- Author: Emily C. Dooley, UC Davis
Outbreaks similar to El Niño-influenced issues of the 1990s
The wave of atmospheric rivers that swept across the state this winter has created the right conditions for plant pathogens that haven't been seen for decades in California. University of California, Davis, plant pathologist Florent “Flo” Trouillas is getting more calls from growers and farm advisors concerned about potential crop damage.
“Generally, whenever you have rain events, you're going to have problems,” said Trouillas, a Cooperative Extension specialist who is based at the Kearney Agricultural Research and Extension Center in Parlier. “In wet years we get really busy because most pathogens need and like water.”
Trouillas is like a disease detective. He splits his time between the field and the lab, working to diagnose pathogens, diseases and other ailments that strike fruit and nut crops such as almonds, cherries, olives and pistachios.
On a recent visit to an almond orchard near Fresno, Trouillas joined Mae Culumber, a nut crops farm advisor for UC Cooperative Extension Fresno County. A few weeks earlier, the two had walked the orchard, taking note of the base of some trees that had gumming — a thick, jelly-looking substance indicating a pathogen had taken hold.
“A lot of what Florent is doing is trying to assess patterns on a landscape,” Culumber said. “Sometimes things may look like they are one thing, but it could be another problem.”
When the two returned weeks later, the amber-colored gumming had moved into the canopy, looking like gumballs stuck to branches, some of which were already dead. “It's getting out of control from before,” Trouillas says. “This branch was killed. This is widespread.”
From the field to the lab
Lab testing confirmed what Trouillas believed was the culprit: Phytophthora syringae, a pathogen that can affect almond crops but is rarely seen in California. If it is found, generally the site of infection are wounds caused by pruning, but that is not the case here, where the infection began in the canopy at twigs, or small branches.
It is a threat to a key crop, which according to the California Department of Food and Agriculture, generates $5 billion annually. The last time Phytophthora syringae hit California was in the 1990s after a series of El Niño-influenced storms. Trouillas, who has a photographic memory, remembered reading about it in an old manual.
“It's rare for California and one that we see mostly following atmospheric rivers,” he says.
“The disease will only happen following these extremely wet winters.”
Phytophthora is soilborne, mostly found in tree roots, and doesn't generally spread up into branches. But the intense storms created the right conditions for the pathogen to “swim” up trunks as winds blew spores into the air and rain dropped them back down into the canopy, Trouillas said.
Some of the trees in this orchard will die; others can be saved by pruning infected branches and applying a recommended fungicide, he said.
Identification, diagnosis, education
Trouillas is one of more than 50 Cooperative Extension specialists at UC Davis and each is charged with identifying problems and developing solutions for those issues in support of agriculture, the ecosystem and communities throughout the state.
In his role, Trouillas focuses not only on pathology and research but also on educating growers, nursery staff, pest control advisers and others in agriculture about ways to manage potential threats and how to prevent crop damage.
“His role is very crucial,” said Mohammad Yaghmour, an orchard systems advisor for UC Cooperative Extension Kern County. “He's not only on this mission to educate growers but he's also a source of education for us.”
Trouillas typically conducts one or two site visits a week, usually after a farm advisor reaches out about a problem they can't solve on their own.
“This allows us to be at the forefront of disease detections in California,” he said.
He likens these visits to house calls a doctor would make, only to fields instead. And one of those calls recently took him to a cherry orchard in Lodi.
“These guys help me quite a bit,” said Andrew Vignolo, a pest control adviser with Wilbur-Ellis who asked for a consult. “I bug them a lot.”
The visit starts like any consult in a doctor's office, only the questions come fast as they walk around the Lodi orchard where branches are dying, there is gumming and the trees appear stressed. Some look to be sunburned from exposure. Old pruning wounds show cankers, indicating that past disease treatments didn't get rid of whatever was affecting the trees.
