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lynncrenshaw80

What is causing these spots on the zinnias

Check the internet but didn't find any reference to the spots on my zinnias. The spots go straight through the leaf. No signs of insects.

Comments (28)

  • zen_man
    5 years ago

    Hello Lynn,

    That is Zinnia Alternaria Blight. It is caused by the fungus Alternaria zinniae. It can be combatted with a systemic fungicide like Bayer Disease Control for Roses, Flowers, and Shrubs

    ZM (not associated with any product or vendor mentioned or linked)

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  • Lynn in Parkton, Maryland
    Original Author
    5 years ago

    Well, in my zone we are rapidly approaching the end of the season, so it may be too late to do much. Does this fungus stay in the ground waiting for next year too? If so, is it unique to zinnias or will it effect other vegetables / flowers? I planted these zinnias in my vegetable garden because I needed a break from veggie gardening and wanted more cut flowers. I hope I have not introduced something new into my limited space for vegetables.

  • Lynn in Parkton, Maryland
    Original Author
    5 years ago

    Thanks for the links, ZM. Not sure why I couldn't find pictures that looked appropriate before. I have been reading up and have answered most of my questions. Unfortunately, they are not what I want to hear. I guess, I'll be pulling these zinnias out asap as Alternaria affects a lot of vegetables. Darn.

  • zen_man
    5 years ago

    Hello junco,

    " The Bayer might cure the spots but as a "systemic" it will be in the
    leaves and in the pollen of your zinnias and will affect any pollinators
    who feed from them. "

    A systemic fungicide will not cure existing spots, but can prevent further fungus attack.

    You have a right to be concerned about the effects of any systemic product. In the case of the Bayer Advanced Disease Control product, the sole active ingredient is Tebuconazole. Tebuconazole is not an insecticide, but is a fungicide. Your concern that pollinators (butterflies, bees, and such) might be harmed by zinnias treated with Tebuconazole is, as far as I know, unsubstantiated by any actual experiments or observations. The following is a quote from US EPA Memorandum Tebuconazole December 13, 2007

    " Tebuconazole is categorized as practically non-toxic (contact LDso 176 pg a.i./bee) to worker honeybees (Bayer Report 99753, 1987); therefore, the potential for tebuconazole to have adverse effects on pollinators and other beneficial insects is minimal. ...Technical tebuconazole showed no toxicity to earthworms...therefore, there is not potential for risk to earthworms. "

    If you know of any actual experiments or scientific observations indicating that Tebuconazole use is toxic to bees or butterflies, please identify them. In the meantime, I will not hesitate to use it on my zinnias. Incidentally, I have not noticed any harm to butterflies or bees, and in my opinion my use of Bayer Disease Control on my zinnias poses no risk to them.

    ZM

  • zen_man
    5 years ago

    Hi Lynn,

    " I guess, I'll be pulling these zinnias out asap... "

    That's probably best. Disease-ridden zinnias are of questionable ornamental value anyway. Don't throw those on your compost pile. They are now "a bio hazard".

    ZM

  • Lynn in Parkton, Maryland
    Original Author
    5 years ago

    As i walked around the flower beds it appears several patches of zinnias have it. I guess I won't be planting zinnias in those beds for awhile. Between the bugs, fungus, deer and rabbits, gardening Is becoming a significant challenge.

  • Lynn in Parkton, Maryland
    Original Author
    5 years ago

    I will do more research, but is there anything with which I can augment the soil to kill the spores? I've checked now and every bed with zinnias has the fungus. Does this mean no zinnias anywhere for over three years? Yikes!

  • zen_man
    5 years ago
    last modified: 5 years ago

    Hi Lynn,

    " I've checked now and every bed with zinnias has the fungus. "

    As you mentioned, Alternaria Blight is not limited to zinnias. Ironically, there is a good chance your zinnias "caught" the disease from whatever was in those vegetable beds last year.

    However, Zinnia Alternaria Blight can also be spread by spores on the zinnia seeds. Where did you get your zinnia seeds? Commercial zinnia seeds rarely carry diseases, because most of them are treated to prevent that, but zinnia seeds from other sources are very likely to carry one or more diseases, including Alternaria Blight spores. If you save zinnia seeds, or someone you know saves zinnia seeds, they should be disinfected before being planted. And you should wash your hands before handling them.

