By Cindy Watter, UC Master Gardener of Napa County
One day recently, while I was standing in my yard, a passerby asked me if the lemons on my tree were real. The gentleman was a tourist, and he doesn't see lemons adorning trees in January in Minnesota. I gave him a couple of lemons and told him to put them in his tea back at the hotel.
Mine is a Meyer lemon tree. This variety is found all over Napa, if you look. Meyers put out flowers year round but are especially fruitful in late winter and early spring.
I love the taste of Meyer lemons. They have a floral flavor and aren't as sharply acidic as Eureka lemons, the common supermarket variety.
Frank Meyer, who worked for the U.S. Department of Agriculture, imported the Meyer lemon from China to California in 1908. The plant is probably a hybrid of orange and lemon. It was intended as an ornamental tree, as it is very attractive and grows well in containers.
The Meyer lemon became popular because it is resistant to extremes of temperature, is relatively easy to grow, and the fruit is tasty. However, it has never caught on as a commercial crop beyond local markets because the thin-skinned Meyer doesn't handle storage and shipping well. I think access to Meyer lemons is a good reason to remain in California.
That 1908 casual crossing of international borders with plants would not be possible today. In fact, parts of some counties in southern California are under federal quarantine order because of citrus diseases that are highly contagious. Sections of Los Angeles, San Diego, Santa Barbara, Riverside and Orange Counties can't allow their citrus to cross the county line.
One particularly virulent citrus disease is caused by the Huanglongbing bacterium (Candidatus liberibacter asiaticus), which is spread by a psyllid, a tiny insect. The disease first appeared in Florida and has affected most of the citrus crops there. The psyllid, or vector, was seen in southern California in 2008. Huanglongbing disease came four years later.
When HLB strikes, the citrus leaves are mottled, the fruit is shrunken and discolored and the seeds are killed. It is devastating for commercial growers.
Research on how to fight HLB is ongoing, but the current treatmen is to put all trees under screenhouses and use insecticides on the psyllid. Interestingly, the first Meyer lemons were symptomless carriers of the tristeza virus. Because of this, the variety is banned in some citrus-producing areas. However, breeders have now given us the Improved Meyer lemon and virus-free clones.
HLB is a serious threat to a major part of California's agricultural economy. For this reason, you should only buy citrus trees, rootstock and budwood for grafting from reputable nurseries and university programs.
HLB was discovered in California on a grafted pomelo tree. Just say no to your friend from Santa Barbara who offers you budwood from her backyard. Don't even consider purchasing those tantalizing trees for sale by the side of the road down south. Planting them is too risky.
Spring and fall are the best times for planting citrus trees. Once you have your Improved Meyer lemon tree from a reputable source, planting is not difficult. Identify your yard's warmest area. Dig a hole as deep as the root ball and twice as wide so the roots can spread and form a sturdy base. University of California advisors do not recommend adding amendments to the soil unless it is almost pure clay.
If your tree comes in a plastic sleeve, lower the tree into the hole and cut the sleeve vertically to remove it. (Recycle it, of course). Pat the soil around the roots. Don't pack it in, but don't leave big air holes, either. If you cover the top of the root ball, use sand or sawdust so water will pass through rapidly.
Citrus trees have many shallow roots, so you shouldn't disturb the soil around them. Water the tree immediately after planting. Keep the root ball moist but not soggy until the roots grow into the surrounding soil.
Citrus trees like nitrogen fertilizer, but don't apply it until after the last spring frost Do not fertilize after the summer, as you don't want to encourage tender new growth in the fall.
Citrus trees are both beautiful and functional, and they can add value to your landscape. They are attractive all year round, with their shiny green leaves, fragrant blossoms and, of course, their fruit. They attract pollinators, too, so they benefit the environment.
The University of California at Riverside College of Natural and Agricultural Sciences website is a wonderful source of information and advice about citrus. The UCR Citrus Experiment Station, founded in 1908, is a tourist attraction today.
Read about the most promising research for treatment of HLB, from UC Riverside:
Got Garden Questions? Contact our Help Desk. The team is working remotely so please submit your questions through our diagnosis form, sending any photos to firstname.lastname@example.org or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email.
For more information visit https://napamg.ucanr.edu or find us on Facebook or Instagram, UC Master Gardeners of Napa County.
By Susanne von Rosenberg, UC Master Gardener of Napa County
If you're observant and you own citrus trees, you may have noticed that they usually have three flushes of growth each year–in spring, summer and fall. Young citrus trees and lemons tend to flush periodically year-round.
During the flushes we need to be extra vigilant. Why? Those new leaves are especially attractive to the Asian citrus psyllid (ACP), which is a carrier for a devastating citrus disease called huanglongbing (HLB). HLB eventually kills the trees it infects, and there is currently no cure. Before it kills the trees, it affects the quality of the fruit. The fruit becomes misshapen and the juice bitter.
