Ask Dr. Hort: Answers to citrus questions on bay area readers' minds

Time running out on tangerine tree's chances

Q: Our tangerine tree, which for many years has produced very good-tasting fruit, started to lose its leaves after the cold winter. Now it has only a few dead leaves. I have scraped back some bark, which shows green underneath, and the branches are not brittle even at the ends. Will it recover? I have put fertilizer around it and Epsom salts at the dripline. Bruce Hood, Palmetto

A: Citrus has leafed out now with its new spring coat, followed by flowers. If this is not the case, give it a few more weeks, and if there is no flush of growth, it's time for a new tree. Citrus succumbs to many diseases as it ages and some are more subtle than others.

Lack of blossoms likely connected to planting

Q: Two years ago I purchased a pink grapefruit tree. It produced fruit, but after the crop was picked and spring approached, the tree never produced blossoms for more fruit. We also have a lemon and an orange tree that have produced for years. They have had no problem blossoming. Judith Ann

A: There are a couple of possibilities. In the first three to five years after planting, a citrus tree is busy putting out a root system. Container size can be relevant. The larger the container, the longer the establishment period. Providing the tree is in full sun, it should flower next season. Tree growth should be noted: If there is no growth, it was planted too deep. With your hand, dig around the stem and feel for the first lateral root, meaning level with the ground. If it's not level, dig the tree up and set it at grade level or just a little higher.

Lemon tree with unusable fruit probably was grafted

Q: We have a lemon tree and I love lemons, but I have not been able to use them. We bought the house a few years ago and some of the lemons were good, while others were tart. They are big, like oranges, and have gotten even more bumpy in texture this past year. No lemons were good this year. What can we do? Debbi Gilmer

A: From examining the photos you sent me, your tree appears to be rough lemon, a common rootstock used for citrus grafting, especially 20 to 30 years ago. Grafting means a seedling of one variety is chosen (in your case rough lemon) for its vigor, disease resistance and adaptability to soil type, but not fruit quality. Then a bud from a quality fruit is joined to the seedling. When we have hard freezes the top of the tree may die and the rootstock grows to become the "new tree." This seems to be your scenario. If you like lemons, you should remove your existing tree and plant a Meyer, a very juicy lemon well adapted to our area.

Two are in need of Persian lime tree TLC

Q: I've had a Persian lime tree in a 2-gallon pot for about two years. It has given me a few limes. Right now it has lots of white buds. Is a particular time of year best for planting it in the sand in my back yard, and can you give me care instructions? Thank you. Andrea Jaeger

• • •

I just planted a second Persian lime tree; the first one died. Now I need advice on caring for the new tree. You're referenced in information available online from the University of Florida. Can you give me details? Thank you. Victor Huff, Safety Harbor

A: April is a perfect time to plant a lime tree, which gives the tyke seven to eight months to establish before cold weather arrives. Place directly into the planting hole with no amendments (potting soil, newspaper, peat moss), being sure to cut the rootball with sharp shears to get rid of encircling roots. Plant with the top of the rootball slightly higher than the existing soil, water into the hole, then backfill with soil. Create a soil saucer, a soil ridge 6 inches high, around the outside of the planting hole and pack tightly. Fill it with water every other day for six to eight weeks, then twice a week unless there is regular rainfall. Fertilize after six weeks with a quality citrus fertilizer, and again in August and October. You may observe some fruit drop because of the planting shock, but the loss of a few fruit now will reward you with a bounty next year.

The University of Florida's IFAS extension website — IFAS stands for Institute of Food and Agricultural Sciences — has a multitude of information on the culture and care of citrus and much more. Go to edis.ifas.ufl.edu.

The care and feeding of lemon trees

Q: I have a few questions:

• My citrus fertilizer instructions say "feed 1 cup in year 1, feed 2 cups in year 2," etc. Is that the first year in the ground or the first year of the tree's life? And how do I fertilize if I have landscape fabric around the citrus (it goes to the dripline of the tree, but not to the trunk)?

• I have Meyer lemon trees, but would a Eureka lemon tree do well here? And would my trees be cross pollinators for my newly planted Minneola tangelo?

• Should I pick the fruit off of these trees in the first few years? Thank you. Gina Acosta

A: The fertilizer clock starts at year one after planting. Apply fertilizer from the dripline (the outermost circumference of the tree's branches) on top of your fabric.

