Identify These leaf spots?

[JoeHibiscus]

My Hibiscus plants have the black spots shown in the attached picture. Can anyone tell me; are they bad? What are they? They are on the undersides of older leaves. New leaves remain clean for many months but eventually develop the spots.

The spots never move, overtime the number and size of the spots increases. The plants drop approx one leaf every 2 weeks. However they grow many more than they drop. The plants are indoors. I live in Washington state where it is always rainy and cloudy - so there is very little bright light and never sun - even in the best window.

The plants seem generally happy otherwise and flower constantly all year.

Thank you.

[Darkhorse]

It does look like your plant has some kind of leaf disease.  Have you tried spraying the entire plant with Bayer Insect, Disease, and Mite control?  This may help.  Plants deal with bacterial, viral, and fungal diseases just like animals do. 

I haven't dealt with them personally, but apparently leaf diseases don't normally pose a big threat to a plant.  The problem should be taken care of, however.  Sorry I can't say more but this is just from what I remember reading at some point.

[blupit007]

I would like to hear what this is as I also have one plant with this...

[blupit007]

I see that no one else has a solution for you, hopefully I can get some help as well.  I have some spots on one of my plants that is quite a mystery to me.  I just pluck them off.  This plant was put in a Light box about a month ago, I would think that it is used to the intense lights in there by now, but these came within just the last few days.
The other leaf photo is a newer growth, that has the edges turned up and the body of the leaf is ribby.

[roadrunner]

Joe, I've also had a problem with black spots that look very similar to the pics that you posted. Are the spots on the undersides of the leaves raised and shinny?  That is how they appear in your pics.  I have an earlier post from August in this section titled "Yellowing leaves with black spots" which includes a few pictures and some comments by other posters as well as Charlie. The spots spread much faster on mine than what you describe for yours so I wonder if it's because your use of Wilt Proof that you described in your previous post may retard their spread to uninfected leaves.   Unfortunately I don't have a solution either as I'm still dealing with the problem and my latest attempt at eliminating it was spraying the entire collection yesterday with the Bayer 3 in 1. I've also had an insecticide resistant whitefly problem all year that may have a connection to the spots so hopefully the Bayer will take care of both problems.

dave

[JoeHibiscus]

blupit007, there is no question, you have spider-mites. I'd know their evil damage anywhere.

Roadrunner, yes the black spots are raised, and they do not come off at all with que-tip or otherwise. They are shiny cause plant is prayed with wilt-proof. So I'm guessing they have a weird leaf fungus of some sort. I don't have high humidity, but I have very low light and low heat. I'll have to watch to see if the spots are worse in the winter when temps are low and light is at lowest. Not sure what else I'll do about it because it does not seem to be seriously harming the plants.

[helixturnhelix]

I have seen this on my plants too, I just added a fan to the growing area and it seems to have gone away.  I think that good air movement is key for keeping this fungus at bay.

[Charlie]

We have to expect some leaf drop from hibiscus. It is their main way to react to stress in the environment. They also naturally replace older leaves with new leaves on a regular basis. As old leaves die they show weird signs of their demise as chlorophyll decreases, yellowing increases, and opportunistic fungi attack. Insects can breach the leaf surface which also allows fungi and bacteria to get a toe-hold, so to speak. As long as the leaf drop is moderate it's usually not a symptom of a bigger problem.

In looking over the Wilt Pruf web site I see that there are claims made for suppressing various leaf fungus diseases. I'm liking this stuff more and more and look forward to testing it to see if it works in my conditions that allow for rapid mite build up due to high temperatures and relatively dry air. Have to wait for spring to come for that but other than very expensive miticides this is the first promising approach I've heard in quite awhile.

Charlie

[roadrunner]

Charlie I see that you just added a post while I've been typing this one. I'm posting this one as is.  I don't know if anything in my post is something we haven't gone over before for this problem.

