A question came in this week to Ask Gardenerd that I have been asking myself for awhile, but never felt compelled to research the answer. Now I have no excuse:
“Hello! The leaves of many of my herbs have white speckles on them
lately. (It almost looks like they’re variegated). It’s definitely not
on the leaves, but more so ‘in’ the leaves and is appearing on many of
the varieties, such as thyme, basil, and cilantro. Any ideas on what
might be the cause? Many thanks!!” 
I’ve seen this in my own garden – and this web forum not only has a great picture of the damage to several different types of herbs, but also offers a possible cause and solution:
White Spots on Herbs – take note of the homemade spray recipe listed in the forum.
It’s possible that you have either leafhoppers or thrips.
Leafhoppers
Various Leafhoppers. Photo courtesy of Illinois Natural History Research
Leafhoppers come in many shapes and colors, but they are usually small and deftly jump off your plants just when you think you might be able to catch them. They have sucking mouth-parts and can transmit diseases to plants, though most commonly they just damage them in the way you have experienced.
Thrips
Image courtesy of IPM Labs
It seems like there’s a specific type of thrip for every veggie out there. I’ve experienced damage from onion thrips, found larvae on my strawberries, and obviously the herbs are well acquainted with thrips as well. They are harder to find, but the damage is easy to spot. Some of them pupate on the leaf, but most seem to reproduce and pupate on the ground.
UPDATE: It could also be spider mites. See this newsletter for a solution.
Control
While most plants will out-produce the damage, it’s still annoying, so there are a couple things you can do:
Sticky Traps
– These yellow traps help with all kinds of small insects, including thrips and soil gnats, aphids and more.
Moisture – keeping your plants well watered will help, as thrips and leafhoppers like dry conditions.
Natural Predators – lacewings, ladybugs and parasitic wasps tackle your leafhopper problem, so plant beneficial flowers that attract them to your garden.
I hope this helps. Thanks for writing in, and keep us posted on your results.
Hi, i live in florida, and I am having the same problem too, what kind of remedy I can use for the white spot in my herbs?
Elba, any of the remedies listed in the blog post will help you. Click through for the recipe, and click the newsletter link to get more help.
please let me know what the recipe is for the herb spray, I can’t find it on the page.
Thank you
Thanks for bringing this to our attention, Betsy. We’ve fixed the link and if you scroll down you’ll find a recipe for home made spray. Keep in mind that we now opt for putting down worm castings first, and applying a good quality compost tea (with microbes that help control the lifecycle of spider mites) over insect sprays, but if you don’t have access, this is a good option.
I have these too. Just thought it was a disease i haven’t learned about, yet. Now I know, too.