There are three true lemons grown in Florida: Bearss, Eureka and Lisbon. Bearss is vigorous, practically thornless, but is susceptible to the most diseases. Eureka is slow-growing, practically thornless, but the shortest-lived. Lisbon is vigorous, produces large crops, but is very thorny. Lisbon is the most widely planted in Florida, but I would use a fruit picker to harvest the fruit to save on blood loss.

As for your Minneola, which is a great selection, it is self-pollinating.

And you're right, it is a good idea to pick off the young fruit for the first couple of years to keep the plants' energy focused on growth rather than making babies. For more information, go to edis.ifas.ufl.edu.

Dieback isn't related to nearby tree exfoliation

Q: My neighbor's trees began exfoliating two years ago. To protect mine, last year I used a multipurpose spray, but a section of leaves turned yellow and the branches fell off. This year I sprayed just before bloom, but I noticed leaves turning yellow toward the top of the tree, a much larger area than last year. I would spray again, but not until after it's done blooming, because I don't want to harm the bees. What can I do to save my tree? Is this disease, frost damage or something else? Barb Matthews, Trinity

A: Although the exfoliation (the peeling away of bark) in your neighbor's trees indicate it's time for their removal, they are not affecting your tree.

There are many causes for branch dieback, some worse than others. Prune out any dead wood and keep close watch to see if the problem continues to spread. If the rest of your tree looks healthy and no further problems arise, call a pest control company that specializes in trees and get an accurate diagnosis and program of care. Spraying a tree without knowing the cause of the problem may sometimes do more harm than good.

Diagnosing the cause of key lime's fruit drop

Q: A key lime tree we planted about five years ago develops flowers but no limes; fruit forms and grows to about 1/4 inch and then falls off. We planted a tangerine tree next to it a couple of years ago and that produces fruit. What's going on with our lime tree? Citrus fertilizer is applied. Denise Wrentmore

A: There are many physiological causes for citrus fruit drop, including sudden changes in temperature or humidity, poor nutrition management, hormonal imbalance and improper soil moisture.

There is also a fungal disease that hits key lime trees very hard. It doesn't sound like fungal disease because you mention that the tree looks healthy; in a fungal disease the flower petals turn brown, and some brown lesions, or streaks, on leaves and stems also occur.

Temperature and humidity could be a possibility, but not five years straight. Key limes are sensitive to uneven moisture, so regulate your watering from when flowers begin to form to when fruit sets. Nutrition doesn't sound plausible because you are fertilizing and the tree looks healthy. But if you are fertilizing during the time that flowers set, that could be the culprit. If the fruit drops off perfectly green, not slightly yellow (which would indicate a moisture problem), it is hormonal and there is no cure.

Symptoms point to tree's severe decline

Q: My Valencia orange once had dark green leaves and abundant fruit. But since 2009 the leaves are sparse, lighter in color and there is hardly any fruit. The fruit that is there is also small and hard. Wayne Huneke

A: Your tree is in severe decline, from either viral or fungal pathogens (disease-causing organisms) and will continue to produce smaller and smaller crops. It's time for removal, but you may replace it with any citrus variety without harm to the new tree.

Citrus greening now leading citrus disease

Q: Would you please give us more information about citrus greening?

Pat Maison

A: We all thought citrus canker was bad. Citrus greening is now the world's leading citrus disease. It first popped up in South Florida in 2005 and landed in the Tampa Bay area in 2008. The bacterial disease, which slowly weakens and kills all types of citrus trees (sometimes within two years), causes fruit to become lopsided and taste bitter. The bottom of the fruit stays green even as the top is ripe, hence its name. The leaves become blotchy yellow and over time can turn entirely yellow and die along with the twig. There are many nutritional deficiencies that look similar so gardeners shouldn't freak out at every yellow spot. When a citrus tree has problems, consider all the symptoms.

Citrus greening is spread by a tiny 1/8-inch brown and gray insect called the Asian citrus psyllid (Diaphorina citri Kuwayama), the University of Florida reports. The nonnative insect sucks juice from a leaf with a spearlike mouthpart that, if infected, can transmit the disease to a healthy tree. For more detailed information, go to the UF website edis.ifas.ufl.edu/hs383. If you suspect citrus greening in your yard, take several quality photographs to your local extension service for positive identification. Keep all citrus in your yard, just in case.

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Ask Dr. Hort: Answers to citrus questions on bay area readers' minds 04/15/11 [Last modified: Friday, April 15, 2011 11:37am]

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