White 'dust' on fresh rosemary

[Curlz]

I have a small rosemary bush in a pot (about 1.5' tall) that friends gave me for a Channukah gift (LOVE my friends)...in the last few days, I've noticed a white dust on some of the leaves. If I blow on it, it goes away, but I'm wondering if it's a mold of some sort and of course, whether or not it's safe to keep using it.

Fwiw, the plant is in my kitchen window, and I've kept it well-hydrated (daily) as per the instructions. I've also got a ton of new growth on it, but the white stuff is appearing on the older leaves, not the new ones.

This is not just a dusty plant--it's something else. Any thoughts???

[Sugarella]

Does it actually look like dust? It could be something in your air that's settled.

Is it sticky?? If so, it's likely droppings or secretions from a parasite. Throw the plant out. (

If not, try washing the plant off under tepid water, then leave it alone for a week or so and see if it reappears again.

[little ms foodie]

My outdoor rosemary plant has the same stuff. I always just wash it before using it. Have never had problems but now I'm wondering......

[andiesenji]

If it is sitting where it is exposed to higher temps with little air circulation, the essential oils in the leaves will be exuded onto the surface. The oil will then dry into a very fine opaque dust.

(Windows do concentrate heat from the sun.)

If you have a very fine brush, try picking some up on the tips of the bristles and see if it has the scent of rosemary. This is the easiest way to see if that is the case.

Outside, the air moving over the plants carries this dust away as soon as it dries, however if there is little or no air circulation where you placed it, then it will simply remain on the leaves.

Similar plants, with a high content of volatile oils, will do the same. Sage, for instance, however it usually is found on the underside of the leaves, where most of the oil cells are concentrated.

Edited January 28, 2006 by andiesenji (log)

[Curlz]

Good info, Andie--thanks! I've not used a brush, but have lightly touched the stuff with my finger, and it's like powder..and my hand smells wonderful--from rosemary--after I've done it.

Finally (headsmack) thought to post a photo...have a look:

The light spots that look like they're overexposed are where the white stuff is; that's the best shot I could get with or without the flash...hope it helps explain what I'm talking about! It looks like it (fake) snowed on parts of the plant!

[andiesenji]

That's a bit too much, not what I was describing. This might be a type of fungus.

You might try this, I have used it on the one little bay bush I bring inside.

First cut off as much of the affected stems that you can. You can use it, just wash it well then dry it in a very low oven

Now for the plant itself.

Cover the dirt in the pot completely with a plastic bag, tape it tightly around the base stem and stuff some paper towels in there to catch any liquid that drips down.

Make a very weak solution of bleach - 1/2 tablespoon to a quart of water - put it in a spray bottle and carefully spray the foliage, being careful to cover all of it, wait 10 or 15 minutes then wash it well with clear water. You can turn it on its side, keeping pressure on the plastic covering the dirt, to make sure it doesn't get too much water into the roots.

I do this to my bay bush in a bathroom tub, using a sprayer.

There are fungicides available but most are specific for certain organisims and I am always leery about using them on food plants, particularly herbs.

I know the bleach treatment is safe and it usually works on mild infestations.

In this area, at certain times of the year, the rosemary is attakced by spittle bugs, which are a pest, but really don't do much harm to the plants. My rosemary bushes are extremely vigorous - the "dwarf" varieties are twice the size they are supposed to be and the Tuscan Blue was 10 feet tall before my gardener trimmed it back to 6. It looked more like an Italian cypress than a rosemary bush.

Edited January 29, 2006 by andiesenji (log)

[Smithy]

In this area, at certain times of the year, the rosemary is attakced by spittle bugs, which are a pest, but really don't do much harm to the plants.  My rosemary bushes are extremely vigorous - the "dwarf" varieties are twice the size they are supposed to be and the Tuscan Blue was 10 feet tall before my gardener trimmed it back to 6.  It looked more like an Italian cypress than a rosemary bush.

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Andie, what do spittle bugs look like? I've had what look like little white flies on my rosemary - kept indoor for the winter - and in some years they've clustered almost as heavily as on Curlz's photo above. This year when I spotted them I used a food-safe bug spray, and judicious washing, and seem to have gotten them to go away. I'd still like to know what they are.

