althea - Knowledgebase Question

saucier, Mi
Question by katykat1944
January 21, 2010
plant is about 8 years old. is full of buds every year but does not open. 2009 one bloomed. rest fell off. plant also has a gray lichen or moss on the trunk

Answer from NGA
January 21, 2010


The lichen or moss really won't hurt your plant but it can look unattractive. If you don't like seeing it, an application of lime/sulphur (sold as Bordeaux and used as a dormant spray for fruit trees). The lime sulphur will kill off the lichen and it will eventually weather away. Of more concern is the bud drop. Failure to bloom and bud drop seem to be common problems with Rose-of-Sharon, but we don't know exactly why. Sometimes water stress issues can cause this and sometimes the problem is due to a bud worm. These little pests start out when an adult moth or flying insect lays an egg just beneath the surface of the sepal. When the egg hatches the little larvae feeds on the unopened flower. When it has finished it makes a little exit hole and drops down into the soil to pupate. After this process it hatches into an adult and starts the process all over again. It's difficult to control this pest because it flies around rather than stays on the plant where you can pick it off or spray it off. Try checking the unopened buds for worms or exit holes. I just pick a few off the plant and cut them open with a razor blade. Or you can harvest some of the plump buds and place them in a sealable plastic baggie. Leave them out in the sun. In a day or two, if any are inside, the little worms will emerge and you'll know for sure if this is the problem. Sometimes you can break the lifecycle by cultivating the soil beneath the plants to expose the pupa to the elements. Other times you can simply place a nice thick layer of organic matter beneath the plants to keep the worms from pupating in the soil.

Best wishes with your Rose of Sharon.

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