hope to research and develop more effective and practical methods that can help growers find a balance of light for improving tree health and yields in the era of HLB.
Christopher Vincent and Yu Wang are assistant professors, Joon Hyuk Suh is a research assistant scientist, and Anirban Guha is a postdoctoral research associate — all at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.