So, my cousin/housemate has spearmint that she grows and makes tea from and also uses the leaves in a salad she likes to make. The soil where it grows is fairly poor, and its watering is uneven.

It always has a few white spots on the leaves. I've never worried about it and know we have major work to do on the soil, which is underway.

But another cousin received a plant of our spearmint as a gift and was asking if this white speckle on the leaves was something to be concerned about. I realized I had no clue what it is. The look is as if someone spattered the plant with white flecks.

My guess is it's either a soil deficiency or an effect of uneven watering that has caused the leaves to develop unevenly.

I have no picture right now but will try to get one.

Anyone have any clues?

Thanks!

Kyla, the picture will give us a lot more clues as to what the spots might be. Mint really doesn't have much insect or disease problems.

But you could try putting a division of the plant in a pot (you could grow it on the windowsill for the winter) and see if better soil and regular water make the spots go away.

I should be able to get a good picture tomorrow. Thanks!

Thrip damage?
Spider mites?

Not the greatest picture but it might help.

I managed to focus on an area with lots of the white spots. Not all leaves are this affected.

Can you also add photos of the undersides of the leaves?

I'll see what I can do!

Does anything fly or hop out when you disturb the plants? I can't see the pic quite close enough but it looks like it could be sage leafhopper damage:

http://bugguide.net/node/view/...

That sure looks like a match Sue. And it seems they would abound in an area that was water stressed.

Honestly, I have not worked over there a whole lot. That spearmint is my cousin's baby.

I'll check into that about the leafhopper, it sounds likely to me too. My other cousin was primarily concerned as to whether there was any danger to using the leaves for tea or in food.

She also said the spots didn't appear right away but showed up suddenly shortly after she potted this up. She has potted another mint from somewhere else right next to these and it does not have the white spots. I don't know if it is in the same container or separate.

*goes to google up sage leafhopper*

(I will try to get a shot of the leaves underside later on.)

Uh oh, either she took the insects with her when she potted up the plant, or it was damage from a fungal infection that just showed up later. In either case, the leaves are fine to use.

Are the white spots bumps on the leaf, or are they depressed? I can't tell from the picture.

Yes, Elaine, and thank you, that's just what happened I feel sure.

The spots are not raised bumps; they are flat. I see similar white spots now that I am looking for them on a small dahlia in a different bed, and also on some calamint I planted way down the yard. Though much less on the calamint. This soil is in very bad shape in most places and the watering has not fully made up for lack of rain.

I'll try to get more pictures tomorrow or next day. (Things are busy right now!)

thanks again, all!

Okay, here are a couple more pictures. I pulled off a little sprig so it would be easy to focus on.

Here are the leaves, topside:



And here is that same sprig turned over to show the underside:



I chose one with maximum damage. Most leaves have only one or two specks and some leaves are clear of them. I have not seen leafhoppers however. I've also not read the URL posted up-thread yet! I need to do that soon (I did look at the picture and save the link, though.)

thanks again, everyone.

It looks to me like spider mite damage, although they don't usually go after herbs. IF you run your finger along the underside of the leaf, does it feel sandpapery? In any case, there is an easy, cheap, non-toxic solution to try - soapy water spray.

Mix up 1/2 teaspoon of dish soap (not dishwasher detergent, liquid soap you use in the sink) with a quart of water in a clean spray bottle. Spray the plants thoroughly, making sure to hit the undersides of the leaves especially. Spray again at least twice a week, also after watering or it rains, as the soap will rinse off. Do this for a couple of weeks and see if the damage stops. You need to repeat the spray a few times, hence the two weeks time frame because even if you kill off the adult mites, the eggs will continue to hatch for a week or two.

Be sure to rinse off the leaves before you use them. They will be nice and clean.

The only other thing that might make spots like that is overspray of some chemical blown in from a neighbor's yard. But that wouldn't be hit or miss, every leaf would show damage and it would only happen once, not continuously. Also it wouldn't have turned up on the plant your cousin potted up.

I tend to say it's spider mites too, especially since she said it 's so dry there. Spider mites love hot, dry weather.

Thanks, I am thinking now that spidermites is more likely than the leafhopper. I'm not too worried about it; but it's good to get confirmation that it isn't anything noxious.

The soapy water, I already have some mixed up that I used on some aphids. Don't think I can do this with the mint though, as it gets clipped and the hung to dry by my cousin, so washing it is not likely and there would be soapy tea

I'm hoping that as the soil is improved and the watering becomes more consistent, they'll have less reason to be there. As I said, most leaves are not that affected.

Update:

Since the original question, the white spots have also appeared on my calamint, and just the other day I noticed them on the leaves of the little thyme starts I planted out (which I grew from seed.)

Here is the white spotting on the calamint (with a fly who, I am sure, is unrelated, though pretty.)



Here is the thyme. One plant also has black "stuff" near the white spots.



I'm not really concerned, just quite curious. I've always felt herbs were proof against so many issues that other plants are vulnerable to, because of their strong scent perhaps -- but this? seems to target the strongly scented plants specifically!

Edit: I look at the backsides of these leaves and see nothing. From some appearances it looks similar to leafminers, but I'm sure it is not. White dots, not channels, and nothing showing on the leaf underside. It does kind of look like egg laying in there though. In mint and thyme? So odd.

Kyla, you're right, most herbs are resistant to bugs and fungi because of the aromatic oils in the leaves.

Your spotty situation is very mysterious! Did you try a little soapy water on some of them? (tell your roommate which ones you spray with it, so she can rinse them off before she dries them).

The other thing to try that is somewhat preventative, and non-toxic is a solution of baking soda and water, 1/2 tsp. soda in a quart spray bottle. If the cause is a fungus, the baking soda spray will prevent it from continuing to spread.

As you say, it doesn't seem to be doing much harm to the plants overall, and they're going to start winding down pretty soon.

I did try the soapy water on the thyme just after I took those pictures, but now, thank goodness, it is raining! And of course that's washing off the soapy water, whatever might have been left. I may not have enough soap in there, either.

If this continues to spread, I'll try the baking soda. That's a new one on me.

I'm not going to concern myself with the mint, it's too complicated and she's not worried about it, so I'm not going to bother.

My theory of the day is, whatever is going after these herb leaves is doing so precisely because they are concentrated. The bugs need the nourishment?

Makes as much sense as anything else.

I have the exact same problem. (It's the reason I logged on.) My mint patch is four feet by four feet. Each white dot is a dry spot. Each spot looks as though a bit of chemical burned away the liquid right out of the leaf. So frustrating. I can't gift it to friends this way. I used some on mine to make extract so I figured the alcohol will kill any bad guys as the hot water will in the tea, but I would rather not have white spots on my mint!