[mukki]

In this area, at certain times of the year, the rosemary is attakced by spittle bugs, which are a pest, but really don't do much harm to the plants.  My rosemary bushes are extremely vigorous - the "dwarf" varieties are twice the size they are supposed to be and the Tuscan Blue was 10 feet tall before my gardener trimmed it back to 6.  It looked more like an Italian cypress than a rosemary bush.

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Andie, what do spittle bugs look like? I've had what look like little white flies on my rosemary - kept indoor for the winter - and in some years they've clustered almost as heavily as on Curlz's photo above. This year when I spotted them I used a food-safe bug spray, and judicious washing, and seem to have gotten them to go away. I'd still like to know what they are.

←

I'm obviously not Andie, but I've had spittle bugs on my rosemary. It basically looks like a little wad of foamy spittle attached to a stalk. If you wash off the spittle, you'll find a bug or bugs inside. I had a few one year and washed them off with the hose and they never returned.

Hilary

[iguana]

It looks like powdery mildew to me. Here's an informative article from Taunton's Fine Gardening about rosemary-- it says lack of air circulation on indoor plants can promote powdery mildew.

http://www.taunton.com/finegardening/pages/g00060.asp

The article says to run a fan to discourage mildew. If you do that, trim off all the affected foliage as it's covered in spore packets and fanning will just encourage spread.

[bjones9942]

Andie -

I had to look at where you live ... my rosemary was supposed to get to 4 feet. Six to eight feet later, both in height and width, I find I can no longer make my way down the side of my house (I was thinking small hedge along the house when I planted all 14 of them). I also no longer have the desire to use rosemary when cooking, although I still love the smell.

[andiesenji]

Andie -

I had to look at where you live ... my rosemary was supposed to get to 4 feet.  Six to eight feet later, both in height and width, I find I can no longer make my way down the side of my house (I was thinking small hedge along the house when I planted all 14 of them).  I also no longer have the desire to use rosemary when cooking, although I still love the smell.

←

I still love rosemary in many things, however it can become overwhelming. A little goes a long way. I have several varieties and most have great culinary value, however a couple are not. One is a cedar/pine-scented rosemary that I use in my closets and often toss a sprig on the dashboard of my van as it counteracts the sometimes unpleasant odor that develops when the van is sitting in the very hot sun for long periods.

This area is the high desert, over 2500 ft altitude and we get very hot summers and very cold winters similar to the area where rosemary originated. It loves it here. Many of the housing developments in the hills use prostrate rosemary for ground cover on hillsides to prevent erosion and it develops into a very dense mat only about 4-6 inches high.

Iguana, I think you are right about the powdery mildew - note that in my first post I mentioned lack of air circulation and excessive heat.

However I have found that the mild bleach bath does work to destroy the residual (unseen) spores that remain on seemingly unaffected plant parts.

I also use a very diluted spray of insecticidal soap, water and Listerine (or a cheaper generic) as recommended by Jerry Baker in one of his print gardening newsletters (long before the internet) to which I subscribed for years.

The spittle bugs seem to blow in on the wind, and can be an annoying pest but seem to do very little damage to healthy plants (Mine are like The Day of The Triffids) but I use the homemade spray in a small (half-gallon) pressure sprayer, followed a short time later with a blast of water and they rarely return.

Edited February 12, 2006 by andiesenji (log)

[bjones9942]

I think rosemary is one of those strange plants that grows for people it likes! Seattle is far from having hot summers / cold winters - but my tuscan blue grows like a weed. Eastern exposure with only morning sun. Perhaps it was the 3 inches of steer manure I tilled into the soil before I planted them? I get a kick out of the little $2 bags of rosemary the store sells.

Anyway, back to topic ... I don't have the fungus problem, but I do occasionally see the spittle bug evidence. And spiders. Generally a fungus problem is due to too much water and poor circulation. After the bleach treatment, I'd see about putting it somewhere with a little more breeze.