    The other source of fungal contamination is organic material on or in the soil. Was there any kind of mulch on your soil, or had you incorporated any kind of organic matter as a soil amendment? Can you post a picture or pictures of your soil in its present state? Including at the base of your spotted zinnias.

    " Does this mean no zinnias anywhere for over three years? "

    Just waiting three years is no guarantee. If that were all that is required, you probably shouldn't have had a problem this year. Lets take a close look at that problem soil. The first thing you need is really good situation awareness.

    ZM

  • Lynn in Parkton, Maryland
    Original Author
    5 years ago

    Does anyone know of anything I can use on the soil to kill the spores? I really don't want to wait three years before being able to plant zinnias.

  • Lynn in Parkton, Maryland
    Original Author
    5 years ago

    Your post came up after I posted last. I am not sure why. Anyway, got your message now.

    The plants in the flower beds were from a local nursery purchased as annuals and all three beds have three different kinds of zinnias and they all have the fungus to a different extent. Those beds were all mulched this spring.

    The ones in the veggie garden came from purchased commercial seed. There is no mulch in the garden, but I did have trouble with tomatoes in that spot last year due to a fungus which is one of the reason I planted flowers there instead of veggies. I moved the tomatoes to pots in another part of the garden. They are fine.

    Our weather has been very wet of late - started out with a drought for most of the summer and now plants are drowning. I have very clay soil. We got 5 inches of rain over several days three weeks ago and have had 1.5 to 2 the last two weeks. The spots showed up after the rain, I think. At least that is the first time I noticed them.

  • Lynn in Parkton, Maryland
    Original Author
    5 years ago

    Oh, and we usually till horse manure in to the garden rows (straight from the critter, although we select aged manure from the pile). However, this year we did not use anything, just tilled it as is before planting.

  • zen_man
    5 years ago

    Hi Lynn,

    " Does anyone know of anything I can use on the soil to kill the spores? "

    Methodology involves many things, including practicality, individual circumstances. and personal belief systems. What works fine for one person may not work at all for another. A lot of good information is available on the Internet, but unfortunately there is also disinformation. I never cease to be amazed when the subject of Powdery Mildew on zinnias comes up and the advice is always to avoid overhead watering so as not to get the foliage wet. Rain or even dew is going to wet the zinnia foliage, totally out of your control. And, oh, by the way, water actually kills the Powdery Mildew spores. Sprinkling the zinnia foliage is one PM control method, and the so-called "experts" are dead wrong. Surprise, surprise.

    But there are a lot of experts on the Internet who are actually paid to be experts on gardening methodology -- they draw a salary and it is part of their job description. I am just an amateur gardener and I won't engage in controversy involving politics or religion or controversial aspects of gardening like organic vs inorganic. And that kinda includes discussing what you can use on your soil to kill the spores.

    ZM

  • Lynn in Parkton, Maryland
    Original Author
    5 years ago

    Here are some pictures. You suggested they might help in diagnosis. The zinnias are dying pretty quickly. I'm going to pull them all out this weekend. The first pictures are the flower beds with mulch. The last are the veggie garden. I understand your unwillingness to commit to recommendations as I have been witness to strong feelings expressed on this site. I thank you for whatever advice you feel you can offer. I am just learning and am very much an amateur. Of late everything has been a struggle. I am starting to feel as if gardening at the level I want my place to be, is out of reach - besides the deer eating everything even deer resistant plants, depleted clay soil that will not drain, and bugs of all kinds, the fungus is finishing off my enthusiasm.


    Even the blanket flowers seem to have a white fungus now.




    On a happier note

  • zen_man
    5 years ago
    last modified: 5 years ago

    Hi Lynn,

    This is a detail I cropped from your first photo. Click and F11 for a larger view.

    That black mulch may be your culprit. At a very minimum, it is a good harboring place for fungal organisms. It's odd that your zinnia stems seem to be bare on their lower portions. Did you prune them and, if it wasn't you, why do you think the stems are bare like that? It almost looks like something ate the lower limbs of those zinnia plants. It may be that the Alternaria Blight may be what "ate" the missing limbs. Have you seen any slugs in your zinnias?

