Apple Tree Fungus & Sour Oranges

Question:

 I'm concerned about a greenish fungus growing on the stems and trunk of my apple tree. What do I go about treating it?

Answer:

  • The light green growth is not a single fungal organism but a combination of algae and a fungus called Lichen. It is a common occurrence in the Bay Area growing on both healthy and declining trees. I've seen it growing on almonds, apricots, plums, and cherries.
  • Lichen can be a light green color, or it can have a blueish tint. It grows on the surface of the host plant and doesn't penetrate it.
  • The host plant is nothing more than a resting place. With apples, it's relatively flat, while on other trees, it raised and flares out like cabbage leaves. Lichens will grow on pretty much on any firm, well-lit surface like the bark of trees. It grows best when exposed to full sunlight, and dead or dying trees can be the perfect habitat.
  • On healthy trees, you more likely to find it on the southwest side of the side the receives the majority of the sunlight.
    • Lichen is never a cause for a tree's decline. Each Lichen has fungal cells that make up the main body and algae or cyanobacteria. This gives its green or blue color. The fungal part of a lichen cannot create its own food; thus, it relies on photosynthesis in the algae cells for the energy it needs to grow. In turn, the fungus provides the algae with water and minerals and prevents it from drying out.
    • This mutually beneficial relationship is called symbiosis. They only use the bark on the tree as a place to live and grow. Trying to scrape lichens off of the bark will likely do more harm than good, and applying a fungicide has absolutely no effect at all.

Note: I’ve been told that there is an upside to having lots of lichens on your trees. Lichens are extremely sensitive to air pollution and are only found growing in places with good air quality. Hence, you rarely see them growing along city streets.

Question:

How do I get my orange to be sweet? The tree is two years old, gets plenty of sunshine, and is healthy with green leaves and plenty of oranges, but they're sour. Besides Citrus Food, would Epsom Salts help?

Answer:

  • Sour oranges are not a fertilizer problem, so no Epsom Salt is not a solution. The sourness indicates that oranges have not matured. It has more to do with growing location. Getting oranges to sweeten up is a problem in areas where the summer is mild. It isn't a problem inland with the warm summer days but is the closer you get to the ocean.
  • The simple solution is to be patient and let the fruit hang of the trees for an extended period. I'm assuming this is a Navel Orange which typically ripens December through March. Every two to three weeks, pick one and taste test for sweetness. Your tree