- Author: Lauren E. Parker, USDA Climate Hub
- Author: Tapan Pathak, UC Cooperative Extension specialist
CalAgroClimate web tools help farmers prepare for frost events
A cold snap damaged almond blossoms across the Central Valley, resulting in more than $44 million in crop insurance claimsin late February 2018. A multi-day frost event wiped out roughly 75% of California's citrus crop and severely damaged avocados in January 2007. Frost can damage crops, impact growers' bottom lines and drive up food prices for consumers. With advance notice, farmers may be able to use heaters, wind machines, irrigation and other tactics to lessen some of the impacts of cold weather, such as damaging near-ripe citrus fruit or killing the bloom in almonds.
CalAgroClimate is a new farmer-focused website that can help growers anticipate weather-related risks and make plans for taking defensive action. Growers and crop consultants can use CalAgroClimate's crop and location-specific tools and resources to help prepare for upcoming frost events. The website's tools can also support on-farm decisions for managing heat, crop development and pests.
Future holds less frost
The risk of frost damage to crops and the need to prepare for that risk is top-of-mind for many farmers today, but will it always be so? To examine what climate change might mean for future frost risk, researchers at UC Davis, UC ANR and the USDA California Climate Hub conducted a study examining the incidence of temperatures below multiple “frost thresholds” during the months of critical development phases for three frost-sensitive California crops: almonds, avocados and navel oranges.
The researchers found that even during the coldest winters and springs, the incidence of frost exposure declined under projected mid-21st century climate conditions by more than 50% for almonds and oranges, and by more than 75% for avocados. While farmers in 2050 will not find frost risk to completely be a worry of climates past, they will not have to contend with the same frost concerns that farmers face today.
Few aspects of climate change are considered “positives,” and although the warming winters and springs that result in reduced frost temperatures could also come with increased pest pressure, reduced chill accumulation and other challenges, the reduction in frost exposure is a silver lining.
However, until this frost-free future arrives, growers still need to be prepared to protect their orchards from frost. To assess frost risk for the next seven days for your location, check out the new interactive Frost Advisory Tool at CalAgroClimate.org.
- Author: Help Desk Team
Are you noticing that the leaves on your citrus trees are looking yellow, and wondering if now is the time to fertilize? We have some answers for you.
Should You Fertilize Now?
First of all, don't be too worried about the yellow leaves. The yellowing, especially the yellowing of the leaf veins, is related to a lack of nitrogen. Citrus leaves are frequently yellow in the winter due to the trees' inability to take up nitrogen in cold weather. But now, as the days get longer and the soil begins to warm, the trees are getting ready to pick up nitrogen from the soil which means we are getting closer to the start of the citrus tree fertilization process.
Citrus trees are typically fertilized at three points in the year. The first is in January or February just before the trees begin to bloom. Exactly when will depend on your microclimate and the trees' readiness. Given the climate differences In Contra Costa County, in west county, you may need to apply the first fertilizer in late January, while the trees in central and east county may not be ready until mid- to late-February.
The next application time is in May, with a third application in June if necessary. And that is it for the season. Avoid fertilizing any later in the year, since late-season fertilization can have adverse effects on the fruits, including reduced fruit quality, delayed fruit coloring, and rough rinds. Late-season fertilization can also cause off-season growth making the trees more susceptible to diseases, disorders, and pests. Frost damage and leaf miner infestations are two common problems with late-season fertilization.
What Kind of Fertilizer Should You Apply?
Nitrogen is the main nutrient that you need to provide. Contra Costa soils are typically deficient in nitrogen and citrus trees are heavy nitrogen users. There are many sources of nitrogen. An easy choice for the home gardener is an organic citrus fertilizer. Fertilizers are labeled with three numbers on the front of the package, indicating percentages of N (nitrogen), P (phosphorous) and K (potassium). Look for a fertilizer where the first number (nitrogen) is the highest of the three, e.g., 7-3-3.
Citrus can also suffer from micronutrient deficiencies including zinc or iron. Most organic fertilizers contain these micronutrients, but if the leaves on your citrus have yellow patches between green veins you may need to correct these deficiencies by applying a foliar application of a liquid chelated micronutrient solution as the new growth emerges in the spring.