    " I am just learning and am very much an amateur. Of late everything has
    been a struggle. I am starting to feel as if gardening at the level I
    want my place to be, is out of reach - besides the deer eating
    everything even deer resistant plants, depleted clay soil that will not
    drain, and bugs of all kinds, the fungus is finishing off my enthusiasm. "

    It's understandable that you are feeling discouraged. However, I don't see any obvious deer damage in your photos, nor any deer tracks either. Do your neighbors also experience deer damage?

    Actually, some of your zinnias don't look too bad from a distance. You can always plan for better gardening next year. Maybe apply a little gypsum to that clay soil to loosen it up. I would get rid of that black mulch. Maybe buy some sand to use as a clean "dust mulch".

    I strongly recommend that you not throw those diseased zinnias onto a compost pile. Dispose of them as trash. Send them to a landfill mixed in with your other trash. Get a "Bug Book" to help you study your insects. Have a conversation with your County Agent. Possibly join a garden club. And maybe plan on growing a greater variety of sunflowers next year. Plant breeders have done a lot with sunflowers. You might even decide to breed them yourself.

    ZM

  • Lynn in Parkton, Maryland
    Original Author
    5 years ago

    Thanks for your encouraging words. I am hoping to retire next spring which should give me the time and energy to tackle these issues with more energy and determination. Something to look forward to.

    The mulch looks blacker than it really is due to it being wet. It is hardwood mulch and looks brown when dry. We have had a lot of rain lately.

    Yes, I have slugs, deer, and just about everything else. Slugs are usually hanging out where it is damp, particularly on whatever is left of the hostas the deer haven't eaten. Deer are my most direct problem. I have had a fawn born within 12 feet of my deck. We used to have a green screen of arborvitae but now it looks like lollipops as they have been eaten to the trunks as far up as a deer can reach. Lilies, roses, and hostas are deer candy around here. I live up against a state park where hunting is limited. The population is out of control. I usually buy a plant, wait to see if the deer eat it, and if they don't, I'll buy another. However, when the winter is bad, they will eat just about anything. :)

    Those sunflowers were also grown inside the hot wired veggie garden because the deer take the whole flower head when they start chewing on them. They don't seem to like zinnias, marigolds, and dahlias. Zinnias were my go to for color.

    I will certainly take your advice and I appreciate you taking the time to communication and advise me. Thanks again.


  • zen_man
    5 years ago

    Hi Lynn,

    " The mulch looks blacker than it really is due to it being wet. It is
    hardwood mulch and looks brown when dry. We have had a lot of rain
    lately. "

    A lot of recent zinnia problems that were reported and discussed on this forum have occurred in black (dark) mulch. This is one example: What is happening to my Zinnias? Brown leaves overnight.

    That is just one example of several recent zinnia problem threads in which it developed that the diseased zinnias were living in a black organic mulch. It seems to me that the mulch is causing more problems than it is solving. As I have suggested before, I recommend getting rid of your mulch. I use a sand mulch myself, but anything inorganic might do, like a pebble mulch. I think bare soil would be preferable to a rotting organic mulch for zinnias and other annuals.

    I notice in your last series of photos that your zinnias that aren't in "black hardwood mulch" seem to have significantly less disease. The two photos at the top of that group have the black mulch and also the worst disease. I don't think that is a coincidence. I have found that washed river sand (equivalent to children's play sand) is an effective hygienic trouble-free mulch. And as various circumstances cause it to be mixed into the soil, the sand serves as a good soil amendment.

    " Those sunflowers were also grown inside the hot wired veggie garden
    because the deer take the whole flower head when they start chewing on
    them. "

    I assume that by "the hot wired veggie garden" you infer that you have an electric fence around your veggie garden. Depending on how close your neighbors are, and whether they have children or not, you might want to consider putting up a warning sign or signs of some sort. A kid getting shocked on an electric fence would be possible cause for a lawsuit. When I was a kid on the farm, more than a few years ago, we had electric fences to control where the cattle grazed, and they (the fences) could inflict a very painful shock. Occasionally we would skin the leaves off of a tall Marestail weed and touch the stem to the fence to get a controlled shock. Touching the fence directly was painful and scary enough to discourage a repeat performance. Just make sure you are covered legally on that electric fence. Depending on where you are, it might even be illegal. Some people use motion sensors to turn on a sprinkling system as a deterrent to animal invasion.