Trouillas asks about the cultivar of the trees because some varieties are more susceptible to pests or diseases. He focuses on stress because that opens the door to disease.
Do they prune in the dormant winter months or in summer when pathogens are more prevalent? Does the soil get tested? How old are the trees? What about nutrition?
“I'm trying to figure out how they got infected so bad,” Trouillas said, walking the orchard. “Bacterial canker is a very mysterious disease.”
He thinks it might be a bacterial canker disease and shaves some bark to take to the lab for testing. He wants to come back next winter to take some samples to see where the pathogen is overwintering.
“We'll know in a few weeks if we have a fighting chance,” Vignolo said.
Be it Lodi, Fresno or elsewhere in the state, Trouillas focuses on local conditions. But what is learned in one field can be passed on to others, providing early warnings or advice for those in similar situations. “All these efforts at collaboration, from the field, to the lab, going through research projects, there's only one goal here — to help the farmers of California.”
/h3>/h3>/h3>- Author: Trina Kleist, UC Davis
Growers invited to participate in study by sharing their experiences
A multi-state team led by Patrick J. Brown has been awarded nearly $3.8 million over the next four years for a project to improve pistachio production as the industry faces warmer winters and scarcer water.
“We are at this unique point in history where we can do this,” said Brown, an associate professor in the UC Davis Department of Plant Sciences.
The project aims to ensure the industry can thrive in coming decades despite the challenges faced. Growers are invited to participate in the study, sharing what they already are trying in their own fields or supporting any aspect of the project. To discuss the possibilities, contact Brown at pjbrown@ucdavis.edu or (530) 752-4288.
The project includes research to ensure pollination, experiments to calculate irrigation needs amid water shortages, creating tools to improve public breeding programs, developing more efficient harvesting equipment, and economic analyses to ensure future pistachio cultivation is economically rewarding. Researchers hope to offer a guide for growers deciding whether to plant new orchards or remove existing ones.
“The success of California's pistachio industry, which is the top producer of the nuts in the world, has always relied on a strong collaboration between UC researchers and pistachio growers,” said project participant Florent Trouillas, a UC Cooperative Extension specialist in the UC Davis Department of Plant Pathology. “Research efforts must continue to address enduring and new challenges, improve sustainability and ensure the profitability of pistachio farming.”
The tasty, green nuts have blossomed into a $5.2-billion industry in California, thanks to their greater tolerance of dry lands and salty soils. The project aims to further improve their climate resilience by finding a rootstock that can thrive despite growing water scarcity and declining water quality projected over the next half-century. With millions of genetically distinct pistachio trees growing in the state, "we already have out there what may be the industry's next great rootstock," Brown said. "It's probably in some grower's field already. We just have to find it."
Researchers seek to pair that new rootstock with high-yielding scions – the producing part of the tree grafted onto the rootstock – to develop new combinations that can thrive in the different conditions across the state.
Trouble with “boy meets girl”
Pistachios, like many other tree crops, have male and female trees, and they require hundreds of hours of wintertime temperatures below 45 degrees Fahrenheit for the trees to flower in the spring. Wind blows the pollen from male flowers to female flowers, creating nuts.
Complicating the timing: Boy flowers and girl flowers generally require different amounts of winter cold to bloom. After a sufficiently cold winter, boys and girls flower together. But if the winter is warm, most of them will flower at different times, reducing pollination.
That happened in the winter of 2014-15, which saw unusually warm winter temperatures. The following fall, farmers harvested only half their expected crop, losing more than $1 billion, Brown said. Climate change is expected to provoke progressively warmer winters in the future, on average.
An additional complication: The boy scions come from a single variety, or cultivar, and the girl scions come from another single cultivar. "In California part of the problem is that we have been relying on a single male and single female cultivar," Brown explained.
A key part of this project will be to test new scions that can pollinate efficiently despite warmer winters. “We now have additional male and female scions released in the last 10 to 15 years, but we need more information on their chill requirements,” Brown said.