You can check here on the signs of different nutrient deficiencies to get an idea of what you are dealing with: https://ipm.ucanr.edu/PMG/C107/m107bpleaftwigdis.html
No matter which product you are applying, make sure that you carefully follow all label directions on the amounts and timing of the fertilizer application. Avoid over fertilizing which can cause excessive new growth, making the trees susceptible to other disorders such as bacterial blast.
Micronutrient deficiencies can also occur if the soil is too acidic or too alkaline. Citrus trees can tolerate a pH in the range of 6.0-7.5, with 6.5 being optimum. Contra Costa soils tend to be on the higher, alkaline side. If you have taken the actions above and are still not seeing the results you want, a soil pH test may be your next step. You can use an off-the-shelf home soil test kit or send a soil sample to a commercial soil test company.
How Should You Apply the Fertilizer?
The fertilizer should be scattered evenly on the soil under the tree's canopy. Make sure that you distribute the fertilizer at least as far out as the drip line. Avoid the area near the trunk. Lightly scratch the fertilizer into the surface of the soil and then irrigate.
For more information on citrus fertilization, including guidelines on the amount of nitrogen needed based on the age of the tree, see: https://ipm.ucanr.edu/PMG/GARDEN/FRUIT/CULTURAL/citfertilization.html
For a full set of tips on growing citrus, see: http://ipm.ucanr.edu/PMG/GARDEN/FRUIT/citrus.html
We wish you the best with your citrus trees. Proper fertilization and care should provide you with healthy trees and tasty fruit.
Help Desk of the UC Master Gardener Program of Contra Costa County (ECS)
- Author: Ben Faber
Organic Citrus Growing Short Course
February 9-12, 2023
Course Overview
Seasoned citrus growers will provide detailed information appropriate for a range of growers, focused on a diverse range of citrus production. Presenters include Chadwick Garden Manager Orin Martin, Farm Garden Manager Christof Bernau, and Daniel Paduano Farm Manager and Co-owner of Abounding Harvest Mountain Farm.
This course will begin with an online introductory lecture on February 9th. Instructor Orin Martin will share a presentation on getting started with citrus that will include video demonstrations.
On February 11th, participants will begin the day at the UCSC Farm to learn about citrus planning, planting, pruning, and care with instructors Christof Bernau and Orin Martin. Participants will then spend an afternoon session at the Chadwick Garden on the UCSC campus. Orin Martin will tour participants through the garden's citrus trees from recent plantings to 50-year old trees to discuss rootstock/tree size and bearing, care/consideration for small citrus block, orchard floor management, seasonal ripening, irrigation delivery systems, and more.
The final session will take place on February 12th at Abounding Harvest Mountain Farm in the Santa Cruz Mountains. Daniel Paduano will tour participants through his citrus grove at this certified-organic farm specializing semi-tropical fruit and summer vegetables, sharing information on varietal differences, orchard management, irrigation, fertility, and more.
About the Instructors
Orin Martin is the author of Fruit Trees for Every Garden: An Organic Approach to Growing Apples, Peaches, Plums, Citrus and More (2020 American Horticultural Society Book Award Winner). Since 1977, he has taught classes, lectures, and workshops to thousands of students and other learners.
Christof Bernau has extensive experience in citrus management and has been teaching students, apprentices, home gardeners, and budding farmers with the Center for Agroecology since 1999.
Daniel Paduano is a graduate of the Center for Agroecology's Apprenticeship Program. Since 2006 he has managed Abounding Harvest Mountain Farm, which specializes in semi-tropical fruit including citrus.
