Rosemary with Burnt Looking Stems
Answered by: Conrad Richter
Question from: Julie
Posted on: March 19, 2004

I purchased 2 rosemary bushes about 10-12" tall in November 2002. They lasted beautifully for 9 months. Then the stems began to turn dark and looked burnt but the leaves still appeared healthy. I still have the plants and they have a few very healthy looking, leaf bearing branches. They are in large pots and have full sun for half of the day. I live in Ga. Obviously, I have little experience in gardening. Can you tell me the cause of the burnt look and also how to replant or save the remaining healthy stems? I have just learned through your site that I probably do not have enough drainage for these plants.

That "burnt" look is a sure sign of an infestation. Tiny fungi that feed on the exudation of certain insects will cause stems, and eventually leaves, to turn black as if covered with soot.

Scale insects, mealybugs and aphids are some of the insects that produce exudations that fungi later colonize. In this case, I suspect you have scale insects because they are hard to see to the untrained eye. The hard shell of the scale insect blends in very well with the brown stems, and the shell adheres so tightly to the stem that it appears to be a natural bump in the stem at first glance.

Scale insects are a serious problem for woody plants such as rosemary and indoor house plants. If a retailer or a commercial grower does not pay attention to scale he or she can cause a lot of grief to their customers because scale is very difficult to eradicate, especially on edible plants such as rosemary, and scale spreads to other plants. Sometimes the only safe solution is to discard infested plants.

We at Richters pay very close attention to pest problems. Our monitoring program has been so succcessful that we have not had outbreaks of scale or mealybugs in years. The kind of intense monitoring we do is expensive to implement, but we feel that it is better to avoid problems early than to give our customers a unpleasant surprise later.

You can try to treat the scale. For more information return to the "Q&A" section of our website and enter "scale" in the search box.


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