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How to Treat Disease with Citrus Trees

Ask This Old House landscape contractor Roger Cook helps a homeowner treat a citrus tree that’s been affected by citrus greening


  1. To identify if a citrus tree is diseased, check the fruit and the leaves of the tree. Small, green fruits indicate that the tree isn’t receiving proper nutrients. Pinched leaves indicate that psyllids have been feeding off the tree and spreading disease.
  2. Check the root tips. If the roots are brown, they should be cut off to allow for new root growth. Take a shovel and cut down 4-6” around the base of the tree at the dripline to do this.
  3. Spread a layer of fertilizer around the base of the tree to help nourish the roots.
  4. Sprinkle the plant sugar on top of the fertilize to stimulate the microbes in the fertilizer.
  5. Make compost tea to coat the leaves of the tree. Fill the bucket a little more than halfway with water. Then, take a sock and fill it with compost. Tie the sock closed and stick it in the bucket of water.
  6. Stick the fish tank pump tube into the water and leave the pump out of the bucket to aerate the tea. Allow the tea to brew for 24 hours.
  7. Add a cup of molasses to the tea to feed the microbes in the tea.
  8. Use the paint mixer to mix the molasses into the tea.
  9. Scoop out some of the compost tea and connect it to the hose sprayer. Spray the tea onto the tree leaves.
  10. Apply an organic pesticide to prevent psyllids from returning to spread disease without deterring helpful insects, like bees, from the trees.


Roger visited a commercial orange grove to learn about Citrus Greening, or Huanglongbing, a disease that’s killing citrus trees across the state. Roger and Benny McLean, a citrus expert, then presented an organic solution to prolonging the life of a diseased backyard orange tree.

Citrus greening is spread by an insect called a psyllid. Applying neem oil, a botanical oil available at garden centers, will smother the eggs of the psyllid to help control the population.

Citrus greening also prevents the transportation of nutrients from the soil to the tree. Benny did some root pruning with a shovel and applied composted cow manure to the root zone. He also sprayed a compost tea onto the foliage.

While this method, the life of the tree can be prolonged, but the disease is still fatal.
Expert assistance with this project was provided by Uncle Matt’s Organics.