Ask a Question forum: Rose - discoloration of leaf and black dots on back

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Hong Kong
JohnNg
Dec 22, 2016 6:31 PM CST
Hello,

Some leaves of my rose (in pot) are discolorating, showing some yellowish spot and the surface is a bit grayish. Besides, there are some black dots (protruding) on the back which can be wiped off with a damp cloth. The discoloration is quite even over a leave (as in picture), instead of showing patches of discoloration while other area looks normal.

Here's the picture.

Could somebody help identify what is the disease with this rose?
Thumb of 2016-12-23/JohnNg/1b3fb9

Thank you very much.

Name: Daisy I
Reno, Nv (Zone 6b)
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DaisyI
Dec 22, 2016 8:14 PM CST
Welcome!

Can you wipe the discoloration off the front of the leaf also?
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Hong Kong
JohnNg
Dec 23, 2016 12:28 AM CST
Hi Daisyl,

Unfortunately, the front discoloration cannot be wiped off.

Thank you

Name: Lyn
Weaverville, California (Zone 8a)
Garden Ideas: Level 1 Garden Sages Celebrating Gardening: 2015
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RoseBlush1
Dec 23, 2016 2:54 AM CST
@JohnNg ...

I am not sure what part of the world you where you are gardening. If you are gardening in the United States, roses are dormant this time of year. The leaves on your plants are old and are not truly functioning to serve the plant. Photosynthesis slows down in roses when temps hit around 70F. So, it makes sense that they do not look like healthy functioning leaves. The plant is not supporting them right now.

The reason the leaves are hanging on is that modern roses, roses with china and tea in their lineage do not go completely dormant and hang onto the leaves even when the leaves are not working to serve the plant.

In spring, when you do your regular pruning, you will want to remove those leaves and new growth will come in and your rose leaves will look like healthy leaves again.
I'd rather weed than dust ... the weeds stay gone longer.
Name: Sue
Ontario, Canada (Zone 4a)
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sooby
Dec 23, 2016 5:40 AM CST
Welcome! Just wondering if you've seen any insects that look like the pictures in these links (thrips) since they leave black specks on leaves (their droppings):

https://www.google.ca/search?q...

https://www.google.ca/search?q...
[Last edited by sooby - Dec 23, 2016 5:42 AM (+)]
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Hong Kong
JohnNg
Dec 23, 2016 7:41 AM CST
@RoseBlush1 thanks. I live in Asia, it is currently about 70F and 60~80%RH. I am not sure about the what is the species of the rose. Definitely hope the symptom is normal, but since it appears on a few leaves while the other looks normal, and the plant is still growing flowers, it worries me.

@sooby thanks. there are a few black flying insects around. will spraying the leaves to kind of wash them do any good or harm to the plant?

thanks all.
Name: Porkpal
Richmond, TX
Charter ATP Member I was one of the first 300 contributors to the plant database! Keeper of Poultry Farmer Roses Raises cows
Garden Ideas: Level 2 Celebrating Gardening: 2015 Plant Identifier
porkpal
Dec 23, 2016 7:49 AM CST
Washing the leaves sounds like a good idea to me.
Porkpal
Name: Sue
Ontario, Canada (Zone 4a)
Daylilies Birds Enjoys or suffers cold winters Native Plants and Wildflowers Butterflies Annuals
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sooby
Dec 23, 2016 9:37 AM CST
John, whether it will harm the plant depends on what you use. It should be something that is compatible with roses and will kill thrips, if that's what they are. If it is thrips it is often recommended to use a systemic insecticide but if you don't want to do that you could try an insecticidal soap which you will probably need to repeat. Spinosad is also often recommended for thrips. @RoseBlush1 can probably advise what is safe for roses.

Would it be possible to post a picture of the whole plant so we can see the over-all effect of the problem? Does the greyish seem to be an actual greyish substance on the leaf or is it just that the leaf has a greyish look to it that seems more internal? Also if you can get a picture of the flying insects we may be able to tell if they are thrips or something else.
Name: Lyn
Weaverville, California (Zone 8a)
Garden Ideas: Level 1 Garden Sages Celebrating Gardening: 2015
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RoseBlush1
Dec 23, 2016 6:59 PM CST
John, thank you for letting me know where you are gardening.

Unfortunately, I cannot give you any advice as to any products you may use to control insect damage on your roses as I have a no spray garden.

Since you did mention that this is just impacting a few leaves instead of the whole plant, if the leaves that are looking damaged are "old", it may be that the rose is just abandoning the leaf because it is no longer performing its function of photosynthesis. If this is true, it's just a rose being a rose. However, if you do have an insect infestation, you generally will find damage on the old leaves as well as younger leaves.

Until you identify the insect, washing down the plant is a good practice.

I'd rather weed than dust ... the weeds stay gone longer.
Hong Kong
JohnNg
Dec 24, 2016 12:35 AM CST
Hello all,

Here are more pictures of the rose.
With a further inspection,
1. I found a tiny bug under a leaf,
2. some leaves wrinkles and with brown patches on the back.
3. the grayish thing on top looks like something is breaking off the surface of the leaves

I am thinking of spraying/washing the plant with tap water only.

