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Growing Wise
Citrus tree greening bad news
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The first symptoms of greening are vein yellowing and an asymmetrical yellowing referred to as “blotchy mottle.”
Something new for Florida citrus growers to worry about: a deadly tree ailment known as citrus greening, Huanglongbing or yellow dragon disease that first showed up in Miami-Dade County in 2005 and is being spread by an invasive insect, Asian citrus psyllid. It destroys production, appearance and value of citrus trees, produces bitter, inedible, misshapen fruit and, worst of all, has no cure and is fatal to citrus trees.

Naturally, commercial citrus growers are extremely concerned. According to a recent study by the University of Florida, since 2006 citrus greening has cost the state approximately $3.63 billion in lost revenues and 6,611 jobs. It is now threatening the entire U.S. citrus market and the thousands of jobs it supports. 

Unfortunately, backyard citrus trees are also subject to greening. Here’s what to look for and what to do.

The first symptoms of greening are vein yellowing and an asymmetrical yellowing referred to as “blotchy mottle.” The blotchy mottle is the most diagnostic symptom of the disease, especially on sweet orange trees. Yellowing can appear on a single shoot or branch then spread throughout the tree over a year, especially on young trees. Affected trees may show twig dieback, causing the productivity to decline within a few years.

Trees with citrus greening usually don’t produce much fruit and if they do, they are often small, may be lopsided with a curved central core, fail to color properly and drop prematurely. A yellow stain may be present just beneath the stem on a cut fruit. Affected fruit often contains aborted seeds and have a salty or bitter taste.

Since other citrus problems, such as nutrient deficiencies, root rot, citrus tristezia virus, citrus blight, leafminer tunnels or water logging, can be mistaken for greening, it’s important to know the greening symptoms. You can find helpful pictures of greening at this University of Florida website:

Once greening is diagnosed, the tree should be removed immediately and the stump also treated with an herbicide to prevent any new shoots from forming. Infected trees act as a reservoir for the disease, helping to spread it. Once the Asian citrus psyllid is infected with the bacterium that causes the disease it carries it for the rest of its life and spreads it from tree to tree as it feeds.

Homeowners and consumers can play an important part in limiting the spread of the Asian citrus psyllid by:

• Planting only certified citrus trees that are known to be free of Citrus Greening Disease.

• Inspecting citrus trees monthly for Asian citrus psyllid adults, nymphs or eggs and removing those that are infected.

• Getting rid of orange jasmine and orange boxwood since both are hosts for the psyllid and the greening bacterium.

It is also important to eliminate the movement of citrus around the state or outside of the state as this could also spread the disease. While researchers are seeking a cure you may want to plant a different type of fruit tree. See this publication for a list of other tropical and subtropical fruit crops:

There is hope for a solution. The U.S. Senate Finance Committee recently passed legislation sponsored by Sen. Bill Nelson, D-Fla., that establishes a multimillion-dollar trust fund dedicated to finding cures for citrus diseases and other threats to the industry. The trust fund would be financed by tariffs that foreign producers already pay to import citrus into the United States. The money would primarily be used for research and development on citrus greening.

“If we don’t stop this now, we’ll end up paying five bucks for an orange – and it’ll be one imported from someplace else,” Nelson said.

Nelson will now seek to get the legislation through the full Senate.

Jane Morse is a UF/IFAS Extension Agent, Pinellas County.
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