Lichen & Scale Insects

Karen Cambre, Sharpe, Kenneth W.

News article for December 31, 2018:

The winter months get long for gardeners. There is too much inside time and not enough digging in the soil and getting dirty.

There are still tasks to be performed and some of them are specific to the dormancy of winter.

There are two problems that I get a lot of calls about each year that are most easily taken care of now. The first would be control of scale insects. There are hundreds of scales in the environment that grow on plants.


In general, scales will be seen as hard shelled, circular dots on the back of your leaves, twigs and branches. The insect is living protected from predators under the shell most of the time and is hard to control. The scales I most frequently see are white, gray, pink, red or yellow, although they are not limited to these colors. Their size varies greatly from the size of a pin head to ones I have seen on magnolia trees that looks like a large wad of chewed yellow bubble gum.

A tell-tale sign of scales can be sooty mold, although not all sooty mold is caused by scales. Sooty mold is the black flaky material that covers the leaves of your plants.

The most frequent plants that I see that have scale this time of the year are citrus, camellias, euonymus, variegated privet and fatsia. These are evergreen plants that I would definitely check, but do not limit your inspection to just these plants.

Scales attach themselves to the leaves and twigs and suck plant juices. They can cause a general decline, lack of flower and fruit production and they can kill the plants.

This time of year is the easiest time to control scales because you can use dormant oil (which is not an insecticide) to suffocate the scales. The oil would burn the foliage if you wait for the warmer weather. You should note that dormant oil can burn the foliage if applied within 48 hours of a freeze, so watch your weather reports. You can also enhance the action of the spray by adding the insecticide, Malathion in with the oil.

Check you plants in a few weeks and make sure the scales are not still attached, if they are repeat your spray so you can start the growing season off scale free.

Another frequent concern is about lichen. Lichen in the greenish gray mossy growth you see on trees and shrubs. It grows on the branches and trunks and can appear as a flat, flaky growth or it can appear as a more hairy moss.


The lichen is not really a problem for the health of the plants since if fixes nitrogen from the air and produces its own energy. Some plants that have lots of lichen can look bad but usually the lichen is a secondary issue. Lichen will also grow on any stationary non-living object, such as rocks, fence posts, wood siding and outdoor furniture.

Lichen grows on almost every tree here and does not need to be controlled. If you want to control lichen then now would be the best time. Spray with a copper fungicide such as Bordeaux mixture, tri-basic copper sulfate or Kocide before the leaves emerge in the spring. Copper can burn foliage in warm weather, so it is best applied in the winter.

Do not expect the lichen to fall off immediately. It adheres very tightly to the bark and will take a few months to fall off. Once you spray the lichen it will turn a copper color and this will let you know that you have been successful.You have probably heard the old saying, “moss doesn’t grow on a rolling stone”, that may be applicable here. Fertilize plants that have excessive lichen in the spring to get them actively growing.

For more information on these or related topics contact Kenny at 225-686-3020 or visit our website at

12/20/2018 4:15:22 PM
Rate This Article:

Have a question or comment about the information on this page?

Innovate . Educate . Improve Lives

The LSU AgCenter and the LSU College of Agriculture