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All of my rosemary plants are infected with rosemary mites, which are some kind of variety of spider mite. These invisibly tiny insects cause unsightly yellow mottling on the leaves of the rosemary, and (more importantly to me) are detrimental to the flavor of the rosemary. Oddly, though, they don't prevent the rosemary from continuing to grow.

Since I use this rosemary for culinary purposes, I do not want to use any toxic pesticides, or anything which is hard to wash off (like pepper wax or cinnamon oil). There are three solutions I've seen recommended for this and I wanted to ask if anyone had tried them and what your results were:

  • Neem Oil
  • Rosemary Oil
  • Ladybugs

The second solution seems ideal. However, I've had trouble locating rosemary oil in pesticide quantities; everywhere I've seen it has been in the neighborhood of 4oz for $14, which won't work for the applications I need to do. My second issue with applying oils is that it's hard for me to get good coverage on a 4' tall, 4' diameter rosemary bush.

So, here's the answers I'm looking for:

  • the best method you've tested for removing spider mites from rosemary
  • advice on finding rosemary oil in pesticide quantities (e.g. 32oz) and prices
  • advice on oil application for a large rosemary plant

Thanks!

  • Ladybugs sounds good, though I don't have any experience :-/ – πάντα ῥεῖ Sep 15 '14 at 19:54
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There's a type of ladybug that specializes in spider mite control. It's called a spider mite destroyer lady beetle, or Stethorus picipes. They work well, but regular ladybugs just fly off. However, they weren't the most thorough, so I usually use neem oil, or insecticidal soap.

Soap and water is very effective, but more damaging to the plant, than neem oil, but both generally bring good results. I don't know about rosemary oil, but it seems to be very variable pricewise. I see a lot for about $2 an ounce.

Do not use chemicals like sevin. They were shown to speed reproduction, and aren't very effective.

For the application of insecticidal oil, I usually mix it with water at about 2%, and spray the entire plant until runoff.

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Do you not suffer with Rosemary Beetle (Chrysolina americana) in San Francisco? Maybe not, we have it here in the UK.

Otherwise, just a word about Rosemary Oil - it's expensive because it's difficult to produce without it being infected with botulism, but even if you found a cheap source, it's unlikely to work on whatever pest is troubling your plant because it obviously likes rosemary and won't be repelled by the oil.

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