    " They don't seem to like zinnias, marigolds, and dahlias. Zinnias were my go to for color. "

    Talk to your County Agent and local gardening experts. There are preventions for zinnia diseases, but you may find it easier to grow an alternate ornamental that doesn't need them, provided the deer don't like it.

    ZM

  • Lynn in Parkton, Maryland
    Original Author
    5 years ago

    Thanks again Zen.

    I took the zinnias out today and bagged them for the dump. Too bad, but better than spreading the fungus. I cleaned up any leaves I could find. I think you are right about the mulch as the ones in the garden looked much better, but all are gone none the less.

    No worries over the fence. No children in the neighborhood and no one comes on the property without our knowledge. It stings, but not the way the old ones used to. You are right, they were pretty powerful. This one is solar powered. If I touch it, I quickly remember it is on but the shock is minor. I think it works because the deer can "feel" the electricity and hear the soft clicks. A couple of years ago, we ran the wire further around the house to see what would happen and the deer just walked down the drive way and came in that way, so we gave up on that. (I have a game camera so I can watch them at night :)

    Just curious... what zone are you in?


  • zen_man
    5 years ago

    Hi Lynn,

    " Just curious... what zone are you in? "

    I think it is 5b. Climate change may promote me to a 6a. Since I am a zinnia hobbyist/breeder I grow zinnias year round, by growing zinnias indoors November-March. This year some of my best new hybrids appeared indoors. I have been "going after" new zinnia flower forms, like this specimen from last Winter. Click and F11 these photos for larger versions.

    That one had tubular petals with "fingers" at the end. I also like narrow tubular petals that create a starburst effect.
    Even narrower tubular petals can increase the drama of the bloom.
    I make hybrids between hybrids for greater variation. Creating new zinnias can be a lot of fun. Zinnias are relatively easy to breed, because their flower parts are easily accessible, zinnias are easy to grow, and they grow fast. I also like it that their seeds are relatively large and easy to handle. When you breed your own zinnias, you are not limited by what is commercially available. Zinnias can "do" a lot of interesting things that you don't normally see. They never cease to surprise and amaze me.

    ZM


  • Lynn in Parkton, Maryland
    Original Author
    5 years ago

    They are beautiful!!!

    I am sure it is very satisfying and rewarding to be able to use your imagination and breeding skills and then be able to see your creations come to life.

    Maybe when I retire I will be able to find something as interesting to do with my time. I would love to be able to create something as lovely.





  • Lynn in Parkton, Maryland
    Original Author
    5 years ago

    May I indulge you for one more question? I have been thinking...since I have planted zinnias in those flower beds for a few years and never had an issue before could I have bought infected plants? I know the ones in the veggie garden were from commercial seed and probably caught the fungus from the soil where I already knew I had an issue with a fungus on the tomatoes plants (which is why I planted flowers). But, I had never had an issue in the flower bed previously.

  • zen_man
    5 years ago

    Hello Lynn,

    " ...since I have planted zinnias in those flower beds for a few years and
    never had an issue before could I have bought infected plants? "

    That is actually likely. The conditions in which commercial plants are moved around and cared for provides ample opportunities for them to transmit diseases (and pests) ti each other. Zinnias are common plants and Zinnia Alternaria Blight is a very common fungus disease of zinnias. There is no need to despair because your beds got infected. There are a variety of ways of combating or controlling most zinnia diseases. Potassium bicarbonate is a common component of baking powder, so it is nontoxic and safe to use, and it is the active ingredient in Green Cure, which is effective against a long list of plant diseases. And we all have probably eaten Potassium bicarbonate in our food. As I mentioned before, plain water can be very effective in controlling Powdery Mildew.

    " Maybe when I retire I will be able to find something as interesting to
    do with my time. I would love to be able to create something as lovely. "

    It's not too early to be thinking about things to do when you retire. I enjoy photography, art, home computers, and gardening. Part of which involves breeding zinnias for fun. You might want to dabble in zinnia breeding, just to see what it is like. Grow some zinnias, save seeds from your favorites, and those seeds will please you more than the original commercial seeds. And it is really easy to cross pollinate zinnias to create your own hybrids.