HLB has been found in Southern California since 2012, and the state is working hard to contain and control it. The goal is to buy time for scientists to find a cure. At this point, University of California researchers have identified one promising predator of ACP, Tamarixia radiata. Tamarixia strongly prefers ACP nymphs and can significantly reduce psyllid populations. Tamarixia and other natural enemies have reduced ACP populations in Southern California, but they have not eradicated it and have not halted the spread of HLB.
The most effective way to buy more time is to control the spread of the psyllid. Without its carrier, HLB cannot spread. An ACP nymph (immature insect) takes the bacteria causing HLB into its body when it feeds on infected plants. When it flies away as an adult, the bacteria-carrying psyllid can feed on a healthy tree and inoculate it with the bacterium. It only takes a few psyllids to spread the disease.
You might ask why we look for ACP when we could just remove the infected trees. Detecting infected trees is difficult because it can take several years for symptoms to show. Meanwhile, psyllids can pick up HLB bacteria and spread them only a few weeks after the tree is infected.
We've been lucky in Napa County. There have been no confirmed cases of HLB in Napa County nor any confirmed detections of ACP. There were a few detections of ACP in our vicinity, but none recently.
In Florida, where HLB spread widely, citrus production has been cut by more than half. California is doing its best to avoid that fate for its citrus industry and the many California homeowners who have citrus trees.
All of us need to do our part to help prevent the spread of HLB. The most important things you can do are to monitor your citrus trees for the psyllid and comply with citrus quarantine rules.
When your trees put out new growth, check for evidence of the psyllid. ACP feeds on all varieties of citrus and several closely related ornamental plants, including calamondin, box orange and Indian curry leaf. Inspect the tiny, newly developing leaves on your citrus trees. Walk around each tree and check for signs of psyllid feeding and damage, including notched leaves, nymphs, honeydew, sooty mold or adult ACP.
If you think psyllids are present, use a magnifying glass to look for the sesame seed-sized yellow nymphs with their waxy tubules. Nymphs feed only on tender new leaves and don't fly, so looking for nymphs on citrus flush is most effective.
Each nymph produces a waxy tubule from its back end to help expel the sugary waste from feeding on sap. The tubule's shape—a curly tube with a bulb at the end—is unique to ACP and can be used to identify it. Adult ACP are tiny, mottled brown and about the size of an aphid or a grain of rice. Adults perch with their hind quarters angled up. (No other insect feeds like this.)
Other psyllids such as Eucalyptus psyllids, tomato psyllids and Eugenia psyllid can be found in home gardens. You can find images of the Asian citrus psyllid and its life stages on the UC ANR website at http://ucanr.edu/acp. If you find signs of the insect, call the California Food and Agriculture Exotic Pest Hotline at (800) 491-1899.
To comply with quarantine rules, do not transport citrus plants, budwood or plant material such as leaves out of your area. It's okay to move clean, washed fruit free of any leaves or stems. Also, please purchase the trees only from reputable nurseries. Do not accept tree cuttings or budwood from friends or relatives.
Drying out or double-bagging citrus waste after pruning or cutting down a citrus tree ensures that live psyllids won't ride into another region on the foliage. Controlling ants in and near citrus trees with bait will also help. Ants protect ACP from its natural enemies, as they do for aphids.
Food Growing Forum: Last Sunday of the month through October. Register to get Zoom link at: http://ucanr.edu/foodgrowingforum2020
Sunday, September 27, 3 pm to 4 pm, ”Harvesting Your Bounty and What Else to Do Now”
Sunday, October 25, 3 pm to 4 pm, “Planting Onions, Leeks and Other Alliums and What Else to Do Now”
Napa Library Talks: First Thursday of each month. Register to get Zoom link.
Thursday, October 1, 7 pm to 8 pm, “Creating Wildlife Habitat” http://ucanr.edu/wildlifehabitat2020
Pollinator Gardening, Sundays, 1 pm to 2 pm. Register to get Zoom link.
September 20– Introduction to Gardening for Pollinators
September 27 – Pollinators and the Plants They Love
October 11 – Caring for Your Pollinator Garden http://ucanr.edu/2020pollinatorpart4care
Got Garden Questions? Contact our Help Desk. The team is working remotely so please submit your questions through our diagnosis form, sending any photos to email@example.com or leave a detailed message at 707- 253-4143. A Master Gardener will get back to you by phone or email.
INTERESTED IN BECOMING A UC MASTER GARDENER OF NAPA COUNTY VOLUNTEER? Send us your information through our website request.
For more information visit http://napamg.ucanr.edu or find us on Facebook or Instagram, UC Master Gardeners of Napa County./table>