Growing importance of pistachio sector
With nearly 520,000 acres planted in California in 2021, pistachios are the fastest-growing tree nut crop in the state. Growers have doubled their plantings over the past decade, due to pistachios' drought tolerance and higher gross returns compared to other nuts, experts report. California dominates the industry, growing 99 percent of the nation's crop and nearly 60 percent of the world's crop, employing people in 47,000 full-time-equivalent jobs and creating $5.2-billion of total economic impact in 2020, according to American Pistachio Growers.
Brown's team is part of a wider effort at UC Davis to support the sector's growth and adaptation to climate change. Other department members participating in the project include co-directors Louise Ferguson, a UC Cooperative Extension pomologist, and Richard W. Michelmore, a distinguished professor and director of the UC Davis Genome Center. Also participating are Giulia Marino, a UC Cooperative Extension specialist; and Grey Monroe, an assistant professor.
Other UC Davis participants include Trouillas and Brittney Goodrich, a UC Cooperative Extension specialist in the Department of Agricultural and Resource Economics. The project also includes researchers from UC Merced, New Mexico State University and Purdue University.
The four-year project was among nearly $70 million in Specialty Crop Research Initiative grants awarded this fall by the National Institute of Food and Agriculture. The Department of Plant Sciences landed three of the 25 grants.
Read the NIFA grant summary.
/h3>/h3>/h3>- Author: Ed Perry
If you do not prune your trees enough, they will become too tall to harvest, even with a tall ladder. If you have an unpruned fruit tree in your garden, you know that most of the fruit grows in the top. Yearly pruning is necessary to keep the tree at a reasonable height, for instance, no more than 10 or 12 feet high. If your tree is already overgrown, you may want to reduce its height gradually, say over a two-year period.
The main objectives of pruning mature fruit trees are to reduce the number and increase the size of the potential crop, to develop new fruit wood, to remove interfering and broken branches, and to contain tree height and spread for convenient harvest. Most fruit trees, when not pruned, produce more fruit than they can size and mature properly. You can prevent such overproduction with yearly pruning.
Persimmons, many figs, quinces and pomegranates bear fruit on current season's growth. When you prune these trees, remove old and weak branches, leaving some younger branches to produce new growth and fruit the coming year. Overcrowding and lack of sunlight will cause branches to die, so you need to thin out some branches to allow light infiltration into the tree so that the fruit wood stays healthy.
Nut trees such as almonds and walnuts do not need as much pruning for height control as fruit trees. You harvest nuts by knocking them down with a long pole, rather than by hand picking, so the trees can be much taller.
Fruit Tree Resources
Fruit Trees: Training and Pruning UC ANR Publication
The California Backyard Orchard For more details about training and pruning deciduous fruit trees.
Citrus and Avocado Trees Require Little Pruning For information on pruning citrus and avocado trees.
Ed Perry is the emeritus Environmental Horticultural Advisor for University of California Cooperative Extension (UCCE) in Stanislaus County where he worked for over 30 years.
/h3>
- Author: Kathy Low, UC Master Food Preserver of Solano and Yolo Counties
One of the many wonderful things about California's climate is that in many regions of the state you'll find orchards of walnut, almond, pecan, pistachio or chestnut trees. You may be growing or planning to grow one or more of these trees in your yard so you can enjoy consuming the nuts. But do you know how to safely store, and preserve these fresh nuts?
There are just a few simple steps to follow. First, be sure to promptly remove the hull (the fibrous outer covering) that may still be remaining on some of the nuts. (If you have hulled walnuts before you will know they'll stain your hands brown, so you should wear gloves to hull walnuts.)
During this time of COVID-19, you may be tempted to wash your fresh nuts, but don't. Washing the nuts in their shell could increase their moisture and provide the environment for mold or bacteria to grow. Although not required to safely store the nuts, to decrease the likelihood of walnuts, almonds, pecans and pistachios developing mold, you may want to dry them. For walnuts and almonds, spread them out preferably single layer on a flat screen or tray that allows good air circulation. To prevent birds and other critters from making off with them while they are drying, cover them with another screen or plastic netting. Stir and move the nuts around daily.
