Remember the citrus canker outbreak from about 1986 to 1994 that was declared eradicated but still pops up here and there? Millions of trees were burned in groves and many were cut down in homeowners' yards, all in an effort to stop the spread of the worst disease to hit Florida citrus, an industry worth about $9 billion annually — not to mention the trees in your own back yard. • Turns out it wasn't the worst disease to hit citrus. • There's a new kid on the block, and it's a whole lot worse than citrus canker. Like canker, the disease is caused by a bacterium, but unlike canker, it has escaped with no control in sight, killing young, healthy trees in just a few years. It takes a little longer to kill mature trees after symptoms are first noticed. • The disease is called "citrus greening," also known as huanglongbing (HLB) or yellow dragon disease, one of the most serious citrus diseases in the world. • It was found by farmers in southern China in the early 1900s (citrus is native to China), and was first detected in Florida in 2005.
What causes citrus greening to spread?
Like Texas Phoenix Palm Decline, citrus greening (shown right) is transported by a sucking insect that moves the disease from tree to tree. The insect in question is called the Asian citrus psyllid, a tiny, odd-looking critter only 1/16-inch long, mottled brown and white, with wings up in the air making the insect look like it is doing a headstand. Looking closely, they can be seen in mass feeding on new growth, causing some stunting of the leaves. So monitor your trees closely whenever there's new growth.
If noticed, spray weekly with horticultural oils and Neem oil, preferably at 100 percent. Reducing psyllid populations is a key to slowing the spread of the disease.
Symptoms of citrus greening
The first notable signs of the disease are small yellow leaves on one branch somewhere in the tree canopy, followed by many leaves appearing variegated or mottled, displaying several shades of green and yellow. This has been termed "blotchy mottle."
The disease may also cause small, narrow leaves and short stems that give plant growth a bunched appearance. As the disease progresses, twigs and then branch dieback are followed by poor flowering and fruit set.
The fruit is small, often misshapen, and typically has some green color on the bottom when ripe. Many fruit drop prematurely. Infected fruit tastes either bitter or sour.
Stunted, chlorotic leaves and tip dieback also can be caused by micronutrient deficiencies, root-rotting diseases and viruses, so every mottled leaf is not citrus greening. Positive identification is imperative. If you think your tree or trees have "citrus greening," look at as many pictures on the Internet as possible for comparison. This link will get you started: freshfromflorida.com; search "citrus greening.".