Thumb of 2016-12-24/JohnNg/e85a57
Thumb of 2016-12-24/JohnNg/942b76
Thumb of 2016-12-24/JohnNg/37a7fb
Thumb of 2016-12-24/JohnNg/348009
Thumb of 2016-12-24/JohnNg/4be43e
Thumb of 2016-12-24/JohnNg/d9a885

Thanks all.
Name: Sue
Ontario, Canada (Zone 4a)
Daylilies Birds Enjoys or suffers cold winters Native Plants and Wildflowers Butterflies Annuals
Region: Canadian Keeps Horses Dog Lover Plant Identifier Garden Sages
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sooby
Dec 24, 2016 6:58 AM CST
Thanks for the pictures. The bug is definitely not a thrips, it looks more like a mite but hard to see for sure. The black specks do look like some kind of bug droppings though. The curly leaf could also be from a pest. The plant looks a little tall and stretched, maybe just the cultivar or is it growing in the shade? Are the leaves with the problem mostly the oldest ones or are they scattered?
Name: Lyn
Weaverville, California (Zone 8a)
Garden Ideas: Level 1 Garden Sages Celebrating Gardening: 2015
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RoseBlush1
Dec 24, 2016 11:35 AM CST
Thank you for the photos, John.

The brown patches can be caused by several things when you are growing roses ... and other plants ... in containers. There are a lot of variables. Here are a few examples:

1. Keeping a container plant with even moisture throughout the growing season is not aways easy. If the container dries out for even one day, you may see brown patches as a sign of water stress.

2. They could also be caused by "fertilizer burn". You may have used a little bit of too strong of a solution or mixture of fertilizer during one of your feedings.

One rule of thumb in feeding container grown roses is to water the plant heavily the day before feeding and to feed lightly and more often.

3. They could be caused by "salt build up" in the container. To simplify, fertilizers are salts which are broken down by soil bacteria into a form which the plants can take up by reverse osmosis. Periodically it is wise to flush the soil by heavy watering to reduce the salt build up in the soil in the container.

Also, with roses and other plants, general practice is to replace the soil every 3 to 4 years because this refreshes the soil and gives you an opportunity to do a root prune, if necessary.

I'd rather weed than dust ... the weeds stay gone longer.
Name: Philip Becker
Fresno California (Zone 8a)
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Philipwonel
Dec 25, 2016 11:59 AM CST
I'd wash em with soapy water every 2 or 3 days for about 10 days or more. If bad infestation. Or ownce a week otherwise. 1 tablespoon regular ivory or dawn dish soap to gallon of water. In morning so they dry off and dont get mildew. Thumbs up
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Name: Lyn
Weaverville, California (Zone 8a)
Garden Ideas: Level 1 Garden Sages Celebrating Gardening: 2015
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RoseBlush1
Dec 25, 2016 1:04 PM CST
Philip ...

That is only necessary if there is truly an insect infestation, which would show up by all of the leaves on the plant being impacted instead of just a few.

Just washing the plants with water is sufficient. Soap leaves a film on the leaf and can impair the photosynthesis process. Generally, just washing the plant with plain water daily for a week will interrupt the breeding cycle of most insects. Then washing the plants weekly keeps any new infestation from getting a foothold.
I'd rather weed than dust ... the weeds stay gone longer.
Name: Elaine
Sarasota, Fl
The one constant in life is change
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dyzzypyxxy
Dec 25, 2016 1:38 PM CST
Looks somewhat like spider mite damage to me. Washing the plant down with a spray of soapy water then rinse off with tap water is a good idea. Be sure the soapy spray hits all the undersides of the leaves as well as stems, and the soil surface too. About 1/2tsp. dish soap to a liter of water is enough.

This is a good thing to do for any plant grown indoors in winter because the dry conditions of our heated homes favor spider mites.
Elaine

"Success is stumbling from failure to failure with no loss of enthusiasm." –Winston Churchill
Name: Lyn
Weaverville, California (Zone 8a)
Garden Ideas: Level 1 Garden Sages Celebrating Gardening: 2015
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RoseBlush1
Dec 25, 2016 2:53 PM CST
Elaine ...

As I mentioned above, I use just plain water to control spider mites, too, in my garden of about 100 roses. My summer climate is spider mite heaven and washing the roses even without soap is sufficient to control any possible infestation.

What I am trying to share is that you really don't have to have a special spray routine to control many insects in the garden.

I know that controlling spider mites indoors is much more difficult.
I'd rather weed than dust ... the weeds stay gone longer.
Name: Elaine
Sarasota, Fl
The one constant in life is change
Cat Lover Master Gardener: Florida Tropicals Multi-Region Gardener Vegetable Grower Region: Florida
Herbs Orchids Birds Garden Ideas: Level 2 Garden Sages Celebrating Gardening: 2015
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dyzzypyxxy
Dec 25, 2016 4:04 PM CST
So right, Lyn and I have you to thank for the health of my Brugs in the garden. I hose them off once or twice a week if it doesn't rain and have no more problems with mites at all.

But as you say, indoors it's a bit more difficult. Hauling a big plant to the shower stall if it's too cold outside to use the hose is a real pain. The soapy treatment is just a little bit of help, I think.
Elaine

"Success is stumbling from failure to failure with no loss of enthusiasm." –Winston Churchill
Name: Sue
Ontario, Canada (Zone 4a)
Daylilies Birds Enjoys or suffers cold winters Native Plants and Wildflowers Butterflies Annuals
Region: Canadian Keeps Horses Dog Lover Plant Identifier Garden Sages
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sooby
Dec 25, 2016 4:27 PM CST
Just to add that John is in Asia and I'm not sure that this plant is indoors since the temperature is in the 70s, although it's obviously in a pot. Also there may be pests there that we don't have in North America. There are black bugs flying around and what look like droppings on the leaves, not that that necessarily precludes spider mites and there does look to be a single mite of some kind on one of the pictures. Whatever, spraying with water won't do any harm (other than maybe encourage fungal diseases) but it would be useful to know what the flying black things are if not thrips because if they're a pest they won't be affected by water or soap unless they land on the plant while it is still wet.
[Last edited by sooby - Dec 25, 2016 4:28 PM (+)]
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