FAQ's

1. What is Citrus Greening?

Huanglongbing (HLB), also referred to as Citrus Greening, is a systemic bacterial disease that affects all citrus varieties and other plants in the Rutaceae family. Ornamental plants can also be infected, including boxwood and orange jasmine. 

2. What causes Citrus Greening?

HLB is caused by the bacterium, Candidatus Liberibacter asiaticus. The bacteria are located in the part of the tree vascular system known as the phloem and are harmless to humans. The Asian citrus psyllid can also acquire the bacteria from an infected tree and is the vector of the disease. The bacterium reproduces in the plant and in the psyllid.

3. Why is greening so bad?

In a plant, water moves through the xylem, and sugar and minerals move through the phloem.

The bacterium that causes Citrus Greening resides in and damages the phloem, causing the tree to be unhealthy. You can relate this concept to the movement of blood throughout a human's veins and arteries. The effects of citrus greening are comparable to what happens when the human vascular system is damaged and blood flow is restricted. In the case of Citrus Greening, the flow of sugar and minerals to the rest of the plant is restricted.

The tree roots are also affected by the bacteria. Even before leaf symptoms are visible, the bacteria is already damaging the tree roots; therefore, the tree cannot function as if it were a healthy tree. Once the root damage has occurred, the tree tries to grow new roots to replace the damaged ones, but at that point the damage has already occurred and the overall tree health will only continue to decline.

Ultimately, an infected tree will become unproductive over time. A smaller tree will succumb to the infection more quickly than a larger tree. As tree health declines, it should be removed.

4. How does citrus greening spread?

HLB is spread by two methods, the Asian citrus psyllid (ACP) and grafting. The most frequent method is the ACP. The insect has piercing, sucking mouthparts that allow it to acquire and transmit the bacteria to and from the plant phloem, part of the tree's vascular system.

Budding (grafting), the other method for disease spread, is illegal for Florida homeowners to perform. This regulation is in place to prevent unintentional disease spread. Only certified nurseries may graft/bud citrus trees from certified mother trees determined to be clean stock. The disease is not seed transmissible.

DISEASE IDENTIFICATION

1. How can I diagnose citrus greening?

Fruit and leaves have different symptoms. Fruit symptoms include lopsided, misshapen, and small green fruit. As the fruit begins to mature (ripen), it may display a color inversion. Healthy fruit colors from the blossom end (bottom) toward the calyx button (where the fruit attaches to the stem); whereas, in HLB infected fruit the color begins to change from the top end (calyx button) downward toward the blossom end. 

The most characteristic symptom of HLB is the blotchy mottle pattern on leaves. This blotchy mottle pattern presents as an asymmetrical pattern across the midvein on both sides of the leaf. Other leaf symptoms include yellow veins or corky veins. Broken or girdled limbs and another disease called Phytophthora may also cause yellow veins. Corky veins are also a symptom of Boron (B) deficiency. 

This information provided by the University of Florida (Ask IFAS)