    ZM

  • Pam
    3 years ago

    There is quite a bit of misinformation here. The disease is identified correctly. Comments on systemics are not correct. It depends on the type of systemic as to how long it is active and to whether it affects insects and what is mixed with it. Some systemic are only good for 7-10 days and must be reapplied. In addition many fungicides are very low toxic to bees but are when mixed with pesticides or herbicides or growth regulators then cause an issue. This particular product called -Bayer Advanced Disease Control for Rose, Flower and Shrubs Concentrate contains Tebuconazole and is strictly a fungicide and is very low in toxicity to bees. Note while lower for honey bees, bumblebees may be more sensitive to this active ingredient.. All fungicides and pesticides use demands following directions carefully and be applied precisely how and when directed. Usually it is best to apply late evenIng/night. Pollinators are asleep and not feeding and the foliage has time to dry off before early morning. Below is a link that gives most of the insecticides and fungicides and their bee toxicity. The tables you will want to look at is further down the article.- this is done by Michigan State University called Minimizing Pesticide Risk to Bees in Fruit Crop.

    https://www.canr.msu.edu/uploads/resources/pdfs/Minimizing_Pesticide_Risk_to_Bees_in_Fruit_Crops_(E3245).pdf

  • Pam
    3 years ago

    Alternaria leaf spots and blights are common leaf pathogens on many crops. Sometimes the Alternaria species is specific to a particular crop; often Alternaria alternata is the pathogen involved; this species is common, has a wide host range, and can occur as a secondary invader of senescent or injured tissue. Alternaria zinniae is the fungal species responsible for leaf spot, stem canker, flower blight, and foliar blight of garden Zinnia. Cultural control measures include rotation to non-susceptible crops for two years, control of susceptible weeds, and removal of crop debris from the planting area or prompt incorporation of refuse after harvest. Careful attention to the timing of irrigation (avoid late afternoon or evening) and proper plant spacing to reduce the amount of time during which the plants remain wet can reduce disease spread. Treat with protective fungicides at regular intervals. Among the compounds registered for use on ornamentals are chlorothalonil, thiophanate methyl, copper compounds,and mancozeb. The effectiveness and number of sprays required will vary with weather conditions.

    Here is a link to the Missouri Botanical Garden that speaks to this issue with zinnias. This disease can start with the seeds and may need to be treated to prevent it getting started. In attention, as the spores remain, the plants need to be removed and burned or bagged and sent to the dump. I prefer to burn if I can do it immediately. Never, ever compost any diseased plant material unless you can insure your pile is big enough and turned daily with the right mix to maintain temps over 140-160 degrees F for 30 days. Even then some spores and bacteria may be missed so it is safer to only compost healthy material. Read about safe composting.

    https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/diseases/fungal-spots/alternaria-blight.aspx

    https://pnwhandbooks.org/plantdisease/host-disease/zinnia-alternaria-blight

  • Pam
    3 years ago

    All fungicides, pesticides,herbicides, growth regulators need respect in their use but we need to realize which are the bad ones, and which are the serious to our environment that need to be banned - many of those are the neonicotinoids. We are using them like they aren’t an issue because we don’t spray them in the air. some short term products are fine in this regard, these nicotine like products are not. Much of Europe has banned wide use, the USA seems oblivious. Many of the plants you buy and decide to raise organically in your pollinator gardens are already contaminated and may stay so for months and years.

    Let’s talk about a real killer of bees that is in so many products out there. You probably have at least one of the main 7 of this group - in your garden shed right now. But it isn’t just honey bees. Bumble bees can be more sensitive than honey bees to many pesticides. And song birds, other pollinators and hummingbirds are most likely being affected. Plus keep in mind that honey bees range long distances in a day...so local bee keepers whose honey you may buy most likely is contaminated with these neonicotinoid. Testing has already confirmed that many sources of honey are affected in some manner. You will have to research where this testing was done and what the results are. In addition, the bees dying and having reproductive issues affect the quantity and maybe the quality of the honey if they aren’t able to produce as normal...this makes honey cost more and ends up in us.

