Yikes! It's whitefly blight!
White fly larvae on a leaf of the Lisbon lemon tree.
Well, apparently the lemon tree was very lucky all these years, with no diseases. But now it is under siege of whiteflies! I look at the tree every weekend, so you can imagine my shock when suddenly a couple of weeks ago, early on a Sunday evening, I noticed on some of the leaves this fuzzy stuff that resembles mold.
We immediately looked this up online, and sure enough it's whitefly. The larvae lives on plants, and, like aphids, they suck the nutrients from the plant's circulatory system.
And they are hard to get rid of. Their only natural enemies seem to be ants.
Naturally we don't want to use any chemicals or toxic stuff, especially since our local bees are pollinating the lemon flowers and birds like to hang out in the tree.so after a lot of research we decided to go with the home-made concoction that should help. One should spray the leaves (better yet, the whole plant), especially the under sides later in the day, as in early evening, while there's still some natural light. You want to make sure there are no pollinators still active in the area.
The oil in this mixture will prevent the larvae from hatching, it basically smothers them.
Because this is not a heavy-duty chemical mixture, you will probably need to apply several times within a 2 week period. After that you can just spray with water.
We've sprayed the tree leaves twice in a 2 week period. So far, it looks like we might have the blight under control. In the meantime, the lemons are growing and the tree is still producing blossoms. Keeping our fingers crossed...
Here is what you need:
dish detergent (we use Dawn dish liquid, since it is used to clean oiled wild birds, so shouldn't be toxic to them)
1/2 tablespoon dish detergent to 1/2 cup cooking oil (we use canola oil) to 1 gallon of water
To apply to the leaf surfaces, you should purchase a 2 gallon sprayer tank that has a pump and shut-off valve and includes a hose and spray wand. The one we purchased (photo below) works really well and cost about $20. It's a good investment because you can always use it later for other purposes.