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Ask Dr. Hort: Ailing grapefruit tree is victim of 'citrus greening; how to care for pentas; maximize tea olive fragrance by minimizing pruning

There's no cure for 'citrus greening'

Q: I have a grapefruit tree that is about 13 years old. It appears to be dying. Many of the branches are dead and the leaves have been falling. Most of the fruit this past year did not mature and many rotted on the tree. Any idea what is wrong? Dave Bowman

A: Your description of rotting fruit on the tree (mummified) and the yellow leaves that I could discern, makes me think your tree is dying from a relatively new bacterial disease to hit Florida citrus called "citrus greening," which kills a tree in short order. Unfortunately, there is no cure. To further match up your grapefruit trees symptoms, visit edis.ifas.ufl.edu and search "citrus greening." If you suspect citrus greening, cut the tree down immediately, or it will infect other citrus trees in the area through a sucking insect called the citrus psyllid. As it feeds on an infected tree it picks up the bacterium and redeposits the organism into a healthy tree, just as a mosquito would transmit malaria.

Once pruned, shoots rise from pentas

Q: My question concerns the care of several pentas. I read somewhere that they should be thinned out occasionally. The ones I have are not quite a year old in this location and are doing quite well as they have many blooms and buds. There is also a lot of new growth visible at the bottom. Could they just be pruned, and if so how much and when? A few weeks ago they were fed with Osmocote. Virginia Melidosian, Palm Harbor

A: Many herbaceous perennials (nonwoody green stems) of which Pentas spp. are classified, do well by being heavily pruned each spring (down to about 8 to 10 inches). You will see a whole set of new shoots rising from the base of the plant, which you mentioned. This type of pruning eliminates tall, leggy growth.

Tea olive should get very little pruning

Q: It's difficult to see in the pictures the white blooms of the tea olive which came about recently. How do I prune and when is a good time? Grace Ricalde, St. Pete Beach

A: Fragrant tea olive, Osmanthus fragrans, is a much underused shrub, hollylike in appearance but in the olive family, being a winter bloomer and having a heavenly fragrance. It does, however, have a rather open appearance, is slow-growing and flowers on old wood. Prune as little as possible because excessive new growth will reduce the following winter's bloom or cause no bloom at all with the plant's energy going to growth instead of flowering. It is finicky that way. When pruning, use a thinning cut (prune back to a side branch), which eliminates a branch with no regrowth. A heading cut (simply cutting a branch back, reducing length) promotes new branches. The more natural you let the plant grow, the more fragrance you'll enjoy.

Need help? Dr. Hort (Greg Charles) answers questions about garden problems. Email him at drhort@tampabay.rr.com or mail questions to HomeLink, Features Department, Tampa Bay Times, P.O. Box 1121, St. Petersburg, FL 33731. Describe problem in full, and include your name, city of residence and contact information. If possible, include a good-quality photo. Fuzzy ones won't do. Photos cannot be returned.

Ask Dr. Hort: Ailing grapefruit tree is victim of 'citrus greening; how to care for pentas; maximize tea olive fragrance by minimizing pruning 04/14/12 [Last modified: Saturday, April 14, 2012 4:31am]
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