I have a small (3') ruby red grapefruit tree that I bought at Home Deport last year and planted in the ground in May of '06. In august it had about 9 or 10 blossoms with 1 going on to maturity this winter and 5 maturing about half way. During this time some black dust (mold?) appeared on some of the leaves. Can anyone tell me how to get rid of this? Also, I am going to try and attach some pics I took yesterday of the tree. Three pictures of different angles. There must be 50 to 60 blossoms! What do I do? The tree is only a little over 3' high! Will some fall off? Some have already been pollenated and have little B-B sized fruit starting. Will I need to prune some of them off? If even 80% grow to fruit the tree will be lying on the ground from the shear weight. You can probably tell I am a neophyte, beginner backyard citrus grower. Also, I fertilized it once every 3 months. It's due again in April. Thanks for any info you can provide. Oh yea, I am located in East Central Florida.
As a newbie citrus grower like you I can only address your black dust problem. If it is mold it will be sooty mold. It won't kill your tree directly but will cover the leaves and prevent photosynthesis. That will lead to a slow decline of the tree. Sooty mold is a side effect caused by one or more of several insects. Look for scale (small hard mounds on the stems or leaves), mealybugs (white cottony bits) although unlikely because the pics look good, or aphids. All these insects are very common and excrete a liquid called honeydew. It is excess sugar and water from the sap they suck out of your plant. The sooty mold grows on this. Your best cures are spraying with an insecticidal soap for aphids or mealybugs and horticultural oil for the scale. The insecticidal soap can be purchased at garden centers and big box stores. It works by cracking and dissolving the wax coating on the insects. They are unable to heal like we do and will dehydrate. Horticultural oil will suffocate the scale. The actual insect is inside the scale and most insecticides can't get inside. Be very careful which oil you use. In Florida you probably want to use a very light oil sometimes called a summer oil. It is possible to burn your leaves with it so follow directions carefully for optimal temperatures and sun levels for spraying. Look carefully on your tree for an abnormal number of ants. The ants will farm these insects for their honeydew. It is a food for them. You may need to follow ants back to their nest and destroy the nest. It will make keeping the critters off the tree easier. If you Google the insects you can find some really great images to help you figure out if this is what is wrong. Hope this helps.
As to your question of flowers-- only a small percentage will set fruit and even then the tree will drop excess fruit that it cannot support. Skeet
Thanks for all the good info. Sabagal - I don't see any of the indicators that you suggest to look for regarding the black substance on the leaves. I have noticed that over time the black substance turns dry and will actually flake off the leaves. In Florida, we get black mold and I believe this is what it might be. I am going to a few of the nurseries around here to see if they have a solution to offer.