It will take several days for them to dry. To determine when they are sufficiently dry, remove the shell from several nuts. Break apart the almond kernels, or walnut meat. If they are rubbery, they're not dried sufficiently. If they are crisp or brittle when broken, then they are dried adequately.
For pecans, they should be dried slowly in air temperatures 75–85 degrees Fahrenheit to prevent the shells from cracking. A fan blowing on the nuts will speed up the drying process, which can take up to 10 days. The pecans are dry when they're brittle and the membrane between the kernel halves separate easily from the kernels.
Pistachios can be dried in the sun on a plastic tarp, or they can be dried in the oven at 140–160 degrees Fahrenheit for 10–14 hours. They are dried when the kernels are crisp, but not brittle.
Before consuming or storing at room temperature, fresh home-grown walnuts, almonds, pecans, pistachios or chestnuts, or those bought at farm stands, pasteurize them to kill any insects or insect eggs. To pasteurize, simply place them in the freezer for 48 hours. (Make sure your freezer is set at 0 degrees Fahrenheit or lower.)
To store your walnuts, almond, pecans or pistachios, place them in clean moisture free, odor tight packaging, such as glass or plastic jars or other containers. The nuts can be stored shelled or unshelled. They can be stored up to a year in your refrigerator set at 40 degrees Fahrenheit or lower. Almonds can be stored in your freezer (set at 0 degrees Fahrenheit or lower) for a year or more, walnuts and pecans for two years plus, and pistachios for three years.
Chestnuts are different from the other nuts because they're more like potatoes than tree nuts. They usually develop mold within two weeks if stored at room temperature. Unshelled chestnuts can only be stored for two to three months in the refrigerator, but shelled chestnuts can be stored for a year in the refrigerator. Both shelled and unshelled chestnuts can be stored in the freezer for one year or more.
Enjoy your stored nuts throughout the year!
For more information about the UC Master Food Preserver Program, including the Food Preservation Video Library, visit mfp.ucanr.edu.
- Author: Ben Faber
Here's an example of the kind of information that can be both exciting and disappointing - forecasts of the future of the citrus and avocado industries and many other fruit and nut crops. The latest forecasts are available form the USDA - Economic Research Service:
https://www.ers.usda.gov/webdocs/publications/92731/fts-368.pdf?v=7239.3
Wednesday, April 24, 2019
Imports play a significant role in meeting the U.S. demand for avocados. Since the mid-1990s, imports of avocados have grown sharply as per capita consumption has grown, representing 87 percent of domestic use in the 2017/18 marketing year. USDA forecasts that imports will make up an even larger share of supply in 2018/19, mainly because California's crop is expected to be smaller than in recent years. Contributing factors to this reduced crop include record-breaking heatwaves in July 2018 followed by record-breaking wildfires, as well as recent rains and cold weather, and the general alternate-year-bearing nature of avocado trees (whereby a large crop one year is followed by a smaller crop the next year). Because over 80 percent of all U.S.-produced avocados each year are from California, California's low harvest in 2018/19 should boost U.S. demand for imported avocados (especially from Mexico) even higher than it has been in recent years. If USDA's forecast is realized, imports in 2018/19 will represent 93 percent of the domestic avocado supply. This chart appears in the ERS Fruit and Tree Nuts Outlook newsletter, released in March 2019.
Fruit & Tree Nuts
Provides current intelligence and forecasts the effects of changing conditions in the U.S. fruit and tree nuts sector. Topics include production, consumption, shipments, trade, prices received, and more.
https://www.ers.usda.gov/webdocs/publications/92731/fts-368.pdf?v=7239.3
Can the past foretell the future?
/h3>/h2>