    We did have a ban on these types of pesticides in all federal lands so they could clear out or remain untainted if not yet affected. However, President Trump has lifted the ban and the government and people with federal land leases are able to use these again.
    There are 7 main neonicotinoid insecticides - look at any products you have or are thinking of buying to see if you see these names. Write them down and carry in your wallet. Be precise and don’t decide just because another product sounds or looks like one of these - they are the same.

    • Acetamiprid.
    • Clothianidin.
    • Dinotefuran.
    • Imidacloprid.
    • Nitenpyram.
    • Thiacloprid.
    • Thiamethoxam.

    Neonicotinoids are classified by the EPA as both toxicity class II and class III agents and are labeled with the signal word “Warning” or “Caution.” Because the neonicotinoids block a specific neuron pathway that is more abundant in insects than warm-blooded animals, these insecticides are more selectively toxic to insects than mammals. Of the neonicotinoids, imidacloprid is the most toxic to birds and fish. Both imidacloprid and thiamethoxam are highly toxic to honeybees. The most available toxicity data of the neonicotinoids is with imidacloprid. They are all neurotoxins.

    At least read the first link. It is very detailed but I feel it is worth your time. Download the full pdf report and read during breaks in your time.

    From Xerces Society -
    https://xerces.org/neonicotinoids-and-bees/

    PBS
    https://www.pbs.org/newshour/science/neonicotinoid-pesticides-slowly-killing-bees

    Audubon Society
    https://www.audubon.org/magazine/spring-2017/the-same-pesticides-linked-bee-declines-might

    Below is a link that gives most of the insecticides and fungicides and their bee toxicity. The tables you will want to look at is further down the article.- this is done by Michigan State University called Minimizing Pesticide Risk to Bees in Fruit Crop.

    https://www.canr.msu.edu/uploads/resources/pdfs/Minimizing_Pesticide_Risk_to_Bees_in_Fruit_Crops_(E3245).pdf

    Lynn in Parkton, Maryland thanked Pam
  • Curious Girl
    5 months ago

    zen_man You mentioned disinfecting seeds that may carry fungal infection before planting. Can you advise how to do that?

  • zen_man
    5 months ago
    last modified: 5 months ago

    Hi CG,

    Seed companies disinfect the seeds they sell you using heat treatment using special equipment that prevents over-heating and damaging the seeds. So commercial seeds don't carry a fungal infection. But seeds that you save can and probably do. But no seed treatment can solve your problems, because you have to plant the seed into a growing medium and water it, and as soon as you even handle a seed to plant it, you risk infecting it. The growing medium can contain infectious organisms, and the water or fertilizer that you water the seeds with can also contain infectious organisms. So nothing that you can do to the seeds themselves will solve your problems.

    People have tried adding hydrogen peroxide to the water that they moisten the growing medium with, with various degrees of success. I have tried hydrogen peroxide, Physan 20, and commercial systemic antifungals, with various degrees of success, and failure. (I suspect that hydrogen peroxide decomposes Physan 20 and commercial systemic antifungals, so it is best to use those things separately.)

    Oxine is what I am using currently, and I am using it alone. It is what I initially water the growing medium with, as well as in all subsequent applications of liquid nutrients. Oxine is effective in very dilute amounts. I am currently using just 1/2 teaspoon of Oxine per gallon of water or liquid nutrients, and that is considered to be a strong Oxine solution. Many users of Oxine deal in just drops per gallon. (My son uses it to prevent disease in the drinking water for his chickens and guineas, at only 4 to 6 drops per gallon.) I have gotten zinnia plants from seeds that were saved from plants that died of disease, so Oxine seems to be very effective. But I think it is too early for me to be recommending that people depend on Oxine to solve their plant problems. I plan to continue using Oxine until I have some kind of noticeable failure with it.

    ZM

  • Curious Girl
    5 months ago

    Thanks SO much, zen_man! I wasn't sure I'd get a response since this is an old thread. This is very helpful information. My zinnias often end up with Alternaria Leaf Spot. I prefer not to use chemicals if I don't have to. But I recently treated my impatiens beds with Daconil because of what I'm almost sure was rhizoctonia. It seems to have done the trick for that problem. It's a never ending battle to keep all these plants healthy! I'm excited to have an alternative to try that is organic approved!

    CG