Ndpitch
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Help with watermelon disease!

Hi there-

Can anyone help identify this potential disease I have on my watermelon vines? I just recently noticed these blackish spots propagating along the leaves. So far the fruit seems unaffected but I imagine this is only going to get worse.

I attached a picture of a bad leaf, and one of a somewhat normal leaf.

Is it a fungus of some sort? Anything I can do to save the plant and the harvest?

Thanks for any help anyone can provide.
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rainbowgardener
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Re: Help with watermelon disease!

Not looking good! :(

Where are you located? There are hardly any garden issues that can be discussed without regard to location and climate/ weather. Are you somewhere, like me, where there has been a lot of rain? That is very conducive to fungal and other diseases.

Can you rub the black stuff off? Do the lesions show on the under side of the leaves? Are there any marks on the stems? Answers to these questions will help determine which disease it is, but I do think it is probably diseased.

To start with, I would remove and destroy all affected leaves (not in compost pile). Mulch well to prevent soil contact. Try spraying what is left after you remove affected leaves (including under sides of leaves) with hydrogen peroxide, which is anti-bacterial and anti-fungal. The H2O2 that is sold in stores is 3% and it can be sprayed right from the bottle.

Good luck!
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Ndpitch
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Re: Help with watermelon disease!

We are located in Buffalo, NY.

It's been an on and off summer. Long periods of cool damp weather, followed by periods of hotter weather. I'm no expert gardener, and just recently learned that my overhead irrigation probably wasn't helping, either.

In answer to the other questions, the lesions are visible on both sides of the leaves. The black does not rub off. The spots are only on the leaves as of now. They have not extended onto the stems/vines or fruit (yet). Upon closer examination of the rest of the garden, there are tiny amounts of smaller black spots starting to show on the lowest and most mature leaves of my tomato plants. It's possible the cucumbers are starting to be effected as well.

After doing some of my own research, I think it could be anthracnose. If it's anthracnose, should I still stick with H2O2, or try something like a chlorothalonil spray? Or, does anyone have some other brand name remedy that has worked on vegetable/fruit gardens for fungus issues? I'm afraid if I don't do something fast it could get out of control and wipe out the whole garden :x

Thanks!

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rainbowgardener
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Re: Help with watermelon disease!

Yes, now that you point me in that direction, I think you are right. I didn't think about anthracnose in watermelons, but one of the devastating things about this fungal disease is that it seems it can attack practically anything.

It is a fungal disease and the hydrogen peroxide is an anti-fungal. Baking soda solution is another.

Whether you want to use the chlorothalonil depends on how you feel about spreading environmental poisons around.
If chlorothalonil leaches into waterways, it is highly toxic to aquatic organisms, even at very low levels. Although animal studies have provided sufficient evidence to classify chlorothalonil as a probable carcinogen, it is not known if it is a human carcinogen or not. It is not directly toxic to birds, but it reduces their reproduction -- egg production, hatching survival, etc. Its degradate SDS-3701 (compound it breaks down into) is much more toxic. Berries treated with it were found to still have residue 76 days later. It can inhibit growth in plants treated with it
https://www.cdpr.ca.gov/docs/emon/pubs/f ... alonil.pdf Department of Environmental Toxicology, College of Agricultural & Environmental Sciences, University of California, Davis, CA 95616-8588, USA
It's part of the same chemical family, organochlorines, as the banned pesticide DDT. It is known to cause severe eye and skin irritation in humans if handled improperly. Chlorothalonil's label says not to spray it directly on waterways, so the researchers did not do that. Instead, they used a federally approved formula that calculates how much of a concentration would run off of a farmer's field and wash downstream into a nearby waterway. It killed nearly 90 percent of the frogs, no matter what species
https://www.tampabay.com/news/environmen ... gs/1162355

It is not acutely toxic to honey bees, but
Fungicides used on apples and other crops lower the honey bees’ ability to defend against a potentially lethal parasite linked to bee colony deaths, a study found. Commercial honey bees exposed to the fungicide chlorothalonil had a three times greater risk of being infected by the parasite linked to Colony Collapse Disorder than those not exposed to the chemical used to fight off fungus, according to research today in the journal PLoS ONE.
https://www.bloomberg.com/news/articles/ ... tudy-finds

and so on....
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imafan26
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Re: Help with watermelon disease!

I would pick off and destroy the infected leaves. Make sure you clean tools and hands afterwards so you do not transfer sap to other plants. Destroy crop residues after harvest and do not save the seeds.

If your watermelon is close to harvest it may still be o.k. to get a crop.

chlorothalanil usually is a weak fungicide and works better when paired with another fungicide like sulfur or Dithane.

If the problem is widespread it is hard to control. Most fungal control should begin as soon as the wet humid weather arrives. Fungal issues are always easier to manage by preventive sprays.

If the disease is widespread and the vines are young, it will be difficult to salvage.
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rainbowgardener
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Re: Help with watermelon disease!

Dithane is a similarly toxic chemical, carcinogenic, endocrine disrupting, goiter inducing, highly poisonous to warm water fish and toxic to other aquatic animals, developmental/ reproductive toxin,

https://pmep.cce.cornell.edu/profiles/ex ... b-ext.html
https://www.pesticideinfo.org/Detail_Che ... Id=PC35080

And it likely doesn't matter what you treat it with. Anthracnose can be prevented, but not really cured, even with poisons.

