aefernandez
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White and black spots on herb garden

I have a small herb garden in my kitchen windowsill and over the past few days have noticed that all of the leaves have small white and black spots, and are starting to shrivel. Mostly on the basil, oregano, and thyme (pictured) but also a bit on my spearmint and rosemary.

I didn't see any bugs and I haven't changed my watering or fertilizing patterns so I'm not sure what the issues. Does anyone know what the issue might be? Hoping there's something I can do to save the plants!
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applestar
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Re: White and black spots on herb garden

I think these are signs of thrips damage — I hope someone else can confirm.

In the meanwhile try putting the pot of herb in the sink and using strong sprays of water from hand sprayer or kitchen sink sprayer to thoroughly rinse the underside of the leaves. This is a good idea as regular practice — once or twice a week.
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rainbowgardener
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Re: White and black spots on herb garden

The white "spots" are definitely the marks left by some kind of sucking insect. Check the undersides of the leaves. Try shaking the leaves over a piece of white paper. Should help you determine what pest you have.
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imafan26
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Re: White and black spots on herb garden

Thrips are common pests and many of them are very tiny and you would need a magnifier to see them. The plants are indoors and indoor plants are more stressed than outdoor ones. Predators also won't be able to get in. Horticultural oils and soaps are usually safe, and spinosad may also be an option, but it is best to check by spot spraying first on just one leaf to make sure it won't make the plant worse (phytotocixity).

Since these are herbs, you will be very limited in other chemicals you can use. Most herbs will not be listed on the label and the label is the law.


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pepperhead212
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Re: White and black spots on herb garden

You also mention black spots (though I didn't see those), which appear especially on basil as soon as it gets cold out, but not necessarily frosted. Where are you located?
Dave

aefernandez
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Re: White and black spots on herb garden

Thank you all! I shook the leaves over a white envelope and noticed very tiny bugs - almost didn't even see them until I noticed them moving.

I'm concerned there's been too much damage to save the herbs. I was going to try neem oil, but will I be able to bring the plants back to their healthy state?

Thanks, again! Still very new to indoor gardening.

pepperhead212
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Re: White and black spots on herb garden

I missed that the pot was on the windowsill - sorry. If I had seen that it was indoors, I would have immediately thought of aphids on mint. I have tried 3 times to grow spearmint indoors, in hydroponics, and each time the mint would grow like crazy, yet get covered with aphids, and only on the stems! The leaves would have white specks, but only because of the aphids molting, and the white was the empty "shells", or skins of the aphids. The basil around them would also get a few of them, from spillover, but as soon as I removed the mint each time, the aphids would disappear. Peppermint, OTOH, does not attract aphids indoors or out, and spearmint, which I have a huge patch of every season, never gets any bugs at all outside. Go figure!
Dave

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applestar
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Re: White and black spots on herb garden

Good thing about herbs is that in most cases, they will re-grow rapidly after being trimmed. So go ahead and trim off and discard leaves or lengths of stems with leaves that are too bug-eaten ugly to eat yourself. New shoot buds will form from leaf nodes and they will grow, bushier.

As long as you have taken steps to eradicate the pests, the new tender shoots and leaves will grow and fill out.

A couple of my favorite ways to eradicate pests on edibles — obtain and release natural predators (my 1st choice) — ladybugs, predatory mites, predatory wasps...etc.

...then...

(if not utilizing natural Garden Patrol and am not concerned about killing the good guys — typically only on indoor plants)
  • Horticultural/food grade diatomaceous earth is effective for most bugs if they are not too small like mites (not sure about thrips), I use a soft paint brush and dust the plant
  • ... I use natural liquid soap called Dr. Bronner’s — I like peppermint for washing hands and use it at all the sinks — it is very strong so I use it cut in half with water in liquid soap dispensers. I wet my hands, suds up my hands with this, wet the herbs with water, put the suds on the herbs, and then rinse off. Probably all within less than 5 minutes. Very un-scientific. I think of it like giving them a “wash” and am more concerned about burning the plants by leaving the soap on too long. The way I’m doing it, the soap bubbles suffocate the bugs and make the weakened but often not quite dead bugs let go of the plant more easily when rinsed off. :twisted:
    Depending on the herb and how they are potted, I fill a container with tepid water and dunk the stems and leaves and swish around to rinse. If needing to hold the pot upside down, I wrap the pot and soil with plastic — put in plastic bag with opening twisted around the stem or use food wrap — so the soil (and plant) doesn’t fall out.
  • I also take a spray bottle — about 8 oz to 16 oz, fill with water, a (dribble) of the diluted liquid soap, a drop or two of light salad oil like sunflower or safflower oil, maybe canola/rapeseed oil, and a drop or two of clear alcohol like vodka or rum, shake well and spray. I sometimes add a pinch of baking soda. I think actual recipe is something like a teaspoon to a quart or a tablespoon to a gallon. If oil is added, I don’t use when the plants are/will be in direct sunlight. If spraying, I follow by thoroughly spraying with filtered water or rinse off in the sink.
When there is a pest infestation, you need to dedicate yourself to treating the plants at least twice a week for a couple of weeks to break their life cycle and eliminate adults and eggs and newly hatched nymphs. If you need to wash them often, you need to be careful not to overwater, especially herbs that prefer drier conditions. You will also need to modify/reduce your watering regimen after cutting them back since there is less leaf surface to support and less to evaporate.
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