Question

Grapefruit   QUESTION: All of a sudden my grapefruit tree is producing fruit with large brown areas and there is increased fruit drop.  Photo attached

ANSWER: The problem with the grapefruit may be caused by a fungus and there are many possible culprits.  The brown areas on the fruit appears somewhat leathery so my best guess would be a disease called brown rot.  You did not mention if there are any spots on the leaves or any other symptoms such as wilting, dieback, etc.  If there are additional symptoms, these may help determine the cause of the problem.

You may want to put some of the fruits in a sealed plastic bag with a damp paper towel.  If the problem is caused by a fungus, fuzzy growth should be evident in a few days.  Sometimes the color of the fungal growth can help determine which fungus may be involved.

At this point, it is probably too close to harvest to try to treat the tree with a fungicide.  Next year, you will probably want to treat the tree with a protectant fungicide such as copper hydroxide.

Without knowing the exact organism involved, I can make recommendations as to some things you can do to help with the problem next season. You should remove and discard all of the damaged fruits.  Any fruits that remain on the ground after harvest should be raked up and discarded.

When watering the tree, you want to provide adequate moisture but avoid over watering.  Avoid watering with sprinklers that spray the underside of the tree and wet the canopy.  If possible, water the tree in mid-morning rather than afternoon or later in the day.  It may be helpful to remove branches that hang low to the ground.  

Hopefully, this information is helpful.  If you note any other symptoms or would like to submit additional images, I would be happy to take a second look.

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QUESTION: I checked again, and there are some leaves with brown spots, but there are very few of them with this symptom. Almost all the leaves have a good green color. However, there is some dieback. There is one whole branch of the tree that appear that is dead. I also noticed that some of the wood have a light greenich/yellowish spots. Appreciate your comments

Answer
Hi Sophia,

I think that you may be at the point where you want to have your plant tested for plant pathogens.  Since the damage you have observed on the fruit is accompanied by other symptoms (leaf spot, dieback) this suggests there may be a pathogen problem.  You may find out that environmental factors are to blame, but if it is something greater than it is good to have the problem checked out.  I think that the light greenish/yellowish spots may be lichens which are normal.

I am not sure where you are at in the United States.  I suggest that you go to the National Plant Diagnostic Network website:  www.npdn.org   
When you go to this site, if you scroll down you will find a list of states.  When you select your state, it should take you to another website where you will be able to find information about the Plant Diagnostic Laboratory in your state.  In some states, the services are free while in other states there may be a fee.  You may want to try to send a sample directly to the lab but it is usually best to work with your local county extension office.  

Most states have a Cooperative Extension office in each county.  They are usually located near the county courthouse or fairgrounds.  The phone number and address can often be found in the phone book or you can locate it on the internet.  You could take a sample to the county office and often the Extension Educators (aka County agents) are well trained and might be able to solve your problem without going through the laboratory (so there is no charge).  If necessary, they will tell you what type of sample to collect and will assist you in submitting it for testing.

If you have any trouble finding about the diagnostic lab in your state or in locating your county extension office, please let me know.  The symptoms on your plant suggest many possible problems, so this is the best way to get a conclusive diagnosis.