Prevention includes spacing plants well and ensuring good air circulation, don't get water on the leaves, grow in full sun, clear away all leaf litter, don't leave anything for spores to over winter in. Mulch well - the disease is easily spread by splashback of irrigation water or rain. Spray with fungicide (whatever you are using) preventatively from the beginning of the season, every 7 - 10 days. Keep your plants as healthy and un-stressed as possible. Plants become much more susceptible to anthracnose (and other diseases and pests) when stressed.
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imafan26
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Re: Help with watermelon disease!

Agreed, there are issues with using chemicals. I have used dithane before on orchids but not on vegetables. I prefer to use sulfur or baking soda or an oil spray if I can do it before it rains. It is actually hard to find wettable sulfur in powder form. I can only find copper sulfate which I do not like to use because copper can be toxic as well.

I do try to use cultural controls like resistant cultivars and spacing and timing planting to avoid the rainy season. Sometimes the weather won't cooperate and I know if I do not use the preventive sprays, I may as well be prepared to pull everything in a few weeks. If I am doing a lot of spraying I do gear up with a disposable painters overalls, chemical resistant gloves, pesticide respirator and safety glasses. For prevention, I usually am using oil spray or sulfur (they must not be used within two weeks of each other). Before it rains horticultural oil sprays help to wick water off the leaves. Sulfur helps prevent most of the common fungal problems in the vegetable garden.

Most chemicals are harmful to bees and aquatic life so care should be used to avoid water contamination no matter what you use. Long sleeved shirts, long pants, chemical resistant gloves, and boots are minimum for spraying anything to avoid skin contact. Glasses or googles for eye protection and I like to use the respirator for dusts and sprays and workng with perlite, which is also a known respiratory irritant. Clothes should be dedicated for garden use and washed separately. This is why I prefer to use the disposable painter's suit. It is very hot but I just double bag it when I am done with it. Acccording to the msds sheet on chlorothalanil there is limited evidence that it is a carcinogen. Everyone should read the labels of whatever chemicals they are using and follow the directions for storage, mixing and safety precautions.
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applestar
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Re: Help with watermelon disease!

Lots of great information from your own research as well as rainbowgardener and imafan.

Wow it really sounds pretty scary. Have you removed all the affected leaves yet? That would be the first step whatever you decide to do. Keeping an atomizer or small sprayer of rubbing alcohol on hand to spray cutting tools and your hands often is a good and simple way to minimize transfer. I have also read that rinsing hands in milk can be effective. Some people use water with bleach (too harsh for me).

Don't forget to treat your garden boots -- a bucket and change of footwear outside the bed.

I find that, often, removing the leaves will give you a better perspective of the extent of the damage. Once worst of the damaged leaves are gone, the bed may look manageable and hopeful that spraying with some kind of fungicide or preventive could be enough.

For my own garden, I only spray with milk solution alternated with AACT (actively aerated compost tea) and recently added willow tea to the possible spray regimen (supposed to improve general plant immune response and health). If these don't work and they get worse and continue to get worse then I pull the plug on them.

If the leaf removal seems endless and there's practically nothing left, then yeah, might as well give up on them. -- Better to clear the bed and see if you can grow something else before the end of this season. In the heat of the summer, there might be chance to try solarizing the bed, etc. too.

So sorry to see something like this. Hoping for the best.
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Ndpitch
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Re: Help with watermelon disease!

Thank you so much for all of the help and advice so far. Here is my current update.

I removed the most severely affected leaves. Some of the remaining leaves do have disease on them, but it's not as severe as the disease you see in the picture in my first post.

I did some research on the best fungicide that is safe and won't harm bees and other beneficial insects.

I was between the baking soda solution, and the serenade garden spray.

I ended up going with the Serenade Garden spray because most people that have used it seem to report good results. I have a bottle of it on overnight arriving sometime today. I plan on giving the whole garden a good treatment once a week or so, and hopefully the existing disease will be contained and not spread. It's listed as being fully organic, and the bacterial strain in it isn't supposed to harm the plants and other surround life.

Hopefully that will allow me to harvest the best that I can without having to destroy the plants early.

imafan26
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Re: Help with watermelon disease!

Serenade is less toxic, and worth a try. But it did not list anthracnose on the label so it may be of limited effectiveness.

The reason I mentioned dithane and chlorothalanil is because it is what is listed on the Stanford IPM site for managing anthracnose in cucurbits.

https://www.ipm.ucdavis.edu/PMG/r116101411.html

Fungicides and biofungicides in particular work better if they are alternated. That is why I use and oil spray as a preventive before it rains since it does not wash off as easily as a water based product and it helps the leaves wick off water better.
Happy gardening in Hawaii. Gardens are where people grow.

Ndpitch
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Re: Help with watermelon disease!

HI all-

Just figured I'd update everyone.

Success! After removing the most affected leaves and getting rid of them, treating with serenade, and weekly treatments with baking soda spray, the melons came roaring back to life.

Out of my 4 vines, I have about 9 melons to harvest. Here is a picture of one I just recently cut. Delicious.

Thanks for all the help!



IMG_0857.jpg

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applestar
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Re: Help with watermelon disease!

Yay! :clap:

So happy to hear that you are enjoying the fruit(s) of your labor. :> :wink:
Learning never ends because we can share what we've learned. And in sharing our collective experiences, we gain deeper understanding of what we learned.

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