Citrus Greening Disease: Symptoms & Treatment

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Citrus greening is a devastating disease. In this lesson, we will discuss the history of the disease, symptoms you can identify on infected trees, and what people are doing to try and manage it.

Citrus Greening

When I was growing up my grandmother lived in Florida, and every winter she would send us a box of fresh oranges and grapefruits. I lived in Michigan where winters are harsh and cold, and this box of tasty fruit was like a ray of sunshine for us!

I now live in Florida myself, but that's not the only thing that has moved into the region. Huanglongbing, also known as HLB or citrus greening disease, has also taken up residence in the state. HLB is a bacterium that is transmitted by tiny insects called psyllids. The disease attacks the vascular system of plants, and once infected there is no cure that can save them. In some cases, trees can die within a few years.

Citrus damaged by citrus greening disease.
citrus damaged by citrus greening disease

History of Citrus Greening

I think of Florida when I think of citrus greening because Florida produces 66% of the United States' citrus. But citrus greening is actually a world-wide problem. It was first reported in China in 1919, in the Philippines in 1921, in Thailand in the 1960s, in Brazil in 2004, and in Florida in 2005. It has since spread to other states such as Louisiana, Georgia, and South Carolina. It has also been found in other nearby countries like Cuba and Mexico. Southern Africa, India, and the Saudi Arabian peninsula are also victims of the disease.

The psyllid that transmits the disease first arrived ahead of the disease in Florida in 1998. But these tiny vectors, or organisms which helps spread a disease, are not the only way the disease can be spread. Years before, in 1965, it was discovered that HLB can also be spread through grafting, or transplanting one piece of a plant onto another so they can grow together.

Small insects called psyllids are one of the main vectors for transmitting citrus greening disease.
citrus psyllid

Symptoms & Treatment of Citrus Greening

The symptoms of citrus greening are many and can easily be seen on an infected tree. Some things you might notice are:

  • Twig dieback
  • Leaf yellowing
  • Green, misshapen fruit
  • Blotchy mottle on leaves (a random yellowing pattern)
  • Yellow leaf veins
  • Salty, bitter tasting fruit
  • Off-season blooming
  • A curved central core inside the fruit

Once your citrus tree is infected, there's really nothing you can do about it. But steps are being taken to eradicate this devastating disease. Researchers are working hard to figure out how to control both the disease and the psyllid that transmits it. They're even working on developing citrus varieties that are resistant to HLB.

Leaves on a tree yellowed by citrus greening disease.
leaves on a tree damaged by citrus greening

But until then, management is the best method. Keeping the disease out through quarantine regulations, which is what California is doing, is one preventative action. Other tactics include removing infected citrus plants, applying insecticides, and planting/grafting HLB-free citrus plants.

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