Every year my nastriums g... - Ask Extension
Every year my nastriums get overtaken by tiny black dots on the underside of the leaves. Since I use the leaves and flowers as food garnishes do not ...
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Every year my nastriums g... #173179
Asked April 04, 2014, 2:11 PM EDT
Every year my nastriums get overtaken by tiny black dots on the underside of the leaves. Since I use the leaves and flowers as food garnishes do not know how to protect from this. Have tried to wash plants with soapy water but does not help. Any advise? Thank you.
Delaware County Ohio
Expert Response
It sounds like your nasturtiums might be being attacked by aphids. There are many types of aphids and some are black. Also, aphids excrete “honey dew”, a sticky substance which can then attract sooty mold, which might be the black you are seeing. Some gardeners actually use nasturtium plants as a “trap crop” for aphids, to attract them away from more important vegetable plantings. Reliable sources advise that the most innocuous way to control aphids is to wash them off with a strong spray from the hose. If your infestation has developed the sooty mold, this might be the reason you aren’t haven’t luck with washing them away. Or perhaps you aren't catching the infestation in its earliest stages, when washing or soap treatment can be most effective. Natural predators, such as lady bugs, eat aphids. You can spray insecticidal soap, a few drops of dish detergent diluted in water, or neem oil on them, too. But since you want to use your nasturtiums as edibles, the plain water spray is probably the best approach. Try using the water spray before you actually see any infestation. Be sure you are hosing off both the tops and the undersides of the leaves and flowers. Also, it’s recommended to do the spraying early in the day so the plants can dry out quickly in the sun. If the infestation of aphids and/or sooty mold is so severe controls don’t work, you may have to pull up the plants .If this is an annual occurrence and spray and soap haven't been successful, how about giving up using the nasturtiums as edibles for one season and experimenting with an oil control? That might at least answer the question of exactly what is attacking your flowers, determine if the problem can be controlled chemically, and help you decide how to proceed in the future.Here are some informative fact sheets on aphids and their control:OSU Extension http://ohioline.osu.edu/hyg-fact/2000/2151.html University of Kentucky http://www2.ca.uky.edu/entomology/entfacts/ef103.asp University of California, Davis http://ucipm.ucdavis.edu/PMG/PESTNOTES/pn7404.html