The spots on mine are raised and shinny and that's before spraying them with anything.  This started inside the house last winter in sunny windows and continued inside the greenhouse this summmer. The greenhouse is very well ventilated with a door at one end and a window at the other end both open and a box fan circulating air throughout each day. I tried isolating the infected plants, then removing all the spotted leaves, spraying with various insecticides, horticultural oil, neem, and fungicides, and a couple of other things that don't come to mind at the moment.  On a few the spotting then started showing up on all the new growth which became stunted.  This occurred after all the above steps were taken and was the beginning of the end for 3 plants so far.  I guess the badly infected plants had gotten too weak and I've lost Love Story, Heaven Scent, and Bluebird just died this week.  Cherry Appaloosa appears to be next in line as it has been in steady decline for the last 3 months.  Rosalind, Cindy's Heart, and Blonde Ambition all have it but still look strong.  Overall most of the collection shows no signs of it.  Several times I've thought I had eliminated it, but it comes back.  Yes it does appear it could be spider mite related but the visual damage doesn't appear typical of the pictures that I've seen for that.  I've had an ongoing problem with spider mites and whiteflies as I've mentioned earlier, but not at major infestation levels, but I suppose they could be the source or a contributing factor for this.  Charlie believes this is secondary in nature.  I'm wondering if it is bacterial or viral instead of fungal and the spider mites and whiteflies are spreading it.  Anyway I'm trying the Bayer 3 in 1 now since I finally have it and will go to the Greenlight Tree & Shrub with Safari next for the feeding pests if necessary.  Cheez, it's almost like the neverending battle with blackspot on roses, except I've never lost a rose to that.  

dave
 

[Charlie]

Dave, I sympathize. It can drive you nuts trying to figure out a knotty hibiscus problem. Having never seen this particular problem, I don't have much to offer that is specific for it.

A few observations, for whatever use they may or may not be:

Air circulation at night is more important than air circulation during the day. Lots of problems are solved with that simple fix.

Cindy and I have noticed that after having the systemic Kontos in our indoor pots for many months the hibiscus are noticeably lush and green and lacking leaf blemishes and problems. That has led me to believe that a lot of leaf problems are caused by insects whether we ever see the actual insects or not. The Safari you mentioned will take care of the whitefly problems you mentioned. The 3 in 1 will likely stimulate an increase in mite population that will become noticeable about 3 weeks after using it while helping with some types of leaf fungus. You might want to try the Wilt Pruf at the same time or take other mite precautions after using the 3 in 1.

Bacterial leaf diseases are among the most difficult to cure. One called Xanthamonas gave a commercial grower in Florida a lot of trouble a few years back. Hopefully your plants don't have such a problem. Virus problems show in a different way, such as yellow rings or larger spots.

I sure hope you get it figured out and do not suffer more losses! I know it's not the most pleasant solution to your space problem but is a solution. 

Charlie

[roadrunner]

I strongly doubt it is a circulation problem since the window in the greenhouse is left open at night during the summer and the greenhouse actually has very good air circulation because it isn't very air tight.  That's one of the reasons I haven't tried to heat it during the winter time.  It's too leaky air wise. Technically it probably isn't really a greenhouse. 

I'm confused about one thing that you wrote though.  The Bayer 3 in 1 is the product that you have been recommending for eliminating spider mite infestations before you started using Kontos.  I thought it was the Bayer Tree & Shrub systemic that stimulates the mite egg laying, not the Bayer 3 in 1 which has a miticide in it.

dave

[Charlie]

Dave, you bring up a sticky issue about the Bayer products containing imidacloprid. When the pesticide imidacloprid was first introduced over a decade ago it was considered almost a miracle product. Very low toxicity for mammals but highly lethal to sap sucking insects and a long lasting systemic to boot. I was fighting white flies when I first heard about it but after one application they completely disappeared. Meanwhile this chemical found its way into all sorts of products, including dog shampoos for fleas, and is one of the mainstay ingredients in many of the Bayer insecticide formulas. After some years people began to notice that spider mite outbreaks followed applications of imidacloprid like clock work. I made it standard practice to apply a miticide during the week following any applications of imidacloprid and that took care of the problem.

Anyway, much later Bayer introduced the 3-in-1 product containing imidacloprid, a miticide, and a fungicide. That sounded great but the chemical they call a miticide is only fair at controlling mites, definitely not one of the better miticides. We considered it better than no miticide and decided to recommend the product since it was better than having people use imidacloprid without dealing with the mite issue at all. This was the best solution available to people not using agricultural grade pesticides. We also recommend Tree & Shrub (imidacloprid only) because it is formulated for long lasting systemic effect, much longer lasting than the 3-in-1 spray even though both contain imidacloprid. When using Tree & Shrub the user should always consider the mite stimulating effects and take precautions.

Then along came Safari. This chemical kills sap sucking insects systemically without stimulating mites. We recommend it for sap sucking insects but it does not control spider mites (nor stimulate them). For that the best commonly available pesticide product is still the Bayers 3-in-1 but unfortunately it is not very good at controlling mites. This is why we have been looking at alternatives for mite control. Also why Wilt Pruf is sounding so good at this point. One suggestion for you - find the smallest, cheapest bottle of Wilt Pruf you can find and give it a try on one or more plants. See if the test plant(s) do any better than the other plants nearby.

If any of this is not clear please let me know.

Charlie