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Brown spots and holes on leaves on my mint and basil plants

Mint    United States

Hello,

I bought and planted some herbs in pots that I keep on my porch about 2 weeks ago. I am starting to see holes and brown spots on all of my plants: peppermint, spearmint, and basil. I have looked up a lot of information and pictures about what potentially might be causing the issue, but have not been able to figure out if it is an insect, slugs, or some kind of fungus. I have not yet been out at night to see if there are slugs or beetles on the plants, but I have not seen traces of slugs in the mornings.
The mint plants still have lots of healthy looking leaves, but the Sweet Basil plant has taken a real beating.
I sprayed the plants with insecticidal soap a few days ago, but am not sure if it is working.
Any advise would be greatly appreciated.

Many thanks,

Monica


Posted by: Monica (1 point) Monica
Posted: May 19, 2015




Answers

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The holes certainly seem to suggest that an insect is chewing the plant. Hard to say exactly what but likely some kind of caterpillar or, as you say, slugs. Scout the plants carefully for any signs of the pest. Turn over the leaves and check the stems too. Caterpillars can be safely treated with Bacillus thuringiensis (BT or Bt for short) application but is best to confirm what the pest is before selecting treatment.


Posted by: Lindsay McMenemy (2 points) Lindsay McMenemy
Posted: May 19, 2015


Monica commented,
Thanks Lindsay! It might be caterpillars. I have found a few small ones in the house, which I assume fell on us when we were outside. So far I have not been able to see any bugs on the plants. I'll keep looking! If I do find caterpillars, is a product like Safer Brand Garden Dust the right thing to use?
over 4 years ago.

Lindsay McMenemy commented,
Yes, safer brand garden dust contains BT and would be ideal
over 4 years ago.



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It looks like caterpillar damage to me too. It also (in one image) looks older because of the brown discoloration around the hole where the leaf has died. It seems a low level of damage and you have used a soap. So, keep checking but may have reduced the herbivory.

update: May 28th 2015
I heard from someone on twitter* that soapy water on Basil is not a good idea. Suggestion was to pick off eaten leaves. The new leaves look good.

From Nicky Kyle who grows a lot of produce and is clearly an expert http://www.nickykylegardening.com/


Posted by: David Hughes (43 points) David Hughes
Posted: May 20, 2015


Monica commented,
Thank you David. I have finally seen insects on my herbs, and especially on the potting mix in the chives pot. They are small black ones, that kind of look look like little fruit flies. Any idea what these are and how to get rid of them?
over 4 years ago.

David Hughes commented,
do they have wings? Flies do not chew leaves. They do lay eggs that turn to grubs, but they too do not chew leaves. This looks like a caterpillar damage

do you see many insects?

over 4 years ago.

Monica commented,
They do look like they have wings, but I am not 100% sure. I saw quite a few, but most of them are on the potting soil, and not on the plants. I have never seen a caterpillar on any of the plants. Do they mainly feed at night time?
over 4 years ago.

David Hughes commented,
If the insects are on the potting soil and have wings, they are not the culprits. It may be that the soil is damp and attractive for them. They might be feeding on fungi growing there.
The original damage is likely a caterpillar and yes they can feed at night. Are you getting more holes developing

over 4 years ago.



0
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Thanks David, that's good to know! I'll have to remember to go out at night with my flashlight to look for caterpillars. I've seen a few more holes on the mint, but not on the basil. I have sprayed with the insecticide soap again, but guess I should get that powder with BT for caterpillars if I manage to catch any of them in action. Thanks again for responding to my questions.


Posted by: Monica (1 point) Monica
Posted: May 28, 2015


David Hughes commented,
see my edits on the original answer
over 4 years ago.



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