Pre-registration for the course is required. The course carries extension credit from UCSC Extension and has a $200 fee. REGISTER FOR THIS COURSE
Scholarship Information
Scholarships are available. APPLY NOW FOR A SCHOLARSHIP
Course Schedule
- Thursday, February 9th, 5:30-7:00pm — Online introductory webinar
- Saturday, February 11th, 9:00am -12:00 pm — UCSC Farm; 1:30-4:00pm — Alan Chadwick Garden
- Sunday, February 12th, 9:00 am-12pm —Abounding Harvest Mountain Farm
See Also
- Author: Ben Faber
If the citrus fruit has a swollen stem end, it's called "sheepnose" and it's a swollen nipple or blossom end, it's also called "sheepnose". A swollen nipple is much more common. The fruit also tends to be coarse and the skin thick. Both terminal end conditions are thought to occur from too much vigor, low fruit numbers on a tree, high nitrogen, high temperatures at fruit set and early fruit formation and tends to occur more commonly with certain grapefruit and lemon varieties and rootstocks. Overlay that background with general tree care associated with irrigation and pruning and it's not always clear what the overriding factor is that creates these fruit. So then what brings all these factors together and how to prevent the condition is not at all clear. It doesn't appear every year in the orchards where it is occasionally found.
Tangelos and dekopons naturally have that necky stem end, and that's how you know you got one.
'Minneoloa' tangelo
- Author: Saoimanu Sope
Sugar-feeding ants protect pests that infect trees and damage the fruit they bear. Insecticides are often a go-to solution, but may kill beneficial insects in the process, too. Thankfully, Mark Hoddle, University of California Cooperative Extension entomologist and biological control specialist at UC Riverside, together with UCR colleagues in chemical engineering, developed a biodegradable hydrogel baiting system that targets ant populations, which protect sap-sucking pests from their natural enemies. Control of ants allows beneficial parasitoids and predators to greatly reduce pest populations.
Deciding to expand Hoddle's research was a “no-brainer” according to David Haviland, UC Cooperative Extension farm advisor in Kern County.
Haviland is investigating active ingredients that can be effectively used in hydrogel baiting systems. His research builds on Hoddle's use of alginate gels, also known as water beads, soaked in sugar water to control Argentine ants.
“What we're doing in California can benefit places like Florida, Texas, Mexico and beyond,” Haviland said.
The Hoddle lab conducted two years of orchard research showing that when ants are controlled, the amount of citrus flush infested with Asian citrus psyllid (ACP), a mottled brown insect that vectors the pathogen causing citrus greening, decreases by 75%. Citrus flush refers to newly developed leaves.
“But benefits are not restricted to just ACP with Argentine ant control, as natural enemies destroy colonies of other sap-sucking pests too,” said Hoddle. “For example, citrus mealybug infestations on leaves were completely eliminated by natural enemies, 100% control, while densities of fruit infested by mealybugs were reduced by 50%.”
The Hoddle lab's success inspired Haviland to consider how this approach will fare in different regions of the state where there are different crops, different pests and different ant species.
Haviland has worked for many years on solid baits that are effective and affordable for ants that feed primarily on protein, like fire ants in almonds, but successful control measures for sugar-feeding ants that drink their food have been elusive.
“Therefore, we're using hydrogels to essentially turn a liquid bait into a solid, making it effective and commercially adoptable,” Haviland said. He and his team are assessing whether active ingredients that undoubtedly work against ants, like thiamethoxam, maintain their effects in a hydrogel system.
Unlike Hoddle's biodegradable alginate gels, Haviland is relying on acrylamide gels that are similar to the absorbing material you would find in a diaper. These gels are not organic, but are currently accessible on a commercial scale, and have been shown to be effective in wine grapes on the North Coast by a Cooperative Extension advisor in Napa County, Monica Cooper. Haviland's current research efforts are focused on citrus, table grapes and wine grapes in the San Joaquin Valley, and on lemons on the coast.
The primary challenge now is navigating pesticide regulations and registration.
“This is cutting-edge research,” Haviland said, and manufacturer labels for the products being used need to be updated to include hydrogels as an approved use. This process takes time. Additionally, adding new product uses needs to make economic sense for the manufacturer.
Hoddle and Haviland's research can provide data for adding these methods to the product labels.
“If we can show that this tech works against lots of pests, lots of ant species, in lots of different crops across California, hopefully we'll achieve a critical mass of benefits that motivates product manufacturers to make modifications to their labels,” said Haviland.
Haviland is hopeful about the process, and said he believes that UC ANR is in a prime position to lead innovation for an issue that requires collaboration among specialists, advisors and the industry.
